Building Retrofits for Increased

Protection Against Airborne

Chemical and Biological Releases

Andrew Persily

Robert E. Chapman

Steven J. Emmerich

W. Stuart Dols

Heather Davis

Priya Lavappa

Amy Rushing

NISTIR 7379
NISTIR 7379

April 2006

U.S. Department of Commerce

Carlos M. Gutierrez, Secretary

Technology Administration

Robert Cresanti, Undersecretary of Commerce for Technology

National Institute of Standards and Technology

William A. Jeffrey, Director

Building Retrofits for Increased

Protection Against Airborne

Chemical and Biological Releases

Andrew Persily

Robert E. Chapman

Steven J. Emmerich

W. Stuart Dols

Heather Davis

Priya Lavappa

Amy Rushing

Building and Fire Research Laboratory

Prepared for:

U.S. Environmental Protection Agency

Research Triangle Park, NC

Funded under IAG DW-13-93010301-0 by the U.S. EPA National

Homeland Security Research Center (NHSRC), Decontamination

and Consequence Management Division (DCMD) 

March 2007

iii

ABSTRACT

Due to concerns about potential airborne chemical and biological (chembio) releases in or near

buildings, building owners and managers and other decision makers are considering retrofitting 

buildings to provide some degree of protection against such events. A wide range of technologies

and approaches are being proposed with varying levels of efficacy and cost, as well as varying 

degrees of applicability to particular buildings and ventilation systems. This document presents

the results of an effort to evaluate chembio retrofit options for buildings. A number of retrofit

options are identified, and their potential to protect building occupants from a number of generic

contaminant releases is evaluated using building airflow and contaminant transport modeling. In

addition, a case study is presented in which specific retrofit options were considered for two 

actual buildings and pre-installation designs and cost estimates were developed. Based on the

analyses performed, the results of the case study and other available information, guidance on the

application and effectiveness of various retrofits are presented. An economic analysis software

tool employing life cycle cost analysis techniques was developed as part of this project, and its

use is described in an appendix to this report.

The retrofit options considered fall into two categories, the first being stand-alone technologies

or devices such as enhanced particulate filtration that are installed and implemented as

purchased. The second category includes retrofit approaches that employ operational strategies

or building modifications to increase building protection, such as outdoor air purging or building 

envelope airtightening. The guidance section describes each retrofit technology and approach in 

some detail, presenting relevant performance data and the level of protection that might be

expected from the retrofit. Potential disadvantages and knowledge gaps are also discussed for

each technology. The retrofit technologies considered include enhanced particle filtration,

sorbent based gaseous air cleaning, ultraviolet germicidal irradiation, photocatalytic oxidative air

cleaning, and work area air capture and filtration equipment such as mail handling tables. The

approaches include ventilation system recommissioning, building envelope airtightening,

building pressurization, relocation of outdoor air intakes, shelter-in-place (SIP), isolation of

vulnerable spaces such as lobbies, system shutdown and purge cycles, and automated heating,

ventilating and air-conditioning (HVAC) operational changes in response to contaminant

sensing. The filtration and air cleaning options are noted to have an advantage of always being 

operational, which is an advantage as long as the systems are properly designed, installed and 

maintained. However, the lack of standard test methods for sorbent-based gaseous air cleaning 

and other air cleaning approaches is identified as a critical issue in the application of these

technologies. Building envelope air sealing and pressurization can be quite effective in

protecting against outdoor releases as long as effective filtration against the contaminant of

concern is also in place. The protection provided by operational changes such as system

shutdown and purging are shown to be very dependent on the timing of their implementation,

with the possibility of increasing occupant exposure if the timing is inappropriate. Isolating 

vulnerable zones and other system related modifications are highly dependent on the building 

layout and system design, and their implementation must be well conceived to be effective under

the range of conditions that exist in buildings. Finally, many retrofits are noted as also providing

additional benefits of increased energy efficiency and improved indoor air quality, which should 

be included in the life-cycle cost comparison of different options to the degree possible.

Keywords: air cleaning, building protection, CBR, chembio, filtration, indoor air quality, lifecycle costs, terrorism
iv

Use of Non-SI Units in a NIST Publication

The policy of the National Institute of Standards and Technology is to use the International

System of Units (SI units) in all its publications. However, in the North American construction

and heating, ventilating and air-conditioning (HVAC) industries, certain non-SI units are so 

widely used instead of SI units that it is more practical and less confusing to include values in

non-SI units in portions of this publication.
v

TABLE OF CONTENTS

1. INTRODUCTION.......................................................................................... 1

1.1. Project Description...................................................................................... 1

1.2. Retrofit Options........................................................................................... 2

1.2.1 Retrofit Technologies.................................................................................. 2

1.2.2 Retrofit Approaches................................................................................... 4

2. TECHNICAL EVALUATION........................................................................... 7

2.1 Description of Simulations............................................................................... 7

2.1.1 Building Models......................................................................................... 7

2.1.2 Contaminants and Release Scenarios................................................................10

2.1.3 Retrofits................................................................................................. 11

2.1.4 Simulations and Analysis............................................................................. 16

2.2 Results of Simulations.................................................................................. 17

2.2.1 Single zone Building.................................................................................. 17

2.2.2 Two-story Office Building........................................................................... 22

2.2.3 High-rise Office Building............................................................................ 36

2.3 Summary of Simulation Results....................................................................... 43

3. CASE STUDY........................................................................................... 45

3.1 Description of Buildings and Retrofits Considered................................................ 45

3.2 Retrofit Design.......................................................................................... 47

3.3 Economic Evaluation .................................................................................. 50

3.4 Technical Evaluation ................................................................................... 51

3.5 Discussion of Case Study.............................................................................. 56

4. GUIDANCE............................................................................................... 57

4.1 General Guidance........................................................................................ 57

4.2 Retrofit Technologies................................................................................... 60

4.3 Retrofit Approaches..................................................................................... 78

4.4 Guidance Summary..................................................................................... 99

5. CONCLUSIONS........................................................................................ 103

6. ACKNOWLEDGEMENTS............................................................................ 105

7. REFERENCES........................................................................................... 106

APPENDICES

A. Life-Cycle Cost Analysis Tool for Chem/Bio Protection of Buildings: Software Primer..... 111

B. Case Study Retrofit Design Documentation......................................................... 143

C. Case Study Retrofit Costs Per Unit of Floor Area.................................................. 157
vi

LIST OF ACRONYMS

A&E: architectural and engineering, with reference to firms that do both types of design work

ASHRAE: American Society of Heating, Refrigerating and Air-Conditioning Engineers

ASZM-TEDA: military grade carbon sorbent, impregnated with copper, silver, zinc,

molybdenum and triethylenediamine

BASE: Building Assessment, Survey and Evaluation (EPA study of 100 U.S. office buildings)

BFRL: Building and Fire Research Laboratory (part of NIST)

CMU: concrete masonry unit (type of wall construction block)

CONTAM: NIST-developed multizone airflow and contaminant dispersal simulation program

CSEPP: Chemical Stockpile Emergency Preparedness Program (FEMA program)

ELA: effective leakage area

EPA: Environmental Protection Agency

FEMA: Federal Emergency Management Agency

GPAC: gas-phase air cleaning

HEPA: high-efficiency particulate air filters

HVAC: heating, ventilating and air-conditioning

IAQ: indoor air quality

LCAT: Life-Cycle Cost Analysis Tool, NIST-developed software for comparing retrofit options

LCC: life-cycle cost, method for economic comparison of retrofit options

MERV: minimum efficiency reporting value, metric of particle filtration efficiency based on 

ASHRAE Standard 52.2

NIST: National Institute of Standards and Technology

OAE: Office of Applied Economics (part of BFRL)

PCO: photocatalytic oxidation

PVNS: present value of net savings, method for economic comparison of retrofit options

SIP: shelter-in-place

TAB: testing, adjusting and balancing; procedure for confirming ventilation system operation 

relative to design

ULPA: ultra low-penetration air filters

UV: ultraviolet

UVC: C-band wavelength of UV radiation, generally less than 280 nm

UVR: UVGI rating value

UVGI: ultraviolet germicidal irradiation
1

1. INTRODUCTION

Due to concerns about potential airborne chemical and biological (chembio) releases in or near

buildings, building owners and managers and other decision makers are considering retrofitting 

buildings to increase protection against such events. A range of technologies and approaches are

being proposed with varying levels of efficacy and cost, as well as varying degrees of

applicability to particular buildings and ventilation systems. While a number of useful guidance

documents have been published (ASHRAE 1993, NIOSH 2002 and 2003), most of these do not

the address the selection of appropriate and cost-effective retrofits for specific buildings. In order

to address this need for better guidance on building retrofits to increase protection against

chembio releases, the Building and Fire Research Laboratory (BFRL) at the National Institute of

Standards and Technology (NIST) undertook the project described in this report.

1.1 Project Description

The purpose of the project is to provide building owners, managers, engineers, and other

decision makers with information about retrofit options to improve the safety of buildings

against airborne hazards and with economic analysis tools for use in selecting cost-effective

approaches to mitigating those hazards. This project was organized around a number of tasks, the

first two of which were to identify the retrofit options to be considered in the project, and to 

establish the methods to use in the technical and economic evaluations of the retrofit options.

The next task was to conduct a technical evaluation of the protection impacts of the retrofits

using building airflow and contaminant transport modeling. This evaluation is described in

Section 2 of the report. These simulations involved the analysis of three buildings subjected to

generic particle and gaseous releases to determine the reduction in occupant exposure as a result

of implementing the various retrofits. Section 3 of the report presents a case study in which 

specific retrofit options were investigated for two buildings and pre-installation designs and cost

estimates were developed. Finally, guidance on the application and effectiveness of various

retrofits is presented in Section 4.

A key effort within the project was to formulate methods for economic analysis that provide lifecycle cost (LCC) information about retrofit options to assist decision makers in choosing how to

improve the safety of their buildings. An economic analysis software tool was developed 

(available for download at www2.bfrl.nist.gov/software/LCCchembio/index.htm), with a

software primer included in Appendix A to this report The economic analysis methodology 

includes the following considerations: the assumptions and information requirements necessary 

to compute the costs of each retrofit option; the methodology for combining information about

first costs with operations, maintenance, and repair costs and with other costs to compute the

life-cycle costs of the retrofit options; and specifying the appropriate circumstances for applying

this methodology to cost analyses of retrofit options. The economic analysis methodology 

includes two metrics of the cost effectiveness of alternative investments, life-cycle cost and 

present value of net savings.

It is important to note that every building and its ventilation systems and every contaminant

release scenario are unique. Therefore the information presented here must be considered in the

context of a specific building’s characteristics, including layout, system type and design, and 

occupancy. The level of protection in a given situation is highly dependent on these

characteristics and the nature of the contaminant release, and it is extremely difficult to make

general statements about what strategies will be effective in a given situation and to what degree.

Nevertheless, this project is based on the philosophy that better protection is a worthy goal, even 

if the degree of protection cannot be characterized in general terms.
2

1.2. Retrofit Options

The first task in this project was to identify candidate retrofit options for consideration in the

technical evaluations of the study and for potential inclusion in the resultant guidance itself.

These options are divided into two basic categories, specific technologies, such as filtration and 

air cleaning devices, and more generic approaches to increasing building protection such as

building pressurization strategies and isolation of areas of potential concern (e.g. mail rooms).

These options have been identified based on information in the published literature, information

from vendors, and interactions with researchers, consultants, government agencies, building

contractors, HVAC experts, and other knowledgeable individuals. The options that are

considered are limited to engineering-based retrofits as opposed to building and personnel

management options such as building security and evacuation. Obviously, building management

practices can play a major role in increasing building protection, but they are not within the

scope of this project. In addition, the options considered are restricted to those that are “off-theshelf” or commercially available today. While much research and development is currently in

progress that will result in more options in the future, only currently available technologies are

being considered.

This section presents the technologies and approaches that have been identified, including a

discussion of the performance data that is relevant to the simulations planned for the project and 

a summary of other issues related to the retrofit that are relevant to the study.

1.2.1 Retrofit Technologies

A number of technologies have the potential to increase building protection against chembio 

agent releases. Most of these are in the particle filtration and gaseous air cleaning categories.

Other technologies for building protection include systems for use in mail rooms, and other

spaces that may be more vulnerable to agent releases, to capture and remove the agents before

they are able to migrate to other portions of the building.

Enhanced particle filtration

Particle filtration is currently employed in most commercial and institutional buildings, primarily 

to limit dirt buildup on cooling coils and other wetted surfaces in order to reduce the potential for

microbial growth and to maintain good heat transfer between the air and the coil surfaces.

However, typical levels of filtration are not always very effective in removing particles of the

sizes associated with many biological agents, i.e., on the order of 1 μm. Nevertheless, dramatic

increases in removal rates can still be achieved through enhanced filtration without the use of

very high levels of efficiency (NIOSH 2003). Particle removal efficiencies are fairly well

established based on the use of ASHRAE Standard 52.2 (ASHRAE 1999), which provides a

rating method referred to as Minimum Efficiency Reporting Value (MERV).

The implementation of enhanced filtration involves a number of important issues. First, the

particle size of interest must be considered. Biological agents vary in size, but the bacteria and 

spores of most interest are generally on the order of 1 μm to 10 μm. In addition, the installation 

of more efficient filters will generally result in an increase in the pressure drop across the filter.

Depending on the increase in filter efficiency and the type of filter installed, the increase in 

pressure drop may or may not be particularly large. In some cases, the air handling equipment

will need to be modified due to the increased pressure drop.
3

Sorption based gaseous air cleaning

Sorption based gaseous air cleaning is currently employed in a number of applications to control

odorous, corrosive or otherwise undesirable gases generated within or outside of buildings. A

variety of sorbents are employed including activated carbon, alumina and sorbents impregnated 

with compounds to enhance their ability to remove specific contaminants (NIOSH 2003,

ASHRAE 2003). These sorbents have varying degrees of removal effectiveness depending on 

the particular sorbent-contaminant combination, and they capture contaminants through either

physical adsorption or chemisorption. Some sorbents employing the former mechanism can be

regenerated through heating or other processes. Adsorbents using a chemisorption process

generally rely on catalytic (continuously self-regenerating) reactions that chemically decompose

the threat gases into less toxic or non-toxic gases. The effectiveness of sorbent-based air cleaners

also depends on temperature, humidity, the concentrations of the contaminant of interest as well

as other contaminants, and the residence time of the airstream in the air cleaning unit. Gaseous

air cleaning devices are not typically employed in commercial and institutional buildings but are

seeing increasing use in a number of applications. There are no standard test methods for

determining the contaminant removal efficiency of gaseous air cleaning equipment for use in

selecting and sizing these systems. Manufacturers have performance data and experience that can 

be useful, but efforts to develop the equivalent of a MERV rating for gaseous air cleaning are

still being pursued.

In general, gaseous air cleaning systems are associated with a more significant pressure drop 

than particle filtration devices and require more space than typical filtration equipment. These

increased pressure drops can in turn affect system airflow rates and may require significant

system modifications. These devices must be changed at intervals that depend on their capacity,

the concentrations to which they are exposed, and the degree of temperature and humidity

control in the system.

Ultraviolet germicidal irradiation (UVGI):

UVGI systems have been used for many years to kill airborne infectious agents in healthcare

facilities and other venues, primarily to control the transmission of tuberculosis. These devices

use ultraviolet irradiation in the 250 nm to 260 nm wavelength range and are generally installed 

in the upper portions of a room with shielding to protect the occupants or in ductwork where

such shielding is not required. This application is distinct from the use of UVGI to kill biological

contamination on exposed cooling coils resulting from dirt accumulation and condensation.

The effectiveness of these devices is primarily a function of device geometry, intensity of the

light source, microbial resistance and residence time of the agents of concern. Inactivation or

“kill” rates can be predicted with a fair level of reliability based on these parameters (VanOsdell

and Foarde 2002). However, there is no standard test method for determining the effectiveness of

these devices and they are not generally supplied with the performance data to determine kill

rates. These devices are associated with electrical energy consumption and require some level of

maintenance to keep them operating effectively.

Photocatalytic oxidation air cleaning (PCO)

PCO is an air cleaning approach in which titanium dioxide (TiO2) acts as a photocatalyst when 

irradiated by UV light, removing organic chemicals including both chemical and biological

agents. If the photocatalytic reaction is 100 % complete, the byproducts include water and carbon 

dioxide, but complete conversion is difficult to achieve in practice.
4

Various PCO devices are available as either portable, stand-alone units or in-duct devices.

However, the lack of test methods for gas or biological removal limits the availability of

performance data.

PCO systems generally have low pressure drops in comparison to particle filters and sorption

based gaseous air cleaning. However, questions exist as to the useful life of the catalysts in 

practice and the production of undesirable byproducts associated with incomplete photochemical

reactions.

Work area treatment

A variety of devices are available for capturing and removing particulates from work areas, e.g.

mail opening stations. These devices are essentially air capture hoods combined with highefficiency filtration systems. Some of these devices also incorporate anti-microbial elements,

gaseous air cleaning components and UVGI.

The performance of these devices is generally expressed as a filter efficiency at a specific

particle size and an airflow rate. Units with anti-microbial or gaseous air cleaning capabilities are

impacted by the lack of standard test methods noted earlier. Another important parameter is the

contaminant capture effectiveness, but this is not generally covered in the product specifications.

1.2.2 Retrofit Approaches

In addition to the specific technologies described above, there are a number of retrofit options

that also have the potential to increase building protection against chembio releases. This section 

describes options that do not involve a specific technology but rather a general strategy for

building and system design or operation.

System recommissioning

Assessing the vulnerability of a building to a chembio release and using the ventilation system as

part of a protective strategy require that the system design be understood and that the system be

operated as intended. Ventilation system recommissioning is a process by which a system’s

operation is brought into line with its design intent. Depending on the system, recommissioning 

can involve a number of items including the following: airflow testing and balancing; calibration 

of temperature, humidity and other sensors used to control system operation; checking dampers

for proper operation; reviewing system operating schedules; and confirming system capacity 

relative to current loads.

The impacts of a recommissioning effort will depend on the design of the ventilation system and 

the degree to which the system has “drifted” away from its design specifications. In addition to

increasing building protection, building recommissioning can also increase energy efficiency,

improve indoor air quality and extend equipment life.

Envelope tightening

Based on the available data, the exterior envelopes of U.S. commercial and institutional

buildings are fairly leaky (Emmerich and Persily 2005). This leakage in combination with

indoor-outdoor pressure differences caused by weather and system operation can lead to 

significant infiltration rates and the entry of exterior chembio agents without the possibility of

removing them through filtration or air cleaning. Therefore, tightening of building envelopes has

the potential to increase building protection.

Envelope tightening can also improve building energy efficiency by reducing heating and 

cooling loads due to infiltration (Emmerich et al., 2005a and 2005b, Emmerich and Persily 
5

1998). In addition, building indoor air quality can improve due to the reduction in unfiltered and 

uncontrolled infiltration.

Building pressurization

This approach involves protecting a building against outdoor chembio releases through the

overpressure of the building interior relative to outdoors and the removal of the outdoor agent

from the intake air via filtration or air cleaning. The idea behind this strategy is for the building 

to be pressurized continuously under normal operation, not as a response strategy in the event of

a release. To be effective, the amount of air must be sufficient to overcome negative pressures

that can be induced by weather and the operation of other systems. This approach is more likely

to be effective in a building with a tight envelope than a leaky one.

This approach is characterized by the net amount of outdoor air intake relative to exhaust or spill

air, the envelope airtightness, the weather conditions and the filter/air cleaner removal efficiency.

The cost and maintenance issues associated with filtration are also relevant to this approach. In

addition, ventilation system airflow rates and controls may need to be modified to achieve the

desired levels of pressurization. As with envelope tightening, this approach can have a positive

impact on indoor air quality (IAQ) by reducing infiltration of contaminated air.

Relocation of outdoor air intakes

Unless otherwise protected, ground level air intakes are more likely to be exposed to the

intentional release of a chembio agent relative to more inaccessible intakes. One potential

solution is to relocate the intake to a higher elevation that will presumably be harder to access.

There is no quantity that characterizes the degree of accessibility of an air intake, but presumably 

an intake that is located at a higher elevation is less likely to be subject to a ground level release.

Locating outdoor air intakes well above ground level also reduces the entry of contaminants

associated with landscaping and other activities. There is clearly a cost associated with relocating

air intakes, which in some cases can be quite significant. In addition, the relocation may modify 

the airflow resistance associated with the intake, thereby requiring other modifications to the air

handling system.

Shelter-in-place (SIP)

In the event of an exterior release, and in some cases an interior release, the building occupants

can move to a designated space that is isolated from the rest of the building and offers protection 

from the airborne agent. The degree of protection will increase if the space is well isolated in

terms of airflow by having tight boundaries and even more if it is equipped with a filtration and 

air cleaning system to remove contaminants that have entered the space. Self-contained filtration 

and air cleaning system for use in SIP spaces are currently commercially available.

The primary variables describing this approach include the airtightness of the interior partitions

and, if filtration or air cleaning is employed, the supply airflow rate to the space and the filter/air

cleaner removal efficiency. There is some cost involved in setting up such an arrangement,

particularly in terms of any airtightening involved and the equipment costs for an oversupply and 

cleaning system. The system will also require some maintenance to ensure it will function 

properly in the event it is needed.
6

Isolation of special-use spaces

Due to the potential vulnerability of mail rooms, loading docks and lobbies to chembio releases,

keeping these spaces at a lower pressure than adjacent portions of the building can provide some

protection. Such isolation can be achieved through ventilation airflow control, e.g., exhaust fans,

and will generally be easier to achieve if these spaces are served by a dedicated system. This

approach is more likely to be successful if the boundaries between the vulnerable space and the

rest of the building are tight.

There may be some initial costs associated with airtightening or with modifications of system

airflow rates to achieve the desired pressure relationships. The latter will require maintenance in 

terms of periodically checking the system balancing to verify that these pressure relationships are

still in effect. In some cases a new air handling system may need to be installed, as well as

controls to modulate the system airflows in response to the real-time pressure monitoring 

between the space and an adjacent space.

System shutdown and purging

In some circumstances, shutting down a building ventilation system or operating it at 100 %

outdoor air intake (purging) may help protect the building occupants from exposure to a chembio 

release. However, realizing these benefits requires knowledge that the release has occurred, that

one of these options is the appropriate response, and switching to the desired ventilation mode

quickly. A dedicated control that implements the operational strategy is one means of making the

change relatively quickly, though a fast shutdown requires quick-acting and tight-sealing 

dampers, fan braking mechanisms and specially-constructed ductwork to prevent ducts from

collapsing, all of which are not typically employed in commercial building ventilation systems.

Also, running a building in a purge mode can result in pressure differences that make it difficult

for building occupants to open and close doors.

Automated HVAC response

Given a timely and reliable signal from a contaminant sensor, or perhaps an occupant generated 

signal, a building’s automated control system could modify the ventilation system operation in a

manner that contains the contaminant in the zone of release, or prevents it from entering a

building in the case of an outdoor release, and maintains the rest of the building and egress paths

at low contaminant concentrations. These modifications could include stopping and starting fans,

repositioning dampers, or securely closing doorways. This is the concept behind automated

smoke control systems that have been used for many years (Klote and Milke 2002) to contain

smoke in the fire zone and provide a safe evacuation route for the building occupants. The

manner in which a system’s configuration and operation should be modified depends on the

building and system design and layout, and the nature of the contaminant release.

In theory, if the sensors and system capabilities were available, and the building and system

airflow dynamics were well understood, this approach would be able to provide a high level of

protection. However, sensors that are fast, reliable and inexpensive enough are not currently

available for any applications other than very high security buildings where the costs are

justified.
7

2. TECHNICAL EVALUATION

In order to support the guidance to be developed as part of this project, technical evaluations of

the retrofit options were conducted to estimate the impacts of the retrofits on occupant exposure.

These evaluations employed simulations of generic building and system configurations, with

contaminants intended to represent generic chembio agents, as described below.

2.1 Description of simulations

The technical evaluations of the retrofits involved simulations of airflow, contaminant transport

and occupant exposure in selected buildings using the multizone airflow and indoor air quality

model CONTAM (Walton and Dols 2005). The general concept of the evaluations is to simulate

generic contaminant releases within or outside a building and calculate the occupant exposure,

and then to repeat the process for the same building and release scenario with one or more

retrofits in place. The cases without the retrofits are referred to as the baseline cases. The

measure of retrofit performance is based on the change in occupant exposure, i.e., the retrofit

exposure as a percentage of the baseline exposure.

The CONTAM simulation program was used based on its demonstrated ability to model

multizone airflow and contaminant transport in building systems, as well as the project team’s

familiarity with the program. CONTAM considers a building as a system of interconnected 

volumes or zones, each at a uniform temperature and contaminant concentration. These zones

can be rooms, hallways, floors of a building, stairwell shafts, etc. Airflow paths between zones,

and between zones and the outdoors, are specified in the building model along with other

relevant information such as ventilation system airflows, weather, and wind pressure coefficients

on exterior surfaces. Using these inputs, CONTAM calculates airflow rates between each zone,

under either steady state or transient weather and system operation conditions, based on a

simultaneous mass balance of air in each zone. Given additional information on contaminant

sources and removal mechanisms and outdoor contaminant concentrations, CONTAM

determines contaminant concentrations in the zones based on the calculated airflow rates and 

contaminant-specific information.

2.1.1 Building Models

The project focus on commercial and institutional buildings served to define the buildings

studied in the simulations, which are described in Table 1.

# of stories Floor area, m2 (ft

2

) System Type

1, Single-zone 1 1000 (10 800) Simple air handler

2, Office 2 2600 (28 000) Single air handling system

3, Office 14 11,900 (128 000) Central air handling systems

Table 1 Simulated Buildings

Building #1 is a simple, single-zone model of a building included to examine first order effects

of ventilation, filtration, and infiltration without the complexities of weather, interior zoning, etc.

The various airflow rates are input to the model, rather than calculated as in the other building

models. Only some of the retrofits apply in this building, but its simplicity makes it easier to

understand the impacts of each option. The 2-story office building model is more detailed,

including some interior zoning such as stair and elevator shafts and ceiling return plenums, a

more realistic ventilation system, and the calculation of weather-driven infiltration associated 
8

with envelope leakage. Building #3 contains a lobby, mail room and loading dock, and is

modeled with central air handling systems.

In order to create CONTAM models of these buildings, a number of factors need to be defined,

including the building zoning, occupancy levels, airtightness of the exterior and interior walls,

and ventilation systems. The manner in which these factors are handled in each of the buildings

is described below.

Zones

While the number of stories of each building is listed in Table 1, the subdivision of these stories

into zones in the CONTAM representation of each building must also be defined. In addition,

some of the simulations involve lobbies, mail rooms and loading docks, which must also be

specified in each building model. The buildings are zoned as described below:

1-zone building: single zone, with no lobby, mail room or loading dock.

2-story office: two levels per floor, the occupied space and the return plenum above the

suspended ceiling; two toilet rooms with exhaust airflow on each floor; an elevator and a stair

shaft in the building core, both of which are two stories tall; a lobby zone and loading dock 

door on the first floor, but no mail room; and, a conference room on the second floor.

High-rise office: two levels per floor, the occupied space and the return plenum above the

suspended ceiling; two toilet rooms with exhaust airflow on each floor; two elevator shafts

and two stair shafts, all of which extend from the basement to the 11th floor and one stairway 

which extends through the 13th floor; a Mezzanine level that houses the mechanical ventilation 

systems between the 1stand 2nd floors; a 12th floor mechanical room and 13th floor elevator

room; a main lobby on the 1stfloor, a mail room with a loading dock door on the basement

level; and, conference rooms on all occupied floors from the basement through the 11th floor.

Airtightness

Values for the baseline airtightness of the exterior walls are based on an existing database of

airtightness values obtained from building fan pressurization testing (Emmerich and Persily 

2005, Persily 1999). While there is less information on the airtightness of interior partitions, the

available data were used as a basis for the values in the models (Ivy and Persily 2001). In the

analysis, the exterior wall leakage (effective leakage area at 4 Pa reference pressure normalized 

by wall area) value in the model of the two-story office was 5 cm

2

/m

2

of wall area (0.07 in

2

/ft

2

).

For the high-rise building, the exterior wall leakage area was 8.7 cm

2

/m

2 (0.13 in2

/ft

2

). These

leakage values are fairly typical for office buildings based on the limited measurements that have

been made. Interior partitions are assumed to be leakier, with an effective leakage area of

20 cm

2

/m

2 (0.29 in2

/ft

2

). For the one-zone building model, all airflow rates are defined, so no 

airtightness values are employed to calculate pressure-driven airflows.

Occupancy

The number of people in each occupied zone was based on the default occupant density values in

ASHRAE Standard 62.1-2004, i.e., 5 people per 100 m

2 (1000 ft2

) in office space (ASHRAE

2004). The corresponding number of people is located in each CONTAM zone for the duration 

of each simulation, except in cases where shelter-in-place strategies are evaluated and the people

move during the simulation period.
9

Systems and system models

While the system types in each building are generically identified in Table 1, the details of the

system airflows are based on current ASHRAE Standards (ASHRAE 2004), the results of the

EPA BASE ventilation data analysis (Persily and Gorfain 2004), and actual design values in the

case of the high-rise office building. CONTAM has three options for modeling ventilation 

systems (constant airflows to or from the outdoors; simple air handling systems that allow for

recirculation; and full duct models that include all the details of duct resistance and fan 

performance curves). Simple air handling system models were determined to be sufficient for

these simulations based on their ability to adequately handle system filtration and their ease of

use relative to complete duct models.

The single-zone building model has constant airflow rates, with the outdoor air intake rate equal

to 20 % of an assumed supply airflow rate per unit floor area of 5 L/s•m

2 (roughly 1 cfm/ft2 *

).

These values correspond to typical office building system designs, consistent with those seen in 

the EPA BASE buildings (Persily and Gorfain 2004). The envelope infiltration rate is also 

modeled as a constant airflow corresponding to an air change rate of 0.2 h-1. The baseline system

is assumed to have a MERV 6 particle filter in the outdoor air intake and in the recirculated 

airstream (equivalent to the filter being in the mixed airstream), with a particle removal

efficiency of 16.4 % for particle diameters of 1 μm, but no gaseous air cleaning capability. The

MERV ratings throughout this report are Minimum Efficiency Reporting Values as defined by 

ASHRAE Standard 52.2 (ASHRAE 1999).

The two-story office building model was developed to be more realistic than the single-zone

case, with envelope infiltration rates calculated by CONTAM based on weather and system

induced pressure differences and envelope leakage areas. The outdoor air intake rate of the

system was about 10 % of the supply airflow rate, which corresponds to about 9.2 L/s (19 cfm)

per person for the 130 occupants assumed to occupy the building. The supply airflow rate to the

building zones is based on roughly 5 L/s•m

2 (1 cfm/ft2

) of floor area. The baseline building 

model has a MERV 6 filter in the mixed airstream impacting both the outdoor air intake and 

recirculation air.

The high-rise building model is based on, though not identical to, a portion of an actual office

building. The system outdoor and supply airflow rates are based on the design specifications for

that building, with a minimum outdoor air intake of approximately 23 % of the supply airflow

rate of 4.9 L/s•m

2 (0.96 cfm/ft2

) of floor area. The systems are assumed to have MERV 6 filters

in the mixed airstream, with no gaseous air cleaning.

 * cfm is the conventional non-SI unit for volumetric airflow rate and refers to cubic feet per minute.
10

2.1.2 Contaminants and Release Scenarios

The simulated contaminants include generic particulate and gaseous contaminants rather than 

any specific chembio agents. The particular and gaseous contaminants are referred to as agent P

and G respectively. The particle is modeled as monodispersed with a diameter of 1 μm, and the

gaseous contaminant is assumed to be nonreactive. Particle removal by deposition on surfaces,

including filtration of infiltrating air by the building walls, is not included in the analysis.

Release locations both inside and outside the building are considered, including the following:

Exterior release distant from building

Exterior release at outdoor air intake(s)

Interior release in lobby

Interior release in mail room

Interior release into ventilation system return

Exterior release in vicinity of loading dock, with loading dock door closed.

The simulated releases are described in Table 2. The outdoor release is represented by a constant,

elevated outdoor concentration for a period of 60 s. The release at the intake and the loading 

dock are modeled as a localized increase in the outdoor concentration at that specific location,

again lasting 60 s. The indoor releases are expressed as contaminant release rates per unit time,

and once again last for 60 s in the designated location.

Contaminant Outdoor general Outdoor air intake and 

loading dock Interior

G, gas 1 mg/m3 10 g/m3 16.7 g/s

P, particle 109 particles/m3 109 particles/m3 109 particles/min

Table 2 Contaminant release rates

Only two release scenarios are used for the single-zone building model, indoor and outdoor.

There are more release scenarios for the two-story office building, given its more detailed 

representation. In addition to the outdoor general release, there is also a release at the outdoor air

intake and the loading dock door. Indoor releases occur in the lobby and into a ventilation system

return vent on the first floor. In addition to these releases, the high-rise office building

simulations include a release in the mail room instead of the loading dock.

The calculated concentrations and the assumed release rates have no significance in relation to 

any particular chembio agent but were chosen to yield indoor concentrations in a reasonable

range of interest. Given the generic nature of these contaminants and releases, and in keeping 

with the purpose of the project, the calculated concentrations cannot be used to estimate health

impacts. As a result, the simulation results in terms of the relative concentration or exposure

between the various simulated cases are of far more relevance than the absolute concentration

and exposure values themselves. Also, while radiological contaminants are not specifically 

considered in this study, the results for the particulate contaminant can be considered to represent

the impacts on radiological agents of the same particle size.
11

2.1.3 Retrofits

Like the contaminant releases, the retrofits and the manner in which they are implemented in the

simulations depend on the building in question. The list of retrofits considered in the simulations

is as follows:

1 Air cleaning and filtration options: Separate analyses are performance for these systems

located in the outdoor air intake and in the mixed air (downstream of where the outdoor and 

recirculation airstream merge).

a Enhanced particle filtration: increase from baseline MERV value to retrofit value.

b Gaseous or gas-phase air cleaning (GPAC): include a gaseous air cleaner in ventilation 

system with none assumed present in the baseline case; since there is no standard method of

test for these devices or values provided by manufacturers, the contaminant removal

efficiency is only an estimate for the purposes of the simulations.

2 HVAC System options: The following retrofits include changes in HVAC operation.

a System shut down: model by turning off all ventilation systems including exhausts, thereby 

reducing outdoor air intake to zero; include different initiation times to account for varying 

degrees of warning based on automatic, visual or other means of detection; note that when 

the system is shut down envelope infiltration continues to occur based on weather effects.

b Purging: model by running the ventilation systems with 100 % outdoor air intake; include

different initiation times to account for varying degrees of warning.

c Ventilation system recommissioning: assume the baseline case is consistent with design 

intent and model condition(s) that are “off-design” including the following: reduce the

outdoor air intake by 50 % (referred to as 5 % intake since the “design” value is assumed to 

be 10 %), increase the return airflow relative to the supply such that there is 5 % less supply 

to the building than return (referred to as 5 % undersupply), increase the return airflow from

the ventilated space to 100 % of the supply, i.e. 100 % recirculation, and allow 10 % of the

airflow intended to pass through the filter to bypass around the filter (10 % filter bypass).

Note that recommissioning cases are only applied to the two-story building.

d Relocation of outdoor air intakes: simply assume that the contaminant does not enter the

building if the intake is moved and all exposures are zero; applies only to release at the

intake.

3 Envelope and pressurization options:

a Envelope tightening: tighten the building envelope, but do not modify the ventilation system

operation.

b Envelope tightening/filtration: combine the envelope tightening and enhanced particle filter

in the outdoor air intake.

c Envelope tightening/GPAC: combine the envelope tightening and outdoor air intake GPAC

retrofit.

d Envelope tightening/filtration/pressurization: combine envelope tightening and enhanced 

particle filter retrofit in the air intake with attempt to pressurize the building by doubling the

outdoor air intake relative to the minimum design value.

e Envelope tightening/GPAC/pressurization: combine envelope tightening and air intake

GPAC retrofit with attempt to pressurize the building.
12

4 Local options:

a Shelter in place: move occupants from office space to selected shelter locations in each 

building and turn off all ventilation systems at a specified time; shelters have tighter interior

partition; after a two-hour sheltering period, the occupants leave the building and the systems

are operated with 100 % outdoor air.

b Shelter in place with air cleaning: same as shelter in place, but with a recirculating filtration 

and air cleaning system operating in the shelter during the sheltering period.

c Lobby and mail room isolation: isolate these spaces through combinations of interior

partition tightening and using ventilation systems to induce lower pressures in these spaces

relative to the rest of the building; only applied to high-rise building.

The manner in which these retrofits were implemented in each of the building models is

described below.

Single zone model

Table 3 presents the retrofits applied to each of the release scenarios for the single zone model.

Almost all of the retrofits were applied to both the outdoor and indoor releases, even though not

all of them are expected to have a beneficial impact. For example, shutting down a system in the

event of an indoor release would be expected to increase rather than to reduce exposure.

Nevertheless, all possible cases were analyzed to explore the impacts of both “good” and 

potentially “bad” actions.

Release Scenario

Retrofit Outdoor Indoor

Enhanced outdoor air filtration X --

Enhanced mixed air filtration X X

System shutdown X X

Purging X X

Envelope tightening X X

Envelope tightening and outdoor air filtration X X

Table 3 Retrofit and release scenarios for single zone model

Enhanced Outdoor Air Filtration: The MERV 6 particulate filter on the outdoor air intake is

replaced with a more efficient filter, specifically a MERV 13 filter. This change is reflected in an

increase in the particle removal efficiency at 1 μm from 16.4 % to 89.6 %. In addition, a gaseous

air cleaner with a removal efficiency of 95 % is located in the outdoor air intake; in the base case

there was no gaseous air cleaning. Note that this retrofit does not account for the existence of any 

bypass around the filter.

Mixed Air Filtration: The MERV 6 particulate filter in the mixed airstream is replaced with a

MERV 13 filter, again with no bypass. In addition, a gaseous air cleaner with a removal

efficiency of 95 % is added to the mixed airstream.

System Shutdown: The outdoor air intake is reduced to zero for 2 h starting 6 s, 30 s, 1 min and 

5 min after the start of the contaminant release. At the end of the 2 h shutdown period, the

system operates at 100 % outdoor air intake.
13

Outdoor Air Purge: The outdoor air intake is increased from the minimum value of 10 % outdoor

air intake to 100 % intake, beginning 30 s prior, 30 s after, 1 min after and 5 min after the start of

the release and continuing for the remainder of the simulation.

Envelope Tightening: The constant envelope infiltration rate is reduced from 0.20 h-1to 0.01 h-1.

Envelope Tightening and Enhanced Filtration: The reduced infiltration rate and the enhanced 

outdoor air filtration are combined.

Two-story office model

Table 4 presents the retrofits applied in the two-story office building simulations.

Release Scenario

Retrofit Outdoor

general

Outdoor

intake

Indoor,

lobby

Indoor,

return

Loading

dock

Enhanced outdoor air filtration X X -- -- --

Mixed air filtration X X X X X

System shutdown X X X X X

Purging X X X X X

Envelope tightening X X X X X

Tightening and enhanced outdoor air filtration X X -- -- --

Tightening, OA filtration and pressurization X X X X X

Tightening and enhanced mixed air filtration X X X X X

Tightening, MA filtration and pressurization X X X X X

Shelter-in-place X X X X X

Shelter-in-place with filtration X X X X X

Recommissioning

100 % recirculation X -- X X X

5 % outdoor air intake X X X X X

5 % undersupply X X X X X

10 % bypass of baseline filter X X X X X

10 % bypass of enhanced mixed air filter X X X X X

Table 4 Retrofit and release scenarios for two-story office building model

Enhanced Outdoor Air Filtration: The MERV 6 particulate filter on the outdoor air intake is

replaced with a MERV 13 filter, and a gas phase air cleaner (removal efficiency of 95 %) is

added to the air intake. This retrofit was not applied to the indoor releases since it would not

impact the resulting exposure.

Mixed Air Filtration: A MERV 13 particle filter replaces the baseline MERV 6 filter in the

mixed airstream. and a 95 % efficient gaseous air cleaner is added to that airstream as well.

System Shutdown: The outdoor air intake is reduced to zero for 2 h starting 6 s, 30 s, 1 min and 

5 min after the start of the exterior contaminant release. However, envelope infiltration still

continues during the shutdown, as determined by the outdoor weather conditions. At the end of

the 2 h shutdown period, the system operates at 100 % outdoor air intake.

Outdoor Air Purge: The outdoor air intake is increased from the minimum value to 100 %

outdoor air intake, beginning 30 s prior, 30 s after, 1 min after and 5 min after the start of the

release and continuing for the remainder of the simulation.
14

Envelope Tightening: The exterior wall leakage is reduced from 5 cm

2

/m

2 (0.07 in2

/ft

2

) to

0.7 cm

2

/m

2 (0.01 in2

/ft

2

).

Envelope Tightening and Enhanced Outdoor Air Filtration: The improved envelope airtightness

and the enhanced outdoor air filtration are combined. Applies only to the general outdoor release

and the release at the intake, since the results for the indoor releases are no different from the

envelope tightening retrofit alone.

Envelope Tightening, Enhanced Outdoor Air Filtration and Building Pressurization: The

increased envelope airtightness and the enhanced outdoor air filtration are combined with a

doubling of the outdoor air intake fraction to 20 % in order to pressurize the building and reduce

infiltration of outdoor releases.

Envelope Tightening and Enhanced Mixed Air Filtration: The improved envelope airtightness

and the enhanced mixed air filtration are combined.

Envelope Tightening, Enhanced Mixed Air Filtration and Building Pressurization: The increased 

envelope airtightness and the enhanced mixed air filtration are combined with a doubling of the

outdoor air intake fraction to 20 %.

Shelter-in-place: Occupants are moved to a shelter-in-place zone in the second floor conference

room. Four different cases are included corresponding to different times at which the occupants

move to the shelter: 30 s before the release, and 30 s, 1 min and 5 min after the release starts.

During the sheltering period, the shelter-in-place zones are "sealed" by reducing plenum and 

door leakage, and all ventilation systems are turned off. Two hours after the start of the release,

all occupants are moved out of the building, i.e., they are no longer exposed to the contaminants,

and the systems are run at 100 % outdoor air.

Shelter-in-place with Air Cleaning: This is the same as the shelter-in-place case with the addition 

of an air cleaner to each shelter zone. The air cleaners recirculate air within the room and have an 

airflow rate of roughly 5 L/s•m

2 (1 cfm/ft2

) of floor area with MERV 15 particle filters (99.75 %

removal efficiency for 1 μm particles) and a removal efficiency of 95 % for the gaseous agent.

Recommissioning: Five cases represent a system that isn’t operating properly in order to estimate

the potential benefit from a recommissioning effort. These cases include the following: 100 %

recirculation (no outdoor air intake); reduction of the outdoor air intake to 5 % from the baseline

value of 10 %; an unbalanced system with 5 % more return air from the space than supply air to

the space; 10 % of the supply air bypassing the baseline mixed air filters; and 10 % of the supply 

air bypassing the enhanced mixed air filters.
15

High-rise model

Table 5 presents the retrofits applied to each the five release scenarios for the high-rise model.

As this is a relatively complex model, not all retrofits were applied to all the releases.

Release Scenario

Retrofit Outdoor

general

Outdoor

intake

Indoor,

Lobby

Indoor,

return

Mail

room

Enhanced outdoor air filtration X X -- -- --

Mixed air filtration X X X X X

System shutdown X X -- -- --

Purging X -- X X

Envelope tightening X X -- X --

Envelope tightening and OA filtration X X -- -- --

Tightening, filtration and pressurization X -- -- -- --

Shelter-in-place X -- -- -- --

Shelter-in-place with filtration X -- -- -- --

Lobby partitions -- -- X -- --

Lobby partitions and HVAC isolation -- -- X -- --

Mail room under-supply -- -- -- -- X

Mail room undersupply & return air 

filtration -- -- -- -- X

Table 5 Retrofit and release scenarios for high-rise office building model

Enhanced Outdoor Air Filtration: As in the single zone and two-story models, the MERV 6

particulate filters on the outdoor air intakes of all three air handling systems are replaced with 

MERV 13 filters. Gaseous air cleaners having removal efficiencies of 95 % are also installed in

the intake. Again, this retrofit was not applied to the indoor release cases.

Mixed Air Filtration: A MERV 13 particle filter replaces the MERV 6 baseline filter in the

mixed airstream, and a 95 % efficient gaseous air cleaner is added to that airstream as well

System Shutdown: Four different shutdown scenarios are considered. All systems are turned off

starting 6 s, 30 s, 1 min and 5 min after the start of the exterior contaminant release. Two hours

after the release begins, the systems are turned back on and operated at 100 % outdoor air intake

for the remainder of the simulation. The occupants are assumed to remain in the building

throughout the changes in system operation. Note that envelope infiltration continues during the

shutdown, as driven by the outdoor weather conditions.

Outdoor Air Purge: The outdoor air intake of all three systems is increased from the minimum

value to 100 % outdoor air intake, beginning one minute after the start of the release and 

continuing for the remainder of the simulation.

Envelope Tightening: The exterior wall leakage is reduced from 8.7 cm2/m2 (0.13 in2/ft

2

) to 

0.7 cm

2

/m

2 (0.01 in2

/ft

2

).

Envelope Tightening and Enhanced Outdoor Air Filtration: The improved envelope airtightness

and the enhanced outdoor air filtration are combined. This retrofit is applied only to the general

outdoor release and the release at the intake, since the results for the three indoor releases are no 

different from the envelope tightening retrofit alone.
16

Envelope Tightening, Enhanced Outdoor Air Filtration and Building Pressurization: The

increased envelope airtightness and the enhanced outdoor air filtration are combined with an 

increase in the outdoor airflow rate.

Shelter-in-place: Occupants are moved to shelter-in-place zones on their respective floors of the

building. Four different cases are included corresponding to different times at which the

occupants move to the shelter: 30 s before the release, and 30 s, 1 min and 5 min after the release

starts. During the sheltering period, the shelter-in-place zones are "sealed" by reducing plenum

and door leakage, and all ventilation systems are turned off. Two hours after the start of the

release, all occupants are moved out of the building, i.e., they are no longer exposed to the

contaminants, and the systems are run at 100 % outdoor air.

Shelter-in-place with Air Cleaning: This is the same as the shelter-in-place case with the addition 

of an air cleaner to each shelter zone. The air cleaners recirculate air within the room and have an 

airflow rate of roughly 5 L/s•m2 (1 cfm/ft

2

) of floor area with MERV 15 particle filters (99.75 %

removal efficiency for 1 μm particles) and a removal efficiency of 95 % for gas G.

Lobby Partitions: The lobby is partitioned off from the rest of the first floor with walls having

the same leakage rate as the rest of the interior walls and two doors. The lobby is still served by 

the same ventilation system that serves the rest of the first floor.

Lobby Partitions and HVAC Isolation: In addition to a separate lobby, this retrofit includes an air

handling system dedicated to the lobby. The lobby system has approximately 10 % more return

airflow than supply in an attempt to depressurize this zone relative to the rest of the building.

Mailroom Under-supply: Adjust the mail room return airflow to be 10 % greater than the supply,

in an attempt to depressurize this zone relative to the adjacent zones.

Mailroom Under-supply and Enhanced Return Air Filtration: In addition to the under-supply,

filter the mail room return air with a MERV 15 particle filter and a 95 % gas filter.

2.1.4 Simulations and Analysis

Simulations were performed for the building models and retrofits described above. These

simulations were run for 12 h with a 5 s time step. For the two-story and high-rise buildings,

cases were run with no wind speed or indoor-outdoor temperature difference, i.e., no weatherinduced envelope infiltration. To study infiltration effects, additional cases were run with a wind 

speed of 5 m/s (11 mi/h) and an indoor-outdoor temperature difference of 20 °C (36 °F).

The simulations yield contaminant concentrations as a function of time in each building zone,

which were subsequently used to determine occupant exposures. The exposure of an individual

building occupant is the average contaminant concentration to which they are exposed over the

simulation period in units of mg-min/m3 for the gaseous contaminant G and number-min/m3 for

the particulate contaminant P. In the shelter-in-place cases, the exposure is based on the

occupants’ initial location in the building and then their exposure after moving to the shelter.

They are assumed to leave the building 2 h after the release, at which point there is no additional

contribution to their exposure. The two-story office building is assumed to have 130 occupants,

evenly split between the two floors. The high-rise office building has a total of 285 occupants

distributed among the various floors.

The average exposure for all occupants of the building is then determined from the individual

occupant exposures. These exposures are calculated over 6 h, starting 1 h before the release and 

continuing 5 h after. For each retrofit simulation, the average building exposure is compared with

the baseline exposure to determine the exposure as a percentage of the baseline exposure.
17

2.2 Results of Simulations

The simulation results for each of the building models are presented in this section in terms of

the exposure reduction for each retrofit case relative to the baseline exposure without any of the

retrofits included. In addition, representative plots of concentration versus time are included for

selected cases to help explain the impacts of the retrofits.

2.2.1 Single zone model

Figure 1 is a plot of the calculated concentrations for the single zone baseline and retrofit cases

subject to the outdoor particle release. As described earlier, this release corresponds to an

increase in the outdoor concentration from (0 to 109) particles/m3 occurring at t = 1 h and lasting 

for 1 min. Therefore, all the concentrations are zero for the first hour. The baseline case is the

solid line with a peak concentration of 2x104 particles/m3. The other lines show the impacts of

selected retrofits, with the combination of enhanced outdoor air filtration and envelope

tightening resulting in the lowest peak concentration. Envelope tightening alone has a less

significant impact due to the low baseline infiltration rate relative to the outdoor air intake rate

and the low baseline filter efficiency. Less contaminant enters the building at the lower

infiltration rate, so the initial concentration is slightly lower than the baseline case. However, the

lower air change rate causes the contaminant to remain in the building for a longer time,

resulting in similar concentrations to the baseline case after about 45 min. The enhanced outdoor

air filter significantly reduces contaminant entry and therefore concentration, while the enhanced 

mixed air filter reduces concentration even further due to the continued filtration of the

recirculation airstream.

The four shutdown cases show the importance of timing, with timely implementation of the

shutdown having a much more significant impact than a delayed shutdown. (Note that the

shutdown cases all exhibit a discontinuity at a time of 3:00 when the system resumes operation at

100 % outdoor air intake.) The 6 s and 30 s shutdowns reduce contaminant entry and the initial

concentrations, but the lower ventilation rate during the shutdown leads to higher contaminant

concentrations than the baseline case later on during the shutdown. The two late shutdown cases,

1 min and 5 min, result in significantly higher concentrations than the baseline case because the

ventilation rate is reduced after the agent has entered the building. The purge retrofit doesn’t

reduce the initial concentration, but the increased ventilation rate the contaminant at a relatively

high rate. The timing of the purge cycle also impacts the concentrations, but only the 1 min

purge results are displayed in this figure; the other results are presented below in Table 6.

Analogous transient concentration data exist for the gaseous contaminant G and for the indoor

release scenarios, and these results are also summarized in Table 6.

The single zone exposure reductions, relative to the baseline case, for the indoor and outdoor

particle releases are presented in Table 6 and plotted in Figures 2 and 3. The exposures are

presented as a percentage of the baseline exposure; therefore, a retrofit that does not change the

exposure corresponds to a value of 100 %. Lower percentages correspond to a reduction in 

exposure. As noted in the discussion of Figure 1, the combination of outdoor air filtration and 

decreased infiltration results in the lowest initial concentrations for the outdoor release, but the

mixed-air filtration retrofit results in the lowest exposure. Envelope tightening alone increases

exposure to the indoor release due to the lower dilution rate, but has only a small impact on 

exposure to the outdoor release. Retrofits that are particularly effective, i.e., decreasing exposure

to about one-third or less of the baseline, include outdoor air filtration (for the outdoor release),

mixed air filtration, envelope tightening with outdoor air filtration (outdoor release), outdoor air

purge for an indoor release, and purging after the release is complete.
18

The 6 s shutdown reduces exposure to the outdoor releases by about one third, but the later

shutdowns actually increase exposure to the outdoor release. These results indicate that unless a

shutdown can be implemented very early in response to an outdoor release, it may be better to

leave the system running. All the shutdowns increase the exposure to an indoor release, as would 

be expected, pointing out the importance of reacting to an event based on good awareness of the

circumstances. The change in exposure for the purge cycle given an indoor source is not strongly

dependent on timing, but it is for an outdoor release. Of course, purging is not a reasonable

response to an outdoor release, but it could conceivably happen given poor awareness. After an

outdoor release is over, however, purging is an effective means of removing the contaminant that

did enter the building. Figures 2 and 3 display the relative exposures for the gaseous and 

particulate contaminants respectively. The results are similar in the two figures, with the only

differences resulting from the lack of a gaseous air cleaner in the baseline case and differences in 

the removal efficiencies for the particulate and gaseous filter retrofits.

Figure 1 Single-zone simulation results for an outdoor particulate release
19

Exposure Relative to Baseline (%)

Gas G Particle P

Case

Indoor 

source

Outdoor 

source

Indoor 

source

Outdoor 

source

OA filtration 100.0 18.4 100.0 26.8

Mixed air filtration 19.7 3.6 35.2 9.4

Shutdown (6 s) 220.7 68.1 171.9 58.8

Shutdown (30 s) 220.6 135.5 171.5 108.3

Shutdown (1 min) 219.7 219.6 170.0 170.0

Shutdown (5 min) 208.7 208.8 158.7 158.8

Purge (30 sec prior) 22.6 100.1 33.2 144.0

Purge (30 sec after) 22.8 62.6 33.6 90.6

Purge (1 min after) 23.6 23.6 34.7 34.6

Purge (5 min after) 30.5 30.5 44.5 44.5

Envelope tightening 115.3 99.9 108.5 91.7

Envelope + OA Filtration 115.3 5.8 108.5 12.1

Table 6 Single zone retrofit effectiveness values

Figure 2 Single-zone exposure results for gaseous contaminant G
20

Figure 3 Single-zone exposure results for particulate contaminant P

In order to determine the importance of the input parameters in the single-zone simulations, a

simple sensitivity analysis was performed in which the baseline and retrofit simulations were

repeated with selected inputs varied (decreased) by 10 %. The results of that analysis are

presented in Table 7, with the impacts on the baseline case exposures in the upper portion of the

table and the impacts on the retrofits in the lower portion. In the latter cases, the parameters

associated with the retrofit (e.g. filter efficiency) were decreased by 10 % and the value in the

table is the change in exposure relative to the retrofit case. Most cases show either essentially no 

impact of the variation or an approximately linear (i.e., about 10 %) impact. For example,

varying the zone volume has no impact since it increases both the contaminant concentrations

and the air change rate, resulting in no change in exposure. Larger differences are seen for the

filter efficiency retrofits, for example a 44 % increase in exposure for the gaseous contaminant

and a 33 % increase for the particulate contaminant for an outdoor release in the case of the

outdoor air filter retrofit. This “amplified” sensitivity occurs because the exposure is impacted by 

1 minus the removal efficiency, and therefore a 10 % change in the efficiency is a larger change

in one minus the efficiency.
21

Exposure Relative to Case without Input Varied (%)

Gas G Particle P

Parameter varied

Indoor 

release

Outdoor

release

Indoor 

release

Outdoor

release

Baseline

Zone volume 0 0 0 0

OA intake rate 9 0 5 -3

Infiltration rate 1 0 1 -1

Filter efficiency -- -- 4 6

Release amount -10 -10 -10 -10

Release duration -10 -10 -10 -10

Retrofits

Outdoor air filter efficiency -- 44 -- 33

Mixed air filter efficiency 30 57 9 45

Reduced infiltration rate 0 0 0 0

Table 7 Single zone sensitivity analysis results
22

2.2.2 Two-story office building

Figure 4 is a plot of the calculated concentrations for the two-story office building subject to the

outdoor particle release with no weather effects (i.e., zero wind speed and no indoor-outdoor

temperature difference). As described earlier, the outdoor release corresponds to a 60 s increase

in the outdoor concentration from (0 to 109) particles/m3 at t = 1 h. The concentrations for the

baseline case are shown by the solid black line with a peak concentration just below

7.5x106 particles/m3, which begins to decay immediately after reaching that peak. The

concentrations for the envelope tightening case are identical to the baseline case because there is

no infiltration under no-weather conditions. The lack of weather-induced pressures in 

combination with the building being positively pressurized (i.e., supply airflow greater than 

return plus exhaust) leads to no infiltration through the envelope. The other lines in the plot show

the impacts of selected retrofits, with the mixed air filtration retrofit (open black triangles)

resulting in the lowest concentrations. Combining envelope tightening with outdoor air or mixed

air filtration yields identical results to enhanced filtration alone, again because there is no 

envelope infiltration. Therefore these two cases are not shown in the figure. Tightening the

envelope and increasing the outdoor air intake to induce pressurization increases the

concentration for both filtration cases, because the additional outdoor air brings more

contaminant into the building. Given that the building is already pressurized and there is no

infiltration, there is no reduction in contaminant entry due to reduced envelope leakage.

The four shutdown cases show the importance of timing such actions. (Note that the shutdown 

cases in Figure 4 all exhibit a discontinuity at a time of 3:00 when the system resumes operation 

at 100 % outdoor air.) The contaminant concentration is constant during the shutdown period

because there is no air change under no-weather conditions. The 6-s shutdown significantly

reduces contaminant entry, and once the purge begins the contaminant is quickly removed from

the building. The 30 s shutdown also reduces contaminant entry and the initial concentration

relative to the baseline case, but the contaminant concentrations are higher than the baseline later

during the shutdown. The two late shutdown cases, 1 min and 5 min, result in significantly 

higher concentrations than the baseline because the shutdown retains the contaminant in the

building. Only the results for the purge case starting 1 min after the release are shown, and these

exhibit a quick reduction in the contaminant concentration as expected. Analogous concentration

data exist for the gaseous contaminant G, and for the indoor releases.

Figure 5 is a plot of the two-story office building concentrations subject to the outdoor particle

release with weather effects included, i.e., a nonzero infiltration rate. The concentration for the

baseline case is the solid black line that peaks around 1.25x107 particles /m3. Note first that this

peak is higher than in the no weather case because more contaminant enters the building due to

infiltration. The building air change rate for the no weather case is 0.38 h-1, while it is 0.60 h-1

with weather-induced infiltration. The roughly 60 % increase in air change rate is close to the

increase in the peak concentration. Upgrading the outdoor air filtration efficiency from MERV 6

to MERV 13 reduces the concentrations by about one half relative to the baseline case, while

upgrading the filtration in the mixed airstream reduces the concentration even further. Tightening

the envelope, which reduces the building air change rate from 0.60 h-1 to 0.39 h-1, decreases the

concentrations somewhat but not as much as filtration. The combination of enhanced outdoor air

filtration and envelope tightening (solid red line) significantly reduces the concentration, while

locating the filter in the mixed air (solid blue line) reduces them even more. While not shown in 

the figure, increasing the outdoor air intake in an attempt to induce pressurization increases the

concentration relative to the other outdoor air filtration cases, because the additional outdoor air

brings more contaminant into the building. The four shutdown cases once again show the
23

importance of the timing of the shutdown. However, the existence of significant envelope

infiltration reduces the effectiveness of shutdown strategies relative to that seen in Figure 4 with 

no weather because contaminant continues to enter the building during the shutdown. Again,

only the purge case starting 1 min after the release is shown, which exhibit a quick reduction in

the contaminant concentration after the release. Analogous transient concentration data exist for

the gaseous contaminant G and for the indoor release scenarios.

Figure 4 Two-story simulation results for an outdoor particle release (no weather)

Tables 8 through 11 present the exposure reductions for all the retrofit cases for the two-story 

building, with the first two covering contaminant P (particle) and the second two covering G

(gas). Each value in the table is the change in occupant exposure over 6 h relative to the baseline

case. Therefore, a value below 100 % corresponds to an exposure reduction, which a value

greater than 100 % means the retrofit actually increases exposure. Table 8 contains the relative

exposure for contaminant P with no weather effects, i.e., no envelope infiltration. There are no 

entries in the loading dock column (with one exception noted below) because with the outdoor

air intake rate exceeding the exhaust airflow rate and no weather to drive air into the building, no

contaminant enters at the loading dock door. Upgrading the outdoor air filtration from MERV 6 

to MERV 13 reduces occupant exposure by almost 90 % for the outdoor releases. The results for

the general and intake releases are identical since there is no envelope infiltration. This filter

upgrade has no impact on exposure to the two indoor sources, and therefore these cases were not

run. Using a MERV 13 filter in the recirculation airstream is more effective in reducing 

exposure, with the retrofit exposure less than 5 % of the baseline. The mixed air filter has a

larger impact than the intake filter on the outdoor sources because now the recirculation air is
24

filtered on each pass through the air handler. The upgraded mixed air filter also results in similar

exposure reductions for the indoor sources.

Envelope tightening has almost no impact on exposure for any of the sources given the lack of

any weather-induced driving pressures. Combining enhanced outdoor air filtration with envelope

tightening is therefore identical to the filtration retrofit alone, as is the case for enhanced mixed 

air filtration plus tightening with only a minor exception for the lobby release. As noted in the

discussion of Figure 4, supplementing these retrofits with increased outdoor air intake in an

attempt to pressurize the building increases exposure to outdoor sources. However, combining

outdoor filter enhancement and pressurization reduces exposure to the indoor sources by roughly

one third due to the increased air change rate. Adding pressurization to the mixed air and 

envelope retrofit roughly doubles the exposure relative to these combined retrofits with no

pressurization for the outdoor sources, but has little effect for the indoor sources.

Figure 5 Two-story simulation results for an outdoor particle release (with weather effects)

The five “recommissioning” cases appear in Table 8 after the various “envelope” retrofits. The

100 % recirculation case has roughly 20 % higher exposures for the two indoor releases due to 

the lower total air change rate. There is a roughly one-third reduction for the outdoor general

case because the reduced contaminant entry has a larger impact than the lower dilution rate. The

situation is similar for the 5 % outdoor air intake case for both the general outdoor release and 

the intake release, i.e., less entry is more significant than less dilution leading to a decrease in 

exposure. The indoor sources have somewhat higher exposures due to the decrease in the

building air change rate. When there is 5 % less supply than return, the infiltration rate increases

from 0.0 h-1 to 0.40 h-1, and the total air change rate roughly doubles. In this case, the outdoor

general exposure increases because of the increased contaminant entry, but the exposure
25

decreases for the intake and two indoor source cases due to the higher dilution rate. Because the

building is now depressurized, contaminant enters at the loading dock, which results in nonzero

exposure even with no weather. In this case, the 9.1 % exposure metric is relative to the baseline

intake source case since there is no baseline loading exposure for comparison. Assuming 10 %

bypass around the baseline filter increases exposure by about 10 % in all cases. If the same

bypass fraction is assumed for the mixed air filtration retrofit, the exposure relative to the

baseline is still low, but the exposure relative to the mixed air retrofit itself roughly doubles.

Exposure Relative to Baseline (%)

Retrofit Outdoor,

General

Outdoor

Air Intake

Indoor,

Lobby

Indoor,

return vent

Loading

Dock

Outdoor air (OA) filtration 12.4 12.4

Mixed air (MA) filtration 3.3 3.3 4.2 3.3

Envelope tightening 100.0 100.0 98.3 100.0

Envelope, OA filtration 12.4 12.4

Envelope, OA filter, pressure 19.7 19.7 63.4 73.1

Envelope, MA filtration 3.3 3.3 3.8 3.3

Envelope, MA filter, pressure 7.1 7.1 3.3 3.3

100 % recirculation 65.7 120.9 115.5

5 % OA intake 85.8 53.2 108.8 106.4

5 % Undersupply 151.0 76.6 69.9 66.1 9.1*

10 % baseline filter bypass 108.5 108.5 108.3 108.5

10 % MA filter bypass 6.8 6.8 7.6 6.8

6 s Shutdown 31.7 31.7 0.9 30.7

30 s Shutdown 155.0 155.0 1.2 154.1

1 min Shutdown 303.0 303.0 2.9 302.1

5 min Shutdown 236.2 236.2 46.5 236.2

Purge – 30 s prior 262.8 262.8 0.9 0.0

Purge – 30 s after 146.0 146.0 0.9 11.8

Purge – 1 min after 24.3 24.3 1.0 24.3

Purge – 5 min after 27.3 27.3 4.8 27.3

SIP – 30 s prior 0.1 0.0 0.0 0.0

SIP - 30 s after 137.6 137.5 1.2 136.7

SIP - 1 min after 269.5 269.5 4.3 268.7

SIP - 5 min after 215.2 215.2 49.8 215.3

SIP AC – 30 s prior 0.0 0.0 0.0 0.0

SIPAC - 30 s after 12.2 12.2 0.3 12.1

SIP AC - 1 min after 24.9 24.9 0.6 24.9

SIP AC - 5 min after 28.4 28.4 5.9 28.4

* Exposure relative to the baseline outdoor air intake case.

Table 8 Two-story retrofit effectiveness values (Contaminant P, no weather)
26

As noted in the discussion of Figure 4, the earlier shutdowns are more effective than those that

are delayed. In fact, only the 6 s shutdown reduces the exposure below the baseline case for all

but the lobby source. The later shutdowns for the other sources actually increase the relative

exposure, with the 1 min shutdown exposure being three times the baseline value. In this

particular case, the system shuts down after the contaminant has entered the building and the

dilution rate reduces to essentially zero. The 5 min shutdown is also not very timely, but there

are 4 min of ventilation and filtration after the release ends and before the shutdown begins. The

indoor lobby releases have much lower exposure because there are no occupants in the lobby 

when the release occurs, and the contaminant is not as effectively transported to the rest of the

building from the lobby as it is from the return.

The impacts of the purge cycle are also a strong function of timing. Early purges are more

effective for the indoor releases. However, as expected, purging is not effective for the outdoor

releases when done before or during the release, as such timing brings more contaminant into the

building. Later purging does help clear the outdoor contaminant from the building and reduces

exposure by about 75 %. Again, less contaminant spreads from the lobby to the rest of the

building when the purge cycle begins, and therefore the purge is more effective in removing the

contaminant for this case. Note that purging reduces exposure more than system shutdown for

the interior releases.

The shelter-in-place cases, like the shutdown and purge cases, show the importance of timing.

For all sources, moving the occupants to the shelter 30 s before the release occurs eliminates

essentially all exposure due to the lack of weather-driven air movement in the building.

Instigating the shelter strategy halfway through the release increases exposure by about 40 %,

with the exception of the lobby source, because of the contaminant that enters the shelter space

and then remains there during the low air change sheltering conditions. In the lobby case, the

source is not transported effectively to the shelter, and therefore the exposure decreases for that

case. The 1 min and 5 min cases also increase exposures for other than the lobby source.

However, adding a recirculating air cleaner to the shelter reduces exposure significantly in all

cases, with later initiation of sheltering, resulting in greater exposure.

Table 9 contains the exposure relative to baseline for contaminant P with weather included, i.e. a

wind speed of 5 m/s and an indoor-outdoor temperature difference of 20 °C. The existence of

weather-driven pressure differences results in an envelope infiltration rate of 0.22 h-1, which 

when added to the outdoor air intake rate of 0.38 h-1 yields a total air change rate of 0.60 h-1.

With the existence of infiltration, contaminant from the loading dock source now enters the

building, and the rightmost column of the table contains results. The existence of infiltration 

results in a difference between the impacts for the outdoor general and outdoor air intake sources

for the outdoor air filtration retrofit. The former case has less of an exposure reduction because

contaminant entering the building via envelope leakage is not filtered, while the reduction for the

intake source is identical to the no-weather case. Adding a MERV 13 filter to the mixed 

airstream is again quite effective in reducing exposure, with similar reduction values as those

seen in the no-weather cases. However the reductions are smaller for the outdoor general release

because of unfiltered contaminant entry due to infiltration. The reduction for the loading dock

release is smaller because of the exposure that occurs before the contaminant gets to the mixed

air filter.
27

Exposure Relative to Baseline (%)

Retrofit Outdoor,

General

Outdoor

Air Intake

Indoor,

Lobby

Indoor,

return vent

Loading

Dock

Outdoor air (OA) filtration 48.6 12.4

Mixed air (MA) filtration 15.4 3.8 4.9 3.8 35.7

Envelope tightening 72.4 121.8 120.3 121.6 4.3

Envelope, OA filtration 9.9 15.1

Envelope, OA filter, pressure 14.1 24.0 78.4 89.3 0.0

Envelope, MA filtration 2.7 4.1 4.7 4.0 1.3

Envelope, MA filter, pressure 5.1 8.7 4.2 4.0 0.0

100 % recirculation 75.8 124.8 118.9 180.6

5 % OA intake 88.3 54.5 112.5 109.2 125.0

5 % Undersupply 118.4 85.4 78.1 73.7 83.0

10 % baseline filter bypass 106.4 107.3 107.2 107.3 104.9

10 % MA filter bypass 18.9 7.8 8.8 7.8 38.3

6 s Shutdown 160.5 21.4 13.0 20.5 391.7

30 s Shutdown 184.5 105.2 14.1 103.6 343.3

1 min Shutdown 211.7 207.0 17.2 204.5 278.2

5 min Shutdown 177.3 171.5 55.3 170.0 220.8

Purge – 30 s prior 190.3 304.0 1.1 0.0 33.4

Purge – 30 s after 111.3 169.1 1.2 13.6 33.4

Purge – 1 min after 28.8 28.2 1.3 28.0 33.5

Purge – 5 min after 33.0 31.7 5.8 31.7 36.7

SIP – 30 s prior 16.5 0.0 24.2 0.0 42.2

SIP - 30 s after 106.1 156.9 26.6 155.8 35.6

SIP - 1 min after 196.5 308.5 33.4 307.3 40.8

SIP - 5 min after 187.5 255.7 97.9 255.4 75.3

SIP AC – 30 s prior 2.7 0.0 4.8 0.0 7.9

SIPAC - 30 s after 11.4 15.6 5.1 15.5 6.8

SIP AC - 1 min after 22.2 32.1 5.9 32.0 12.4

SIP AC - 5 min after 30.8 36.8 13.6 36.7 10.8

Table 9 Two-story retrofit effectiveness values (Contaminant P, with weather)

Envelope tightening now reduces the exposure for the outdoor general source because less

contaminant enters via infiltration. However, for the intake case, the same amount of

contaminant enters the building as in the baseline case, but the dilution rate is lower with the

tighter envelope and the exposure therefore increases. The situation for the two indoor sources is

similar, and the exposure also increases by about 20 %. Because tightening the envelope

increases the level of building pressurization, less contaminant enters at the loading dock door

and there is a large exposure reduction for that case. Combining enhanced outdoor air filtration 

with envelope tightening increases the exposure reduction for the outdoor general source relative

to the no-weather condition due to the reduced contaminant entry. There is less reduction for the
28

intake source because of the lower dilution rate. Increasing the outdoor air intake in an attempt to

pressurize the building increases the relative exposure for both the outdoor general and intake

sources, relative to tightening and filtration alone, because more contaminant enters. Increasing 

outdoor air to pressurize the building eliminates all contaminant entry at the loading dock door,

resulting in zero exposure. Combining envelope tightness with enhanced mixed air filtration

reduces exposure for the outdoor general and loading dock cases relative to enhanced filtration 

alone, and has little impact on the other three cases. The exposure reductions for these combined 

retrofits are much more significant that for envelope tightening alone. Increasing outdoor air

intake for pressurization again increases exposure for the two outdoor sources, relative to 

tightening and enhanced mixed air filtration alone. The combination of these three retrofits has

little impact on the two indoor sources, but the addition of pressurization does eliminate

contaminant entry at the loading dock.

The results for the first two of the five “recommissioning” cases, 100 % recirculation and 5 %

outdoor air intake, are similar to those for the no-weather cases. The 100 % recirculation case has

roughly 20 % higher exposures for the two indoor releases, and there is a roughly 25 % reduction 

for the outdoor general case. The loading dock exposure increases significantly because the

building is at a lower pressure with no outdoor air intake. Under 5 % outdoor air intake for the

general outdoor release and the intake release, the decrease in contaminant entry is more

significant than the decrease in ventilation, leading to a decrease in exposure. The indoor and 

loading dock sources have somewhat higher exposures due to the decrease in the building air

change rate. When there is 5 % less supply than return, the infiltration rate roughly doubles, and 

the total air change rate increases by about one third. In this case, the outdoor general exposure

increases because of the higher entry, but the exposure decreases for the other cases due to the

higher dilution rate. Assuming 10 % bypass around the baseline filter increases exposure by 

somewhat less than 10 % in all cases. If the same bypass fraction is assumed for the mixed air

filtration retrofit, the exposure is still reduced relative to the baseline, but the exposure relative to 

the mixed air retrofit itself increases by as much as 100 %.

The shutdown cases again show the impact of timing. However, the early shutdown does not

reduce exposure for the outdoor general and loading dock sources because contaminant enters

the building at a higher rate after the shutdown starts. The contaminant entry increases with the

system off because the system flows tend to pressurize the building relative to outdoors. The

reductions for the 6 s shutdown are similar for the intake, lobby and return vent sources relative

to the no weather cases. The two later shutdowns have less relative exposure than the no weather

case for all but the lobby source given the higher post-release dilution rates due to the extra

infiltration airflow. Again, the indoor lobby releases have lower relative exposures under

shutdown because there are no occupants in the lobby and the contaminant is not effectively 

transported to the rest of the building.

The two early purge cycles increase exposure for the outdoor sources because more contaminant

enters the building. The exposure reductions for the later purge cycles are similar to those seen in 

the no-weather cases. It is interesting to note that the reductions for the loading dock source are

relatively independent of timing. The exposure changes and timing trends for the shelter-in-place

cases are similar to those seen for the no-weather cases, except that infiltration causes

contaminant to enter the building for the cases where the shelter strategy is implemented before

the contaminant release starts. Therefore, the exposure reduction for the 30 s prior case is no

longer 100 %, except for the outdoor air intake and return vent sources. In the latter case, the

contaminant released into the vent does not migrate to the rest of the building before the purge is

implemented. Adding a recirculating air cleaner to the shelter again reduces exposure
29

significantly in all cases, with later initiation of sheltering resulting in greater exposure, but still

with reductions over 80 % relative to the baseline case.

Exposure Relative to Baseline (%)

Retrofit Outdoor,

General

Outdoor

Air Intake

Indoor,

Lobby

Indoor,

return vent

Loading

Dock

Outdoor air (OA) filtration 5.0 5.0

Mixed air (MA) filtration 5.0 5.0 0.9 0.6

Envelope tightening 100.2 100.2 98.7 100.2

Envelope, OA filtration 5.0 5.0

Envelope, OA filter, pressure 5.7 5.7 46.1 52.5

Envelope, MA filtration 0.6 0.6 0.8 0.6

Envelope, MA filter, pressure 1.2 1.2 0.7 0.6

100 % recirculation 79.0 145.4 139.8

5 % OA intake 93.6 61.7 115.9 113.8

5 % Undersupply 113.1 58.7 54.2 50.6 5.8*

10 % baseline filter bypass

10 % MA filter bypass 1.8 1.8 2.1 1.8

6 s Shutdown 13.9 13.9 0.3 13.4

30 s Shutdown 67.9 67.9 0.5 67.5

1 min Shutdown 132.8 132.8 1.2 132.4

5 min Shutdown 106.4 106.4 20.6 106.4

Purge – 30 s prior 115.1 115.1 0.3 0.0

Purge – 30 s after 64.0 64.0 0.3 5.2

Purge – 1 min after 10.7 10.7 0.4 10.6

Purge – 5 min after 12.2 12.2 2.1 12.2

SIP – 30 s prior 0.0 0.0 0.0 0.0

SIP - 30 s after 60.3 60.2 0.4 59.9

SIP - 1 min after 118.1 118.1 1.6 117.8

SIP - 5 min after 96.9 96.9 21.5 96.9

SIP AC – 30 s prior 0.0 0.0 0.0 0.0

SIPAC - 30 s after 5.6 5.6 0.1 5.5

SIP AC - 1 min after 11.4 11.4 0.2 11.4

SIP AC - 5 min after 13.2 13.2 2.6 13.2

* Exposure relative to the baseline outdoor air intake case.

Table 10 Two-story retrofit effectiveness values (Contaminant G, no weather)

Tables 10 and 11 present the relative exposures for the no-weather and weather cases for the

gaseous contaminant G. These results are very similar to those seen in Tables 8 and 9 for

contaminant P, except as impacted by the different gaseous removal efficiencies for the baseline

and retrofit efficiencies relative to those for the particle filters. For example, the exposure

reductions for the outdoor air and mixed air retrofits are larger for contaminant G because the gas
30

filter has a higher efficiency than the enhanced particle filter and the baseline gaseous removal

efficiency is zero. In general, the relative exposures for contaminant G are lower than for the

particulate agent, but there are a few exceptions such as the 100 % recirculation and 5 % outdoor

air intake “recommissioning” cases, which accentuate the lack of gaseous air cleaning in the

baseline case.

Exposure Relative to Baseline (%)

Retrofit Outdoor,

General

Outdoor

Air Intake

Indoor,

Lobby

Indoor,

return vent

Loading

Dock

Outdoor air (OA) filtration 40.0 5.0

Mixed air (MA) filtration 6.3 0.8 1.2 0.8 18.3

Envelope tightening 91.0 142.8 140.5 142.6 5.0

Envelope, OA filtration 5.6 7.1

Envelope, OA filter, pressure 5.1 8.2 66.5 75.2 0.0

Envelope, MA filtration 0.6 0.8 1.1 0.8 0.7

Envelope, MA filter, pressure 1.1 1.7 1.0 0.8 0.0

100 % recirculation 87.6 159.2 152.8 235.8

5 % OA intake 96.2 65.2 123.3 120.3 135.3

5 % Undersupply 102.9 75.9 69.9 65.5 149.5

10 % baseline filter bypass

10 % MA filter bypass 7.8 2.4 2.9 2.4 19.6

6 s Shutdown 75.3 11.0 5.7 10.5 205.5

30 s Shutdown 90.8 53.6 6.1 53.2 183.1

1 min Shutdown 108.9 105.5 7.6 105.2 148.2

5 min Shutdown 94.0 90.6 26.8 89.9 119.9

Purge – 30 s prior 104.1 156.1 0.5 0.0 17.8

Purge – 30 s after 60.4 86.8 0.5 7.0 17.8

Purge – 1 min after 14.8 14.5 0.6 14.4 17.9

Purge – 5 min after 17.4 16.7 2.9 16.7 19.9

SIP – 30 s prior 7.6 0.0 10.5 0.0 22.5

SIP - 30 s after 57.5 80.6 11.6 80.1 19.0

SIP - 1 min after 107.5 158.5 14.6 158.0 20.2

SIP - 5 min after 104.8 90.6 46.6 135.0 50.8

SIPAC – 30 s prior 1.3 0.0 2.2 0.0 4.4

SIPAC - 30 s after 6.4 8.4 2.3 8.4 3.7

SIPAC - 1 min after 12.5 17.3 2.7 17.2 6.8

SIPAC - 5 min after 17.2 20.0 6.7 20.0 6.4

Table 11 Two-story retrofit effectiveness values (Contaminant G, with weather)
31

Exposure Relative to Baseline (%)

Retrofit Outdoor,

General

Outdoor

Air Intake

Indoor,

Lobby

Indoor,

return vent

Loading

Dock

Outdoor air (OA) filtration 546.5 81.8

Mixed air (MA) filtration 648.9 94.2 96.0 94.1

Envelope tightening 101.0 99.6 99.5 99.5

Envelope, OA filtration 111.2 99.6

Envelope, OA filter, pressure 100.0 100.0 100.5 100.0

Envelope, MA filtration 113.5 99.9 98.7 99.9

Envelope, MA filter, pressure 100.0 100.0 104.7 100.0

100 % recirculation 161.0 N/A 83.9 84.3

5 % OA intake 143.5 83.8 84.0 84.0

5 % Undersupply 109.4 91.1 90.9 91.3 147.9

10 % baseline filter bypass 136.9 80.9 80.4 81.0

10 % MA filter bypass 388.3 93.7 94.2 93.6

6 s Shutdown 706.7 55.2 1214.1 54.7

30 s Shutdown 166.1 55.5 915.1 55.1

1 min Shutdown 97.5 55.9 488.2 55.4

5 min Shutdown 104.7 59.4 96.7 58.9

Purge – 30 s prior 101.1 94.6 106.9 *

Purge – 30 s after 106.3 94.7 106.7 94.5

Purge – 1 min after 165.3 94.7 105.7 94.7

Purge – 5 min after 168.8 95.1 97.8 95.1

SIP – 30 s prior 36859.9 * * *

SIP - 30 s after 107.6 93.3 1841.6 93.3

SIP - 1 min after 101.7 93.6 632.5 93.6

SIP - 5 min after 121.6 97.2 159.7 97.2

SIPAC – 30 s prior 39241.1 * * *

SIPAC - 30 s after 131.1 105.2 2349.2 105.2

SIPAC - 1 min after 124.0 105.3 805.5 105.3

SIPAC - 5 min after 151.1 105.8 187.3 105.8

* The exposure with no weather is zero, and therefore the ratio is infinite.

Table 12 Ratio of exposure with weather to exposure without, contaminant P

The impact of envelope infiltration on contaminant entry and, in some cases, retrofit

effectiveness has been mentioned. Table 12 shows the impact of weather-induced infiltration

more explicitly by comparing the exposure to contaminant P with weather to the exposure

without weather. The entries in this table do not compare the relative exposure to the baseline for

each retrofit, but rather compare the exposures for each case with and without weather. The

outdoor general source shows the greatest impact of weather-induced infiltration with only a few

exceptions. The two filtration retrofits have more than five times greater exposure due to the

unfiltered contaminant entry when infiltration is occurring, while the cases with filter bypass
32

have less dramatic increases in exposure with weather impacts included. The two cases with 

reduced outdoor air entry (100 % recirculation and 5 % outdoor air intake) are also strongly 

impacted by weather-induced contaminant entry. The two early shutdown cases have increased 

exposure for the outdoor general source and the lobby source. In the first case, the increased 

exposure is due to contaminant entry with the infiltration air, even after the shutdown occurs. In 

the lobby case, the weather induces airflow within the building, which moves the contaminant to

the occupied zones more effectively than it does without weather. The 30 s prior SIP cases show

dramatic increases in exposure, due to interzone airflow driven by the weather-induced pressures

in the building. Some cases have reduced exposure with weather versus without, but none of the

reductions are particularly large.

Figures 6a through 6c present the two-story office building particle exposures, relative to the

baseline case, for the with-weather condition. Figure 6a presents these results for the filtration

retrofits for all five source locations. Figure 6b presents the results for the shutdown and purge

retrofits, while Figure 6c presents the SIP results. Examination of these figures leads to some

broad categories of exposure reduction. While the divisions are somewhat arbitrary, the

following categories of exposure level relative to baseline are helpful in considering the results:

25 % or less, about 50 %, about 100 %, and more than a 25 % increase in exposure. The only 

retrofits that consistently fall in the lowest exposure category, roughly 25 % or less of baseline,

are envelope tightening with enhanced outdoor air or mixed air filtration, the fastest

implementation of sheltering without air cleaning, and the two fastest with air cleaning. The only 

exception is for the loading dock source, where early sheltering increases contaminant entry into 

the building. The purging response is fairly consistently in the 25 % or less category for the two

later purge times, except in the case of the lobby source where purging is more effective.

Outdoor sources, both general and air intake, are of particular interest in buildings with good 

perimeter security and those that may not be targets themselves but may be near a target. For the

two outdoor sources, retrofits that reduce exposure to roughly 25 % or less of baseline include

the following: mixed air filtration alone; envelope tightening combined with outdoor or mixed 

air filtration; the two later purging cycles; the earliest implementation of SIP without air

cleaning; and, all but the very slowest implementations with air cleaning. The intake release, but

not the outdoor general release, falls in this lowest relative exposure category for outdoor air

filtration alone and for the earliest shutdown. Outdoor air filtration reduces the relative exposure

by roughly 50 % for the outdoor general release. Most of the other retrofits result in only small,

20 % or less, reductions in the relative exposure for the outdoor releases, while several cases

actually increase exposure, in some cases by a significant amount.

Another distinction worth noting is the consistency in the exposure reductions across sources.

For example, mixed filtration has a fairly consistent reduction for all five sources, as does the

shelter-in-place with air cleaning. Most of the other retrofits are beneficial for some sources, but

not for others.
33

Figure 6a Relative exposure for filtration retrofits with weather, particle releases

Figure 6b Relative exposure for system operation retrofits with weather, particle releases
34

Figure 6c Relative exposure for SIP retrofits with weather, particle releases

The recommissioning cases were run to investigate the importance of system installation,

operation and maintenance on exposure. While only a small number were considered, and only

for specific values of the relevant parameters, they do provide some useful insight. Figure 7

shows the relative exposure for the five recommissioning cases for the particle releases with 

weather effects. For 10 % filter bypass around the baseline filter, there is an increase in exposure

relative to baseline for all releases, but due to the low baseline filter efficiency the increase is

small. However, with the same 10 % bypass around the higher efficiency retrofit filter, the

increases are larger, particularly for the intake, lobby and return vent releases. The last three

recommissioning cases all relate to system airflow controls. If there is no outdoor air intake

(100 % recirculation), the relative exposure increases for the two indoor sources and especially 

for the loading dock release. The outdoor general source is associated with less exposure because

there is no outdoor air intake, which also makes the intake source irrelevant to this case. If the

outdoor air intake is reduced by 50 % of its intended value, the exposure to outdoor sources is

reduced accordingly while the exposure to indoor sources increases given the lower rate of

dilution. Finally, if the building becomes more negative due to an undersupply of 5 % relative to 

the return flow, there is more contaminant entry for the outdoor general source, but all other

exposures are reduced given the higher overall air change rate of the building. The important

point of the recommissioning cases is that filter bypass and poor airflow control can increase

exposure, presumably by much larger amounts than shown in these cases if the problems are

particularly bad. These results demonstrate the importance of operating a system as designed and 

the value of good system maintenance.
35

Figure 7 Relative exposure for recommissioning cases with weather, particle releases
36

2.2.3 High-rise office building

Figure 8 is a plot of the calculated concentrations in the high-rise office building for selected 

cases subject to an outdoor particle release with no weather-induced infiltration. Note that in the

high-rise building, the average exposure includes occupants of the lobby, mail room and other

spaces that can have a large impact on the average depending on the source location and 

contaminant transport dynamics. The baseline results correspond to the solid line that peaks

around 3x104 particles/m3 and decays immediately thereafter. The building air change rate for

the baseline case with no weather, i.e., driven by mechanical intake alone, is 1.12 h-1. For the noweather conditions, the results for the tight envelope case are identical to those for the baseline

case, as indicated in the plot’s legend. Tightening the envelope has no effect on the air change

rate for the no-weather case because the system flows already pressurize the building. Enhancing

the outdoor filtration decreases the concentrations significantly. Those results are also identical

to the results for the case that combined envelope tightening and enhanced outdoor air filtration,

and are barely distinguishable from the case that combines outdoor filtration, tightening and 

pressurization with additional outdoor air intake. Increasing the mixed air filtration efficiency 

decreases the concentration more than the enhanced outdoor air filter. The impact of the

shutdown cases is similar to the impact seen in the other buildings, with timing being critical.

Figure 8 High-rise simulation results for an outdoor particle release (no weather)

Figure 9 shows the same cases as Figure 8, but with weather conditions inducing envelope

infiltration. In this case the building air change rate is 1.35 h-1, an increase of 0.23 h-1relative to

the no-weather case. The peak baseline concentration of just over 3x104particles/m3 is slightly

higher than the no-weather case because the non-zero infiltration results in more contaminant

entry. The peak concentration for the envelope tightening case is just barely lower than that of
37

the baseline case because the decreased contaminant entry tends to balance the decreased 

dilution rate. The four filtration retrofits all decrease the concentrations significantly, with the

mixed air filter resulting in the greatest reduction. The four shutdown cases now show the

concentration decaying during the 2 h shutdown.

Figure 9 High-rise simulation results for an outdoor particle release (with weather)

The high-rise building is more complex than the other two buildings due to its mix of systems,

the non-uniform occupant distribution in the building, and the existence of the lobby and mail

room. These features lead to somewhat unique contaminant transport and exposure patterns. For

example, Figure 10 shows the concentrations in the Lobby and the 1stand 2nd floors for a lobby

release of contaminant P with no weather. The baseline case has no interior partitions between 

the lobby and the rest of the 1stfloor, and the concentration peaks around 2.5x105 particles/m3 as

indicated by the solid black line in the figure. Almost none of the contaminant released in the

lobby is transported to the rest of the building, and therefore no line is seen for the 2nd floor

baseline concentration. Partitions that separate the lobby from the rest of the 1stfloor increase the

lobby concentrations (open blue squares) to a peak concentration of almost 2x106 particles/m3,

and decrease the concentrations on the rest of the 1stfloor (solid blue line) relative to the baseline

case. However, after about 15 min, these concentrations are the same as in the baseline case.

Again the concentrations on the 2nd floor are so low that no line is seen. Finally, when the lobby

is further isolated through the use of a dedicated ventilation system, the lobby concentrations

(open red squares) are slightly higher than in the partitioned case. Now the concentrations on the

rest of the 1stfloor, as well as the 2nd floor, are zero. Therefore, as the cases progress from

baseline to partitioned lobby to HVAC isolation of the lobby, the lobby concentrations and the

exposure for the small number of lobby occupants increases, but the concentrations and 
38

exposures in the rest of the building decrease. The difference between average and local

exposure are highlighted in Table 13, which shows the average exposure for the occupants of the

lobby, the rest of the first floor, the second floor and above, and the entire building for the lobby

release and retrofits. In the baseline case, there is only a single zone on the first floor, i.e., the

lobby is not a separate zone. There is some exposure throughout the building due to contaminant

transport upward from the lobby. Installing partitions increases the exposure of the 3 lobby 

occupants, but reduces it for the rest of the first floor occupants and those in the higher floors.

Finally, isolating the lobby through ventilation reduces the exposure outside the lobby to zero.

Figure 10 Lower levels of high-rise building for lobby release of contaminant P (no weather)

Average exposure (particle•min/m3)

Lobby Rest of 1st

floor

2nd floor &

above

Entire 

building

Number of occupants 3 22 230 285

Baseline 6.38 × 106 * 6.38 × 106 1105 5.60 ×105

Lobby partitions 1.71 × 107 4.52 × 106 758 5.30 × 105

Lobby partitions & HVAC isolation 1.73 × 107 0 0 1.81 × 105

* In the baseline case, the lobby is not a separate zone but is part of the 1stfloor zone.

Table 13 High-rise exposures for lobby source and retrofits (Contaminant P, no weather)
39

Tables 14 through 17 present the relative exposure for all the retrofit cases for the high-rise

office building, with the first two covering P (particle) and the second two covering G (gas).

Each value in the table is the average occupant exposure over 6 h relative to the baseline case

expressed as a percentage. Therefore, a value below 100 % corresponds to a reduction in

exposure. Given the varied occupancy and complex zoning of this building, there is a range of

exposure values among the various occupant locations that is not revealed by the average

exposure as noted in the discussion of Table 13.

Table 14 contains the relative exposure for contaminant P with no weather-induced infiltration.

Enhanced outdoor air filtration decreases exposure to about 12 % of the baseline value, with no

difference between the general outdoor and intake releases. A mixed air filter is more effective.

This retrofit is not particularly effective for the mail room release because the filters are in the

main handlers that don’t serve this space and because the mail room exposures are so high. The

shutdown cases show the impact of timing discussed previously, but even the fastest shutdown 

reduces exposure to the outdoor sources by only about 25 %. Purging reduces exposure by about

70 %, while envelope tightening has little impact on the outdoor sources. Shelter-in-place is

fairly effective, with timelier sheltering being more so. Adding filtration to the shelter greatly 

increases the exposure reduction. The mail room retrofits prevent contaminant from moving to

the rest of the building, but the exposure of the mail room occupants is still high, leading to only

a 15 % reduction in the average exposure.

Exposure Relative to Baseline (%)

Retrofit Outdoor,

General

Outdoor

Air Intakes

Indoor,

Lobby

Indoor,

return vent

Mail

room

Outdoor air filtration 12.4 12.4

Mixed air filtration 4.9 4.9 32.0 4.0 92.1

6 s Shutdown 72.7 72.7

30 s Shutdown 350.8 350.8

1 min Shutdown 677.2 677.2

5 min Shutdown 471.1 471.1

100 % OA purge 36.9 26.0 29.2

Envelope tightening 100.2 100.2 91.1 95.5

Envelope, OA filtration 12.4 12.4

Envelope, OA filter, pressure 13.5

SIP – 30 s prior 5.1

SIP - 30 s after 8.6

SIP - 1 min after 16.7

SIP - 5 min after 41.1

SIPAC – 30 s prior 0.4

SIPAC - 30 s after 0.1

SIPAC - 1 min after 1.7

SIPAC - 5 min after 26.1

Lobby partitions 94.6

Lobby partitions, HVAC isolation 32.4

Depressurize mail room 86.6

Depressurize mail room, filter return 86.6

Table 14 High-rise retrofit effectiveness values (Contaminant P, no weather)
40

Table 15 contains the exposure reductions for contaminant P with weather effects, i.e., a nonzero envelope infiltration rate. The exposure reduction associated with enhanced outdoor air

filtration in the general case is now lower than for the intake release. Most of the other cases are

not impacted very significantly by the inclusion of weather, with some exceptions. The mail

room release with the mixed air filter has a more significant reduction in the exposure, though

the relative exposure is still fairly high. All of the shutdown cases are impacted by infiltration,

with an increase in exposure for the 6 s shutdown with the general release but a larger decrease

for the intake source. All of the other shutdown cases have lower exposures relative to the

baseline than the no-weather cases due to the nonzero dilution rates during the shutdown periods.

Envelope tightening reduces exposure from the outdoor general release due to less contaminant

entry via infiltration, but increases exposure from the other three sources due to the lower

outdoor air dilution rate. The shelter-in-place reductions are also lower, particularly without the

filtration and air cleaning systems.

Exposure Relative to Baseline (%)

Retrofit Outdoor,

General

Outdoor

Air Intakes

Indoor,

Lobby

Indoor,

return vent

Mail

room

Outdoor air filtration 24.5 12.4

Mixed air filtration 9.4 5.2 33.3 4.1 73.3

6 s Shutdown 140.7 41.9

30 s Shutdown 268.2 204.2

1 min Shutdown 418.8 397.8

5 min Shutdown 321.1 302.3

100 % OA purge 38.3 30.4 30.5

Envelope tightening 93.8 108.9 104.3 107.8

Envelope, OA filtration 11.6 13.5

Envelope, OA filter, pressure 12.6

SIP – 30 s prior 34.8

SIP - 30 s after 32.0

SIP - 1 min after 38.6

SIP - 5 min after 63.8

SIPAC – 30 s prior 3.2

SIPAC - 30 s after 3.1

SIPAC - 1 min after 3.9

SIPAC - 5 min after 24.4

Lobby partitions 99.5

Lobby partitions, HVAC isolation 27.4

Depressurize mail room 87.8

Depressurize mail room, filter return 69.6

Table 15 High-rise retrofit effectiveness values (Contaminant P, with weather)
41

Tables 16 and 17 contain the contaminant G results, without and with weather, for the high-rise

building. As was the case in the two-story office building, the results are essentially identical to

the results in Tables 14 and 15 for contaminant P, except as impacted by the different removal

efficiencies for the gas relative to the particle. For example, the outdoor air and recirculation 

retrofits have lower relative exposures for contaminant G because the gas filter has a higher

efficiency than the enhanced particle filter.

Exposure Relative to Baseline (%)

Retrofit Outdoor,

General

Outdoor

Air Intakes

Indoor,

Lobby

Indoor,

return vent

Mail

room

Outdoor air filtration 5.0 5.0

Mixed air filtration 1.2 1.2 16.5 0.8 85.5

6 s Shutdown 47.7 47.7

30 s Shutdown 230.2 230.2

1 min Shutdown 445.0 445.0

5 min Shutdown 324.4 324.4

100 % OA purge 24.2 14.1 15.9

Envelope tightening 100.2 100.2 88.5 92.4

Envelope, OA filtration 5.0 5.0

Envelope, OA filter, pressure 5.0

SIP – 30 s prior 2.8

SIP - 30 s after 5.4

SIP - 1 min after 11.0

SIP - 5 min after 27.7

SIPAC – 30 s prior 0.2

SIPAC - 30 s after 0.1

SIPAC - 1 min after 1.2

SIPAC - 5 min after 14.4

Lobby partitions 95.9

Lobby partitions, HVAC isolation 27.7

Depressurize mail room 80.6

Depressurize mail room, filter return 80.6

Table 16 High-rise retrofit effectiveness values (Contaminant G, no weather)
42

Exposure Relative to Baseline (%)

Retrofit Outdoor,

General

Outdoor

Air Intakes

Indoor,

Lobby

Indoor,

return vent

Mail

room

Outdoor air filtration 17.2 5.0

Mixed air filtration 3.9 1.4 18.7 0.9 58.2

6 s Shutdown 86.0 28.9

30 s Shutdown 176.3 140.6

1 min Shutdown 283.5 274.2

5 min Shutdown 226.3 217.7

100 % OA purge 26.2 17.9 18.0

Envelope tightening 99.7 114.3 113.5 120.1

Envelope, OA filtration 5.0 5.7

Envelope, OA filter, pressure 5.0

SIP – 30 s prior 20.2

SIP - 30 s after 19.4

SIP - 1 min after 24.4

SIP - 5 min after 42.7

SIPAC – 30 s prior 2.0

SIPAC - 30 s after 1.9

SIPAC - 1 min after 2.6

SIPAC - 5 min after 17.0

Lobby partitions 102.2

Lobby partitions, HVAC isolation 34.7

Depressurize mail room 83.6

Depressurize mail room, filter return 55.4

Table 17 High-rise retrofit effectiveness values (Contaminant G, with weather)
43

2.3 Summary of Simulation Results

Multizone airflow and contaminant transport simulations were performed in three buildings to

estimate the impacts of selected retrofits on occupant exposure to generic chembio contaminants.

The general approach of these simulations is to model a generic contaminant release within or

outside a given building and calculate the average occupant exposure to the contaminant, and 

then to repeat the process for the same building and release scenario with one or more retrofits in

place. Therefore, the measure of retrofit performance is based on the change in average occupant

exposure relative to the baseline case. As noted earlier, the assumed contaminant release rates

and the calculated concentrations have no particular significance in relation to any particular

contaminant, and therefore the calculated concentrations cannot be used to estimate any health

impacts. Nevertheless they do provide useful insights into the impact of the retrofits considered 

and the factors (e.g. weather, building features) that determine these impacts.

One key issue to note is that the results presented and the conclusions reached are strongly

dependent on the particular building models, sources, systems and other features of the

simulations. While a large number of cases were examined, it is always true that each building,

system and retrofit application is unique, and the effectiveness in any particular circumstance

needs to be determined based on the associated details. Note also that the changes in exposure

reported here are based on average exposures, and the effectiveness of a particular retrofit can be

locally quite variable in the case of an indoor source. In addition, the modeling approach used in

these analyses does not consider within-room concentration gradients.

The results for all three building models showed that the most significant and consistent

exposure reductions were associated with enhanced filtration, either of the outdoor airstream

alone for exterior releases or the mixed airstream for indoor and outdoor releases. The benefits of

filtration were also evident in the shelter-in-place strategies. The size of the reduction depended 

primarily on the removal efficiencies of the baseline and retrofit filters. Because the amount of

contaminant that passes through the filter, and therefore contributes to exposure, depends on one

minus the removal efficiency, small changes in efficiency can have relatively large impacts on 

exposure. For example, a 1 % absolute reduction in the efficiency of a 90 % efficient filter

(resulting in 89 % removal) increases the associated exposure by 10 %.

While filtration can be quite effective, the impact of filtering the intake air can be degraded by 

the presence of envelope infiltration in the case of a general outdoor release (not localized to the

outdoor air intake). The importance of infiltration has been identified previously as an issue with 

building protection strategies based on outdoor air filtration (Persily 2004). Due to the strong

dependence of infiltration on building envelope airtightness, weather conditions and ventilation

system airflow rates, the extent of such degradation cannot be generalized. Strategies based on 

building pressurization to minimize infiltration will be similarly impacted by envelope leakage.

Effective filtration and pressurization strategies require low envelope leakage values. Envelope

tightening alone is not a particularly effective retrofit, but achieves its value when combined with 

effective air filtration.

The impacts of shutdown strategies are highly dependent on their timing relative to the start of a

release, with higher effectiveness for earlier implementation. This unsurprising result leads to the

question of how a building manager or operator knows when a release is occurring, or has just

occurred, and that a system shutdown may be advised. Given the current state of sensing 

technology and the inherently unpredictable nature of such releases, it is unclear how realistic it

is to rely on a shutdown strategy. And as noted in the simulations, a late shutdown retains the

contaminant in the building and increases exposure. Therefore, the risk of implementing a

system shutdown too late in the event timeline needs to be considered in response planning.
44

The use of 100 % outdoor air purging, while potentially effective in removing a contaminant, is

also a function of the timing of implementation relative to the release. However, purging was

found to be more effective than a system shutdown for most cases simulated. The “ideal”

strategy for many cases might be a shutdown before or during a release followed by a purge once

the release is over. However, implementing such a two-stage approach would again require

knowledge of the timing of the release, which in general is not expected to exist. In contrast, one

reason for the effectiveness of the filtration strategies as modeled is that they are ‘always on’. In

other words, contaminant removal occurs as soon as the source begins, since filtration requires

no human or automated intervention. Some have proposed strategies in which the air cleaning 

capability would be available in an alternate HVAC flow path, which would require, for

example, switching the affected airstream from one duct to another. The effectiveness of such a

system would therefore again rely on the timing of implementation.

The use of shelter-in-place is generally effective in reducing exposure, but far more so when a

recirculating filtration/air cleaning system is employed in the shelter. While early 

implementation of sheltering is more effective than later sheltering, timing appears to be

somewhat less critical than for a shutdown response. Again, these conclusions are true for

average exposures, and there can be localized impacts that result in much higher exposures in 

certain zones of a building. Therefore, quicker sheltering is better, which raises the same

notification questions identified in the discussion of system shutdown. Also, while later

sheltering still might be effective on average, there can be an issue with exposed occupants

bringing contaminant into the shelter on their persons, which is not addressed in this analysis.

Additionally, knowledge of when to leave a shelter would be required as eventually occupants in

a shelter without air cleaning receive the same exposure as unsheltered occupants.
45

3. CASE STUDY

A case study was conducted as part of this project to investigate the application of building 

protection retrofits in two actual buildings. Specifically, the case study involved identifying and 

designing retrofits to these buildings given their particular floor plans and HVAC system

designs. In addition to designing the retrofits, the performance of the retrofits was evaluated 

using the simulation approach employed in the technical evaluation of the retrofits. The case

study also included an economic analysis in which the costs of the retrofit measures were

identified and quantified. The cost data were estimated for illustrative purposes as well as to

provide sample data for the economic evaluation software developed as part of the project. Two

office buildings, with very different floor plans and ventilation system designs, were selected for

the case study. One is a high-rise office building with central air-handling systems, in addition to

other features of interest including intakes near ground level, a loading dock, a mail room, and a

public-access lobby. The other building is a one-story office building with multiple rooftop air

handling units and no spaces other than offices.

The retrofit design and cost estimation were performed by an architectural and engineering

(A&E) firm and were based on a list of candidate retrofits identified by NIST. The A&E firm

then proceeded with the design work, producing detailed designs for implementing the retrofits.

As part of this effort, the A&E firm reviewed the existing mechanical and control systems in the

two buildings, including all original architectural, structural, mechanical, and electrical plans and

any modifications of these plans. The firm also conducted field inspections of the buildings and

systems and then performed the design work and prepared detailed descriptions and drawings of

the proposed retrofits. They prepared cost estimates for the retrofit work including the following:

Retrofit installation costs (including equipment, materials and parts, required demolition,

labor, and performance testing)

Annual filter replacements costs (including material costs and labor, based on an assumed 

frequency of replacement)

Cost of additional electricity associated with filtration options that significantly increase

system pressure drop

These retrofits, and the associated cost estimates, are specific to the buildings examined in terms

of the available options and the details of implementation. While the designs and costs are of

interest to the general question of building protection, they cannot be applied to other buildings.

Determining retrofit options, designs and cost estimates for a specific building always requires

consideration of the unique features of that building.

3.1 Description of Buildings and Retrofits Considered

High-rise Office Building

The high-rise office building is part of a larger complex of buildings built in the early-1960s. In

addition to the office space, the building has an elevator penthouse, basement and sub-basement

with a total floor area of about 12,100 m

2 (130,500 ft2

). The east and west facades of the building 

are faced with grey face brick; insulated porcelain spandrel panels and fixed aluminum frame

windows enclose the north and south facades. There are six field assembled air handlers located 

on the mezzanine level of the building (above the 2nd story). Each unit has a mixing box with 

outdoor air louvers and dampers (including minimum outdoor air dampers) and a return air duct.

These units also have a filter rack, upstream of the coils and accessible from the mixing box,

with 10 cm (4 in) deep pleated filters rated at MERV 6 (ASHRAE 1999). The outside air intake
46

louvers for these air handlers are located about 6 m (20 ft) above ground level. The temperature

controls are pneumatic, and each unit is started and stopped manually or by means of time

clocks. However, the systems operate 24 h every day of the year.

The building has a lobby area with a 4.3 m (14 ft) ceiling and a floor area of about 325 m

2

(3500 ft

2

). The lobby has glass curtain walls on two sides and marble-finished walls on the other

two and is accessed from a glass-enclosed 14 m

2 (150 ft2

) vestibule with a series of two rows of

four balanced glass doors. The lobby is open to the elevator bank serving the building and 

another wing of the complex. The lobby does not have a dedicated air-conditioning system, but

is served by one of the six air handlers located on the mezzanine, which also serves the corridors

adjacent to the lobby.

The building has a mail room in the basement, with a floor area of about 334 m

2 (3600 ft2

). The

mail room has a suspended acoustical ceiling system and is enclosed by concrete masonry unit

(CMU) walls and modular metal partitions. One wall is solid to the ceiling, two walls have doors

to interior corridors, and the fourth wall is an exterior wall with a roll-up door to a loading dock 

area. The mail room does not have a dedicated air handler and is served by a unit in a basement

mechanical room that also serves several adjacent spaces. The basement mechanical room

contains six other air conditioning units serving other basement and first floor spaces and is

fairly crowded with storage tanks, pumps, ductwork and other services. The ceiling plenum

above the mail room is also very congested with ductwork, piping and other services.

One-story Office Building

This building is a contiguous group of large, one-story trailers that have been joined to form a

single building of about 1600 m

2 (17 000 ft2

). The building is about 4.6 m (15 ft) tall with six

exterior doors, sixty-seven fixed double-glazed windows, and a crawl-space containing electrical

and plumbing services. The building is served by twenty-eight rooftop heat pump units that

provide heating, cooling and ventilation. Each unit has a 2.5 cm (1 in) MERV 4 filter and is

controlled by a single thermostat in the occupied space.

Candidate Retrofits

Based on an initial assessment of the buildings, NIST provided the A&E firm with the following

lists of candidate retrofits for consideration in the two buildings.

High-rise building:

Enhanced particle filtration consistent with current air handlers (currently MERV 6)

Enhanced particle filtration with air handler modifications to handle increased pressure drop

Enhanced particle filtration and gaseous air cleaning with air handler modifications

Envelope tightening

Quick shutoff switch

Quick purge switch

Shelter-in-place: tighten shelter spaces, local filtration/air cleaning units

Isolate/depressurize lobby: install partitions, dedicated system to depressurize

Isolate/depressurize mail room: tighten interior partitions, dedicated system to depressurize

Relocate ground level intakes to higher elevation

HVAC system testing, adjusting and balancing
47

1-story building:

Enhanced particle filtration consistent with current air handlers (currently MERV 4)

Enhanced particle filtration with air handler modifications to handle increased pressure drop

Enhanced particle filtration and gaseous air cleaning with air handler modifications

Envelope tightening

Quick shutoff switch

Quick purge switch

Shelter-in-place: tighten shelter spaces, local filtration/air cleaning units

3.2 Retrofit Design

Based on their review of the building design and condition, along with the retrofits identified by 

NIST, the A&E firm designed a number of retrofits for the two buildings. As noted earlier, these

retrofits and the associated cost estimates are specific to the buildings examined in terms of

available options and the details of implementation. Determining options and costs for a specific

building always requires consideration of the unique features of that building. Also note that the

list of retrofits considered is not comprehensive, and none of these options should be interpreted 

as either providing the best protection or the most cost-effective option possible.

A number of options were considered for each building as follows. For the high-rise office

building, the following retrofits were considered and design work performed:

Filter upgrade #1: Replace all the MERV 6 particulate filters with MERV 11 filters. MERV

11 is the highest efficiency that can be installed employing existing filter frames and requiring 

no changes to the existing fans or motors.

Filter upgrade #2: Replace all the MERV 6 particulate filters with a three-stage filtration

system including a 10 cm (4 in) pre-filter (MERV 8), an 85 % intermediate filter (MERV 13)

and a 99.97 % HEPA filter (MERV 17). This option requires the installation of new HEPA

filter frames, as well as replacing the fans and motors of the air handlers to handle the

increased pressure drop and the main circuit breaker to handle the increased electrical load.

Filter upgrade #3: Replace all the MERV 6 particulate filters with a multi-stage filtration 

system including a 10 cm (4 in) pre-filter (MERV 8), an 85 % intermediate filter (MERV 13),

a 99.97 % HEPA filter (MERV 17), an AZDM-TEDA grade carbon gas phase filter, and a

5 cm (2 in) final filter (MERV 11). This option requires the installation of new HEPA filter

frames, as well as replacing the fans and motors of the air handlers to handle the increased 

pressure drop and the main circuit breaker to handle the increased electrical load.

Tighten the exterior envelope of the building: Seal around interior and exterior of windows,

doors and penetrations of the building envelope. (Note that it is not possible to know the

actual before and after airtightness of the building without conducting fan pressurization tests

of building airtightness. There are often significant leaks in commercial building envelopes at

wall-floor and wall-roof interfaces that might not necessarily be addressed by these retrofits.)

Shut-off and purge switches: Install quick shut-off and purge switches in a central location of

the building, i.e., a guard office that is staffed 24 h/d.

Elevate outdoor air intakes: Extend the outdoor air intakes from the mezzanine level to the

roof. (Note that this option would block more than 100 exterior windows of the building

because there is no available internal space through which to run the new ductwork.)

Lobby retrofit with exhaust filtered to level #2: Isolate the lobby from the rest of the building

(other wings and corridors) by providing tempered glass partitions with self-closing glass

doors. Also install a new air handling unit in the basement mechanical room to serve the lobby 
48

only, with level #2 filtration as described above. The design also includes a new exhaust fan,

drawing from the lobby, and filtration level #2 installed in the outgoing airstream to clean the

air before it is exhausted to the outdoors. This exhaust fan is sized to maintain 10 % more

exhaust air from the lobby than supply air under normal operating conditions. This retrofit

requires a number of electrical modifications to accommodate the new fans and motors.

Lobby retrofit with exhaust filtered to level #3: Same as above, except the exhaust air from

the lobby is filtered to level #3.

Mailroom retrofit with exhaust filtered to level #2: Air seal the partitions between the mail

room and all adjacent zones. Upgrade the filtration in the air handler serving the mail room to

filtration level #2, which requires the installation of HEPA filter frames. Add the same level

of filtration to the exhaust airflow out of the mail room to prevent any agent released in the

mail room from impacting the rest of the building. The filtration upgrade requires higher

horsepower motors and electrical modifications for both the supply and exhaust fans. The

system is to be operated with 10 % more exhaust air from the mail room than supply air.

Mailroom retrofit with exhaust filtered to level #3: Same as above, except the exhaust air from

the mail room is filtered to level #3.

Shelter-in-place: Designate a number of shelter-in-place spaces in the building, with air

sealing of the walls of these spaces. plus a stand-alone, recirculating filtration and air cleaning

unit in each such space.

TAB: Test, adjust and balance (TAB) the existing air handling systems to ensure that they are

being operated at the design airflow rates. This retrofit, while not necessarily resulting in a

direct reduction of occupant exposure to agents, allows the system to be relied on for other

protection strategies with a greater degree of confidence. The retrofit may also reduce energy 

consumption and improve indoor air quality. However, the impacts of such a TAB effort will

depend on the as-is condition of the system, specifically the magnitude of the differences

between system design and performance.

For the 1-story office building, the following retrofits were considered and design work

performed:

Filter upgrade #1: Replace all the existing MERV 4 particulate filters with MERV 11 filters,

employing existing filter frames and requiring no changes to fans or motors.

Filter upgrade #2: Given the power and space limitations of the rooftop units, it is not possible

to upgrade the filtration beyond MERV 11. Therefore, to provide a higher level of filtration,

the designer proposed installing two dedicated outdoor air fans on steel platforms on the roof,

which would provide filtered outdoor air to the rooftop units. These outdoor air units have

filtration consistent with option #2 for the high-rise office building, specifically, a three-stage

system including a 10 cm (4 in) pre-filter (MERV 8), an 85 % intermediate filter (MERV 13)

and a 99.97 % HEPA filter (MERV 17). In addition to the platform, fans, and filters, this

option requires electrical system upgrades.

Filter upgrade #3: Same as above, but with filter option #3 in the two outdoor air fans.

Specifically, this option includes the new support platform, new fans, a multi-stage filtration 

system including a 10 cm (4 in) pre-filter, an 85 % intermediate filter (MERV 13), a 99.97 %

HEPA filter (MERV 17), an AZDM-TEDA grade carbon gas phase filter, a 5 cm (2 in) final

filter (MERV 11), and electrical system upgrades.

Tighten the exterior envelope of the building: Patch roof leaks, seal around windows, provide

doors with gasket hardware, replace door thresholds, and seal around pipe and conduit floor
49

penetrations within the building’s crawlspace. (Note that it is not possible to know the actual

airtightness level without a fan pressurization test. As noted for the high-rise building, there

are often other significant leaks in commercial building envelopes that might not be addressed 

by these sealing efforts.)

Shut-off switches: Install quick shut-off switches in the reception area of the building. (The

systems cannot be operated in a purge mode. Therefore, no purge switch option is

considered.)

More detailed descriptions of the buildings and retrofit designs are excerpted from the A&E

report and presented in Appendix B.
50

3.3 Economic Evaluation

The cost data provided by the contractor for each of the retrofits consists of first costs

(equipment and installation), annual costs for maintaining the retrofit, and annual costs of

additional electrical power required for operation. These costs are summarized in Table 18. The

annual maintenance costs consist of the materials and labor associated with filter replacement.

Table 19 expands on the maintenance cost entries in Table 18 by providing cost per change (e.g.,

labor and materials costs) and the assumed number of changes per year for each filter option.

The values in Table 19 are given for each air handling unit, so the total maintenance costs are

those values multiplied by six. In actual application, the filter-changing schedule is a complex 

function of the outdoor and indoor conditions, and may be different from these assumed 

frequencies in a specific building. The annual operating costs are the increase above the base

case electrical consumption.

Costs (thousands of $)

Retrofit

Initial

cost 

Annual

maintenance

cost

Annual

operating cost

increase

High-rise building

Base case 0.0 2.9 0.0

Filtration upgrade #1 71.4 1.2 0.0

Filtration upgrade #2 291.8 21.1 39.0

Filtration upgrade #3 1111.3 153.0 71.3

Envelope tightening 625.3 0.0 0.0*

Shut-off/purge switches 20.9 0.0 0.0

Extend intakes to roof 225.1 0.0 0.0

Lobby partitions 64.1 0.0 0.0

Lobby partitions & dedicated HVAC system 198.9 1.0 1.5

Lobby retrofits, with filtration level #2 215.6 5.5 8.1

Lobby retrofits, with filtration level #3 273.1 5.8 10.5

Mailroom air sealing 29.1 0.5 0.0

Mailroom air sealing, with filtration level #2 101.3 5.2 18.5

Mailroom air sealing, with filtration level #3 194.1 26.4 35.6

Shelter-in-place spaces 75.8 0.0 0.0

System testing, adjusting & balancing 75.0 0.0 0.0*

1-story building

Base case 0.0 3.6 0.0

Filtration upgrade #1 2.1 6.3 0.0

Filtration upgrade #2 251.3 5.6 20.8

Filtration upgrade #3 368.6 22.6 28.9

Envelope tightening 32.4 0.0 0.0*

Shut-off switch 11.8 0.0 0.0

* May reduce building energy consumption and associated operating costs.

Table 18 Summary of Retrofit Cost Estimates
51

Material

Unit 

Cost ($) Units

Material

Cost ($)

Labor

Cost ($)

Total

Cost ($)

Changes/

Year

Annual

Cost ($)

Baseline (“as is”) system

MERV 6 5 20 100 20 120 4 480

Level 1 filtration: Limited particulate filtration and no chemical air cleaning

MERV 11 8 20 160 32 192 1 192

Level 2 filtration: Enhanced particulate filtration and no chemical air cleaning

MERV 8 5 20 100 20 120 1 120

MERV 13 125 20 2500 500 3000 0.33 1000

HEPA 300 20 6000 1200 7200 0.33 2400

TOTAL 3520

Level 3 filtration: More enhanced particulate filtration and chemical air cleaning

MERV 8 5 20 100 20 120 1 120

MERV 13 125 20 2500 500 3000 0.33 1000

HEPA 300 20 6000 1200 7200 0.33 2400

Gas phase air 

cleaning

4500 20 90,000 18,000 108,000 0.2 21600

MERV 11 8 20 160 32 192 2 384

TOTAL 25504

Table 19 Maintenance Costs of Filtration for High-Rise Building 

More detailed breakdowns of the initial costs for the retrofits are presented in Appendix C. In 

addition, life-cycle costs for each retrofit option are included in the presentation of the technical

evaluation of the retrofits in the following section.

3.4 Technical Evaluation

The degree of protection against generic chembio releases provided by the case study retrofits

was investigated through multizone airflow and contaminant transport simulations using the

CONTAM program (Walton and Dols 2005). As in the retrofit evaluations presented in Section

2, CONTAM was used to estimate occupant exposure for generic indoor and outdoor releases of

both a gaseous and particulate agent, referred to as G and P respectively. The exposure was

estimated for the baseline (as is) building and then for the building with the selected retrofits

installed. For the purposes of these estimates, the exposure was calculated for the occupants over

6 h, with the release of both agents occurring at the beginning of the second hour. Note that

potential particle removal processes such as deposition and filtration of infiltrating air by the

building walls were not included in the analysis. While these processes might be expected to 

impact the estimated exposures, they will have a less significant impact on relative exposures

between cases than on the absolute exposure for a single case. The results of these simulations

are presented in Tables 20a through 20c for the high-rise office building in terms of the ratio of

the exposure with the retrofit to the baseline exposure without. Therefore, the values in the table

are dimensionless and the lower the value the greater the reduction in exposure. The exposure

ratios reported are based on calculated average exposures of all occupants in the building. Table

21 presents the average exposure ratios for the one-story office building.
52

Life-cycle costs of the various retrofits are also reported in Tables 20a, 20b, and 20c for the highrise office building and in Table 21 for the one-story office building. Cost data from Tables 18 

and 19 are used to calculate life-cycle costs. The life-cycle cost figures in Tables 20 and 21 are

based on a 20-year study period and a 7 % real discount rate. The discount rate is used to adjust

future costs for filter replacements (i.e., annual maintenance costs) and additional electricity (i.e.,

annual operating cost increases) to a present value amount. All life-cycle cost figures are

expressed in thousands of dollars. It is important to note that the life-cycle cost figures do not

include any potential cost savings, such as reduced energy consumption due to envelope

tightening or increased worker productivity due to improved indoor air quality associated with 

enhanced filtration.

Exposure Relative to

Baseline (%)

Retrofit Agent G

(gas)

Agent P

(particle)

Life-cycle cost 

(thousands of dollars)

Filtration option #1 100 64 122

Filtration option #2 100 15 899

Filtration option #3 13 15 6283

Envelope sealing 100 97 625

Filtration #1 with envelope sealing 100 56 748

Filtration #2 with envelope sealing 100 0 1524

Filtration #3 with envelope sealing 0 0 6908

Table 20a Relative Exposure and Life-Cycle Cost for Selected Retrofits in High-Rise Building 

(outdoor release with weather-induced infiltration)

Table 20a presents relative occupant exposures for a generic outdoor release for the high-rise

office building. This outdoor release was modeled as a step change elevation in outdoor

concentrations of both gaseous agent G (1.0 mg/m3) and particulate agent P (1.0 × 106

particles/m3) lasting for 1 min. The selected retrofits studied for this release included filtration 

option #1 (upgrade of existing system filters from MERV6 to MERV11), filtration option #2 

(three-stage filtration system including 10 cm (4 in) pre-filter (MERV 8), an 85 % intermediate

filter (MERV 13) and a 99.97 % HEPA filter (MERV 17)), filtration option #3 (multi-stage

filtration system including a 10 cm (4 in) pre-filter (MERV 8), an 85 % intermediate filter

(MERV 13), a 99.97 % HEPA filter (MERV 17), an AZDM-TEDA grade carbon gas phase

filter, and a 5 cm (2 in) final filter (MERV 11)), sealing the building envelope, and then each 

filtration upgrade option in combination with envelope sealing. The weather conditions during 

the simulation period were an outdoor air temperature of 0 °C and a wind speed of 5 m/s in order

to induce a reasonable level of envelope infiltration. The building envelope effective leakage

area (at a reference pressure of 4 Pa) was 5 cm

2

/m

2 before (0.07 in2

/ft

2

) and 0.7 cm

2

/m

2

(0.01 in2/ft

2

) after sealing the envelope. The baseline whole building air change rates were

0.23 h-1 due to infiltration and 1.12 h-1 due to outdoor air intake, for a total of 1.35 h-1. The

envelope sealing completely eliminated infiltration under the conditions modeled, leading to a

whole building air change rate of 1.12 h-1.

As seen in Table 20a, the predicted exposure reductions for an outdoor contaminant release vary 

widely from no impact at all (100 % relative exposure) to very nearly a total elimination of
53

exposure (0 % relative exposure). For the gas agent, the retrofit with the largest reduction is

filtration option #3, which includes a gaseous air cleaner in the outdoor air intakes, combined 

with envelope sealing for a predicted reduction in exposure of essentially 100 %. Without sealing 

the envelope, filtration option #3 is predicted to have a smaller impact, with an exposure

reduction of 87 %. The lower reduction without tightening occurs because of outdoor air entry 

via infiltration that is not impacted by the air cleaning system. Envelope sealing alone has no 

impact on exposure to agent G. The other filtration options do not impact agent G because they 

include only particle filtration.

For Agent P, filtration option #2 (and #3 since it provides equivalent particle filtration) combined 

with envelope sealing is predicted to reduce exposure by essentially 100 %. As with Agent G, the

impact of these levels of filtration is lessened if the envelope is not sealed with a predicted 

exposure reduction of 85 %. The lower filtration upgrade (option #1) has predicted exposure

reductions of 36 % and 44 % with and without envelope sealing, respectively. Unlike Agent G,

envelope sealing alone is predicted to have a small impact (3 % reduction) on exposure because

the baseline building includes a particle filter.

Exposure Relative to

Baseline (%)

Retrofit Agent G

(gas)

Agent P

(particle)

Life-cycle cost 

(thousands of dollars)

Lobby Partitions 101 101 64

Lobby Partitions & Isolated HVAC 34 22 225

Lobby Partitions & Isolated HVAC

& Return Filtration Option #2 34 8 367

Lobby Partitions & Isolated HVAC

& Return Filtration Option #3 8 8 455

Table 20b Relative Exposure and Life-Cycle Cost for Selected Retrofits in High-Rise Building 

(lobby release with weather-induced infiltration)

Table 20b presents the relative exposure for a source in the lobby of the high-rise office building.

The contaminant source was modeled as a 1 min contaminant release of 1 kg of gaseous agent G

and 1.0 × 109 particles of agent P. The selected retrofits studied for this release include the

following 

• Install partitions to separate the lobby from the remainder of the first floor (modeled 

leakage of 1 cm

2

/m

2 (0.01 in2

/ft

2

) at 4 Pa for lobby walls and 150 cm

2 (23.2 in2

) for each 

of 2 doors),

• Install the internal partitions and a separate HVAC system with 10 % undersupply to 

depressurize the lobby relative to the rest of the building,

• Install partitions and a separate HVAC system with 10 % undersupply, plus filter the

lobby return air with filtration option #2 (addition of new outdoor air fans with a threestage particulate filtration system),

• Install partitions and a separate HVAC system with 10 % undersupply, plus filter the

lobby return air with filtration option #3 (addition of new outdoor air fans with a fourstage filtration system including a carbon gas phase filter).
54

As seen in Table 20b, the predicted reductions in the average 6 h exposure to a contaminant

release in the lobby vary from a 1 % increase to a 92 % reduction. For Agent G, the retrofit with

the largest reduction is filtration option #3, which includes a gaseous air cleaner in the lobby

return, combined with the lobby partitions and isolated HVAC. As stated earlier, the calculated 

exposure ratios are based on the average exposure of all occupants in the building. Adding lobby

partitions alone results in an increase in average exposure to both agents because it increases

exposure to occupants in the lobby while only reducing exposure in the remainder of the building 

by 10 % or less. Using isolated HVAC in combination with the lobby partitions results in an 

average exposure reduction of 66 % for Agent G with respect to the baseline case. Adding 

filtration option #2 does not impact agent G because it includes only particle filtration. HVAC

isolation combined with the lobby partitions results in a 78 % reduction in average exposure to 

Agent P. Adding the HEPA filtration (i.e., return filtration options #2 and #3) to the other lobby

modifications further improves the effectiveness for an exposure reduction of 92 %.

Table 20c presents relative occupant exposures for a source in the mail room of the high-rise

office building. The contaminant source was modeled as a 1 min contaminant release of 1 kg of

gaseous agent G and 1.0 × 109 particles of agent P. The selected retrofits studied for this release

included the following:

• Seal the mail room (reduce wall, interior doors, exterior doors and ceiling leakage to

1 cm

2

/m

2 (0.01 in2

/ft

2

) at 4 Pa, 10 cm

2 (1.6 in2

) each, 5 cm

2 (0.8 in2

) each and 2.5 cm

2

/m

2

(0.04 in

2

/ft

2

) respectively) and modify the HVAC system to depressurize the mail room

with 10 % undersupply,

• Seal the mail room as above, modify the HVAC system with 10 % undersupply, and filter

the basement recirculation air with filtration option #2 (addition of new outdoor air fans

with a three-stage particulate filtration system),

• Seal the mail room, modify the HVAC system, and filter the basement recirculation air

with filtration option #3 (addition of new outdoor air fans with a four-stage filtration 

system including a grade carbon gas phase filter).

Exposure Relative to

Baseline (%)

Retrofit Agent G

(gas)

Agent P

(particle)

Life-cycle cost 

(thousands of dollars)

Seal Mail Room & HVAC 

undersupply

78 78 34

Seal Mail Room & HVAC 

undersupply & filtration option #2 in

basement recirculation

78 78 362

Seal Mail Room & HVAC 

undersupply & filtration option #3 in

basement recirculation

78 78 895

Table 20c Relative Exposure and Life-Cycle Cost for Selected Retrofits in High-Rise Building 

(mail room release with weather-induced infiltration)

As seen in Table 20c, the predicted exposure reductions for the mail room contaminant release

are 22 % for both agents and all retrofits. However, as with the lobby case, the exposure is the

average for the mail room occupants and the occupants of the rest of the building. The retrofits
55

increase exposure of the mail room occupants but reduce the exposure of the occupants in the

remainder of the building by 100 %. As in the case of the lobby retrofits, sealing the mail room

and reducing the supply airflow tends to keep the agent from migrating to the rest of the

building, thereby increasing the exposure to the mail room occupants. The filtration upgrades do 

not provide additional protection to the building occupants because they are located in the system

exhaust stream and serve only to prevent discharge of contaminants to ambient.

For the one-story building, CONTAM was again used to estimate occupant exposure for a

generic outdoor release for the baseline building and then for the building with selected retrofits.

This outdoor release was modeled as a step change elevation in the outdoor concentrations of

both gaseous agent G (to 1.0 mg/m3) and particulate agent P (to 1.0 × 109 particles/m3) that

lasted for 1 min. The retrofits studied for this building include filtration option #1 (upgrade of

existing system filters from MERV4 to MERV11), filtration option #2 (addition of dedicated 

outdoor air fans with a three-stage particulate filtration system), filtration option #3 (addition of

dedicated outdoor air fans with a multi-stage filtration system including a carbon gas phase

filter), sealing the building envelope, and each filtration upgrade option in combination with

envelope sealing. The weather conditions during the simulation period were an outdoor air

temperature of 0 °C and a wind speed of 5 m/s in order to induce a reasonable level of envelope

infiltration. The building envelope effective leakage area (at a reference pressure of 4 Pa) is

5 cm

2

/m

2 (0.07 in2

/ft

2

) before and 0.7 cm

2

/m

2 (0.01 in2

/ft

2

) after sealing the envelope. The

baseline whole building air change rates are 0.28 h-1 due to infiltration and 0.89 h-1 due to 

outdoor air intake, for a total of 1.17 h-1. The envelope sealing completely eliminates infiltration 

in this building under the conditions modeled, leading to a whole building air change rate of

0.89 h-1. The filtration removal efficiencies used in the simulations are 0 % for agent G and 5 %

for agent P for the baseline case, 0 % for agent G and 51.4 % for agent P for option #1, 0 % for

agent G and 99.97 % for agent P for option #2, and 99.5 % for agent G and 99.97 % for agent P

for option #3.

As seen in Table 21, the predicted reductions in the relative exposure to an outdoor contaminant

release vary widely from no impact at all up to a greater than 99 % reduction. For the gas agent,

the retrofit with the largest reduction is filtration option #3, which includes a 99.5 % gas air

cleaner in the outdoor air intakes, combined with envelope sealing for a predicted reduction in 

exposure of over 99 %. Without envelope sealing, filtration option #3 is predicted to have a

somewhat smaller impact, with an exposure reduction of about 84 %. Envelope sealing alone has

almost no impact on exposure to agent G. The other filtration options do not impact agent G

because they include only particle filtration.

For Agent P, filtration option #2 (and #3 since they provide equivalent particle filtration)

combined with envelope sealing is predicted to reduce exposure by over 99 %. As with Agent G,

the impact of the improved filtration is lessened if the envelope is not sealed, with a predicted 

exposure reduction of about 82 %. The lower filtration upgrade option #1 has predicted exposure

reductions of about 40 % and 54 % with and without envelope sealing, respectively. Unlike

Agent G, envelope sealing alone is predicted to have some impact (a 9 % reduction) on exposure

because the baseline building includes a particle filter.
56

Exposure Relative to

Baseline (%)

Retrofit Agent G

(gas)

Agent P

(particle)

Life-cycle cost 

(thousands of dollars)

Filtration option #1 100 60 72

Filtration option #2 100 18 538

Filtration option #3 16 18 926

Envelope sealing 100 91 32

Filtration #1 with envelope sealing 100 46 104

Filtration #2 with envelope sealing 100 0 570

Filtration #3 with envelope sealing 0 0 958

Table 21 Relative Exposure and Life-Cycle Cost for Selected Retrofits in 1-Story Office

Building (outdoor release)

3.5 Discussion of Case Study

The primary goal of the case study was to apply simulation and economic analysis to two real

buildings, both to demonstrate the analysis methodologies and to gain further insights into the

retrofits investigated. The case study has provided useful information on the design,

implementation and performance of selected chembio retrofits in two very different buildings - a

high-rise office building with central air-handling systems and a one-story office building with

multiple rooftop units. The technical and economic analysis in the case study highlights the

building-specific nature of the design and analysis of the retrofit options, such as multiple levels

of filtration, and their associated costs and other economic impacts. Additionally, the case study 

analysis shows the possibility of completely eliminating exposure to a threat such as the outdoor

release by applying a combination of improved filtration and envelope sealing. However, the

economic analysis indicates the relatively high cost of accomplishing this level of protection.

Information on potential performance and costs such as those presented here are both critical to 

decision-makers.

In some cases, examination of the results beyond average exposures yields additional insight into

the potential retrofit effectiveness. For example, the lobby retrofits result in reductions in average

exposure of up to 92 %, but the average exposure after retrofit is distorted by differences

between occupant exposure in the lobby zone and occupant exposure in the remainder of the

building. The reduction in exposure to occupants of non-lobby zones ranges from 97 % to more

than 99 % for the cases that include filtration option #3. Thus, this modification achieves nearly 

complete isolation of the lobby, which is its intent. However, the retrofit could not protect the

lobby occupants from a release in that zone.

The results also show the importance of considering effectiveness and costs of potential

combinations of retrofits. For example, sealing the envelope of the one-story office building has

a minimal impact on occupant exposure to an outdoor release of Agent P and no impact on 

occupant exposure to Agent G. However, when combined with filtration, envelope sealing 

substantially improves the effectiveness of the filtration retrofits on both agents while increasing 

first costs by less than 10 % and potentially decreasing operating costs by reducing building 

heating and cooling loads.
57

4. GUIDANCE

This section presents guidance on the application of retrofits to better protect buildings from

chembio releases. The purpose of this guidance is to present available options for retrofitting 

existing buildings for improved chembio protection and to discuss where these options are most

applicable, the potential benefits and associated costs, and the extent of our current

understanding regarding their application and performance. The information in this section is

based on information in the literature, other guidance documents and the results of the technical

evaluations conducted in this study.

When considering the retrofit of a specific building, it is critical to note that the unique features

of the building and its systems must be considered when implementing the retrofit and in 

forming expectations as to the level of protection that will be realized. Also, while it is more

straightforward to define and design protection systems for a particular release (primarily its

location and timing), it is rare that such advance knowledge can be expected to exist. The

undefined nature of the threats that need to be considered make retrofit selection and design far

more challenging and limit the ability to quantify or “guarantee” any particular degree of

protection. Nevertheless, this guidance is based on the philosophy that increased protection is a

goal worth pursuing, even if the degree of improvement cannot be quantified in advance.

In addition to achieving the improved understanding of retrofit options that will result from the

information presented below, there is another key step in the decision-making process regarding 

a specific building. Before one decides which retrofit options to implement, it is critical to assess

the risks to which the building may be exposed. Risk assessment is a well-established process

and needs to be carried out to determine the potential likelihood of an event and the associated 

costs and other impacts if an event does occur. While risk assessment methods and the linkage

between the outcome and the resulting actions are beyond the scope of this report, there is some

useful discussion in ASHRAE (2003) and FEMA (2005).

This section is organized into three parts, beginning with actions that generally make sense under

any circumstance. Most of these actions are consistent with good building and system operation 

and maintenance, and therefore may be considered part of good practice. The next two groups

are organized into retrofit technologies and retrofit approaches. As discussed in Section 1 of this

report, the former category refers to specific off-the-shelf technologies, such as filtration and air

cleaning devices, while the latter refers to more generic approaches to increasing building 

protection such as building pressurization and isolation of spaces of potential concern (e.g., mail

rooms).

4.1 General Guidance

There are a number of actions that can be beneficial under almost any circumstance. In many 

cases they are associated with only modest costs and sometimes yield additional benefits in terms

of reduced energy consumption and improved indoor air quality. Many of these actions have

been advocated in prior publications on building protection (ASHRAE 2003a, NIOSH 2002,

Price et al., 2003). They tend to focus less on specific threats than on sound building operation

and maintenance practices that can support the successful implementation of specific chembio

protection strategies and greatly increase the likelihood that any particular response strategy will

perform as intended.
58

4.1.1 Understand the Building

Regardless of the degree of risk to which a particular building may be subject, it is always a good 

idea to understand the building. In this case, the term “understand” refers to several issues

including the layout of the building, the activities within, and what is going on outside the

building. As every building is unique to some degree, it is hard to develop a general list of

parameters to assess but the following list provides some sense of the type of information that is

relevant. The EPA Building Air Quality manual also provides useful guidance for characterizing 

a building (EPA 1991).

Building layout

Entrances: where do people enter the building, including “nonstandard” entrances such as

loading docks, side entrances and parking garages.

Ground level airflow paths: accessible locations where air can enter a building, including but

not limited to outdoor air intakes. Also consider entrances, loading docks, and emergency 

doors where a negative pressure will pull air into a building.

Space types and occupancy levels: determine what different types of spaces exist in a

building (offices, classrooms, meeting rooms, etc.) and where the occupants are generally 

located.

Building activities

Occupancy patterns: where and when people arrive and leave the building; is there a

predictable schedule; make sure to consider evenings and weekends.

Occupant activities: what people are doing in the building; activities likely to generate

contaminants that might be harmful or perceived as harmful to occupants; when these

activities take place?

Outside the building

Pedestrian and motor vehicle traffic: is the building located in an area of high pedestrian or

motor vehicle activity?

Nearby sources: is the building close to other high-profile buildings, or industrial facilities,

transportation stations, roadways or train tracks where an intentional or unintentional release

could occur?

In terms of building protection in particular, methods are being developed to assess vulnerability 

that will address some of the security-specific issues (LBNL 2004).

4.1.2 Understand the System

Whether or not one anticipates using the building ventilation system as part of a protective

strategy, it is important to understand the system as it is designed to operate and as it is actually 

operating. Again, every building and its ventilation systems are unique to some degree, but there

is some basic information that needs to be assembled and understood. The EPA Building Air

Quality manual again provides some useful guidance on ventilation system characterization 

(EPA 1991). In some cases, these actions may require assistance from individuals that are not

part of the building operating staff, such as TAB contractors or engineering consultants.

System design

Documentation: assemble mechanical drawings and fan specifications; these may not be onsite and are often out of date; if so, current drawings and system specifications are important
59

resources that should be developed as soon as resources can be acquired for such an effort,

which can be quite involved in many buildings; assemble any existing TAB reports.

Air handler design information: design supply, return and outdoor air intake airflow rates;

areas served by each air handler; specified level of filtration.

Exhaust systems: design airflow rates; areas served; operating schedule; location of on/off

controls.

Sequence of operations: how systems are intended to operate per time of day, outdoor

temperature and humidity, season of the year, including modulation of outdoor air intake and

supply airflow rates. This effort also includes understanding fire alarm systems, smoke

control modes and any available purge cycles.

System operation

Airflow rates: supply, outdoor and exhaust airflow rates relative to design values; modulation

of same based on time of day and outdoor conditions, again relative to design sequence of

operations.

Building pressures: indoor-outdoor pressure differences at entrances and ground level airflow

paths under different conditions of weather and ventilation system operation, at a minimum

assess at least the direction of the pressure difference; pressure differences between key 

spaces (e.g., lobbies, mail rooms, parking garages and loading docks) and the surrounding

spaces of the building to determine if air will flow from these spaces into the rest of the

building, which must include consideration of different weather conditions.

4.1.3 Inspect the System

Achieving good system operation requires that the system components be in good working

condition. Again, the Building Air Quality guidance document (EPA 2001) contains sound 

recommendations on the aspects of such an inspection. A more detailed inspection protocol was

developed for the EPA Building Assessment, Survey and Evaluation (BASE) Study (EPA 2003,

Persily 1993). The components that should be considered in such an inspection include the

following:

Outdoor air intakes: cleanliness, open per the operating schedule

Intake dampers and damper linkages: functioning as designed, able to open and close

Fans: general condition

Cooling coils: general condition, including cleanliness

Drain pans: cleanliness, rust, existence of standing water and/or microbial growth

Air filters: general condition, condition of seals and existence of bypass

Temperature, humidity and pressure sensors used by building control systems: general

condition

4.1.4 System tune-up

Based on the information gathered through these efforts to understand the building and its

systems, the next step is to make the adjustments necessary to bring the system operation in line

with the original design intent and current needs. Such “recommissioning” is like to improve

energy efficiency and indoor air quality and is discussed as a retrofit option in Section 4.3.
60

4.2 Retrofit Technologies

This section presents guidance on several specific retrofit technologies. The guidance includes a

brief description of the technology including how it functions and how it’s applied, a discussion 

of existing performance data, the protective impact that can be expected from its application, the

associated costs, and finally information gaps regarding the technology. The information

presented here reflects the current state of knowledge, but much research and other activity is

currently occurring in the area of building protection. It is expected that more information on 

these technologies will be produced in the future and new technologies will become available.

Therefore, it is important that building designers, owners, operators and others responsible for

building protection stay abreast of current developments in this rapidly changing area.

4.2.1 Enhanced Particle Filtration

Objective

To increase the removal of particulate contaminants from HVAC system airstreams through the

use of higher efficiency particle filters than those currently in place.

Description

Assuming that an air handler has at least some minimal level of particle filtration (generally used 

to keep cooling coils and other system components clean), this retrofit involves replacing the

existing filters with higher efficiency particle filters. There are two distinct situations in which

this retrofit can be implemented. In the first case the new filters are installed in the existing filter

racks (perhaps with some slight modifications), such that the pressure drop associated with the

higher efficiency filters is compatible with the existing fans and motors. In other cases, the

pressure drop associated with the new filters is too high for the existing system and the fans,

motors and/or electrical systems need to be modified.

A great deal of information is available on particle filtration, including general discussions of the

technology and its application (ASHRAE 2000, NAFA 2001), as well as guidance specific to

chembio protection of buildings (NIOSH 2003). As noted in these references, there are three

primary types of particulate air filters: mechanical, eletrostatically-charged and electronic.

Mechanical filters, which are sometime referred to as media filters and include familiar panel,

bag and pleated filters, capture particles via three predominant mechanisms. The first mechanism

is impaction, where particles collide with the filter media instead of flowing around the filter

fibers and then become attached to the media. Interception is similar to impaction, but rather

than colliding directly with the filter fiber, the particle comes in close contact with the fiber as it

moves along with the airstream and the forces of attraction result in the particle sticking to the

fiber instead of continuing to move with the airstream. Smaller particles can also be captured by 

diffusion, where random movement of the particles relative to the airstream causes them to come

in contact with the filter media and become attached. Figure 11 shows a generic curve of particle

removal efficiency as a function of particle size or diameter. (An efficiency of 1.0 means that the

filter removes all of the particulate matter that flows into the filter, while a lower efficiency 

removes the corresponding fraction of the incoming particulate matter.) In general, diffusion is

most effective with smaller particles, while impaction and interception are most effective at

larger diameters. This difference results in a dip in removal efficiency in the range of 0.2 μm,

which is a particle size that tends to penetrate fairly deeply in the human respiratory system.
61

Figure 11 Representation of filter efficiency dependence on particle size (NIOSH 2003)

The use of eletrostatically-charged media can potentially increase particle removal through the

interaction of charged media and naturally charged particles. There are multiple approaches to 

charging the media, and in all cases the performance can be impacted by humidity, time of

service, exposure to various airborne contaminants, and dust buildup (or loading) on the filter.

Electronic air cleaners employ electrostatic precipitation in which an electric charge is imparted 

to particles as they pass through an ionizing section of the device. The particles are then 

collected onto alternately charged plates downstream of the ionizing section. The removal

efficiency of these devices is impacted by particle size, air speed, ionizing and collector plate

voltages, spacing of the ionizers and collector plates, and coating of the ionizing wires with

silicon dioxide over time. Another important consideration with these devices is their potential to

emit ozone, particularly if the ionizing wires are damaged.

The particles that are relevant to building security cover a potentially wide range, but the focus is

primarily on biological agents including microbes such as bacteria and fungi as well as toxins. A

great deal of information is available on the range of bio-agents and their unique characteristics

in terms of size, infectiousness, and lethality (Kowalski 2003, Kowalski and Bahnfleth 1999).

The predominant size range of interest for these agents is on the order of 1 μm, but the particle

size ranges from as small as a few tenths of a micrometer to several micrometers. The size range

is important in relation to the dependence of filter efficiency on particle size depicted in Figure

11. Most mechanical filters have higher removal efficiencies in the size range of interest, i.e.,

1 μm or greater, but the existence of smaller particles can still be an issue for some agents.
62

Available Performance Information

Particle removal efficiencies are fairly well established based on the use of ASHRAE Standard 

52.2 (ASHRAE 1999), which provides a rating method referred to as Minimum Efficiency 

Reporting Value (MERV). The MERV ratings are based on particle size specific removal rates

and include the effects of filter loading over time, thereby providing more information than 

contained in the dust spot efficiency and arrestance values from ASHRAE Standard 52.1

(ASHRAE 1992). MERV values range from 1 to 20, with higher values having higher removal

rates. For reference, a 30 % dust spot filter corresponds roughly to a MERV 8 and a HEPA filter

corresponds to values of MERV 17 or higher. Figure 12 shows some sample plots of removal

efficiency as a function of particle size for a range of MERV values. Note that ASHRAE

Standard 62.1-2004 requires the use of at least a MERV 6 filter upstream of all cooling coils or

any other wetted surface. Historically, particulate filters have been installed in commercial

buildings to keep system components clean, which improves the performance of heat transfer

surfaces and reduces the likelihood of microbial growth in ventilation systems, but more recently 

concerns about indoor air quality and now building security have renewed the consideration of

higher levels of filter efficiency (Burroughs 2005a).

Figure 12 Representative curves of particle removal efficiency for various MERV Levels

(Kowalski and Bahnfleth 2002)

While the MERV rating system has been available since 1999, many users and vendors still

speak in terms of dust spot efficiency and arrestance, the performance parameters determined 

with the earlier ASHRAE test method 52.1 (ASHRAE 1992). Table 22 compares the values of

the three parameters, along with some information on the types of filters that provide the various

efficiency values.
63

Approximate values from

ASHRAE 52.1

MERV value per

ASHRAE 52.2

Dust spot 

efficiency Arrestance Filter type

1 < 20 % < 65 %

2 < 20 % 60 % - 70 %

3 < 20 % 70 % - 75 %

4 < 20 % 75 % - 80 %

Throwaway media filters;

washable panel filters;

electrostatic panel filters

5 < 20 % 80 % - 85 %

6 < 20 % 85 % - 90 %

7 25 % to 30 % > 90 %

8 30 % to 35 % > 90 %

Pleated filters (25 mm to

125 mm thick); cartridge 

filters; throwaway media filters

9 40 % to 45 % > 90 %

10 50 % to 55 % > 95 %

11 60 % to 65 % > 95 %

12 70 % to 75 % > 95 %

13 80 % to 90 % > 98 %

14 90 % to 95 % > 98 %

15 > 95 % n/a

16 n/a n/a

Bag and box filters

17 n/a n/a

18 n/a n/a

19 n/a n/a

20 n/a n/a

HEPA/ULPA filters

Table 22 Comparison of generic particulate filter efficiency values (ASHRAE 1999)

There have been relatively few measurements of installed filter removal efficiencies. A recent

field study by Burroughs (2005b) included measurements in several office buildings over 1 year

using particle counts up and downstream of filters of different MERV levels. The results did 

verify that the MERV ratings translated to installed performance, but also found significant

leakage at the filter seals. More such measurements are needed to better understand the factors

that determine installed performance in order to support improved installation, operation and

maintenance practices as needed.

Protective Impacts

Enhanced particulate filtration can reduce the exposure to bioagents, but the impact depends on 

the particle diameter of the agent, the filter efficiency at that diameter, the airflow rate through

the filter, the quality of filter maintenance and the filter location relative to the contaminant

source and the occupants. Given the lack of prior knowledge of the particle size to which one

might be subjected and the prevalence of bioagents in the 1 μm range, one should expect to 

realize significant protection from upgrading filtration. And since larger particles (greater than 

1 μm in diameter) are more readily removed by filtration than smaller ones, high efficiency 

filters (i.e., HEPA) are not necessarily required to remove close to 99 % of 1 μm particles.
64

Whether this level of removal provides an adequate level of protection is a separate, but

important, issue. At the same time, filtration systems must be properly installed and maintained,

just like any other building equipment, to perform as expected over time.

Given the removal efficiency of an upgraded filter relative to the pre-retrofit filter, it is relatively 

straightforward to determine the potential protective impact. However, since a filter will only

remove contaminants that flow through it, the filter location relative to the contaminant source is

critical to the exposure reduction that will be realized. The three generic source locations of

interest are outdoors, at the air intake, and indoors. An outdoor release that increases the ambient

concentration surrounding a building for some period of time will result in contaminant entering

the building through the intake (filtered) and through envelope leakage (unfiltered). (Intake air

that bypasses the filter due to poor filter sealing is discussed below.) The amount of contaminant

that enters the building with the intake air will be reduced by an amount determined by the filter

removal efficiency relative to the pre-retrofit value, but the actual exposure reduction will be

impacted by the amount of envelope leakage or infiltration relative to the amount of air intake.

Assuming that no agent is removed by the building envelope (a conservative assumption because

some agents will be “filtered” by the envelope), and ignoring filter bypass as well as particle loss

due to deposition onto building surfaces, the impact on the exposure reduction depends primarily 

on the ratio of the envelope infiltration airflow to the outdoor air intake airflow.

One can express the “effective” filter efficiency as a function of the rated or nominal efficiency ε

of the filter and the ratio of the airflow entering the building via infiltration QINF to the airflow

entering via the system intake QINT as follows:

Effective filter efficiency =

!

"

QINF

QINT

+1 #

$

%

&

'

(

(1)

The rated efficiency ε is the removal efficiency of the device itself (based on a test performed in

accordance with ASHRAE 52.2), again without any filter bypass, while the effective efficiency 

is the removal efficiency on a whole building scale adjusted for the entry of unfiltered infiltration 

air. In other words, the effective efficiency is the removal efficiency based on the total amount of

air entering the building, not just the intake airflow through the filter.

Figure 13 depicts the dependence of the effective filter efficiency on the rated or nominal

efficiency for different values of the ratio of infiltration to intake airflow for an outdoor release.

Therefore, if there is no infiltration (QINF/QINT = 0), then the effective efficiency is the same as

the rated efficiency. As the infiltration rate increases relative to the intake rate, the effective

efficiency decreases relate to the rated efficiency. For example, if infiltration and intake are

equal, which is a reasonable first order assumption for a typically leaky commercial building, the

effective efficiency will be one-half of the rated efficiency. Envelope infiltration can be thought

of as a form of filter bypass, i.e., air that flows around a filter instead of through it and thereby is

not exposed to the particle removal processes of the filter. When a contaminant is released 

directly at or into an air intake, entry via infiltration no longer plays a role and the impact of the

filter is determined directly by the rated efficiency of the filter.

Depending on the quality of the filter installation and maintenance over time, airflow bypass

around the filter can often be significant (Burroughs 2005a). As in the case of infiltration, airflow

that bypasses the filter will not have any contaminant removed, again degrading the effective

efficiency of the filtration system. Figure 14 is similar to Figure 13, but includes the impacts of

bypass fractions of 5 % and 10 % to show the impacts on effective efficiency. A bypass fraction 
65

of 5 % means that 5% of the airstream intended to go through the filter actually flows around it.

The figure shows that bypass has slightly more significant impact when the infiltration-to-intake

ratio is low, but clearly shows the degradation performance due to filter bypass.

Figure 13 Impact of infiltration on effective filter efficiency

By considering a building airflow system as a single zone, the relative exposure to an outdoor

release given an upgrade in filtration from an efficiency ε1 to a higher efficiency ε2 can be

expressed as follows:

Relative exposure =

!

1"#2 + QINF

QINT

1"#1 + QINF

QINT

(2)

Therefore, if there is no infiltration, the relative exposure is the ratio of one minus the “new”

efficiency divided by one minus the “old” efficiency. For example, in the simulations of the twostory office building presented in Section 4 with no weather (QINF = 0), ε1 = 16.4 % and ε2 =

89.6 %. Equation 1 therefore yields a relative exposure for the higher efficiency relative to the

lower efficiency of 12.4 %, which is the same value as in Table 8. For nonzero values of QINF,

the relative exposure increases, reflecting the degradation in performance for the higher

efficiency filtration. In that same example, with weather included, the infiltration rate is 0.22 h-1,

and the ratio of QINF to QINT is 0.58. Equation 2 now yields a relative exposure of 48 %, which is

very close to the value in Table 9.

Table 23 shows the relative exposure as defined by Equation (2), with lower values

corresponding to less exposure with the “new” filter relative to the “old” filter. The first column
66

shows the before and after MERV levels, while the second shows the relative exposure assuming 

no infiltration. The beneficial impacts are seen clearly, with the most significant reductions seen 

for MERV values of 13 and higher. The third column shows the relative exposure assuming an 

infiltration rate equal to the intake rate for a general outdoor release, which shows that without

addressing infiltration, even the highest filter efficiency retrofits are of limited effectiveness.

Figure 14 Impact of bypass on effective filter efficiency

Relative exposure (%) Filter upgrade

No infiltration Infiltration = Intake

MERV 6 to 8 71.8 87.1

MERV 6 to 11 53.2 78.7

MERV 6 to 13 12.4 60.1

MERV 6 to 16 0.6 54.7

MERV 8 to 13 17.3 69.0

MERV 8 to 16 0.8 62.8

Relative exposure based on removal efficiency at roughly 1 μm as follows: MERV 6 = 16.4 %,

MERV 8 = 40 %, MERV 11 = 55.5 %, MERV 13 = 89.6 % and MERV 16 = 99.5 %.

Table 23 Impact of enhanced filtration on exposure to outdoor release

The impacts of filtration in the mixed airstream, a common location of particle filters in most air

handling systems, can also be quite significant. Generally, the airflow rate that passes through a

mixed air filter is roughly five times higher than the outdoor air intake that passes through an 
67

outdoor air filter (except under 100 % outdoor air operation). Therefore, mixed air filtration can

remove more contaminant from the building for a given level of filtration once the contaminant

has entered the building from an outdoor or indoor release. As seen in the simulations, retrofit

effectiveness values (i.e., exposure with retrofit relative to exposure without) on the order of

10 % or even less can be realized by filtration of the mixed airstream. But the actual reduction is

ultimately a function of the pre and post retrofit filtration efficiency, the airflow through the

system, and of course the quality of the installation and maintenance.

When a contaminant is released within the building, the location of that release relative to the

occupants and the filter location becomes critical. If the occupants are very close to the release,

filtration of the recirculation air may have little or no impact on their exposure. If the release is

located such that the contaminant is drawn back via the return system to the filter before being 

distributed to the rest of the building, then recirculation filtration will be more effective overall.

However, occupants in the immediate vicinity of the release may still be significantly exposed to 

the contaminant.

In addition to the rated efficiency of a filter, the air seal of filter installations is critical to their

installed performance and must be addressed regardless of the current or retrofit level of

filtration (Burroughs 2005b). In fact, improving the seal of existing filters may have a more

significant benefit than replacing the filters with higher efficiency filters without addressing 

bypass. Filter seal is generally addressed in the installation of higher efficiency, e.g. HEPA,

filters, but maintenance of the seal over time is always an issue and routine inspection of the

filter seal should be part of normal maintenance practice.

Costs

Like most building retrofits, the cost of enhanced filtration is a combination of first costs and 

operating costs. Specific examples of both are highlighted in the case study as described in 

Section 3 and Appendix C, and the software tool developed as part of this project provides the

means for properly accounting for all these costs in determining the life-cycle costs of enhance

filtration and other retrofits. These costs, specifically the interactions between first costs and 

operating costs, are discussed in NIOSH (2003) and Arnold et al. (2005).

First costs include the following:

Filters

Design work (in cases where system modifications are required)

Reconfiguration of filter racks (where required)

Modifications of air handling system fans, motors, electrical (where required)

Operating costs include the following:

Filter replacement and maintenance (incremental above replacement costs of existing filters)

Increased electrical consumption (when new filters increase pressure drop and require more

powerful fans)

Enhanced particle filtration has the potential for improving indoor air quality, which has been 

associated with increased occupant productivity (Fisk and Rosenfeld, 1997). While difficult to

quantify, increased productivity would correspond to an economic benefit associated with better

filtration. Better filtration can also reduce dirt build up on heat transfer surfaces and result in

better system efficiencies over time. These benefits are also difficult to quantify but nonetheless

can be quite real. In addition, better filtration can improve overall building cleanliness,

potentially reducing housekeeping costs. In the event that a release occurs, filtration can also 

reduce the extent and cost of the followup decontamination effort.
68

Knowledge gaps

There are several areas where additional information would increase our understanding of the

impacts of enhanced particulate filtration. One is measurement of installed performance as a

function of system type and configuration, filter type and length of time since installation. As

noted earlier, there is very little field performance information, and such measurements provide

the only means of verifying the actual impact of filtration in real buildings. In addition, field 

measurements of filter bypass would also be useful, and could be related to different approaches

to filter installation and sealing. Better understanding of the IAQ benefits of improved filtration

could also lead to better cost-benefit decisions.

SUMMARY

The addition or enhancement of particle filtration can significantly reduce exposure to outdoor

and indoor releases. As revealed by the simulations discussed in Section 2 of this report and in

Table 23, upgrading from typically minimal filtration levels of MERV 6 or 8 to MERV 13 or

higher can reduce the exposure to about 10 % of the pre-retrofit case based on consideration of

contaminant entry through the intake alone. These simulations also show the advantages of

mixed air filtration over outdoor air filtration alone, with the latter not having any impact on 

indoor releases. Contaminant infiltration via envelope leakage can drastically decrease the

effectiveness of improved filtration, though the reduction is difficult to predict without reliable

estimates of infiltration rates. The same degradation in the impacts of improved filtration can 

also occur when filters are poorly sealed in their frames, either initially or over time as seals

deteriorate. It is generally more important to first deal with the integrity of these seals before

upgrading the filters, and the same may hold true for envelope airtightness as well.

The levels to which filtration can be enhanced are dependent on the air handling system. Fan coil

units, small rooftop units and other unitary systems often have limited space for deeper filters

and limited fan power to overcome the increases in airflow resistance associated with better

filters. This situation was seen in the case study of the one-story office building with rooftop

units. When increased protection is needed under such circumstances, it can be a challenge to 

achieve it through filtration. Larger systems are generally more adaptable to higher levels of

filtration, though system modifications to the filter racks and air handler housing, as well as new

fans and motors, may be required.

An advantage of enhanced filtration relative to some other retrofits is that it is always working,

as opposed to strategies that rely on operator-based response such as system shutdown. The

sensitivity of shutdown and other strategies to timing was seen in the retrofit analysis, but no

such timing issues exist for filtration. Also, filtration is relatively simple, in that there are no

moving parts and as long as air is brought to the filter, it will remove contaminant. In addition,

particle filtration is part of current practice and the technology is widely available. Therefore,

there are no dramatically new skills required of designers, installers and operators as there would 

be for some other retrofits. The same applies to maintenance, as filter replacement is also part of

current practice. Finally, unlike some retrofit strategies such as system shutdown in the event of

an interior release, enhanced filtration shouldn’t increase exposure under any scenario.
69

4.2.2 Sorption-based Gaseous Air Cleaning

Objective

To remove gaseous contaminants from ventilation airstreams through the use of adsorptive

media that captures these contaminants physically or chemically.

Description

Sorption based gaseous air cleaning is currently employed in a number of applications to control

odorous, corrosive or otherwise undesirable gases generated within or outside of buildings. A

variety of sorbents are employed including activated carbon, alumina and sorbents impregnated 

with compounds to remove specific contaminants. The effectiveness of these sorbents depends

on the particular sorbent-contaminant combination and the design of the system that brings the

air into contact with them. Gaseous air cleaning devices are not typically employed in 

commercial and institutional buildings, but they are seeing increasing use in a number of

applications such as some manufacturing facilities and museums and are receiving increased 

attention based on concerns about building security. A significant amount of information is

available on gaseous air cleaning, including general discussions of the technology and its

application (ASHRAE 2003, NAFA 2001), as well as its use in chembio building protection 

(Kowalski 2002, NIOSH 2003).

Gas phase air cleaning systems remove contaminants through either physical adsorption or

chemisorption. Physical adsorption is based on the attractive van der Waals forces between the

gas molecules and the sorbent surface, with the removal capacity dependent on the surface area

of the sorbent. That dependency is the reason that porous materials with high surface to volume

ratios, such as activated carbon, are so effective. Physical adsorption is a reversible process, and 

therefore temperature has a strong effect on sorption rates resulting in lower removal efficiencies

at higher temperatures. In addition, other gas molecules will compete for the available sorption 

sites. Water vapor acts as one such competitor, and therefore elevated humidity has a significant

effect on the rate of adsorption, particularly for activated carbon. Chemisorption involves

chemical reactions between the adsorbent surface and the gas molecule, resulting in better

retention of the contaminant than physical adsorption alone. To induce chemisorption,

adsorbents are impregnated with various chemicals that target certain chemical classes such as

acid gases or specific chemicals such as chlorine.

The gaseous contaminants that are relevant to building security cover a wide range, including

nerve agents and toxic industrial chemicals. No single sorbent or chemical impregnant is able to

remove all contaminants effectively, and therefore a combination of sorbents is needed to fully 

protect a building and its occupants. Some common adsorbent materials include activated 

carbon, silica gel, alumna and zeolites, while chemical impregnants include potassium

permanganate, phosphoric acid, copper and silver salts, and zinc oxide.

In addition to the specific adsorbent material and contaminant of concern, the removal efficiency 

of a gas phase air cleaning system depends on surface area of the sorbent particles, the residence

time in the adsorbent bed, and the presence of other airborne compounds that compete for

adsorption sites. The residence time depends on the media bed depth and the airflow rate through

the bed. A deeper bed, while increasing residence time, also increases the pressure drop through

the system. The adsorptive capacity of a system, which translates to service life, depends on the

mass of adsorbent employed and the contaminant concentrations, including humidity, to which

the adsorbent is exposed. These contaminants include both the contaminants the system is

intended to remove and others that compete for adsorption sites.
70

Available Performance Information

There are currently no standard test methods for determining the contaminant removal efficiency 

of gaseous air cleaning equipment for use in specifying and sizing these systems. Manufacturers

have performance data and experience in a variety of forms that can be useful, but there is not

yet the equivalent of a MERV rating for gaseous air cleaning. ASHRAE committee 145P is

working on a method of test for gas-phase air cleaning media, which will hopefully be available

soon for establishing the performance of different media using a consistent methodology. That

committee is also working on a method of testing full-scale air cleaning media beds, which will

also be very helpful in the application and specification of such systems.

Figure 15 Representative breakthrough curve

The performance of gas phase air cleaning is often described in terms of breakthrough curves.

These curves are determined for an adsorbent/contaminant combination using a test apparatus in 

which an airstream containing a known concentration of the contaminant flows through the

adsorbent bed. Breakthrough is generally defined as the condition where the contaminant

concentration downstream of the air cleaning device reaches some specific fraction of the

upstream or challenge concentration, presumably because the air cleaner sorptive capacity has

been exceeded. The breakthrough time is then the time between the initial contact of the

contaminant with the adsorbent and the time when breakthrough has occurred at some fraction of

the challenge concentration, for example 50 %. Figure 15 is a representative breakthrough curve,

which plots the ratio of the downstream concentration to the upstream or challenge concentration 

as a function of time. Initially, very little contaminant gets past the air cleaner, but after sufficient

time, the media capacity is exhausted and the contaminant “breaks through” to the downstream

side of the system. Breakthrough curves are often determined at relatively high challenge
71

concentrations in order to complete the tests in a manageable amount of time. Such breakthrough

test results need to be related to the performance at lower and perhaps more realistic

concentrations. Nevertheless, breakthrough curves can be generated as a function of chemical

properties, bed depth and other system design parameters.

Another key performance parameter is the service life of the filter media, which depends on the

mass of adsorbent in the system, the exposure of the media over time to temperature and

humidity swings, and the exposure over time to contaminants such as those normally found in 

air. Service life can be determined analytically for a single contaminant (NAFA 2001), but the

influence of other airborne contaminants makes the determination more complicated in practice.

Media manufacturers therefore use other approaches such as analyzing a media sample from an 

installation to assess its remaining capacity, in-place gas monitoring or simply experience from

other installations to estimate service life.

Protective Impacts

Gas phase air cleaning can reduce the exposure to chemical contaminants, with the impact

dependent on the removal efficiency and the relative locations of the source, air cleaning system

and occupants as discussed for particle filtration. Also as in the case of particle filtration, gas

phase air cleaning systems must be properly installed and maintained to achieve the intended 

performance.

The discussion of potential protective impacts in the previous section on particle filtration is also 

relevant here. The major difference is that the pre-retrofit removal efficiency is generally zero for

gaseous contaminants and the post-retrofit efficiency is a function of the system employed 

(specifically the sorbent media and its mass) and the specific contaminant being considered.

Depending on the media, contaminant, system design, and time and conditions since installation,

the removal efficiency can vary from 0 % to 100 %. The issues of filter bypass and building

envelope infiltration are the same for gaseous air cleaning as they are for particulate filtration.

Equation 1 describes the relative exposure for an upgrade in particle filtration, given an outdoor

release, as a function of pre and post-retrofit removal efficiency and the infiltration-to-intake

ratio. That expression still applies here, with ε1 = 0 % and ε2 set equal to the gaseous removal

efficiency ε, as follows:

Relative exposure =

!

1"# + QINF

QINT

1+ QINF

QINT

(3)

Table 24 shows the relative exposure for 100 % and 95 % efficient gaseous air cleaning. Again,

envelope infiltration significantly degrades the impact of air cleaning.

Relative exposure (%) Removal efficiency No infiltration Infiltration = Intake

100 % 0.0 50.0

95 % 5.0 52.5

Table 24 Impact of gaseous air cleaning on exposure to outdoor release

When the contaminant is released within the building, the location of that release relative to the

occupants and the air cleaner becomes critical. If the occupants are very close to the release, air
72

cleaning of the recirculation air may have little or no impact on exposure. If the release is located 

such that the contaminant is drawn back via the return system to the air cleaning system before

being distributed to the rest of the building, then air cleaning will be more effective. However,

occupants in the immediate vicinity of the release may still be seriously exposed to the release.

Costs

The cost of gas phase air cleaning includes the first and operating costs listed below. Specific

examples of both are highlighted in the case study as described in Section 3 and Appendix C.

First costs include the following:

Air cleaning system

Additional space for system (in some buildings, there may be costs associated with floor space

based on the loss of rentable space)

Design work (system modifications are generally required for gas phase air cleaning)

Modifications of air handling system fans, motors, electrical

Operating costs include the following:

Media replacement

Increased electrical consumption (associated with increased pressure drop)

In general, gaseous air cleaning systems are associated with a more significant pressure drop 

than particle filtration devices. These larger pressure drops may in turn may require significant

system modifications, including replacement of fans and motors as well as associated electrical

upgrades. As was the case for enhanced particle filtration, gas phase air cleaning also has the

potential for improving indoor air quality, which may increase occupant productivity.

Knowledge gaps

Test standards and associated rating systems are the primary need in the application of gas phase

air cleaning. As noted above, an ASHRAE committee is working on a method of test for media,

to be followed by a full-scale test method. Additional information is also need to better predict

and determine media replacement schedules as a function of system design parameters and

exposure history of the media.

SUMMARY

Gas phase air cleaning in outdoor air intakes can reduce exposure to outdoor releases of gaseous

contaminants based on the removal efficiency for the particular agent of concern. As seen in the

simulations (Section 2) and Table 24, air cleaning can reduce exposure on the order of one minus

the filter efficiency given contaminant entry through the intake alone. Envelope infiltration can

significantly decrease the effectiveness, with the degradation dependent on the ratio of the

infiltration rate to the intake.

Due to the pressure drop and filter depth associated with current gas phase technology, fan coil

units, small rooftop units and other unitary systems are generally not compatible with this retrofit

technology. Larger systems are generally more easily adaptable to gaseous air cleaning, but

modifications may still be required. When designing a gas phase air cleaning installation, it is

important to consider the interactions with other system components. For example, locating

particle filters upstream of the air cleaning system will protect gas phase sorbent media from

being “fouled” by particulate matter. In addition, many adsorption systems are negatively 

impacted by humidity; therefore it is often preferable that cooling coils be located downstream

from the air cleaning system.
73

As was mentioned for particle filtration, gas phase air cleaning has the advantage that it is always

working, as opposed to strategies that rely on operator-based response such as system shutdown.

However, it is important to remember that a gas phase air cleaning system will generally achieve

different levels of effectiveness for different contaminants.

4.2.3 Ultraviolet Germicidal Irradiation (UVGI)

Objective

To kill or otherwise deactivate biological agents through the use of ultraviolet irradiation of the

airstream passing through the device.

Description

UVGI systems have been used for many years to kill airborne infectious agents (viruses,

bacteria, and bacterial and fungal spores) in healthcare facilities and other venues, with many 

applications focused on controlling the transmission of tuberculosis. These devices use

ultraviolet irradiation in the 250 nm to 260 nm wavelength range (the so-called “C” band of the

UV spectrum, sometimes referred to as UVC) and are either installed in the upper portions of a

room with shielding to protect the occupants or in ductwork. The use of these devices in 

healthcare facilities has been described previously and application guidelines have been 

published by the Centers for Disease Control and Prevention (CDC 1994, 1999a and 1999b)

More recently UVGI has been advocated for more general application as an indoor air quality 

control measure to keep ventilation system components, particularly cooling coils, clean by 

reducing microbial growth in air handling units (Dillard 2004). UVGI is also being proposed for

protecting buildings against bioagents in the event of an intentional release (Kowalski and 

Bahnfleth 2003).

Available Performance Information

The effectiveness of these devices is typically expressed in terms of deactivation rate, which is

primarily a function of device geometry, intensity of the light source, microbial resistance of the

bioagent of interest, and residence time of the agent in the field of irradiation. Inactivation or

“kill” rates can be predicted with a fair level of reliability based on these parameters (VanOsdell

and Foarde 2002). However, there is no standard test method for determining the effectiveness of

these devices and they are not generally supplied with the performance data to determine kill

rates. Kowalski (2003) has proposed a UVGI Rating Value (URV) from 8-15 that corresponds to 

an average light intensity expressed in units of mW/cm

2

. Based on the exposure time and the

susceptibility of a particular organism, the URV value can then be converted to a kill rate for that

organism. However, the URV concept has not yet been promulgated in an industry standard, nor

has any other rating system of effectiveness. At this point, UVGI systems are described primarily

in terms of the lamp specifications including the light intensity expressed in μW/m

2

. Efforts are

currently underway by the International Ultraviolet Association (www.iuva.org) to develop 

standards to assess the effectiveness of UVGI devices and systems, as well as installation 

guidelines. In addition, ASHRAE Task Group TG2.UVAS Ultraviolet Air and Surface

Disinfection is another source of information including a future ASHRAE Handbook chapter,

potential standards and several planned research projects. Also, a number of devices have been 

tested as part of the U.S. EPA Technology Testing and Evaluation Program, and reports of this

testing are available at http://www.epa.gov/nhsrc/.
74

Protective Impacts

The protection provided by UVGI against bioagents is analogous to that provided by any other

filtration system, i.e., dependent on the deactivation efficiency for the agent or agents of concern.

However, as noted above, efficiency rating systems have not yet been developed. Until they are,

it is difficult to assess the degree of protection offered. Kowalski (2003) discusses kill rates as a

function of exposure time and light intensity for a number of bioagents and has proposed the

URV referred to above. If this concept becomes accepted by the industry and is used to rate

devices and installations, it will provide a needed means of comparing products and systems.

Even without a rating system, the impact depends on the airflow through the device, the quality 

of maintenance, and the device location relative to the source and the building occupants. Lamp 

output can also degrade over time and is dependent on lamp temperature, therefore both effects

need to be considered in designing systems and planning maintenance. Kowalski (2003) and 

others suggest combining UVGI with particle filtration, since the latter is effective at removing 

larger microbes such as spores that tend to be more resistant to UVGI.

Costs

These devices consume electrical energy and require maintenance to keep them operating

effectively. They are associated with a fairly low pressure drop, which reduces the impacts on 

fan power and the need to reconfigure ventilation systems. Like most building retrofits, their cost

is a combination of first and operating costs.

First costs include the following:

UV lamps, fixtures and associated electrical components

Design work (in cases where system modifications are required)

Reconfiguration of ductwork (where required)

Operating costs include the following:

Electrical energy consumed by lamps

Lamp replacement

As noted for enhanced particle filtration, UVGI has the potential for improving indoor air

quality, which has been associated with increased occupant productivity (Fisk and Rosenfeld,

1997). In particular, UVGI can help control bioaerosols in buildings, which can also decrease

infectious disease transmission, healthcare costs and sick leave. The use of UVGI in the vicinity

of cooling coils has the potential additional benefit of improving heat transfer and more efficient

equipment operation. All of these potential benefits can be difficult to quantify, but nevertheless

they could be quite important.

Knowledge gaps

The most important needs in the area of UVGI are industry standards to rate devices and 

installations, as well as guidance for installation and maintenance. As noted above, efforts are

underway to meet these needs. Field evaluation of installed systems would also be helpful to

better understand maintenance requirements, energy consumption and other parameters.

SUMMARY

The use of UVGI in ventilation systems can likely reduce exposure to bioagents, but until a

rating system is developed and employed by the industry, it will be challenging to design and 

specify these systems. In the interim, there is experience with UVGI application in healthcare

facilities and elsewhere that should be useful in other applications.
75

4.2.4 Photocatalytic Oxidation Air Cleaning (PCO)

Objective

To remove organic chemicals, including bioaerosols, from airstreams by flowing the air past a

photocatalyst irradiated by UV light.

Description

PCO is an air cleaning approach in which titanium dioxide (TiO2) acts as a photocatalyst when 

irradiated by UV light, removing organic chemicals including both chemical and biological

agents. If the photocatalytic reaction is 100 % complete, the byproducts include only water and 

carbon dioxide, but complete conversion is difficult to achieve in practice. While PCO is not

widely used for air cleaning in buildings and there are only a small number of products on the

market, it is viewed as a potentially promising technology. PCO devices are commercially 

available, primarily in stand-alone recirculating units. PCO devices consist of a UV light source

configured such that the airflow passing through the device is exposed to both the light and 

surfaces coated with the catalyst. The photocatalytic reaction oxidizes organic compounds in

chemical agents, and presumably in biological agents as well. The effectiveness of cleaners

based on UV-PCO technology depends on the photoactivity of the catalyst, the UV light

intensity on the catalyst surface, contact time between the contaminated airstream and catalyst

surface, the properties of organic chemicals and biological agents, and environmental conditions

such as relative humidity and temperature. There are concerns that potentially harmful chemical

byproducts may form during operation due to incomplete reaction of the contaminants and that

the catalyst can become “poisoned” by exposure to various airborne substances and thereby 

rendered ineffective. Nevertheless, PCO air cleaners may be expected to have low maintenance

requirements and long service life due to the continuous regeneration of the catalyst during

operation.

Available Performance Information

While PCO devices are commercially available, there are no test methods or rating systems for

gas or biological removal and the performance data that are available are limited primarily to the

results of laboratory research studies (Blake 1994 and 1997, Jacoby et al. 1996, Tompkins and 

Anderson 2003). However, given a removal efficiency for a particular contaminant, the exposure

reductions for a PCO device are analogous to those for other filtration or air cleaning systems.

Specifications for stand-alone devices vary typically include the rated airflow capacity, UV

wavelength of the light source, expected life of the light source, efficiency of any particle

filtration included in the device, and power consumption. However, this information cannot be

used to predict contaminant removal efficiency.

Protective Impacts

The protection provided by PCO is analogous to that provided by other filtration systems, but

without removal efficiencies for particular contaminants, the exposure reduction offered by PCO

systems cannot be determined.

Costs

PCO devices consume electrical energy and require maintenance to keep them operating 

effectively. These devices generally have low pressure drops compared to particle filters and 

sorption based gaseous air cleaning, which would reduce their impact on fan power when 
76

installed in a duct system. However, questions exist as to the useful life of the catalysts in 

practice and the production of undesirable byproducts associated with incomplete photochemical

reactions.

Similar to UVGI, the cost of PCO is a combination of first costs and operating costs.

First costs include the following:

PCO components (light sources, catalyst, associated housings, fans for stand-alone units)

Design work (in cases where system modifications are required)

Reconfiguration of ductwork (where required)

Operating costs include the following:

Electrical energy consumed by lamps

Lamp and catalyst replacement

As discussed for the other filtration and air cleaning retrofits, PCO has the potential for

improving indoor air quality, which has the potential for increased occupant productivity and 

reduced healthcare costs. However, PCO technology and application is not yet sufficiently 

developed and demonstrated to evaluate the magnitude of such benefits.

Knowledge gaps

Similar to UVGI, standards are needed to rate PCO systems, as well as guidance for installation 

and maintenance. However, unlike UVGI, the technology is still under development and no 

standardization efforts are yet underway to meet these needs.

SUMMARY

Photocatalytic oxidation appears to have the potential to reduce exposure to chemical and

biological contaminants, but until rating standards are developed, it will be challenging to design 

and specify these systems. In addition, more experience with the application of PCO in buildings

will be needed to understand the factors impacting installed performance.

4.2.5 Work-area Treatment

Objective

To capture contaminants at susceptible work areas, e.g. in mail rooms, before they have an

opportunity to spread to the rest of the building.

Description

A variety of devices are available for capturing and removing particulates from work areas, e.g.,

mail opening stations, which are generally considered relative to the removal of bioaerosols.

These devices are essentially air capture hoods combined with high-efficiency particle filtration 

systems. Some of these devices also incorporate anti-microbial elements, gaseous air cleaning 

components and UVGI. Some exhaust to the outdoors while others recirculate the filtered air

back into the occupied space. These devices are similar in many ways to biosafety cabinets that

have long been employed in research and medical laboratories to contain potentially hazardous

substances, and which have well-established application and rating protocols. Biosafety cabinets

could conceivably be used for mail opening, but it may be hard to justify the first cost and the

training required in all but the highest risk situations. In such cases, a separate mail opening 

facility is often used instead.
77

Available Performance Information

The performance of these devices can be expressed in terms of the airflow rate and contaminant

removal efficiency, which for particle filters is fairly straightforward as noted earlier. Gaseous

air cleaning or UVGI capabilities cannot be similarity rated due to the lack of standard test

methods, though can be tested to meet the needs of a particular application. Another important

parameter is the contaminant capture effectiveness, but this parameter is not generally covered in

product specifications. Test methods for the capture efficiency of laboratory fume hoods exist

(ASHRAE 1995) and could be applied to these devices as well, but the product literature does

not make reference to capture efficiency or fume hood testing.

Protective Impacts

The protection provided by a work area treatment device will depend on the capture efficiency 

and the filtration/air cleaning removal efficiency for the agent of concern. With good capture and 

filtration, such a device should be able to capture essentially all of the contaminant. The

exposure from any contaminant that is not captured will impact the personnel in the work area

based on the airflow patterns in the room, and then the rest of the building occupants based on 

the quantity that isn’t captured and the interzone airflows within the building. It is good practice

to maintain mail rooms and other such spaces at a lower pressure than the rest of the building,

which should minimize transport to the rest of the building and exposure of other building

occupants. Note that typical locations of mail rooms on the lower levels of buildings make them

particularly susceptible to stack-driven airflows upward within the building.

Costs

The costs of these work area treatment devices include the first cost of the device, the electrical

energy consumed by the fans and the replacement costs of the filter elements. In the event of a

contaminated piece of mail entering a building, these devices can prevent contamination of the

building, and thereby save a great deal of money associated with building decontamination.

Knowledge gaps

It would be helpful if these devices were rated for capture efficiency of gases and particles, so 

that devices could be compared. Also, while particulate removal efficiency can be described, the

performance of gaseous air cleaning and UVGI cannot be quantified for these devices.

SUMMARY

Work area treatment devices offer the possibility of capturing contaminants released by a piece

of mail or other package entering a building. If effective, they can essentially eliminate occupant

exposure. Even if not 100 % effective at capturing the contaminant release, in combination with

depressurization of the impacted space, they can limit exposure of other building occupants.
78

4.3 Retrofit Approaches

This section covers retrofit approaches to increase building protection against airborne chembio 

releases. As described earlier, these approaches do not consist of a single technology but rather

involve a change to a building or its systems or an operational strategy intended to reduce

exposure. As in the previous section, the guidance includes a brief description of the approach, a

discussion of relevant performance data and the protective impact that can be expected from its

application, the associated costs, and current information gaps. As in the case of the retrofit

technologies, it is expected that more information on these approaches will be produced in the

future and that new ones may become available. Therefore, it is important that building

designers, owners, operators and others responsible for building protection stay abreast of current

developments.

4.3.1 System Recommissioning

Objective

To improve building and system performance by evaluating existing systems relative to their

design and current building conditions, and then making modifications to equipment and 

maintenance procedures deemed necessary by the evaluation.

Description

Relying on a building ventilation system to increase building protection from a chembio release

requires that the system design be understood and that the system be operated and maintained as

intended. Ventilation system recommissioning is a process by which a system’s operation is

evaluated and then brought into line with its design. If the building use has changed and the

design needs updating, then recommissioning would also involve design and system

modifications to meet the current building conditions. Depending on the system,

recommissioning can involve a number of items including the following: airflow testing and

balancing; calibration of temperature, humidity and other sensors used to control system

operation; checking dampers for proper operation; reviewing system operating schedules; and 

confirming system capacity relative to current loads. There are a number of state utility programs

and private firms that offer recommissioning services, and the role of commissioning is

identified in the EPA Energy Star program (EPA 2004). ASHRAE (1996 and 2005) also has two 

guidelines that address building and system commissioning.

Available Performance Information

While there have been a number of case studies in which building ventilation systems were

recommissioned, each situation is unique in terms of the system, the degree to which the system

deviates from design, and the magnitude and nature of the resulting modifications. Note that

most of these efforts have been motivated by energy efficiency goals rather than building 

security, but the process is not very different. While each situation is different, some of the key 

performance parameters are listed below:

System outdoor air intake rate

Modulation of outdoor air as a function of outdoor weather (including economizer operation)

System supply airflow rate relative to return airflow rate (relates to building pressurization)

Indoor-outdoor pressure differences across building envelope (not always part of design 

specification, but important in chembio applications)
79

Airflow rates of exhaust fans (e.g. toilet, kitchen)

System operation schedule

Interzone pressures between selected spaces and occupied portions of building (e.g. lobby,

loading dock, mail room, underground garage, bathrooms)

There is no comprehensive database of measured versus design values of the above parameters

based on recommissioning or other field evaluation efforts. The EPA BASE study did include

supply airflow and outdoor air intake measurements, which were compared to design values

when design documentation existed (Persily and Gorfain 2004). These comparisons did show

significant deviations from design values in many cases, which presumably would have been 

eliminated through recommissioning efforts.

Envelope tightness measurements, following by sealing retrofits, can also be considered as part

of recommissioning, but these are covered separately in the following section.

Protective Impacts

The benefits of recommissioning in terms of building protection depend on the extent of the

deviation of performance relative to design. The simulations presented in Section 2 included 

several relevant cases, including no outdoor air intake and an intake rate about half of design. In 

these cases, the exposures to an indoor release were significantly higher than the baseline

condition of design outdoor air intake. Other deviations from design that could increase exposure

are airflow imbalances that depressurize the building, thereby increasing rate of entry of an 

outdoor contaminant via infiltration.

Costs

The costs of recommissioning depend on the size and complexity of the building and its

ventilation systems. No rules of thumb exist that allow an estimate based on floor area. Similarly 

the beneficial impacts of recommissioning in terms of energy efficiency and improved indoor air

quality are also building and system specific, but nevertheless can be significant. A recent report

evaluated a number of commissioning case studies in terms of costs, savings and payback times

in new and existing buildings (Mills et al. 2004). While the studies in the report cover all aspects

of commissioning, the medians results were as follows: cost of $2.91/m

2 ($0.27/ft2

), whole

building energy savings of 15 % and payback time of 0.7 years.

Knowledge gaps

While there is general acknowledgement that recommissioning is a valuable and effective

retrofit, there is not much documentation of its effectiveness in terms of system performance or

economics. Case studies of recommissioning \ would be valuable in providing quantitative

evidence of its value. In terms of building protection, it would be very helpful if these studies

considered inside-outside and interzone pressure differences as well as building infiltration rates

in the pre and post evaluations.

SUMMARY

Given the significant deviations between ventilation system design and performance that have

been shown to exist, recommissioning is likely to have value in many buildings. The specific

problems that will be resolved and the extent of the improvements will always depend on the

building in question. Most importantly, if the ventilation system is going to be relied on for

building protection, a recommissioning effort is essentially required for the system to provide the

intended protection.
80

4.3.2 Envelope Tightening

Objective

To increase building envelope airtightness, thereby reducing the rate of outdoor contaminant

entry associated with air infiltration.

Description

Contaminants that are released outside a building enter the interior through a combination of

intentional outdoor air intake through the ventilation system and unintentional air infiltration

through openings in the building envelope. The latter mechanism is often more significant than 

generally assumed given typical levels of building leakage, potentially resulting in significant

contaminant quantities entering buildings via envelope infiltration. The infiltration rate of a

building is determined by the airtightness of the exterior envelope and the pressure differences

acting across the envelope. These pressure differences are determined by the wind speed and 

direction in combination with the exposure of the building to the wind environment, the indooroutdoor air temperature difference, and imbalances between the ventilation systems airflows into 

and out of a building or space. The dynamics of envelope leakage and infiltration are described 

in ASHRAE (2005). This retrofit approach involves increasing the level of building envelope

airtightness by sealing leaks in the envelope, thereby reducing air infiltration and contaminant

entry given the pressure differences imposed on the envelope.

Available Performance Information

The impact of this retrofit on exposure will be a function of the pre- and post-retrofit airtightness

levels, the corresponding infiltration rates, and the relative fractions of outdoor air entry via

intentional intake (generally with some particle filtration) and infiltration (unfiltered). The

connection between envelope airtightness and exposure can be complex and is always situation

specific. Whole building envelope airtightness is measured through fan pressurization testing in 

which a fan is used to induce a specific indoor-outdoor pressure difference across the building

envelope and the airflow rate required to maintain that pressure difference is measured.

Generally, a series of pressure differences in the range of 10 Pa to 75 Pa is induced in such a test,

and the corresponding airflow rates are measured. The test procedure has been standardized for

many years, and employs either a fan brought to the building for the test or uses the building air

handling systems to induce the test pressures (ASTM 2003, CGSB 1996). The results are

reported as the airflow rate required to induce a certain reference pressure (e.g., 50 Pa or 75 Pa),

typically normalized by building volume, floor area or envelope surface area. These airflow rates

are often converted to an “effective leakage area,” which is the area of an orifice that would 

result in the same airflow as that measured through the building envelope at a reference pressure.
81

Envelope airtightness has been measured in a relatively small number of commercial buildings.

Figure 16 is plot of commercial building airtightness data as a function of year of construction,

where airtightness is expressed as the effective leakage area (ELA) in cm2 at a reference pressure

of 4 Pa divided by the above-grade envelope surface area in m

2 (Emmerich and Persily 2005).

The mean air leakage value for the roughly 150 buildings in the figure is 4.3 cm

2

/m

2

(0.06 in

2

/ft

2

). For reference, a typical U.S. home has a leakage value on the order of about

3 cm2/m2 (0.04 in2/ft

2

), while tight U.S. and tight Swedish homes correspond to roughly

1 cm2/m2 (0.01 in2/ft

2

) and 0.3 cm2/m2 (0.004 in2/ft

2

) respectively. The available data reveal that

commercial buildings are not particularly tight relative to homes on a surface area basis, and

reveal no relationship between year of construction and air leakage, dispelling the myth that new

buildings are “airtight.”

Figure 16 U.S. commercial building airtightness data

The determination of envelope infiltration rates from envelope airtightness values requires

consideration of weather-induced pressure differences and the impacts of ventilation system

airflows, and is best done using multizone airflow analysis methods such as those embodied in 

the CONTAM program (Walton and Dols 2005). While simpler relationships between envelope

airtightness and infiltration have been developed for low-rise residential buildings (ASHRAE

2005), they are not generally applicable to commercial buildings of any complexity.

Nevertheless, all else being equal, a tighter building will have a lower infiltration rate, and a

lower infiltration rate will result in less contaminant entry of an outdoor source.

The impacts of an envelope tightening retrofit are characterized by the change in envelope

airtightness. There have only been limited studies reporting before and after envelope

airtightness data (Shaw and Reardon 1995, Zhang et al. 1995). While limited, these studies and 
82

other experience show that reductions in whole building air leakage as large as 50 % can be

achieved, not all sealing approaches will necessarily be this effective. Commercial building 

leakage measurements have shown that windows and doors generally account for a small

fraction of the total, in the range of 10 % to 20 % (Persily and Grot 1986). More often, it appears

that the dominant leakage sites are at interfaces between different wall sections, wall-floor

connections, corners and the interface between the roof and walls. Depending on the wall

construction, it can sometimes be quite difficult to access some of these leakage sites for repair

and additional experience and guidance is needed to guide retrofit efforts.

Protective Impacts

Envelope tightening can reduce the exposure to outdoor contaminant releases, with the amount

of reduction depending on the change in airtightness, the relative magnitudes of the infiltration 

and intake rates, and the level of filtration of the intake air. As noted above, a tighter building has

a lower infiltration rate and therefore less outdoor contaminant entering a building. At the same

time, the lower building air change rate will cause the contaminant that does enter the building to

remain there longer, which will increase exposure. Ignoring any impact of filtration, these two 

effects balance each other out and the exposure over an extended period of time is independent

of air change rate. This effect is depicted in figure 17, which shows the indoor concentration at

three air change rates corresponding to a short-term increase in the outdoor concentration. While

it may not be obvious from this graph, the areas of the indoor concentration curves, i.e., the

integrated exposure over time, are identical. Of course, if the occupants leave the building soon 

after the release or the building is flushed with higher levels of outdoor air intake, then the lower

rates will indeed result in less occupant exposure.

Figure 17 Indoor concentration for different air change rates
83

Therefore, tightening alone will not reduce long-term exposure to an outdoor contaminant unless

some action is taken to evacuate the occupants or flush the building after the contaminant

episode has passed. However, if the outdoor air intake is filtered, then reducing infiltration will

reduce exposure. The effects of filtration are generally most relevant to particulate contaminants,

since gaseous air cleaning is less common, but the dependency is the same. Equation 4 compares

the exposure for two different levels of filtration for a given ratio of infiltration to intake, and can 

be applied to this retrofit by considering the same level of filtration and two different values of

the infiltration to intake ratio.

Relative exposure =

!

1"# +

QINF" post

QINT

$

%

&

'

(

)/QTOTAL" post

1"# +

QINF" pre

QINT

$

%

&

'

(

)/QTOTAL" pre

(4)

where ε is the filter efficiency of the outdoor air intake, QINF-post is the envelope infiltration rate

after tightening, QINF-pre is the infiltration rate before tightening, QTOTAL-post is the total air change

rate (intake plus infiltration) after tightening, and QTOTAL-pre is the total air change rate before.

Based on this expression, one can calculate the relative exposure after tightening as a function of

filter efficiency, as is done in Table 25 assuming an outdoor air intake rate of 1 h-1and a preretrofit infiltration rate of 1 h-1

. The change in exposure is calculated for a 50 % reduction in 

infiltration and for a more dramatic 90 % reduction, corresponding to post-retrofit infiltration

rates of 0.5 h-1and 0.1 h-1, respectively. The table shows that as the filter efficiency increases, the

exposure decreases proportionally as more of the air entering the building passes through the

filter. However, the reduction is much smaller for the 50 % infiltration reduction than for the 90

% reduction, showing that an envelope tightening retrofit must be significant to impact exposure.

The extreme case of no filtration at all results in no exposure reduction as expected based on the

preceding discussion. These estimates assume no other action such as shelter-in-place,

evacuation or outdoor air purging.

Relative exposure (%)

MERV level

50 % infiltration reduction 90 % infiltration reduction

6 97 93

8 92 80

11 87 69

13 73 34

16 67 19

No filter 100 100

Relative exposure based on removal efficiency at roughly 1 μm as follows: MERV 6 = 16.4 %,

MERV 8 = 40 %, MERV 11 = 55.5 %, MERV 13 = 89.6 % and MERV 16 = 99.5 %.

Table 25 Impact of reduced infiltration on exposure to outdoor release
84

Costs

The costs of envelope tightening as a retrofit have not been well-established. The case study 

described in this report includes some estimates, which tend to focus on window and door

sealing, but an effective envelope tightening retrofit is likely to involve the sealing of more

leakage sites.

First costs will include the following:

Pre-sealing inspection and testing to determine leakage locations

Sealing materials

Labor associated with the sealing efforts

Construction staging such as scaffolding to access exterior leakage sites

Envelope tightening is not associated with any operating costs, but it will result in lower heating 

and cooling costs. The magnitude of this reduction is in general a function of climate, pre and

post retrofit tightness, equipment type and system operating schedule. A study of the energy 

impacts of infiltration in U.S. office buildings showed that infiltration accounted for about onethird of space heating loads on average, while the fraction of cooling loads was about one-tenth 

of that (Emmerich et al. 2005). The reduction in these loads due to tightening was estimated to

be about 25 % for heating and 15 % for cooling (Emmerich and Persily 1998), but again the

reduction achieved will depend on the individual building. However, the potential for energy

reduction and, therefore, cost savings by envelope tightening is very real.

In addition, envelope tightening should also improve indoor air quality by decreasing 

contaminant entry via unfiltered infiltration, which has the potential for productivity increases as

noted earlier for improved filtration. Increases in productivity are of course difficult to quantify,

but are a potentially significant issue in areas with poor outdoor air quality. Envelope tightening 

can also improve moisture control in buildings, decreasing the likelihood of condensation within 

exterior walls and other surfaces and subsequent microbial growth.

Knowledge gaps

There is a need for more studies of the increases in airtightness achievable through envelope

sealing as a function of sealing method and building construction, as well as the costs associated 

with these efforts. Presumably more envelope tightening efforts will occur in order to improve

energy efficiency of existing building, and it is important to collect these data in conjunction

with such efforts. Additional information on the energy impacts of tightening would also be

useful to better assess and predict the cost effectiveness of these sealing efforts.

SUMMARY

Enveloping tightening can reduce the entry of outdoor contaminants. However, exposure

reduction requires that the intake air be filtered or that the building be evacuated or purged with

outdoor air after the outdoor contaminant episode has ended. In general, the exposure reduction 

will be larger for more effective tightening and better filtration of the outdoor air intake.

However, tightening alone is not likely to reduce exposure by more than 50 % unless the intake

air filtration is on the order of 90 % or better and the post-tightening infiltration rate is reduced 

by at least one-half.
85

4.3.3 Building Pressurization

Objective

To eliminate or significantly reduce envelope infiltration and the associated contaminant entry by 

bringing in sufficient amounts of filtered, outdoor air to maintain the building at a higher

pressure than outdoors. In this discussion, the pressurization is intended to occur whenever the

system is operating rather than in response to an event.

Description

Building pressurization involves protecting a building against outdoor contaminant releases

through the overpressurization of the building interior relative to outdoors and the removal of the

outdoor agent from the intake air via filtration and/or air cleaning. To be effective, the amount of

air intake must be sufficient to overcome negative pressures that are induced by weather and the

operation of other systems, and the level of filtration must be sufficient to remove significant

quantities of contaminant. As noted earlier, contaminants that are released outside a building 

enter the interior through a combination of intentional outdoor air intake through the ventilation

system and unintentional air infiltration through openings in the building envelope. The latter

mechanism is often more significant than generally assumed given typical levels of building 

leakage. Building pressurization is therefore intended to counter the latter mechanism by 

eliminating, or at least reducing, the inward pressure differences that drive infiltration.

Commercial buildings are generally designed with more outdoor air intake than exhaust in order

to control infiltration. However, in reality, whether this design goal is achieved or not depends on 

many factors including the amount of outdoor air intake, its distribution, the magnitude of the

pressures that induce infiltration, and the tightness of the building envelope. Very few buildings

have actually been evaluated in terms of indoor-outdoor pressure differences, but given the

magnitude of weather-driven pressures and the levels of building leakage, it is unlikely that this

design goal is being realized in very many circumstances. Cummings et al. (1996a and 1996b)

measured building pressures in a number of small commercial buildings in Florida and found

many buildings under significant negative pressures relative to outdoors, due to combinations of

duct leakage and poor control of system airflows.

Available Performance Information

The parameters relevant to building pressurization include the excess outdoor air intake (intake

minus exhaust), building envelope leakage, building surface-to-volume ratio, and removal

efficiency of the filtration and air cleaning systems for the relevant contaminants. Excess outdoor

air intake is a ventilation system design parameter, but the values during operation are the

relevant parameter. Typical design values for outdoor air intake as a fraction of supply airflow

are on the order of 10 % to 20 % in office buildings (Persily and Gorfain 2004). This percentage

is reduced somewhat when toilet and other exhaust flows are included. Given that commercial

building supply airflow rates are on the order of 5 L/s per m

2 (1 cfm/ft2

) of floor area, typical

excess outdoor air rates are roughly 0.5 L/s•m

2 (0.1 cfm/ft2

). Building envelope leakage values,

discussed in the previous section, range from as low as 0.5 cm

2 of leakage area per m2 of

envelope area (0.01 in

2

/ft

2

) to as high as 10 cm

2

/m

2 (0.14 in2

/ft

2

) and greater. Surface-to-volume

ratios depend on building size and floor plan. It is more straightforward to instead consider the

ratio of envelope surface area to floor area. For a collection of 25 representative U.S. office

buildings (Emmerich and Persily 1998), the surface to floor area ratio ranged from 0.03 to 1.50,

with a mean of 0.44.
86

Based on surface to floor area ratio and building leakage, one can calculate the amount of

outdoor air required to pressurize a building. Figure 18 presents the results of such a calculation 

assuming that there are no weather-driven pressures and no internal resistance to airflow within

the building. The values in the figure are the airflow rates required to achieve a 5 Pa indooroutdoor pressure difference, and the lines correspond to different values for the area ratio. There

is nothing significant about this particular pressure difference; it is simply used for illustrative

purposes. These results indicate that in leaky buildings, especially those with higher area ratios

(smaller buildings), relatively large quantities of outdoor air are required to achieve 5 Pa of

pressurization. In the leakiest and smallest buildings, the quantities required are on the order of

total design supply air capacities. Performing these calculations with weather-driven pressures

would make the required airflows higher, by as much as an order of magnitude under windy and 

cold conditions. Therefore, it is unlikely that a leaky building can be pressurized at design 

minimum outdoor air intake airflows. More importantly, the amount of airflow required to

pressurize a building needs to be based on its geometry, the weather conditions to which it is

likely to be exposed, ventilation system design airflow rates, and building envelope airtightness.

If the latter value has not been measured, than a high value should be used to determine a

conservative estimate. In an existing building, these indoor-outdoor pressures can be measured 

under specific conditions of weather and outdoor air intake to determine whether the building is

being pressurized. When making such measurements, it is important to measure at multiple

points on the building façade, including different sides of the building and multiple elevations.

Figure 18 Airflow required for building pressurization to 5 Pa
87

It should be noted that in some buildings, the ventilation system and controls might need to be

modified to achieve the desired levels of pressurization

Protective Impacts

Building pressurization, when combined with high efficiency filtration and air cleaning, can be

effective in protecting against outdoor contaminant releases. The analysis discussed in the

previous section on envelope tightening can again be used to estimate the change in exposure.

However, the post-retrofit intake rate QINT-post is higher than the pre-retrofit value QINT-post, and 

the relevant expression now becomes

Relative exposure =

!

QINT " post ( (1"#) + QINF" post)/QTOTAL" post

QINT " pre ( (1"#) + QINF" pre )/QTOTAL" pre

(5)

The reduction is now a function of the new infiltration rate and the amount of intake air required 

to reduce it, as well as the filter efficiency ε. This equation is used to calculate the exposure

reductions shown in Table 26 for three retrofit cases. In the first case, the outdoor air intake is

increased by 50 % and the infiltration rate is reduced by 90 %. In the second, the intake is

increased by 75 % and infiltration reduced by 95 %. And in the final case, intake is double and 

infiltration is eliminated. These particular values do not reflect any particular expectations of the

infiltration reduction due to these increases in air intake but are simply employed to demonstrate

the impacts of pressurization. The relative exposure is presented for several filter efficiencies, as

well as for no filter at all. The latter case shows that pressurization has no impact if there is no

filter, as expected. The other cases show the degree of protection from reducing infiltration, with

greater reductions for lower infiltration rates and higher filter efficiencies. However, for the two

lowest filter efficiencies, pressurization has a limited impact on exposure.

Relative exposure (%) Filtration

efficiency 50 % intake increase;

infiltration 90 % lower

75 % intake increase;

infiltration 95 % lower

100 % intake increase;

no infiltration

25 % 87.5 86.5 85.7

50 % 70.8 68.5 66.7

95 % 20.8 14.6 9.5

99 % 14.2 7.4 2.0

99.9 % 12.7 5.7 0.2

100 % 12.5 5.6 0.0

No filter 100.0 100.0 100.0

Table 26 Example impacts of building pressurization on exposure to outdoor release

Before increasing outdoor air intake in an attempt to pressurize the building, it is critical to 

assess the current situation regarding building pressure relative to outdoors. If the building is

already under positive pressure, i.e., the infiltration rate is already zero, then bringing in more

outdoor air increases space conditioning loads and makes the filter “work harder” without any

additional protective benefit. If the filtration is less then 100 % efficient, then the extra outdoor

air will actually result in more contaminant entering the building and an increase in exposure.
88

Costs

The costs of building pressurization arise primarily from the increased energy consumption 

associated with heating and cooling the additional outdoor air required to pressurize the building,

which are a function of climate and outdoor air quantities. Since it takes less outdoor air to 

pressurize a building, these costs should serve as a motivation for envelope tightening.

There may also be some first costs associated with modifying the ventilation system and controls

to bring in the extra amounts of outdoor air. In some cases, the system may require extra heating 

and cooling capacity, which would also add to the first costs. Finally, the cost and maintenance

issues associated with filtration also apply to building pressurization.

Building pressurization has the potential for positive economic impacts due to indoor air quality

and envelope durability improvements associated with reductions in moist outdoor air entering 

the building envelope.

Knowledge gaps

While building pressurization is a fairly straightforward concept, the key parameters are the air

leakage value for the building in question and the weather conditions for the site. More measured 

airtightness data would make the design of building pressurization strategies and controls more

reliable, but when considering a specific building it is preferable to measure the envelope

airtightness of that building.

SUMMARY

Building pressurization combined with effective filtration can reduce exposure to outdoor

releases. The reductions will be higher for higher efficiency filtration and air cleaning. Therefore,

good filtration installation and maintenance are critical to the success of this approach. The

infiltration rate reduction with pressurization in place needs to be based on weather conditions

and building airtightness, such that an appropriate amount of outdoor air is brought into the

building. Simply increasing outdoor air intake with the goal of building pressurization may not

be effective and could make things worse in some situations.
89

4.3.4 Relocation of Outdoor Air Intakes

Objective

To move outdoor air intakes, usually to higher elevations, such that they are less accessible to 

public right-of-ways, therefore making it less likely that an individual can release a contaminant

into the intake.

Description

Outdoor air intakes are sometimes located where they are easily accessed by pedestrians and are

therefore vulnerable to someone releasing a contaminant that will be pulled into the building and 

distributed by the ventilation system. The vulnerabilities created by accessible intake locations

have been identified as an issue of concern and recommendations have been made to move such 

intakes to higher elevations (ASHRAE 2002, NIOSH 2002). The NIOSH document notes that a

height of 3.7 m (12 ft) above the ground will put an intake out of reach “without some

assistance.” NIOSH also recommends a sloped and screened covering to the intake, so that an

item thrown on the intake will roll off. Figure 19 is a schematic diagram of three potential intake

locations, ranging from “vulnerable” to “best.” The second schematic clearly shows a sloped 

intake, while the “best” option stresses elevation instead of slope. Other recommendations noted 

in these documents include providing distance from building elements that could be used to 

access intakes, such as loading dock or entryway roofs, and minimizing obstructions near intakes

that could make it difficult to observe someone in their vicinity. In some buildings, it may be

possible to run the intake ductwork through the building interior to the roof, but that approach 

consumes valuable interior space that may not make it a realistic option.

Figure 19 Schematic of intake location options (NIOSH 2002)

Available Performance Information

There is no quantity that characterizes the degree of accessibility of an air intake, but presumably 

a higher intake is less likely to be subject to a release. The amount of contaminant that will be

drawn into a ventilation system from a release near an intake is a complex function of the airflow

patterns around a building. Even without employing complex analysis of airflow patterns and 

quantitative determinations of accessibility, it is probably reasonable to assume that a release at

the intake will be unlikely to occur if it is relocated sufficiently distant from publicly accessible

locations.
90

The EPA BASE study of 100 randomly selected U.S. office buildings included the

characterization of 141 ventilation systems serving the 97 mechanically ventilated buildings in

the study (Persily and Gorfain 2004). Among many other parameters, that study included the

elevation of the air intakes relative to ground level. The mean value of the intake elevation for

these systems is 5.4 m (18 ft), which may be sufficient in many cases. However, the median

value is 1.5 m (5 ft) and the 25th percentile value is 0.3 m (1 ft), which could indicate that many

intakes are lower than perhaps they should be. Of course, in addition to elevation, vulnerability 

of an intake depends on the public access of the intake and physical security around a building.

Protective Impacts

It seems reasonable to assume that all of a contaminant released directly into an intake will be

brought into a building and that moving the intake to an inaccessible location will eliminate any 

such contaminant entry. However, as noted above, the amount of contaminant that enters from a

release near an intake is more complex and its determination requires complex analysis

approaches. In cases where an existing intake is in an accessible location, the goal should be to 

move it as far from such a location as practical. However, as noted in the discussion of costs, in

some cases it can be very expensive to move intakes in some buildings and the degree of risk to

that building may not justify the cost. As an alternative to moving intakes, closed-circuit

television cameras, security lighting, fences and other means of improving physical security have

been suggested as reasonable alternatives (NIOSH 2002).

Costs

There is clearly a cost associated with relocating air intakes, which in some cases can be quite

significant. In addition, the relocation may modify the airflow resistance associated with the

intake, thereby requiring additional modifications to the air handling system. These costs will be

building and system specific, and therefore cannot be generalized. The case study described in 

this report includes an estimate for a high-rise office building of roughly $250 000, but that is

only one estimate. Costs may be higher or lower in another circumstance. Note, however, that in 

the case study building, relocating the intakes would have blocked more than 100 windows and 

compromised the aesthetics of the building, issues that are difficult if not impossible to translate

into a dollar value.

There can also be potential indoor air quality improvements from raising outdoor air intakes

when there is heavy motor vehicle traffic and other ground level contaminant sources.

Knowledge gaps

Given that this is a relatively effective retrofit, there is little need for detailed analysis of its

effectiveness. However, additional case studies of the associated cost for given building and 

system configurations would be useful to assist building owners in the early stages of retrofit

consideration.

SUMMARY

Relocating accessible outdoor air intakes can dramatically improve the level of building

protection by essentially removing that vulnerability. However, the practicality and cost of this

retrofit can vary among buildings, as well as its importance based on the risks to which that

particular building is exposed. In cases where it is determined that relocating the intakes is not an 

option or won’t be pursued, improving the physical security of the intakes and monitoring

activities in their vicinity will reduce the vulnerability.
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4.3.5 Shelter-in-place

Objective

To reduce occupant exposure to an outdoor release by moving building occupants to a designated 

space within a building. This space, which may be equipped with supplemental filtration and air

cleaning, will experience lower concentrations due to the outdoor release and thereby provide

protection to the building occupants who have moved to this space.

Description

In the event of an exterior contaminant release, and in some cases an interior release, building

occupants can move to a designated space that is relatively isolated from the rest of the building

and offers protection from the airborne agent. During such sheltering, the building HVAC and 

exhaust systems are all deactivated to eliminate intentional outdoor air intake into the building,

leaving only unintentional air infiltration. The degree of protection will increase if the space is

well isolated in terms of airflow by having tight boundaries and even more so if the space is

equipped with a filtration and air cleaning system to remove contaminants that do enter the

space. This approach is also sometimes referred to as “collective protection.”

Shelter-in-place is a well-established concept and has been implemented in a variety of settings

and planning efforts. For example, FEMA’s Chemical Stockpile Emergency Preparedness

Program (CSEPP) has generated much information, guidance and training material for planning

in the event of a chemical release at a chemical storage site or industrial facility (Blewett et al.

1996). As noted in this and other publications, there are four basic approaches to shelter-in-place:

Normal: closing all windows and doors, and turning off all mechanical equipment, such as

HVAC systems

Expedient: applying temporary air sealing measures to a shelter space, such as taping over

vents or placing plastic sheeting over windows

Enhanced: applying permanent air sealing measures to a shelter space

Pressurized: providing filtered/cleaned air to the shelter to achieve an elevated air pressure

relative to outside the shelter, thereby greatly limiting air and contaminant entry

Much of the guidance that has been issued in the selection and preparation of shelter-in-place

spaces in buildings focuses on size, location and accessibility (NICS 1999 and 2001, Price et al.

2003). In many cases, sheltering is envisioned as lasting for hours, until the outdoor contaminant

has cleared and it is safe to leave the building. In situations where sheltering is expected to last

longer, requirements for food, water and other basic needs become important. In fact, as was

discussed for envelope tightening, unless the shelter is provided with filtration and air cleaning,

the exposure in the shelter will eventually approach that experienced outdoors. Therefore,

leaving the shelter and the building when it is safe outdoors is an important aspect of this

strategy. In addition, carbon dioxide will build up in the shelter over time, which is another

reason for short term use of this strategy unless ventilation and air cleaning are employed.

A key aspect of shelter-in-place, as noted in the referenced guidance material, is the training of

the building occupants to move quickly to the shelter when directed. Training drills are noted as

useful exercises, similar to evacuation training drills.

Available Performance Information

Key variables related to this approach include the airtightness of interior partitions of the shelter

and the airtightness of the exterior envelope of the building itself. Existing building airtightness
92

data were discussed under the Envelope Airtightening approach. Even less information is

available on shelter airtightness, but studies are in progress that include such measurements.

If filtration or air cleaning is employed, the airflow rate through that system and the filter/air

cleaner removal efficiencies for the contaminant of concern are relevant. Airflow rates are

generally specified for commercial units or can otherwise be determined for systems designed 

for specific installation. As discussed earlier, particulate removal efficiencies are expressed in 

terms of MERV levels but gaseous air cleaning efficiencies are more difficult to determine.

Protective Impacts

Shelter-in-place can provide significant protection against outdoor contaminant releases, as seen 

in the simulation results in Section 2. Timing of occupant movement into the shelter is critical,

however, as is the timing of their leaving the shelter after the outdoor contaminant has cleared.

The simulations discussed in Section 2 showed exposure reductions on the order of 90 % or more

if the occupants moved into the shelter before the release for a two-hour sheltering period.

Filtration and air cleaning reduce exposure even more. But moving into the shelter after the

release had begun greatly reduces the effectiveness of the sheltering.

The parameters that will determine the effectiveness of shelter-in-place are the exterior envelope

and shelter airtightness values, the outdoor weather driving infiltration and contaminant into the

building, interior zoning and temperatures as they affect internal airflow patterns, the relative

timing and duration of the release and the sheltering, and the existence and effectiveness of any 

filtration and air cleaning employed.

A significant amount of research has also been done on shelter-in-place, but most of it focuses on 

the building itself as the shelter as opposed to a designated space within the building (Blewett

and Arca 1999, Fradella and Siegel 2005, Sohn et al. 2005). Jetter and Whitfield (2005)

examined the protection provided by an interior bathroom of a residence, in which tracer gas

tests were used to estimate airflow rates between the shelter, the rest of the house and the

outdoors. A later experimental study by Jetter and Proffitt (2006) considered the protection 

offered by shelters in commercial buildings. Swansiger et al. (2005) looked at the use of interior

stairwells, pressurized with filtered outdoor air as an SIP option.

Costs

There is some cost involved in setting up a shelter-in-place, particularly airtightening of the

interior partitioning and equipment costs for a filtration and air cleaning system if employed. In 

general, these systems are only employed if needed, and therefore they are not associated with 

any significant operating costs. There are some maintenance costs to ensure that the system will

function properly in the event it is needed.

Knowledge gaps

While shelter-in-place is fairly straightforward, the biggest question regarding its implementation

is knowing that a release has taken place, or is about to take place, and that sheltering is the

appropriate action. A warning system based on contaminant monitoring could answer these

questions, but this type of warning system is not typically available. Therefore, better

information is needed on how to determine that sheltering is called for, and when the occupants

should subsequently leave the shelter and go outdoors. There is also a need for better information

on shelter airtightness values and how these values relate to the degree of protection offered.
93

SUMMARY

Shelter-in-place, especially when implemented in a timely fashion, can reduce exposure to

outdoor releases. The reductions will be higher if filtration and air cleaning are employed in the

shelter. Effective sheltering depends on proper selection of shelter spaces in a building,

airtightening of the partitions to adjacent spaces, and training of the occupants to move quickly 

to the shelters when directed to do so.

4.3.6 Isolation of Special-use Spaces

Objective

To limit contaminant releases in vulnerable spaces from impacting the rest of the building,

thereby reducing exposure to the bulk of the building occupants.

Description

Some building spaces are more vulnerable to interior releases due to public access (e.g., lobbies

and parking garages) or mail and delivery activities (e.g., mail rooms and loading docks). Due to

the increased vulnerability of such spaces, keeping them at a lower pressure than adjacent

portions of the building can provide some protection in the event of an incident. Such isolation 

can be achieved through ventilation airflow control, i.e., exhausting more air than is being

supplied, and will generally be easier to achieve and control if these spaces are served by a

dedicated system. This approach is more likely to be successful if attention is paid to the

airtightness of the boundaries between the space and the rest of the building.

Available Performance Information

The effectiveness of this approach is determined by the magnitude of the negative pressure

achieved in the space relative to adjoining spaces, which is a function of the system airflows to

and from the space and adjoining spaces as well as the airtightness of the space boundaries.

Other important variables include weather conditions as they impact building pressures and the

operation of other ventilation systems in the building. The supply and exhaust airflow differential

and the airtightness of the space boundaries required for effective isolation need to be considered 

on a case-by-case basis as impacted by system airflow rates, weather conditions, and location of

the space in the building. For example, lower level spaces, which include lobbies, loading docks

and many mail rooms, are more subject to stack-driven flows upward within a building.

Multizone airflow modeling is useful in assessing these situations and defining system airflows

and levels of partition airtightness required for effective isolation.

Protective Impacts

If effectively implemented, space isolation will limit contaminant migration to other spaces

within a building. The occupants of the space where the release occurs will be exposed, however,

perhaps to significant quantities of contaminant, and this approach will not protect them.

Examples of this approach were discussed in the case study of the high-rise office building,

where isolating the mail room and the lobby was considered.

Costs

There may be some initial costs associated with airtightening or modifications of system airflow

rates to achieve the desired pressure relationships. The latter will require some maintenance in

terms of periodically checking system balancing to determine that these pressure relationships

still exist. In some cases a new air handling system may be required, which will also involve
94

some operating costs. There may also be some first and maintenance costs associated with 

controls to modulate the system airflows in response to real-time pressure monitoring between 

the space and an adjacent space. The costs of isolating the mail room and the lobby of the highrise case study building are discussed in Section 3.

Knowledge gaps

Additional information on interior partition airtightness, as typically constructed and after

airtightening, would be helpful in the design of isolation strategies. These data would also allow

more specific guidance on the differential airflow quantities required for effective isolation as a

function of building climate as well as floor plan and elevation.

SUMMARY

Isolation of special-use spaces can contain indoor contaminant releases, thereby protecting the

rest of the building from significant exposure. This approach requires consideration of the

pressures that need to be counteracted and will be more effective if the partitions to adjacent

spaces are air sealed.

4.3.7 System Shutdown and Purging

Objective

To effectively implement a quick shutdown of all ventilation systems or to induce a 100 %

outdoor air purge when such actions will reduce occupant exposure to a contaminant release.

Description

In some circumstances, shutting down a building ventilation system or operating it with 100 %

outdoor air intake may help protect building occupants from a chembio release. Shutdown 

involves turning off all ventilation equipment, including makeup air and exhaust fans. It is

important to include all equipment, since leaving on a toilet exhaust system will contribute to 

building depressurization and actually increase contaminant entry for an outdoor release.

Implementing a 100 % purge can be effective in removing an agent that has already been 

distributed within a building. Ventilation systems equipped with economizer cycles are already 

equipped with the necessary controls to implement such an action. However, for both shutdown 

and purging, the circumstances under which such an action will be beneficial are very dependent

on the release location and timing, the amount of time that has passed since the release occurred,

and how much contaminant if any has been distributed within the building and where.

Timing is critical to the effectiveness of a shutdown response, and a single-switch or “panic

button” that implements shutdown all at once instead of having to individually deactivate each 

piece of equipment will support more timely implementation. Such single-switch control is

generally much easier to set up in digital control systems than in pneumatic systems, though the

latter can result in faster transmission of the action to the equipment. The location of the switch

and the protocols for who operates and under what circumstances are critical issues that need to 

be considered in advance of any incident, and training exercises are useful to increase the

likelihood that such a response will be implemented as intended.

Even with good controls and a single switch, it takes time for a typical ventilation system to shut

down due to delays associated with fan spin-down and damper closing. These delays can be

countered by installing braking systems on fans and quick closing, tight dampers, but these items

are not standard in commercial building systems and will increase costs.
95

Available Performance Information

Since both shutdown and purging are building-specific in their implementation and impact, there

are no generic performance data describing these approaches. In a given building, key

performance parameters include the building air change rate, i.e., infiltration under shutdown and 

the intake airflow under purging, and the time it takes to implement the response.

In the case of shutdown, the system-off infiltration rate of a building is a strong function of

weather conditions. This rate can be measured with tracer gas techniques or predicted with

multizone airflow modeling, but these approaches require a certain level of sophistication.

Perhaps more important is to assess and understand the airflow patterns into and within a

building with the system off. These patterns can be assessed through the use of smoke pencils

and the measurement of pressure differences at key locations in the building, including entrances

(including secondary entrances such as loading docks), elevator and stairway doors at multiple

building levels, windows at multiple elevations, and roof access doors. Such an effort can help to

understand where air enters and leaves the building with the system off and thereby result in a

better sense of where contaminants may enter the building and how they might move through it.

It is important to conduct such an airflow assessment under different weather conditions (wind 

and outdoor temperature), as the airflow patterns will be impacted by weather.

Purging airflows are less likely to be impacted by weather, but it is still important to verify that

the implementation of a purge cycle operates as intended. Verification can involve measuring

system airflows, in particular the outdoor air intake rate. A less involved assessment includes

inspecting the intake, recirculation and exhaust dampers and the fan speeds to make sure the

system is in fact operating in a manner that will bring in the maximum amount of outdoor air.

Protective Impacts

The degree of exposure reduction from either a shutdown or purge is dependent on the timing of

the response relative to the release, the location of the release relative to the occupants, and the

building layout and system design. This variability was seen in the simulation results presented 

in Section 2, where timing was seen to be critical and the exposure impacts were quite variable

based on the details of the release.

Shutdown is likely to be most effective if an outdoor release has occurred and there is sufficient

warning to initiate the shutdown before the contaminant is brought into the building by the

ventilation system. In some circumstances, a shutdown may also be effective if an agent has

entered a building or has been released indoors and shutting down the system prevents the

contaminant from being distributed within the building. However, realizing the benefits of a

shutdown in such a situation requires a level of understanding of the release timing and location 

and the building airflow patterns that is not necessarily realistic. Also, system shutdown will lose

the ability to pressurize the building with the system, which will increase contaminant entry if an 

outdoor release is still in progress.

A purge cycle makes sense if a contaminant has already been distributed within a building and 

the best course of action is to remove it as quickly as possible. Such situations include a release

into a system return, or even an intake, or a localized release that has mixed within the building.

However, realizing the benefits of a purge cycle requires knowledge that such an event has

occurred and the contaminant has migrated within the building to a degree that purging makes

sense. There is the associated issue of occupant awareness during such an event. If there is

sufficient awareness of the circumstances of an event that purging is an appropriate response,

then it is likely that evacuation of the occupants is also a reasonable response as well. One

exception might be if evacuation is not an option due to conditions outside the building.
96

Costs

There are costs associated with the controls to quickly convert system operation into a shutdown 

or purge mode, as well as the periodic maintenance to confirm that the controls are operational.

The costs will depend on the system type and complexity, and the controls that already exist in

the building. A detailed design review will be required to determine what work is needed to

implement these controls and the costs involved, as was done in the two case study buildings. If

fan braking systems and quick acting dampers are required, they will increase costs accordingly.

There are no economic benefits associated with shutdown and purge capabilities, but having 

them in place does provide a response that might be appropriate under other circumstances such 

as less extreme indoor air quality incidents.

Knowledge gaps

As noted above, the most important information gaps are how shutdown and purging will impact

airflow patterns and contaminant movement in a specific building under a specific release

scenario. More studies of their implementation in individual buildings should improve our

general understanding of the impacts, as well as how and when to implement these responses.

SUMMARY

As noted above, the degree of exposure reduction from either a shutdown or purge response

depends on the timing of the response, the nature of the release, and the building layout and 

system design. It is unlikely to be entirely clear when either response is advised, but having the

capability is worth considering in the event that it is needed. Even if the controls and equipment

are not modified to speed the implementation of shutdown or purging, it makes sense to know

how to shut down all systems quickly, how to implement a purge cycle using existing controls,

and how either action will impact air movement patterns in a building. Note that in the absence

of reliable information regarding a chembio release, implementing a shutdown or purge cycle

can actually increase rather exposure in some circumstances.

4.3.8 Automated HVAC Response

Objective

To modify the operation of a building’s ventilation system in response to a contaminant sensor in 

a manner that reduces occupant exposure.

Description

Given a timely and reliable signal from a contaminant sensor, a building’s automated control

systems could modify ventilation system operation to contain the contaminant in the zone of an

indoor release, or in the case of an outdoor release to prevent it from entering a building and to 

maintain the rest of the building and egress paths at low and presumably safe concentrations.

These modifications could include stopping and starting fans, repositioning dampers, or securely 

closing doorways. These concepts have been used for many years in smoke control systems to 

contain smoke in the fire zone and provide a safe evacuation route for the building occupants

(Klote and Milke 2002). The manner in which a system’s configuration and operation would be

modified depends on the building and system design, and the nature of the contaminant release.

Available Performance Information

The speed, reliability, and ultimately cost contaminant sensors are key to the application of

automated HVAC response and can be considered the weak link. Given the speed at which air
97

moves within buildings, a very fast sensor is required to initiate a change in system operation

before the contaminant has spread within the building and defeated the goals of the approach.

Also, the sensor must be reliable to avoid both false negatives and positives. Sensors also need to 

have a range of detection capabilities to cover the various chemical and biological agents of

interest. In addition to fast sensors, the system changes also need to be implemented more

quickly than most ventilation systems can change operating modes. This requirement means that

fast acting and tight dampers will need to be installed in place of typical dampers. Fan braking 

systems are also needed to stop the airflows more quickly than is generally possible in typical

ventilation systems.

Protective Impacts

In theory, if the sensors and system capabilities are available, and the building and system

airflow dynamics are well understood, this approach would be able to provide a high level of

protection. However, sensors that are fast and inexpensive enough are not currently available for

any applications other than very high security buildings where the costs are justified. Until

sensor cost and reliability improves, this approach is not a practical option in other buildings.

Costs

The cost of this approach includes the contaminant sensors, which are very expensive at this time

and include both the first and maintenance costs. In addition, the tight dampers and fan braking

systems noted above also involve first costs. Finally, such a system will involve design costs

related to the system and control modifications.

Knowledge gaps

As noted, the biggest need to make this option more realistic is the development of fast, reliable

and affordable sensors covering a range of chembio agents. Much work is in progress in sensor

development, but it will still be some time before the sensors are available to support application

of this approach at a reasonable cost.

SUMMARY

While automated HVAC operational changes can in theory reduce occupant exposures, the

technology to implement this approach does not currently exist. It is not clear when the situation 

will change, but it is likely some years before this option will be widely available.
98
99

4.4 Guidance Summary

This section has reviewed a number of retrofit technologies and options for controlling exposure

to chemical and biological contaminant releases. The guidance provided is summarized in Tables

27 and 28. Note the separate entry in the fifth row Table 27 for filtration and gaseous air cleaning 

that points out the key advantage that these technologies are always in effect, assuming the

systems are properly installed and maintained, and therefore there is no need for proper timing or

implementation decisions. Also, filtration and air cleaning will not increase exposure if

implemented at the “wrong” time, unlike some other responses. The biggest problem with

gaseous air cleaning in particular is the lack of standards for testing and rating these systems, but

efforts are underway that should remedy this situation.

Retrofit Advantages Disadvantages Comments

Enhanced

Particle 

Filtration

Protection against bioagents.

Standard for removal

efficiency, MERV values.

Part of current practice.

General IAQ improvements.

Pressure drop associated

with high efficiency

filters.

Must control filter 

bypass before

upgrade.

Combination with

envelope tightening

provides maximum

protection against

outdoor releases.

Gaseous Air 

Cleaning

Protection against gaseous

agents.

General IAQ improvements.

No standard test method.

Pressure drop associated

with high efficiency

filters.

More design guidance

needed.

Challenge of protecting

against range of 

gaseous contaminants.

UV

Germicidal

Irradiation

Protection against bioagents.

Low pressure drop.

General IAQ improvements.

No standard test method.

Design guidance needed.

Challenge of protecting

against range of 

biological

contaminants.

Photocatalytic 

Oxidation

Protection against bioagents

and gases.

Low pressure drop.

No standard test method.

No standard method to

determine if catalyst has

become poisoned.

Design guidance needed.

Challenge of protecting

against range of 

biological and

gaseous contaminants.

All filtration 

and air

cleaning

technologies

Always operating; no timing

issues.

Doesn’t increase exposure 

for any release scenarios.

Lack of test methods for 

gaseous air cleaning,

UVGI and PCO.

Must address envelope 

air leakage to realize

effectiveness.

Bypass will decrease

effectiveness.

Combination of 

methods needed to

protect against range 

of chembio agents.

Work-area

Treatment

Capture of contaminant

releases associated with

localized activities.

Current equipment not

rated for capture 

efficiency.

Lack of test methods for 

gaseous removal.

Table 27 Summary of Retrofit Guidance for Retrofit Technologies
100

Retrofit Advantages Disadvantages Comments

System

Recommissioning

Improves reliability of 

HVAC systems for other 

protective responses.

IAQ and energy efficiency

improvements.

Provides no additional

protection beyond that

inherent in the design.

Benefits depend on

difference between

design intent and

existing

performance.

Envelope 

Tightening

Protects against outdoor 

releases if effective 

filtration in place.

IAQ and energy efficiency

improvements.

Effective filtration

required to realize

benefits.

More data needed on

cost and

effectiveness of 

sealing retrofits.

Building

Pressurization

Protects against outdoor 

releases if effective 

filtration in place.

Challenging to implement

and maintain under all

conditions in some 

buildings.

Amount of extra 

outdoor air based

on climate and

airtightness.

Pressurization can

lead to envelope

moisture problems

in cold climates.

Relocation of Air 

Intakes

Protects against tampering

with accessible intakes.

Potential IAQ benefits by

avoiding ground level

contaminant sources.

Can be costly and

impractical in some

circumstances.

Shelter-in-place Protects occupants against

outdoor, and some 

indoor, releases.

Timing of occupant

movement critical to

effectiveness.

Need to know that an

incident has taken place 

that merits sheltering.

Occupant training

and

communication

important.

Isolation of 

Special Spaces

Protects bulk of building

from releases in more

vulnerable spaces.

Does not protect those in

space of release.

Requires design

based on driving

pressures and

airtightness.

Lack of clear 

guidance on design

pressure difference.

Shutdown and

Purging

Can protect against

outdoor or indoor 

releases under some 

circumstances.

Poor timing can increase

exposure.

Requires knowledge that

an incident has taken

place that merits action.

Even if proper action

not always

obvious, capability

has value.

Automated 

HVAC Response

Can contain release and

provide occupants with

low contaminant zones.

Requires sensing beyond

current technology.

Proper response depends

on details of system and

release; not always clear.

Wrong timing or action

can increase exposure.

Table 28 Summary of Retrofit Guidance for Retrofit Approaches
101

Given the wide range of potential retrofit options, decisions on which options to implement can 

be confusing. While the appropriate actions in a given building are inherently specific to that

building, Table 29 presents a very simplified framework for considering the various retrofit

options discussed in this report. The table contains four categories, with the first being those

retrofits that may reasonably be implemented in any building. These include recommissioning 

and enhanced particle filtration based on the energy and IAQ benefits. Shelter-in-place is also 

included in this category because it is good to have such a contingency plan in response to a wide

range of events. Shelter-in-place may range from simply designating such spaces in a building,

and perhaps some minimal air sealing, to a more comprehensive effort to prepare a space that

might include high levels of air sealing, provisions for food and water, and filtration and air

cleaning capabilities. The second category includes options that should be considered 

independent of the threats to a given building. The first two are included based in part on their

energy and potential IAQ benefits, but since they can be quite complex and costly in some

facilities, they may not be appropriate in all circumstances. Shutdown and purging are also 

included in the category because they are good options to have available, but may not be readily 

implemented in some systems without costly modifications.

RETROFITS COMMENTS

Implement in any building

System Recommissioning

Enhanced Particle Filtration

Based on energy and IAQ benefits.

Shelter-in-place

Range of options depending on threats and

building.

Consider independent of threats

Envelope Tightening

Building Pressurization

Based on energy and potential IAQ benefits.

Shutdown and Purging

As long as not cost-prohibitive for existing

HVAC system and controls.

Consider if threats indicate and costs

commensurate

Isolation of Special Spaces

Relocation of Air Intakes

Work-area Treatment

Gaseous Air Cleaning

More performance data or technology

development needed for general application

UV Germicidal Irradiation

More likely to be appropriate in healthcare 

facilities.

Photocatalytic Oxidation

Automated HVAC Response

Table 29 Framework of Retrofit Options

The third category includes several retrofits whose implementation must be carefully considered 

based on the threats and costs. This category is probably one of the more challenging situations,

where one must balance the risk of the threats with potentially significant costs. The fourth

category includes two air purification technologies that while commercially available are not
102

associated with a lot of performance data and design guidance. They may be appropriate in some

situations, but it can be difficult to determine at the present time. Automated HVAC response is

also listed in the final category due primarily to the limits of current sensor technology.

Nevertheless, there are some situations where the risks may be so significant that this approach 

needs to be employed despite it cost and challenges.
103

5. CONCLUSIONS

This report has presented and discussed a number of retrofit options for improving the protection 

of buildings against chembio releases, including information as to their potential impact on 

occupant exposure and their cost. This information is intended to help building owners and 

others faced with decisions of how best to protect their buildings from such releases. In order to

make these decisions for a particular building, the responsible parties must begin with an

assessment of the risk of the building and its vulnerabilities, and as a result determine the level of

protection and the associated expenditures that are appropriate. These decisions are difficult,

though some guidance has been developed to assist in making them. But given that a decision

has been made to increase the protection of a building through the application of such retrofits,

the information in this report should be useful in determining which retrofits make sense for a

given building and system and how they should be implemented.

The retrofit options considered in this report focus on commercially available options for

engineering and building system retrofits, as opposed to physical security and other building 

management approaches. The options include filtration and air cleaning technologies, changes in 

ventilation system operation, attempts to reduce the entry of outdoor releases via envelope

infiltration, and shelter-in-place. However, before pursuing any of these retrofit options in a

particular building, it is essential to assess the current condition of the building’s HVAC systems

and to bring their operation in line with the design intent through a so-called recommissioning 

effort. Such an effort should address system airflow rates, control systems and the associated 

sensors, filter fit and air seal, and other aspects of system operation and maintenance. Without a

properly operating ventilation system and a maintenance program to keep it that way, no retrofit

should be expected to provide the level of protection of which it may be capable.

In terms of the retrofits themselves, filtration and air cleaning have the advantage of not relying

on any advance warning of a release and a human or automated response. Particle filtration

benefits from an established method of test that allows one to select filters based on MERV

ratings, while gaseous air cleaning and other air cleaning options do not yet have such a method 

of test. This lack of standards makes it much more difficult to specify such systems and to 

determine the anticipated benefits. For a filtration or air cleaning system to be effective, it must

be properly installed and maintained over time with a focus on controlling bypass around the

filters. When considering outdoor contaminant sources, reducing envelope leakage is critical to

achieving the potential benefits of filtration. If the building has typical levels of envelope

airtightness, the resulting infiltration can defeat the high levels of protection that are possible

with good filtration and air cleaning. Similarly, while reducing infiltration through airtightening

and system airflow control can provide protection against such outdoor releases, these

approaches are much more effective if there is good filtration of the intake air.

Many of the other retrofit options require sound operational decisions during a chembio release

in order to provide effective protection. Such decisions include whether and when to shut down a

system or use it to purge the building, and whether and when to send occupants to a shelter-inplace zone. Making and implementing these decisions depends on knowledge about the event,

training in advance of the event, and communications both before and during the event.

While this effort has provided useful insight and tools for considering chembio retrofits,

additional work would be valuable in increasing the understanding of retrofit impacts for more

building and system types, release scenarios and retrofit approaches. In particular, there are

specific building types that are fairly unique and merit more individual attention such as

educational, healthcare and retail facilities. In addition, unitary systems and fan coil units are

limited in the filtration options that they can accommodate and need to be examined more
104

closely. Finally, there are an infinite number of release and building occupancy scenarios that

may be considered. Further examination beyond the generic cases studied here are likely to 

provide additional insights into building protection. Other ideas for followup work include field

testing to ‘validate’ the simulation results, tools to help with the design and implementation of

the retrofit options, and research to document the indoor air quality and energy efficiency 

benefits of some of the retrofits.
105

6. ACKNOWLEDGEMENTS

This effort was supported by the U.S. Environmental Protection Agency under Interagency 

Agreement No. DW-13-93010301-0, but was not subjected to EPA peer review. The conclusions

in this paper are therefore those of the authors and are not necessarily those of the U.S. EPA. The

authors express their appreciation to John Chang and Jacky Rosati at EPA, as well as Harold

Marshall, Julie Wean, Doug Thomas, and Jatin Patel at NIST. The assistance of Jose Reig and 

Guillermo Ramsey of ESE Architects and Engineers are also acknowledged. The following

reviewers made many helpful suggestions that are greatly appreciated by the authors: William

Bahnfleth, Barney Burroughs, Joan Bursey, Michael Gressel, Patrick Spahn and Steve Treado.
106

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111

Appendix A: Life-Cycle Cost Analysis Tool for Chem/Bio Protection of Buildings:

Software Primer (software available for download at

http://www2.bfrl.nist.gov/software/LCCchembio/index.htm)

Background

The National Institute of Standards and Technology (NIST) is a non-regulatory federal agency 

within the U.S. Commerce Department’s Technology Administration. NIST develops and 

promotes measurement, standards, and technology to enhance productivity, facilitate trade, and 

improve quality of life. In the aftermath of the attacks of September 11, 2001, NIST has taken a

key role in enhancing the nation’s homeland security.

NIST’s Building and Fire Research Laboratory (BFRL) has as its mission to meet the

measurement and standards needs of the building and fire safety communities. A key element of

that mission is BFRL’s commitment to homeland security. Specifically, the goal of BFRL’s

homeland security effort is to develop and implement the standards, technology, and practices

needed for cost-effective improvements to the safety and security of buildings and building

occupants, including evacuation, emergency response procedures, and threat mitigation.

Due to concerns about potential airborne chemical and biological releases in or near buildings,

building owners and managers and other decision makers are considering retrofitting their

buildings to provide better protection against such events. A wide range of technologies and 

approaches are being proposed with varying levels of efficacy and cost, as well as with varying 

degrees of applicability to any particular building or ventilation system.

Through support from the EPA Safe Buildings Program, BFRL’s Indoor Air Quality and

Ventilation Group and the Office of Applied Economics (OAE) are developing guidance on 

building retrofit technologies and approaches to promote increased building protection from

chemical and biological attack. This guidance will provide building owners, managers,

engineers, and other decision makers with information about various retrofit strategies to

improve the safety of their buildings against airborne hazards and with economic tools for use in 

selecting cost-effective approaches to mitigating those hazards.

The Life-Cycle Cost Analysis Tool (LCAT) for Chem/Bio protection of buildings incorporates

and integrates research being conducted by OAE under the EPA Safe Buildings Program and

under BFRL’s homeland security effort. OAE’s research focuses on developing economic tools

to aid facility owners and managers in the selection of cost-effective strategies that respond to

natural and man-made hazards. Economic tools include evaluation methods, standards that

support and guide the application of those methods, and software for implementing the

evaluation methods. OAE’s research has produced a three-step protocol for developing a risk 

mitigation plan for cost-effective protection of constructed facilities. This protocol has three

essential components: risk assessment, identification of potential mitigation strategies, and 

economic evaluation. LCAT is designed to help implement the third step in the protocol,

economic evaluation.

A brief synopsis of the three-step protocol is provided here. Users interested in an in-depth 

description of the three-step protocol are referred to NISTIR 7073. Risk assessment is used to 

identify the risks confronting a facility and includes development of possible damage scenarios,

probability assessments for these scenarios, and identification of the facility’s vulnerabilities and 

critical areas. Identification of mitigation strategies provides performance and cost data for the

possible combinations of risk mitigation strategies. Combinations of risk mitigation strategies are
112

used to create a candidate set of alternatives for in-depth economic evaluation. The third 

component, economic evaluation, enables building owners and managers to evaluate each 

alternative combination of risk mitigation strategies and the sequence of cash flows associated 

with their implementation. The alternative combination that results in the lowest life-cycle cost

is designated the cost-effective risk mitigation plan.

Economic Evaluation Methods

Several methods of economic evaluation are available to measure the economic performance of a

new technology, a building system, or like investment, over a specified time period. Two of

these methods—life-cycle cost and present value of net savings—are especially well suited to the

economic evaluation of Chem/Bio hazard mitigation retrofit strategies. OAE has extensive

experience with both methods. OAE’s research on life-cycle cost analysis spans more than 30 

years. Early work by OAE economists led to the development of an industry consensus standard,

ASTM E 917, for the life-cycle cost method. OAE’s life-cycle cost research was extended to the

economics of protection against natural disasters shortly thereafter. More recent work has

focused on specifying cost-effective responses to terrorist risks. OAE’s research on present value

of net savings paralleled its research on the life-cycle cost method and led to the development of

an industry consensus standard, ASTM E 1074. OAE’s ongoing research links the standardized 

economic evaluation methods with a well-defined cost-accounting framework and software to 

make implementation straightforward. The algorithms “sit” behind the LCAT graphical user

interface. OAE believes most users prefer it that way, so they can focus on only those data

elements required to perform the life-cycle cost calculations. Users interested in mastering the

calculation procedures/algorithms employed in LCAT are referred to NISTIR 7073.

Life-Cycle Cost Method

The life-cycle cost (LCC) method measures, in present-value or annual-value terms, the sum of

all relevant costs associated with owning and operating a building over a specified period of

time. The basic premise of the LCC method is that, to an investor or decision maker, all costs

arising from that investment decision over time are potentially important to that decision.

Applied to Chem/Bio hazard mitigation, the LCC method encompasses all relevant costs over a

designated study period, including the costs of designing, retrofitting, constructing/installing,

operating, maintaining, repairing, replacing, and disposing of a particular design or system. Pure

benefits that result (e.g., increased rental income due to improvements) are also included in the

calculation of LCC.

The LCC method is particularly suitable for determining whether the higher initial cost of a

building or system specification is economically justified by lower future costs when compared 

to an alternative with a lower initial cost but higher future costs. If a design or system

specification has both a lower initial cost and lower future costs relative to an alternative, an 

LCC analysis is not needed to show that the former is economically preferable.

The alternative with the lowest initial investment cost (i.e., first cost) is typically referred to as

the base case. The LCC method compares alternative, mutually exclusive, Chem/Bio retrofit

strategies that satisfy a minimum level of functionality to determine which is the least-cost

means (i.e., minimizes life-cycle cost) of satisfying that level over a specified study period.
113

Present Value of Net Savings Method

Information used to compute LCC can also be used to calculate the present value of net savings

(PVNS). PVNS measures the net savings from investing in a given alternative instead of

investing in the foregone opportunity (e.g., the base case). PVNS equals the difference between 

the LCC of the base case and the LCC of the mutually exclusive alternative under consideration.

Any pure benefits that result (e.g., increased rental income due to improvements) are included in

the calculation of PVNS, since they are included in the LCC calculation. With respect to the base

case, if PVNS is positive, the alternative is economic; if it is zero, the alternative is as good as

the base case; if it is negative, the alternative is uneconomical.

Getting Started

The software includes four case study applications. The four case study applications are: (1) a

high-rise office building; (2) an office building lobby; (3) an office building mail room; and (4) a

single-story office building. Associated with each case study application are two case study files.

One file is a high-level summary of the proposed retrofit alternatives. The second file contains a

detailed listing of cost items associated with each of the proposed retrofit alternatives. The case

study files provide a convenient frame of reference through which you can learn about the

capabilities of the software and experiment with the various means for editing, creating, and 

deleting data elements. The case study files are designed to illustrate a wide variety of software

features through a set of simplified, yet fairly realistic building-related examples.

Tips on Analysis Strategy

Developing a cost-effective risk mitigation plan is a complicated process, entailing two distinct

levels of analysis. This “analysis strategy” systematically adds increased detail to the decision 

problem. The first level is referred to as the baseline analysis. Here we are working with our best

“guess” estimates. The baseline analysis provides a frame of reference for the sensitivity 

analysis, which systematically varies, selected sets of data elements to measure their economic

impacts on project outcomes, such as the life-cycle costs of competing alternatives.

The starting point for conducting an economic evaluation is to do a baseline analysis. In the

baseline analysis, all data elements entering into the calculations are fixed. For some data, the

input values are considered to be known with certainty. Other data are considered uncertain and 

their values are based on some measure of central tendency, such as the mean or the median, or

input from subject matter experts. Baseline data represent a fixed state of analysis. For this

reason, the analysis results are referred to as the baseline analysis. The term baseline analysis is

used to denote a complete analysis in all respects but one; it does not address the effects of

uncertainty. When you open any of the case study files, the data elements displayed on the

various software screens are the baseline values.

Sensitivity analysis measures the impact on project outcomes of changing the values of one or

more key data elements about which there is uncertainty. Sensitivity analysis can be performed 

for any measure of economic performance (e.g., life-cycle cost or present value of net savings).

Therefore, a sensitivity analysis complements the baseline analysis by evaluating the changes in 

output measures when selected data inputs are allowed to vary about their baseline values.
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Overview of the Case Study Applications

The case study applications describe a variety of Chem/Bio retrofit strategies for four

prototypical building renovation projects. Note that the cost estimates are for purposes of

illustration only—actual renovations of different building types will face different costs and 

different risk profiles. The cost data associated with the four prototypical building renovation

projects are presented in Appendix C of this report, where they are presented at two levels of

detail. A “summary” format highlights the key cost items. The summary listing records the type

of cost information that would be suitable for presentation to senior management or other

decision makers. The summary formats provide the basis for the four sets of Summary case study 

files—one for each prototypical building renovation project. A “detailed” format covers the type

of cost information that would be provided as part of a building condition assessment. The

detailed listing of cost items “rolls up” into the cost items listed in the summary format. The

detailed formats provide the basis for the four sets of Detailed case study files.

Assumptions and Cost Data

Each of the four case study applications covers a 20 year period beginning in 2005. Life-cycle

costs are calculated using a 7 % real discount rate for the baseline analysis. Information on cost

items is needed in order to calculate life-cycle costs. Cost items are classified under two broad

headings: (1) protection costs and (2) event-related losses.

Protection costs represent all costs tied to the building or facility under analysis that are not

associated with an event. Protection costs include the initial capital investment outlays for

facilities and site work, future costs for filter replacements and electricity for fan motors, future

costs for space heating and cooling, future renovations, and any salvage value for plant and 

equipment remaining at the end of the study period. Protection costs are classified as either

investment costs or non-investment costs.

Event-related losses are based on annual outcomes, each of which has a specified probability of

occurrence. Each outcome has a non-negative number of cost items associated with it (i.e., an

outcome may have no cost items associated with it if it results in zero losses). Note that although

logic is included within the software tool to handle event-related losses, no estimates of these

losses are included in the case study applications.
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High-Rise Office Building

The objective is to protect an 11 story high-rise office building from external discharge of

contaminants from a single source near the outside air intakes and from a larger cloud 

approaching the building. The floor area of the 11 story high-rise office building is 11 148 m

2

(120 000 ft

2

). The building was erected in the mid-1960s and has a rectangular configuration.

The building has been well maintained and does not show significant signs of aging. The outside

air intake louvers are approximately 6.1 m (20 ft) above the ground. A variety of materials

compose the exterior envelope, including granite, marble, face brick, glass, and extruded

aluminum. The facades on the short axis of the building are faced with grey face brick. The

facades on the long axis of the building are insulated porcelain spandrel panels and fixed 

aluminum frame windows.

The high-rise office building includes a lobby and a mail room. Retrofit strategies to protect the

lobby from a discharge of contaminants carried by an individual and to protect the mail room

from introduction of contaminants in mail packages are handled in separate analyses.

To protect the building from an external release of contaminants, it is desirable to seal the

building envelope and retrofit filters in the air-handling units. The proposed improvements are

presented as three options. Each option has a different filtration level.

Retrofit Alternatives for Protecting the High-Rise Office Building

Option 1 (Filtration Level 1) provides a low level of particle filtration capability and no gaseous

capability. Option 1 involves the following set of improvements. Sealing the exterior windows to 

make the building more airtight. Relocating the outside air intake to the roof. Replacing existing 

Minimum Efficiency Reporting Value (MERV) 6 filters with MERV 11 high capacity filters.

Modifying the electrical feeders to accommodate higher motor horsepower. Providing an 

electrical quick shut off mechanism to stop the air handlers and return exhaust fans as needed 

during an emergency. Sealing and isolating six conference rooms to serve as shelters-in-place

during an emergency.

Option 2 (Filtration Level 2) provides a high level of protection against particles but no gaseous

protection. Option 2 involves the following set of improvements. Sealing the exterior windows to 

make the building more airtight. Relocating the outside air intake to the roof. Replacing existing 

MERV 6 filters with a three-stage filter consisting of: MERV 8 pre-filter, 85 % efficient MERV

13 intermediate filter, and a 99.97 % High Efficiency Particulate Air (HEPA) filter. Modifying 

the electrical feeders to accommodate higher motor horsepower. Providing an electrical quick 

shut off mechanism to stop the air handlers and return exhaust fans as needed during an 

emergency. Sealing and isolating six conference rooms to serve as shelters-in-place during an 

emergency.

Option 3 (Filtration Level 3) provides a high level of protection against particle and gaseous

agents. Option 3 involves the following set of improvements. Sealing the exterior windows to 

make the building more airtight. Relocating the outside air intake to the roof. Replacing existing 

MERV 6 filters with a five-stage filter consisting of: MERV 8 pre-filter, 85 % efficient MERV

13 intermediate filter, 99.97 % HEPA filter, 99.9 % gas phase filter, and MERV 11 post filter.

Modifying the electrical feeders to accommodate higher motor horsepower. Providing an 

electrical quick shut off mechanism to stop the air handlers and return exhaust fans as needed 

during an emergency. Sealing and isolating six conference rooms to serve as shelters-in-place

during an emergency.
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Office Building Main Lobby

The objective is to protect the main lobby from a discharge of contaminants carried by an 

individual. The main lobby is a 4.3 m (14 ft) high space that is approximately 325 m

2 (3 500 ft2

)

in size. The lobby is defined by exterior glass curtain walls on two sides and marble finished 

walls on the other two sides. It is accessed from the exterior through a 14 m2 (150 ft

2

) glass

enclosed vestibule with a series of two rows of four balanced glass doors. The lobby is open to

an elevator bank.

To protect the main lobby from a discharge of contaminants carried by an individual, it is

desirable to isolate the lobby with airtight walls and doors and to provide an air conditioning

system dedicated to the lobby capable of maintaining the entire lobby under negative pressure.

The system must also be capable of purging the lobby—one hundred percent outside air and

exhaust—and filtering the supply and exhaust air. The proposed improvements are presented as

two options. Each option has a different filtration level. The two options link to Filtration Levels

2 and 3 for the high-rise office building. Filtration Level 1 was not considered because it would 

not provide the level of protection desired for the main lobby.

Retrofit Alternatives for Protecting the Main Lobby

Option 1 (Filtration Level 2) provides a high level of protection against particles but no gaseous

protection. Option 1 involves the following set of improvements. Isolate the open side of the

lobby from the rest of the building by installing tempered glass partitions with self-closing doors

that allow building occupants continued access to the lobby. Install a new air handling unit to 

serve the main lobby only. Relocate the outside air intake to the roof. Equip the air handling unit

with a three-stage filter consisting of: MERV 8 pre-filter, 85 % efficient MERV 13 intermediate

filter, and a 99.97 % HEPA filter. Modify electrical feeders to accommodate higher motor

horsepower. Remove the existing exhaust fan and install two new exhaust fans: one to serve as

return/exhaust fan to the existing air handling unit the second to return/exhaust the air to the new

air handling unit and run an exhaust duct from the return duct to an existing louver near the fan 

and install filters at the discharge side of the new exhaust fan. Install a quick shut off mechanism

to stop the fans. Maintain the main lobby under negative pressure with respect to the surrounding

areas and the outdoors during normal operations and during an emergency.

Option 2 (Filtration Level 3) provides a high level of protection against particle and gaseous

agents. Option 2 involves the following set of improvements. Isolate the open side of the lobby 

from the rest of the building by installing tempered glass partitions with self-closing doors that

allow building occupants continued access to the lobby. Install a new air handling unit to serve

the main lobby only. Relocating the outside air intake to the roof. Equip the air handling unit

with a five-stage filter consisting of: MERV 8 pre-filter, 85 % efficient MERV 13 intermediate

filter, 99.97 % HEPA filter, 99.9 % gas phase filter, and MERV 11 post filter. Modify electrical

feeders to accommodate higher motor horsepower. Remove the existing exhaust fan and install

two new exhaust fans: one to serve as return/exhaust fan to the existing air handling unit the

second to return/exhaust the air to the new air handling unit and run an exhaust duct from the

return duct to an existing louver near the fan and install filters at the discharge side of the new

exhaust fan. Install a quick shut off mechanism to stop the fans. Maintain the main lobby under

negative pressure with respect to the surrounding areas and the outdoors during normal

operations and during an emergency.
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Office Building Mail Room

The objective is to protect the mail room from contaminants coming in via mailed packages. The

mail room is approximately 334 m

2 (3 600 ft2

) in size. It has a 2.3 m (7 ft 8 in) high suspended 

acoustical ceiling and is enclosed with CMU walls and modular steel partitions. The mail room

has three interior walls and one exterior wall. One wall and all interior partitions extend to the

height of the ceiling. On two walls, a total of three single and double doors lead directly into 

interior corridors. There is a roll-up door on the exterior wall, which serves as a receiving area

for the mail room.

To protect the mail room from contaminants coming in via mailed packages, it is desirable to 

isolate the mail room with airtight walls and doors and to provide a separate dedicated air

conditioning system capable of maintaining the mail room under negative pressure. The system

must also be capable of purging the mail room—one hundred percent outside air and exhaust—

and filtering the supply and exhaust air. The proposed improvements are presented as two 

options. Each option has a different filtration level. The two options link to Filtration Levels 2

and 3 for the high-rise office building. Filtration Level 1 was not considered because it would not

provide the level of protection desired for the mail room.

Retrofit Alternatives for Protecting the Mail Room

Option 1 (Filtration Level 2) provides a high level of protection against particles but no gaseous

protection. Option 1 involves the following set of improvements. Seal mail room envelope;

walls, ceiling, doors, and slabs. Provide upgraded filtration to the existing air conditioning 

system and provide a new dedicated return/exhaust fan. Equip the existing air handling unit with 

a three-stage filter consisting of: MERV 8 pre-filter, 85 % efficient MERV 13 intermediate filter,

and a 99.97 % HEPA filter. Modify electrical feeders to accommodate higher motor horsepower.

Equip the existing exhaust fan with a MERV 8 pre-filter, an 85 % efficient MERV 13 

intermediate filter, and a 99.97 % HEPA filter. Install a quick shut off mechanism to stop the

fans. Maintain the mail room negative with respect to the surrounding areas and the outdoors

during normal operations and during an emergency.

Option 2 (Filtration Level 3) provides a high level of protection against particle and gaseous

agents. Option 2 involves the following set of improvements. Seal mail room envelope; walls,

ceiling, doors, and slabs. Provide upgraded filtration to the existing air conditioning system and 

provide a new dedicated return/exhaust fan. Equip the existing air handling unit with a five-stage

filter consisting of: MERV 8 pre-filter, 85 % efficient MERV 13 intermediate filter, 99.97 %

HEPA filter, 99.9 % gas phase filter, and MERV 11 post filter. Modify electrical feeders to 

accommodate higher motor horsepower. Equip the existing exhaust fan with a MERV 8 prefilter, an 85 % efficient MERV 13 intermediate filter, a 99.97 % HEPA filter, a 99.9 % gas phase

filter, and a MERV 11 post filter. Install a quick shut-off mechanism to stop the fans. Maintain 

the mail room negative with respect to the surrounding areas and the outdoors during normal

operations and during an emergency.
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Single-Story Office Building

The objective is to protect a single-story office building from external discharge of contaminants

from a single source near the outside air intakes and from a larger cloud approaching the

building. The gross floor area of the office building is 1 612 m

2 (17 350 ft2

). The air conditioning 

system consists of 28 rooftop heat pumps. Each heat pump controls its own outdoor intake

making it necessary to protect 28 air intake locations. The system does not have exhaust fans.

The excess air is relieved through barometric dampers. Therefore, controlled purging is not

possible. In addition, the rooftop units cannot be retrofitted with the necessary filters due to the

low static pressure of the fans and lack of space to install the filters.

The physical arrangement of this building makes it difficult to retrofit the filters. The proposed 

improvements are presented as three options. Each option has a different filtration level. The

three options link to Filtration Levels 1, 2, and 3 for the high-rise office building.

Retrofit Alternatives for Protecting the Single-Story Office Building

Option 1 (Filtration Level 1) provides a low level of particle filtration capability and no gaseous

capability. Option 1 involves the following set of improvements. Seal the exterior envelope to 

make the building more airtight. Replace existing MERV 4 filters with MERV 11 filters. Install

quick shut-off mechanism to stop the rooftop heat pumps.

Option 2 (Filtration Level 2) provides a high level of protection against particles but no gaseous

protection. Option 2 involves the following set of improvements. Seal the exterior envelope to 

make the building more airtight. Provide an outside fan with a three-stage filter consisting of:

MERV 8 pre-filter, 85 % efficient MERV 13 intermediate filter, and a 99.97 % HEPA filter.

Duct the filtered air to the intake of each rooftop unit. Install the fan and filter on a new platform

at roof level with the ductwork on the roof. Install quick shut-off mechanism to stop the rooftop

heat pumps and outdoor air fans.

Option 3 (Filtration Level 3) provides a high level of protection against particle and gaseous

agents. Option 3 involves the following set of improvements. Seal the exterior envelope to make

the building more airtight. Provide an outside fan with a five-stage filter consisting of: MERV 8

pre-filter, 85 % efficient MERV 13 intermediate filter, 99.97 % HEPA filter, 99.9 % gas phase

filter, and MERV 11 post filter. Duct the filtered air to the intake of each rooftop unit. Install the

fan and filter on a new platform at roof level with the ductwork on the roof. Install quick shut-off

mechanism to stop the rooftop heat pumps and outdoor air fans.

The Cost-Accounting Framework

The flexibility of the life-cycle cost method enables us to classify and analyze costs in a variety

of ways. The result is a more focused representation of costs, referred to as the cost-accounting 

framework. The cost-accounting framework provides a convenient means for summarizing all

costs entering into the life-cycle cost calculations. The framework is organized around a Budget

Category classification. The Budget Category classification uses cost types and cost items. The

cost types are used as placeholders for summarizing and reporting aggregated cost information.

Each cost type is a collection of cost items. Each cost item has a unique set of identifiers that

places it within the cost-accounting framework.

The Budget Category classification has three cost types based on which category of the budget

the funds come from. These cost types are: (1) Capital Investment; (2) O&M (Operations and 
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Maintenance); and (3) Other. These cost types correspond to widely used budget categories for

private and public sector cost accounting. It is important to note that the dollar amounts accruing 

to all three cost types are inclusive of any expected event-related losses. In the context of the

previous section, Capital Investment costs accrue to the investment cost category and O&M and 

Other costs accrue to the non-investment cost category. All acquisition costs, including costs

related to planning, design, purchase, and construction, are investment-related costs and fall

under the Capital Investment cost type. Residual values (resale, salvage, or disposal costs) and 

capital replacement costs are also investment-related costs. Capital replacement costs are

usually incurred when replacing major systems or components (e.g., replacing an exhaust fan)

and are paid from capital funds. Cost items falling under the O&M cost type include energy and

water costs, maintenance and repair costs, and minor replacements (e.g., replacing belts and

seals) related to maintenance and repair. O&M costs are usually paid from an annual operating

budget, not from capital funds. Other costs are non-capital costs that cannot be attributed to the

O&M cost type.

Navigating Within the Software

This section gives you a guided tour of Version 1.0 of the Life-Cycle Cost Analysis Tool (LCAT

1.0). The goal of the guided tour is for you to work systematically through the hierarchy of

screens used to input, analyze, and display project-related data.

Opening/Creating a Project File

Launch the software by clicking on LCAT 1.0 icon found on your desktop or by clicking LCAT

1.0 in the Start menu in Programs/Life-Cycle Cost Analysis Tool. The first screen to appear

prompts you to open an existing project file, create a new project file, or open an example

project. Figure A1 is a reproduction of the Prompt window. Recall that the software comes with 

a set of case study files. Thus, even when you launch the software for the first time, there are

already several example project files, any of which you may choose to open. If you select Open 

an Existing Project or Open an Example Project and click the Start button, then you will be

taken to the Open Project window. The Prompt window also includes a View Tips check box. If

you select View Tips and click the Start button, you will be taken to the Software Tips window.

(Throughout this section, software features (e.g., buttons) are highlighted through the use of

italics font.)

Figure A2 displays the Software Tips window. The Software Tips window is designed as a

handy reference for first-time users. It highlights material contained in this Primer as well as

several basic concepts for navigating within the software and for saving results.

As a first step, open one of the case study files and use the File Save As feature to make

additional copies with lcc extensions. Suggested file names are test01.lcc and test02.lcc. Use the

test files to gain familiarity with the software. This way, if you inadvertently change or delete a

data element, or create a new data element, you can go back to the case study file for the

reference solution. When you use the File Save As feature with one of the case study files, the

new file (e.g., test01.lcc) will be saved in the “existing projects” directory. If you exit the

software and later wish to open a user-created “test” file, you will need to select Open an 

Existing Project from the Prompt window.

Figure A3 is a sample Open Project window. Figure A3 lists the various case study files

provided with the software. The Open Project window shown in Figure A3 was opened by
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selecting the Open an Example Project option in the Prompt window and clicking the Start

button. Note that the high-rise office building has two case study files—High-Rise Office

(Summary).lcc and High-Rise Office (Detailed).lcc. The “summary” file is an abbreviated 

version of the high-rise office building case study. It provides a convenient means for

highlighting key features of the software. It is used within the Primer to illustrate these software

features. The “detailed” file demonstrates how to handle a fairly complicated retrofit project. It

focuses on breaking out the various cost items presented in the summary file into their

constituent parts.

Highlighting the desired file and clicking the Open button opens that file. Double clicking on the

highlighted file opens the file as well. The Open Project window includes a Cancel button. If you

click on the Cancel button, you will return to the Prompt window.

Figure A1 Life-Cycle Cost Analysis Tool Prompt Window
121

Figure A2 Software Tips Window

Figure A3 Open Project Window

Cost Summary Window and Main Menu

The Cost Summary window is displayed whenever a new project is started, an existing project

file is opened, or a case study file is opened. When a project is created, the Cost Summary

window is blank. Figure A4 is an example of the Cost Summary window display when starting a

new project. As you enter data into the software, the Cost Summary window displays the current

value of life-cycle costs for each cost type and alternative being analyzed. It is recommended that
122

you keep the Cost Summary window open while working in the software. If you wish to close

the window, it can be reopened at any time by selecting Project from the tool bar and then

selecting Cost Summary.

Figure A4 Cost Summary Window When Starting a New Project

The software is designed to analyze up to four alternatives (see Figure A4). The Cost Summary 

window allows you to select both the cost types and the alternatives to be included in the

economic evaluation. These “choices” are represented in Figure A4 by the “cost type” check 

boxes and the “alternative” check boxes within the Alternatives group box in the lower left-hand 

corner.

A tree on the left-hand side of the Cost Summary window serves as the Main Menu to the

software. The tree contains three top-level nodes: Project, Uncertainty, and Reports. Recall that

software features are highlighted through the use of italics font. The tool bar at the top of the

Cost Summary window provides another means for accessing the three top-level nodes. The tool

bar also includes File and Help options. File options include Save, Save As, Close Project, and 

Exit. Help options include Tips, which opens the Software Tips window, and Help, which opens

an on-line version of the Primer and a Glossary of Terms. If you wish to print the on-line Primer

from the Help menu, click Print the selected topic option from the Print Topics pop-up window

and then select which printer from the pop-up Print window.

Project Information

The options listed under the Project node allow you to enter project information, define

alternatives, and manage cost-related information.

Clicking the Description option on the Main Menu opens the Project Description window. Here

you can enter project information such as the project’s name, a brief description of the project,

the base year selected for all present value calculations, the length of the study period, whether a

constant dollar or current dollar analysis is to be performed, and the discount rate. Note that

when a constant dollar analysis is selected, you must use a real discount rate. When a current

dollar analysis is selected, you must use a nominal discount rate. Within LCAT 1.0, the nominal

discount rate and the real discount rate are linked via a formula that includes a term for general
123

inflation. Figure A5 displays the Project Description window for the high-rise office building 

case study. The descriptive material is designed to help decision makers differentiate among 

multiple projects competing for limited investment funds.

Figure A5 Project Description Window for the High-Rise Office Building Case Study

Clicking the Alternatives option opens the Project Alternatives window, which allows you to add 

and delete project alternatives as well as enter information about the alternatives. Figure A6

displays the Project Alternatives window for the high-rise office building case study. The Base

Case tab is selected. The window is constructed so you can switch from one alternative to

another. The text box in the middle of the window allows you to enter a brief description of the

alternative, which serves to differentiate one alternative from another.
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Figure A6 Project Alternatives Window for the High-Rise Office Building Case Study

Cost-related input screens for the software product are of two basic types: (1) protection costs

and (2) event-related losses. You access these screens by selecting the Cost/Loss option on the

Main Menu.

Protection Costs

Clicking the Cost/Loss option opens the Protection Costs/Event-Related Losses window. This

screen manages the creation, deletion, and editing of protection costs and event-related losses.

Upon entering the Protection Costs/Event-Related Losses window, you must select the

alternative for which information is to be reviewed or input. Both the costs and events portions

of the window are active for the selected alternative. Since our focus is on protection costs,

however, we will address only the cost portion of the window here. The following subsection 

deals with event-related losses. Once the alternative is selected, the Protection Costs/EventRelated Losses window displays all cost items associated with that alternative. Figure A7 is an 

example of the Protection Costs/Event-Related Losses window for the Base Case. Notice that the

protection costs are listed in alphabetical order according to their Budget Category—Investment,

O&M, and Other. If a large number of cost items have been entered, some costs will be hidden,

but can be viewed by scrolling down the list. In this case, no costs are hidden.
125

Figure A7 Protection Costs/Event-Related Losses Window for the High-Rise Office

Building Case Study: Protection Costs for the Base Case

Highlighting and clicking the selected cost item opens the appropriate Cost Information window.

This “edit” feature allows you to review and, if desired, modify any previously recorded

information for the cost item of interest. Figure A8 is an example of the Capital Investment Cost

Information window for the high-rise office building case study. Figure A8 displays information 

on the HVAC Upgrade cost item for Alternative 1 (Option 2, enhanced protection from

biological agents). Figure A9 is an example of the O&M Cost Information window for the

Replacing HEPA Filters cost item for Alternative 1. Figure A10 is an example of the Other Cost

Information window for the Change in Traffic Pattern cost item for Alternative 2 (Option 3,

enhanced protection from chemical and biological agents).

The Protection Costs/Event-Related Losses window is the means through which new cost items

are created. The creation of a new cost item is accomplished by selecting the appropriate Budget

Category cost type button—Add Investment Cost, Add O&M Cost, or Add Other Cost—from the

list on the right. The software then opens the Cost Information window associated with the

selected cost type. The Cost Information windows allow you to name the cost item, generate a

cost estimate via separate entries for quantity and unit cost, and specify the timing of cash flows

and any escalation rates that need to be applied (see Figures A8, A9, and A10).
126

Figure A8 Capital Investment Cost Information Window for the High-Rise Office

Building Case Study: HVAC Upgrade for Alternative 1

Figure A9 O&M Cost Information Window for the High-Rise Office Building Case

Study: Replacing HEPA Filters for Alternative 1

Figure A10 Other Cost Information Window for the High-Rise Office Building Case

Study: Change in Traffic Pattern for Alternative 2

Reference to Figures A8, A9, and A10 record the cost choices that map individual cost items into 

the cost types reported in the Cost Summary window. The Capital Investment Cost Information

window offers three choices for classifying a cost item: (1) Initial; (2) Replacement; and (3)

Salvage. An initial investment cost, as its name implies, occurs at the beginning of the Base Year

(i.e., Year 1 or, in this case, 2005). A capital replacement cost occurs in some future year. Use

the drop down menu to specify the year in which the capital replacement is to take place,

recalling that Year 1 is the Base Year. A salvage value is a negative capital cost (i.e., a receipt)

occurring at the end of the study period. The salvage value is the value of the asset, assigned for
127

tax computation purposes, that is expected to remain at the end of the depreciation period. The

choices for classifying a cost item for O&M and Other costs (see Figures A9 and A10) are the

same: (1) Annually Recurring; (2) Periodic (other than annual); and (3) Aperiodic. Periodic

costs, such as HEPA filter replacements, occur less frequently than annually—say every three

years. Aperiodic costs are one-time costs that occur at some point in the future. If feasible, when

preparing estimates for a cost item, include allowances for design/engineering services, taxes,

overhead, and other indirects.
128

Event-Related Losses

Treatment of event-related losses is an important part of a “balanced” life-cycle cost analysis

whenever chem/bio or other man-made or natural hazards are involved. LCAT 1.0 treats events

as a hierarchy. Associated with an event are outcomes and outcome probabilities. Associated 

with outcomes are outcome costs. The combination of outcome probabilities and outcome costs

are the “losses” associated with a given event.

As noted earlier, clicking the Cost/Loss option opens the Protection Costs/Event-Related Losses

window. This screen manages the creation, deletion, and editing of protection costs and eventrelated costs. Upon entering the Protection Costs/Event-Related Losses window, you must select

the alternative for which information is to be reviewed or input. Both the costs and events

portions of the window are active for the selected alternative. However, we will address only the

event-related costs portion of the window here. Once the alternative is selected, the screen 

displays all events associated with that alternative.

Highlighting and clicking the selected event opens the Event Information window. This feature

allows you to review and, if desired, modify any previously recorded information for the event of

interest. The Protection Costs/Event-Related Losses window is the means through which new

events are created. The creation of a new event is accomplished by selecting Add Event from the

list on the right. The software then opens the Event Information window. The Event Information 

window allows you to name the event, provide a brief description of the event, enter the dates of

first and last occurrence, and edit event-related outcomes. First occurrence and last occurrence

specify the period of time over which a specific set of event-related losses occur. The rationale

behind “breaking” events up into segments over the study period is that some mitigation

measures may affect outcome probabilities. Such mitigation measures, if implemented in the

future, might significantly reduce outcome probabilities and hence event-related losses. Figure

A11 is an example of the Event Information window.

Figure A11 Event Information Window
129

Associated with each event is a set of outcomes. Information on event-related outcomes is

accessed via the Outcomes/Outcome Costs window. This screen is reached by clicking the Edit

Outcomes option in the Event Information window (see Figure A11). Clicking the Edit Outcomes

option opens the outcomes portion of the Outcomes/Outcome Costs window. Figure A12 is an 

example of the Outcomes/Outcome Costs window. This screen manages the creation, deletion,

and editing of outcomes. The Outcomes/Outcome Costs window displays all outcomes

associated with the event of interest. The event/outcome costs portion of the Outcomes/Outcome

Costs window is initially grayed out, indicating that it is inactive. However, once an outcome is

selected, the costs associated with that outcome become active.

Highlighting and clicking the selected outcome opens the appropriate Outcome Information 

window. This feature allows you to review and, if desired, modify any previously recorded 

information for the outcome of interest. The Outcomes/Outcome Costs window is the means

through which new outcomes are created. The creation of a new outcome is accomplished by 

selecting Add Outcome from the list on the right. The software then opens the Outcome

Information window. The Outcome Information window allows you to name the outcome,

provide a brief description of the outcome, assign a probability of occurrence for the outcome

(outcome probabilities are a byproduct of the risk assessment), update the sum of all outcome

probabilities for the event of interest, and edit outcome-related cost items. Figure A13 is an 

example of the Outcome Information window.

Figure A12 Outcomes/Outcome Costs Window
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Outcomes are characterized by their severity and their occurrence probabilities. An event

includes the full range of outcomes from no damage to extreme damage. For a given event, the

sum of all outcome probabilities equals 1.0. Thus the no damage outcome would usually have a

very high probability, corresponding to maintenance of the status quo, whereas an extreme

damage outcome would have a very low probability. Outcome probabilities are the “key” driver

of event-related losses, since these losses are “expected” values. Outcome probabilities are

expressed as annual values. Thus, the “chance” an event-outcome combination occurs in a given 

year equals its outcome probability.

Because event-related losses are expected to have a major influence on which alternative is the

most cost effective, the sum of all outcome probabilities is required to equal 1.0 in order for

either the Data Report or the Results Report to be output. OAE’s objective was to avoid 

situations where losses were either ignored (i.e., a sum less than 1.0) or double counted (i.e., a

sum greater than 1.0). Once an event has been created and one or more outcomes assigned to it,

it is possible to edit the outcome probabilities. Once the sum of all outcome probabilities equals

1.0 (100 % in the Probability Information group box), it is possible to generate both the Data

Report and the Results Report. The Data Report is designed as a check on user-supplied inputs,

so it includes the outcome probabilities.

Figure A13 Outcome Information Window

Associated with each outcome is a set of event-related cost items. Typical event-related cost

items are damage to the facility, loss of use of the facility (e.g., function and contents), and 

medical expenses. For example, if an event-outcome combination produced damage to the

facility, equipment replacements might result. Information on event-related cost items is

accessed by closing the Outcome Information window (see Figure A13), which reveals the

event/outcome cost portion of the Outcomes/Outcome Costs window. This screen manages the
131

creation, deletion, and editing of event-related cost items. The Outcomes/Outcome Costs window

displays all event-related cost items associated with the outcome of interest.

Highlighting and clicking the selected event-related cost item opens the appropriate

Event/Outcome Cost Information window. This feature allows you to review and, if desired,

modify any previously recorded information for the event-related cost item of interest. The

Outcomes/Outcome Costs window is the means through which new event-related cost items are

created. The creation of a new event-related cost item is accomplished by selecting the

appropriate Budget Category cost type button—Add Investment Cost, Add O&M Cost, or Add

Other Cost—from the list on the right. The software then opens the Event/Outcome Cost

Information window. The Event/Outcome Cost Information window allows you to name the

event-related cost item, generate a cost estimate via separate entries for quantity and unit cost,

and specify any escalation rates that need to be applied. Figure A14 is an example of the

Event/Outcome Cost Information window.

Figure A14 Event/Outcome Cost Information Window

Cost Summary Window

Once all data have been input, the Cost Summary window displays the life-cycle costs for each 

alternative. Costs are reported for each cost type and in total. Figure A15 reproduces the Cost

Summary window for the completed baseline analysis for the high-rise office building case

study.
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Figure A15 Cost Summary Window for the High-Rise Office Building Case Study:

Baseline Analysis

The Cost Summary window provides the option for you to view calculated values for a measure

of economic performance other than life-cycle costs. The drop down menu in the Evaluation 

Method box lets you select the PVNS (present value net savings) as an alternative measure of

economic performance. The PVNS values reported on the Cost Summary window are calculated 

vis-à-vis the Base Case. PVNS measures net savings of investing in the given alternative instead 

of investing in the Base Case. Thus when the PVNS method is selected, the only meaningful

values are the ones listed under the column headings Alt. 1, Alt. 2, and Alt. 3.

Sensitivity Analysis

Recall that in the baseline analysis all data elements entering into the calculations are fixed.

Thus, the baseline analysis is a complete analysis in all respects but one: it does not address the

effects of uncertainty. Note that the baseline analysis for the four case study applications

includes only protection costs.

Sensitivity analysis, as implemented in LCAT 1.0, lets you evaluate how changes in a single

variable impact the calculated values of life-cycle costs. The sensitivity analysis feature in LCAT

1.0 is based on techniques presented in ASTM Standard Guide E 1369. Depending on the

variable selected, it may impact a single alternative or it may impact all alternatives.

The Sensitivity Analysis window is entered by clicking the Sensitivity option under the

Uncertainty node. The window, as configured in Version 1.0, has a single tab, Change in a

Single Factor.

The left-hand side of the Change in a Single Factor tab lists the hierarchy of factors that can be

evaluated. Each factor is associated with a node in the hierarchy. Upon entering the tab, the

Project and Alternatives nodes appear at the left. All alternatives evaluated in the baseline

analysis are listed immediately below the Alternatives node. The squares immediately to the left

of each node in the hierarchy are marked with a + (plus sign) or a – (minus sign). A plus sign 

means that additional nodes and/or factors reside beneath that node. A minus sign means that a

node has been opened. Since each project has alternatives associated with it, upon entering the
133

Change in a Single Factor tab, you will note that the Alternatives node has a minus sign in its

square on the left.

Nodes can be opened or closed. For example, clicking the square by the Project node opens the

node and the single factor Discount Rate (7.00 %) appears beneath it. Note that there is no square

to the left of Discount Rate. This means that Discount Rate is a factor that can be selected for

evaluation. Note that the factor line in the hierarchy includes both the factor name (Discount

Rate) and its value (7.00 %). Highlighting the factor Discount Rate (7.00 %) selects that factor.

The right-hand side of the screen includes the Results group box, a drop down menu for percent

changes about the baseline value of the selected factor, and a Compute button. Clicking on the

Compute button causes three sets of values to be computed. Figure A16 shows the results of a

10 % deviation about the baseline value of the discount rate. Note that the name of the factor

appears at the upper left-hand corner of the Results group box. Since the Discount Rate is the

same for each alternative, results for the Base Case, Alternative 1, and Alternative 2 are reported.

Note that the Minimum, Baseline, and Maximum values for the factor, Discount Rate, are

displayed. Reference to Figure A16 shows that the discount rate has a fairly strong impact on the

computed value of life-cycle costs for the Base Case, Alternative 1, and Alternative 2.

Figure A16 Sensitivity Analysis Window: Using the Change in a Single Factor Tab to

Evaluate the Impact of the Discount Rate on Life-Cycle Costs

Figure A17 uses Alternative 2 to illustrate how to open up the hierarchy within a given

alternative. The nodes immediately beneath the Alt. 2: Level 3 Protection (Chemical &

Biological Agents) node are labeled Costs and Events. Additional nodes are listed beneath the

Costs node. Opening the Costs node, we see that 11 nodes are listed beneath it. These nodes

correspond to the cost items entered via the Capital Investment, O&M, and Other Cost
134

Information windows. Note that each of the 11 nodes indicates the budget category it falls under.

One of the 11 nodes has been opened—O&M: Replacing Gas Phase Filters—to reveal factors.

The factor selected for analysis is the Unit Cost of Replacing Gas Phase Filters. Under the Range

drop down menu, we have selected a 10 % deviation about the baseline value of the annually 

recurring Unit Cost of $108 000 (i.e., $648 000 for all six units). Clicking the Compute button

causes three sets of values to be computed. Because this factor only affects Alternative 2, only

values for Alternative 2 are displayed. Reference to the Results group box reveals that this factor

has a strong impact on life-cycle costs.

Figure A17 Sensitivity Analysis Window: Using the Change in a Single Factor Tab to

Evaluate the Impact of the Unit Cost of Replacing Gas Phase Filters on LifeCycle Costs for Alternative 2

Event-related costs are evaluated by opening the Events node for the alternative of interest. If

events have been entered, the nodes listed beneath the Events node are the individual events

defined by the user. Beneath each individual event node are the outcomes. If an outcome had 

costs associated with it, then the event/outcome cost items are listed as nodes beneath it. The

factors—unit cost and escalation rate—appear beneath each event/outcome cost item.

The bottom right-hand portion of the window contains the Save Results for Reports group box.

As its name suggests, the Save Results buttons may be used to save up to three sets of computed 

results. For example, the discount rate had a strong impact on life-cycle costs for the Base Case,

Alternative 1, and Alternative 2. Thus, saving these results might prove useful in supporting a

recommendation for one alternative over another. Any results that you choose to save will appear

in the Results Report. Note that more than one range can be used and saved for a single factor.
135

Reports

The Life-Cycle Cost Analysis Tool produces two types of reports. Although the reports share a

number of similarities in terms of their content, their functions are very different. Each report is

accessed via the Reports node on the main menu. Clicking the Data or Results option under the

Reports node takes you to the selected report type.

The Data Report is intended as a means for checking the accuracy of the information that you

entered into the Life-Cycle Cost Analysis Tool. The Results Report is designed to help you “drill

down” on how individual cost items are distributed across Budget Category cost types. This

approach gives you a snapshot of all of the costs entering the analysis, expressed in present value

terms, which “roll up” into the life-cycle costs recorded in the Cost Summary window. The

Results Report also includes any sensitivity analyses you decide to save. The Results Report is

intended for submission to senior management as part of the documentation supporting the

specific project being considered for funding. The Results Report is sufficiently detailed to

provide a concise snapshot of the underlying data, including the candidate set of alternatives

evaluated, the types of analyses performed, and the results of those analyses.

Clicking on the Data option under the Reports node opens the Data Report. The Data Report

consists of: (1) a Cover Sheet; (2) Background Information on the project (e.g., Project Name,

Project Description, Study Period, and Analysis Information); (3) Alternative Information –

Descriptive Summary (e.g., Alternative Name, Alternative Description, Event Name, Event

Description, Outcome Name, Outcome Description, and Key Parameters); (4) Alternative

Information – Protection Cost Data Summary (e.g., Cost Item and Dollar Amount); and (5)

Alternative Information – Event/Outcome Cost Data Summary (e.g., Event, Outcome,

Event/Outcome Cost Item, and Dollar Amount). Figure A18 reproduces the Cover Page of the

Data Report for the high-rise office building case study.

Verifying the accuracy of input data is essential to ensure that the results of the economic

evaluation are consistent with the underlying data. The Data Report is specifically designed to 

verify the accuracy of the input data. Figure A19 provides information on the protection costs for

Alternative 1.
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Figure A18 Cover Page of the Data Report for the High-Rise Office Building Case Study
137

Figure A19 Protection Costs Data Summary Page of the Data Report for Alternative 1

Clicking on the Results option under the Reports node opens the Results Report. The Results

Report consists of: (1) a Cover Sheet; (2) Background Information on the project (e.g., Project

Name, Project Description, Study Period, and Analysis Information); (3) Alternative Information 

– Descriptive Summary (e.g., Alternative Name, Alternative Description, Event Name, Event

Description, Outcome Name, Outcome Description, and Key Parameters); (4) Summary of LifeCycle Costs; (5) Summary of Costs by Alternative sorted by Budget Category (e.g., Cost Item

and Present Value Dollar Amount); (5) Summary of Annual Costs by Alternative and Budget

Category (e.g., Present Value Dollar Amounts for each Year for Capital Investment, O&M,

Other, and in Total); (6) Summary of Annual Costs by Alternative (e.g., Present Value Dollar

Amounts for each Year for each Alternative); and (6) any saved sensitivity analyses.

Figure A20 reproduces the Summary of Life-Cycle Costs Page of the Results Report for the

high-rise office building case study. When you examine Figure A20, you will note that it is a

reproduction of the Cost Summary window for the baseline analysis. Figure A20 includes the

check boxes to indicate clearly whether any data elements have been excluded from the lifecycle cost totals. Figure A20 is the starting point for the “drill down” analysis of the computed

values for life-cycle costs.
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Figure A20 Summary of Life-Cycle Costs Page of the Results Report for the High-Rise

Office Building Case Study

Figure A21 is the second page of the three-page Summary of Costs by Alternative portion of the

Results Report. Figure A21 covers Alternative 1. All costs are expressed in present value dollar

amounts and include designations for the cost types, which map them into the cost-accounting 

framework. If you wish to examine how a particular cost item contributes to the amounts shown 

on the Summary of Life-Cycle Costs page, choose the cost item, see where it fits in the costaccounting framework, and then trace it back to Summary of Life-Cycle Costs page.

Because event-related cost items are very similar across alternatives (e.g., damage to the facility 

and loss of use of the facility) but differ in their magnitude, it is sometimes desirable to use the

Summary of Costs by Alternative to calculate a “loss differential” between the Base Case and 

one of more of the alternatives. This can be done for either a single event-related cost item, a

combination of event-related cost items, or all event-related losses. For example, if damage to

the facility were the event-related cost item of interest, subtract its value for the alternative of

interest from its value for the Base Case. To do this, you will need to pull values from at least

two Summary of Costs by Alternative sections of the Results Report—one for the Base Case and 

one for each alternative of interest.
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Figure A21 Summary of Costs by Alternative Page of the Results Report for Alternative 1

In developing a cost-effective risk mitigation plan, it is useful to see how costs are distributed 

over time. The Results Report provides two separate means for examining and assessing annual

costs. The Summary of Annual Costs by Alternative and Budget Category provides a detailed 

disaggregated synopsis of annual costs. Thus, if you want to examine how major equipment
140

replacements affect annual costs, examine the entries under the Capital Investment heading and 

look for years in which significant increases in costs occur. The Summary of Annual Costs by 

Alternative provides aggregated side-by-side comparisons of the alternatives being evaluated.

Figure A22 reproduces the Summary of Annual Costs by Alternative page for the high-rise office

building case study. These side-by-side comparisons are useful in determining when a particular

alternative has a “bulge” in costs—say at the beginning of the study period or associated with a

major replacement—or when one alternative’s annual costs begin to escalate at a significantly

higher rate. Both pieces of information are useful in understanding the pros and cons of each 

alternative being evaluated. It is important to recognize that the goal of the analysis is to gain

insights into the decision problem.
141

Figure A22 Summary of Annual Costs by Alternative Page of the Results Report for the

High-Rise Office Building Case Study
142

Next Steps

Now that you have completed the guided tour, use the test files to gain familiarity with the

software. Experiment with the various means for editing, creating, and deleting data elements.

Create simple applications using your own data to master the full capabilities of the Life-Cycle

Cost Analysis Tool. Build more complex applications and use the sensitivity analysis feature to 

evaluate how changing the values of key inputs affect economic performance. Use the Results

Report to learn how to drill down on key cost drivers and use that information to help guide you 

in conducting and saving additional sensitivity analyses. Have as a goal to use the software as a

decision support tool; it is largely self documenting, it lays out the information going into the

analysis, and provides guidance in choosing a cost-effective risk mitigation plan.

Visit the OAE website (http://www.bfrl.nist.gov/oae/oae.html) to learn about future updates and 

pending software releases.

References

ASTM. 2002. ASTM Standard E 1369, Standard Guide for Selecting Techniques for Treating 

Uncertainty and Risk in the Economic Evaluation of Buildings and Building Systems, American 

Society for Testing and Materials.

ASTM. 2005. ASTM Standard E 917, Standard Practice for Measuring Life-Cycle Costs of

Buildings and Building Systems, American Society for Testing and Materials.

ASTM. 2006. ASTM Standard E 1074, Standard Practice for Measuring Net Benefits and Net

Savings for Investments in Buildings and Building Systems, American Society for Testing and 

Materials.

Chapman, R.E., Leng, C.J. 2004. Cost-Effective Responses to Terrorist Risks in Constructed 

Facilities, NISTIR 7073, National Institute of Standards and Technology.
143

Appendix B: Retrofit Design Documentation

Disclaimer

The retrofits presented in this appendix are specific to the buildings examined in terms of the

available options and the details of implementation, and are based on the efforts of a single A&E

firm and are not necessarily optimal for these or any other buildings. While the recommendations

and designs are of interest to the general question of building protection, they cannot necessarily 

be generalized to other buildings. Determining retrofit options and designs for a specific building

always requires consideration of the unique features of that building.

Background

Section 3 of this report described a case study investigating the application of building protection

retrofits in two actual buildings, specifically to identify and design potential retrofits to these

buildings given their particular floor plans and HVAC system designs. Two office buildings,

with very different floor plans and ventilation system designs, were selected for the case study.

One is a high-rise office building with central air-handling systems serving most of the building,

in addition to several other features of interest including intakes near ground level, a loading

dock, a mail room, and a public-access lobby. The other building is a one-story office building

with multiple rooftop air handling units and no spaces other than offices.

The retrofit design and cost estimation was performed by an architectural and engineering

(A&E) firm and was based on a list of candidate retrofits identified by NIST. The A&E firm then 

proceeded with the design work, producing detailed designs for implementing the retrofits. As

part of this effort, the A&E firm reviewed the existing mechanical and control systems in the two 

buildings, including all original architectural, structural, mechanical, and electrical plans and any 

modifications of these plans. The firm also conducted field inspections of the buildings and 

systems and then performed the design work and prepared detailed descriptions and drawings

and cost estimates of the proposed retrofits.

This appendix contains more detailed descriptions of the buildings and retrofit designs that are

excerpted from the A&E report.
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A & E Description of Existing Condition

This case study includes two buildings located in an office/lab complex in a suburban area. The

first building is a high-rise office building with an office tower referred to as Wing A. The scope

of this study covers the tower served by Mechanical Room #4 in the Mezzanine level, the Main 

Lobby of the high-rise office building, and the Mailroom in the basement of Wing B of the highrise office building. Additionally, the scope includes the rooftop heat pumps on the roof of a

second building - a one-story office building.

High-rise Office Building Tower

The high-rise office building, built in the mid 1960s, is an eleven story tower with an elevator

penthouse, basement and sub-basement covering an area of 130 500 ft

2

. At its base, the structure

is flanked by adjoining one and two story wings, which includes Wing B, with a central open 

courtyard.

A variety of materials compose the exterior walls including granite, marble, face brick, glass and 

extruded aluminum. The east and west facades of the tower are faced with grey face brick with

insulated porcelain spandrel panels and fixed aluminum frame windows enclosing the north and 

south elevations.

There are six air-conditioning units (ACU-Al, ACU-A2, ACU-A3, ACU-A4, ACU-A5, and

ACU-A6) installed in the Mechanical Room #4 located in the mezzanine floor of Wing A. The

units are field assembled panel construction. The units are generally in good condition and some

of the coils have been replaced, while others appear to be the original design. Each unit has a

mixing box with outside air louvers, outside air dampers, minimum outside air dampers, and

return air. Each unit has a filter rack holding 20 in x 20 in x 4 in 30 % pleated filters. There were

several manufacturer’s filters represented, but it is fair to assume these are nominal ASHRAE

30 % filters (per ASHRAE Standard 52.1) or MERV 6 filters (per ASHRAE Standard 52.2). The

filters are upstream accessible through an access door located in the mixing section of each unit.

There is also an downstream access door that serves the access section between the filter bank 

and the heating coil section.

With the exception of air handling units ACU-3 and ACU-4, the supply fans are original

installation. All the motors were replaced with high efficiency motors recently.

Exhaust/return fans designated E-A-1, E-A-2, E-A-3, E-A-4, E-A-5 and E-A-6 return the air to

their corresponding air handling unit or exhaust the air depending if the units are operating with

the minimum outside air or under the economizer cycle.

The air handling units are all fed from the Motor Control Centers MCC-A1 and MCC-A2 located 

in the same Mechanical Room. Combination starters and disconnect switches for supply and 

exhaust fans for ACU-Al, ACU-A3, ACU-A4, and ACU-A5, are installed in Motor Control

Center MCC-A1 and starter/disconnects for supply and exhaust fans are installed in MCC-A2.

Mechanical Room #4 is in the mezzanine level and the bottom of the outside air intake louvers

are around 20 ft above the ground. The building has a rectangular configuration, with the north

and south sides full of windows at the floors above the mezzanine and outside air intake louvers

at the Mechanical Room.

The temperature controls are pneumatic and each ACU is started and stopped manually or by

means of time clocks installed in each unit's control panel. The ACUs operate 24 h/d all year

round.
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High-rise Office Building, Main Lobby

The Main Lobby is a 14 ft high space that is approximately 3,500 ft

2 in floor area. It is defined 

by exterior glass curtain walls on the north and east sides and marble finished walls on the south

and west sides. It is accessed from the exterior through a 150 ft

2 glass enclosed airlock with a

series of two rows of four balanced glass doors located on the east wall.

On the southern perimeter, the Lobby is open to the elevator bank of Wing A and an exhibition 

space located in Wing B. The Lobby is also open to Wing E west of Wing A.

The Main Lobby does not have a dedicated air-conditioning unit, but is served by Air Handling

Unit ACU-A2 and return/exhaust fan E-A-2. Air Handling Unit ACU-A2 located in the

mezzanine mechanical room serves the Main Lobby and the adjacent corridors. Four supply air

branches with hot water reheat coils are each connected to the main supply air duct from ACUA2. Two of the ducts run down to the Main Lobby (adjacent to the elevators) and supply air to 

linear diffuser located at the north and east perimeter walls of the Main Lobby. The other two 

supply ducts supply air to Corridor #13, Corridor #14, and the Exhibit area.

The return/relief exhaust air fan E-A-2 returns the air to ACU-A2 or exhausts it depending on the

outdoor conditions. A 50 in x 30 in return duct connected to E-A-2 returns the air from the Main 

Lobby, the adjacent corridors, and the Exhibit area. The duct is connected to an 84 in x 48 in x 

24 in sheet metal plenum in the Lobby's ceiling plenum. A 48 in x 13 in duct returns the air from

the Main Lobby and is connected to the same plenum. 33 in x 20 in, 33 in x 27 in, and 40 in x

7 in ducts return the air from Corridor #13, Corridor #14, and the Exhibit area and are connected 

to the same plenum.

Exhaust fan E-A-2 is located in a space between the two elevator shafts behind exhaust fan E-A8.

The temperature controls are pneumatic and air handling unit ACU A2 and the exhaust/return fan

E-A-2 are started and stopped manually or by means of time clocks installed in the unit's control

panel. The ACU and the fan operate 24 h all year round.

The Main Lobby air handling unit ACU-A2 supply and return/exhaust fans E-A-2 are fed from

the Motor Control Center MCC-A2 located in Mechanical Room #4 on the Mezzanine Floor.

High-rise Office Building, Mail Room

The Mail Room is approximately 3 600 ft

2

and has a 7 ft 8 in high suspended acoustical ceiling 

system. It is enclosed by CMU walls and modular metal partitions. With the exception of the

east, west and south walls, the north wall and all other interior partitions extend to the height of

the ceiling. On the east and west walls a total of three single and double doors lead directly into

an interior corridor. There is a roll-up door on the exterior south wall in the Receiving Area and 

the Mail Room.

The Mail Room does not have a dedicated air-conditioning unit. Air handling unit ACU-BI and 

return fan E-A-2a operate at minimum outside air and have the capability to modulate to 100 %

outdoor air (economizer cycle). Air handling unit ACU-BI is located in the mechanical room on 

the basement of Wing B. ACU-Bl is of field assembled panel construction. The unit is in good 

condition and serves the Mail Room and other surrounding rooms. The mechanical room is

crowded with six ACUs, several exhaust fans, domestic hot water storage tanks, pumps,

overhead ductwork, piping, electrical conduits, etc. The ceiling plenum in the Mail Room is also 

fairly congested with ductwork, piping, electrical conduits, etc.
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The return/relief exhaust air fan E-B-la returns the air from the areas surrounding the Mail Room

to ACU-BI or exhausts the air depending on whether the ACU is operating with minimum

outside air or under the economizer mode. The exhaust air fan E-B-lb exhausts the air from the

Mail Room without returning any air to ACU-BI. Both fans are located in the mechanical

equipment room #2 in the basement of Wing B.

The temperature controls are pneumatic and air handling unit ACU B-I and the return fan E-A-la

and exhaust fan E-B-1b are started and stopped manually or by means of time clocks installed in

the unit's control panel The ACU and the fan operates 24 h all year round.

The Mail Room air handling unit supply and return/exhaust fans are fed from the Motor Control

Center MCC-B1 located in the Mechanical Room #2.

One-story office building

The one-story office building is a contiguous group of large one-story trailers that have been 

joined to form a single building of 17 040 ft

2

. The building is approximately 15 ft high with 6

exterior single and double doors and 67 fixed double glazed windows. Additionally, the floor is

penetrated by a number of plumbing pipes and electrical conduits coming from the crawl space.

Twenty-seven rooftop heat pump units provide heating, ventilation, and air-conditioning to the

one-story office building. Each unit is controlled by a single room thermostat. These units are

built to have 1 in thick throw-away air filters.

The Rooftop heat pumps are currently fed from two panels located in the Electrical Equipment

Room.

A & E Findings and Recommendations

High-rise Office Building Tower

General Findings

Without the benefit of a detailed inspection of the exterior glazed areas of the building, it is

believed that decades of aging and weathering will necessitate substantial resealing around the

glazed surfaces and exterior penetrations.

To extend the six outside air intakes from the mezzanine mechanical room to the roof will

require running ductwork up the exterior walls, blocking around 130 windows and 

compromising the aesthetics of the building. Extending the outside air intakes through the inside

the building with ductwork will require valuable space at each floor.

The installed air filters are MERV 6 with an efficiency of 25 % to 30 %.

The existing Motor Control Center MCC-A1 and MCC-A2 have adequate capacity and available

spare/space modules to accommodate the proposed modifications.

The protection needed against release outdoor or indoor of a biological or chemical attack will

require the installation of quick shut-off switch and quick purge switch to be centrally located in

the guard control office that is manned 24 h. Currently there are no areas designated as sheltersin-place to protect the occupants of the building.
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Recommended Retrofits

SEALING BUILDING ENVELOPE

Seal and reseal, as required, around interior and exterior of windows, doors and penetrations at

the building envelope.

ELEVATE OUTDOOR AIR INTAKES

Extend the six outside air intakes, from the Mezzanine mechanical room to the roof by installing 

ductwork on the exterior.

IMPLEMENT SHELTER-IN-PLACE

To augment the ability of building occupants to shelter-in-place, areas of refuge should be

distributed through out the building. These "shelters-in-place" will be sealed rooms in which the

building occupants will assemble for a defined period of time.

INSTALL SHUT-OFF AND PURGE SWITCHES

Protection against outdoor or indoor release of a biological or chemical attack requires the

installation of quick shut-off switch and quick purge switch to be centrally located in the guard

control office that is continuously manned. The electrical system that will provide an immediate

shutdown of the AHU's supply fans consists of a shut-off switch to be located in the Guard 

Control Office in the basement and will control a multipole relay to be installed in an available

space bucket in the existing Motor Control Center MCC-A1 in Mechanical Room #4. Each relay 

contact is then connected to the corresponding starter of the supply fan in MCC-A1 and MCCA2.

The electrical system that will provide an immediate start-up of the AHU's exhaust fans consists

of a purge switch to be located in the Guard Control Office in the basement and will control a

multipole relay to be installed in an available spare bucket in the existing Motor Control Center

MCC-A1 located in the Mechanical Room #4. Each relay contact is then connected to the

corresponding starter of the exhaust fan in MCC-A1 and MCC-A2.

UPGRADE TO FILTRATION LEVEL I

Upgrade all filters from the current MERV 6 filters to 4 in MERV11 high capacity filters. This

change will result in increased efficiency and longer life relative to the standard capacity filter.

Utilize the existing 20 in x 20 in frames, so major changes to the structure will not be required.

Changes to the fan and motor are not required.

UPGRADE TO FILTRATION LEVEL 2

Upgrade each AHU with a three-stage filter system consisting of 4 in pre-filter, 85 %

intermediate filter, and 99.97 % HEPA filter. Remove the existing filter bank assembly to 

achieve this level of filtration. Install a new field fabricated, build-up bank of HEPA rated frames

within the existing AHUs with new safing on all four sides. The frames will have HEPA

clamping mechanism to achieve 99.97 % seal. Safings will consist of 18/20 gauge galvanized 

steel. Screw in place and seal with an appropriate sealant the frames and safing. To achieve the

maximum amount of filter area the nominal frame size will be 24 in x 24 in and 12 in x 24 in, as

required.

Replace the following fans and motors because of the increase in pressure requirements to meet

the requirements of additional static pressure drop:

a. ACU-Al: Replace the existing 15 hp fan motor with a new 25 hp motor.

b. ACU-A2: Replace the 15 hp motor with a new 25 hp motor.
148

c. ACU-A3: Replace the 30 hp motor with a new 40 hp motor.

d. ACU-A4: Replace the 25 hp motor with a new 40 hp motor.

e. ACU-A5: Replace the 40 hp motor with a 50 hp motor.

f. ACU-A6: Replace the supply fan S-A-6(B) with a new fan and the 20 hp motor with a new

40 hp motor.

The pre-filter should be changed four times per year, one final filter change per year, and one

HEPA filter change per year.

Modify the Motor Control Center MCC-A1 and MCC-A2 by removing existing ACU-Al thru

ACU-A6 combination starters/disconnect switch and associated feeders. Provide for new motors:

a. ACU-Al: Install in MCC-A1 combination starter size 2 and 60 A disconnect switch and 

connect new 25 hp motor with 3 #6 and 1 #10 ground in 1 in conduit.

b. ACU-A2: Install in MCC-A2 combination starter size 2 and 60 A disconnect switch and 

connect new 25 hp motor with 3 #6 and 1 #10 ground in 1 in conduit.

c. ACU-A3: Install in MCC-A1 combination starter size 3 and 100 A disconnect switch and 

connect new 40 hp motor with 3 #3 and 1 #8 ground in 1 1/4 in conduit.

d. ACU-A4: Install in MCC-A1 a combination starter size 3 and 100 A disconnect switch and 

connect new 40 hp motor with 3 #3 and 1 #8 ground in 1 1/4 in conduit.

e. ACU-A5: Install in MCC-A1 a combination starter size 3 and 125 A disconnect switch and 

connect new 50 hp motor with 3 #2 and 1 #6 ground in 1 1/4 in conduit.

f. ACU-A6: Install in MCC-A2 a combination starter size 3 and 100 A disconnect switch and 

connect new 40 hp motor with 3 #3 and 1 #8 ground in 1 1/4 in conduit.

The modifications to the Motor Control Center MCC-A1 and MCC-A2 will result in a

considerable increase in the load. Replace the existing main circuit breaker in switchboard 101-

Al with new 3 pole, 600 A and connect to the MCC-A1 and MCC-A2 with new 600 A feeder.

UPGRADE TO FILTRATION LEVEL 3

Upgrade each AHU with a five-stage filter system consisting of 4 in pre-filter, 85 % intermediate

filter, 99.97 % HEPA filter, 99.99 % gas phase filter, and 2 in post filter. Remove the existing 

filter bank assembly to accommodate this level of filtration. Include ASZM-TEDA military

grade carbon (per US Army standard EA-C-1704) designed for chemical agents as the gas phase

filter bank designed to provide approximately 0.10 s of residence time. Remove the existing filter

bank assembly to achieve this level of filtration. Install two new field-fabricated, build up banks

of HEPA rated frames within the existing AHUs with new safing on all four sides. The frames

will be 14 gauge stainless steel with welded corners and ground filter seal surface. The frames

will have HEPA clamping mechanism to achieve 99.97 % seal. Safings will consist of 18/16 

gauge stainless steel. Weld in place the frames and safing, mechanically fasten, and seal them to 

the plenum with appropriate sealant. To achieve the maximum amount of filter area the nominal

frame size will be 24 in x 24 in and 12 in x 24 in as required to achieve the maximum of filter

area.

Replace the following fans and motors because of the increase in pressure requirements to meet

the requirements of additional static pressure drop:

a. ACU-Al: Replace the supply fan S-A-1(C) with a new supply fan and the 15 hp motor with
149

a 40 hp motor.

b. ACU-A2: Replace the 15 hp motor with a 30 hp motor.

c. ACU-A3: Replace the 30 hp motor with a new 50 hp motor.

d. ACU-A4: Replace the supply fan S-A-4(B) with a new fan and the 25 hp motor with a new

50 hp motor.

e. ACU-A5: Replace the 40 hp motor with a new 75 hp motor.

f. ACU-A6: Replace the supply fan S-A-6(B) with a new fan and the 20 hp motor with a new

50 hp motor.

Modify the Motor Control Center MCC-A1 and MCC-A2 by removing existing ACU-Al thru

ACU-A6 combination starter/disconnect switches and associated feeders. Provide for new

motors:

a. ACU-A1: Install in MCC-A1 combination starter size 3 and 100 A disconnect switch and 

connect new 40 hp motor with 3 #3 and 1 #8 ground in 1 1/4 in conduit.

b. ACU-A2: Install in MCC-A2 combination starter size 3 and 70 A disconnect switch and 

connect new 30 hp motor with 3 #4 and 1 #8 ground in 1 in conduit.

c. ACU-A3: Install in MCC-A1 combination starter size 3 and 125 A disconnect switch and 

connect new 50 hp motor with 3 #2 and 1 #6 ground in 1 1/4 in conduit.

d. ACU-A4: Install in MCC-A1 combination starter size 3 and 125 A disconnect switch and 

connect new 50 hp motor with 3 #2 and 1 #6 ground in 1 1/4 in conduit.

e. ACU-A5: Install in MCC-A1 combination starter size 4 and 175 A disconnect switch and 

connect new 75 hp motor with 3 #2 and 1 #6 ground in 2 in conduit.

f. ACU-A6: Install in MCC-A2 combination starter size 3 and 125 A disconnect switch and 

connect new 50 hp motor with 3 #2 and 1 #6 ground in 1 1/4 in conduit.

The modification to the Motor Control Center MCC-A1 and MCC-A2 results in a considerable

increase in the load. Replace the existing main circuit breaker in switchboard 101-Al with new 3 

pole, 600 A and connect to the MCC-A1 and MCC-A2 with new 600 A feeder.

High-rise Office Building, Main Lobby

General Findings

Given the present configuration, it is not possible to contain a release that occurs within the

Lobby. However, it is important to install airtight physical barriers to limit contaminant spread 

into the rest of the building.

To maintain the air conditioning of the Main Lobby independent from the surrounding areas, a

new AHU (ACU-A-2a) and exhaust fan (E-A-2a) will be required. Currently, ACU-A2 supplies

air to the Main Lobby, Corridor #13, Corridor #14, and the Exhibit area, and return/exhaust fan 

E-A-2 returns air to the unit or exhausts it during the air economizer cycle from these areas. The

amount of air circulated through the Lobby should be removed from ACU-A2 and E-A-2 to

maintain the Lobby independent from the other areas.

To isolate the Main Lobby from the surrounding areas, fan E-A-2 should be replaced by two 

fans: 1) New fan E-A-2 should replace the existing fan and return the air from the non-Lobby

spaces to air handling unit ACU-A-2; and, 2) New fan E-A-2a should be dedicated to 
150

return/exhaust the air from the Lobby to the new ACU 2a. The new air exhaust fan should be

fitted with Filtration Level 2 or 3 to prevent spreading hazardous materials from the Main Lobby 

to the outdoors during an emergency.

There are two options for the new exhaust fan E-A-2a. It should be equipped with Filtration

Level 2 or 3. Installation of Filtration Level 1 is not recommended because it will not provide the

level of protection required when discharging contaminated air to the outside.

The space available to install new air handling unit, exhaust fan, filters, and ductwork is very 

tight and will require removal and relocation of existing ductwork, piping, control and electrical

panels, and electrical conduits. Some of the headroom could be reduced due to installation of

new ductwork under existing ductwork, piping, and electrical conduits. Due to existing 

conditions, the installation of Filtration Level 3 will be considerably more difficult than Level 2,

Recommended Retrofits

ELEVATE OUTDOOR AIR INTAKES

Relocate the outside air intakes to the roof.

PHYSICAL SEPARATION

Isolate the east lobby of Wing A from the rest of the building by providing tempered glass

partitions with self-closing glass doors that will allow the building occupants continued access to 

the Lobby and exhibition spaces. The isolating partitions will also include a matching marble

finish above the glazed areas.

The building is has a sprinkler system, therefore isolating the Lobby in the manner proposed will

not compromise egress requirements, impair visibility or prohibit the transmittance of natural

light.

Accessory door hardware will take into account the style and character of the existing building,

including its door hardware, and will seal potential points of air infiltration and enable the

mechanical system to maintain the designed air pressure differentials between adjacent spaces.

HVAC ISOLATION

Install a new air handling unit (ACU-A2a) in Mechanical Equipment Room #4 to serve the Main 

Lobby only. Provide ACU-A2a with air economizer cycle, air filters, hot water preheat coil,

cooling coil, and supply fan. Install the unit in the southeast corner of the room in front of ACUA-2. Connect the supply duct from the unit to the existing supply duct with hot water reheat coils

serving the Lobby. Install chilled water branches from the nearby mains to the cooling coil and 

hot water branches from the nearby hot water mains to the heating coil. Bring outside air to the

unit from an existing louver installed in the northeast corner of the room.

Remove the existing exhaust fan E-A-2 and instead install two new exhaust fans. One fan (E-A2) to serve as return/exhaust fan to the existing ACU-A2 from the areas surrounding the Lobby.

Also, install a second fan (E-A-2a) to return/exhaust the air to the new ACU-A2a and run an 

exhaust duct from the return duct to an existing louver near the fan. Install filters at the discharge

side of the new exhaust fan E-A-2a.

Select and balance ACU-A2a and E-A-2a to maintain the Main Lobby approximately 10%

negative with respect to the surrounding areas and the outdoors during normal operation and 

during emergency.

UPGRADE TO FILTRATION LEVEL 2

Equip the AHU with a Level 2 filter system consisting of 4 in pre-filter, 85 % intermediate filter,
151

and 99.97 % HEPA filter in a filter section and a 7.5 hp motor.

Install in Motor Control Center MCC-A2 a combination starter size 1 and 20 A disconnect

switch and connect new 7.5 hp motor with 3 #12 and 1 #12 ground in 3/4 in conduit.

Provide fan E-A-2a with Filtration Level 2 system.

Equip the fan with a 5 hp motor to meet the additional requirements of the filters static pressure

drop. Remove in MCC-A2 combination starter/disconnect switch for fan E-A2 and associated 

feeder. Install in place combination starter size 0 and 15 A disconnect switch and connect new

5 hp motor with 3 #12 and 1 #12 ground in 3/4 in conduit. Install in MCC-A2 combination

starter size 1 and 20 A disconnect switch and connect new 7.5 hp motor with 3 #12 and 1 #12 

ground in 3/4 in conduit.

UPGRADE TO FILTRATION LEVEL 3

Equip the AHU with Filtration Level 3 consisting of 4 in pre-filter, 85 % intermediate filter,

99.97 % HEPA filter, 99.99 % gas phase filter, and 2 in post filter in a filter section, and a 7.5 hp

motor.

Install in Motor Control Center MCC-A2 a combination starter size 1 and 20A disconnect switch 

and connect new 7.5 hp motor with 3 #12 and 1 #12 ground in 3/4 in conduit.

Provide fan E-A-2a with a Level 3 filter system consisting of 4 in pre-filter, 85 % intermediate

filter, 99.97 % HEPA filter, 99.99 % gas phase filter, and 2 in post filter in a filter section.

Equip fan E-A-2a with a 7.5 hp motor to meet the additional requirements of the filter’s static

pressure drop. Remove in MCC-A2 combination starter/disconnect switch for fan E-A2 and

associated feeder. Install in place combination starter size 0 and 15 A disconnect switch and 

connect new 7.5 hp motor with 3 #12 and 1 #12 ground in 3/4 in conduit. Install in MCC-A2 

combination starter size 1 and 20 A disconnect switch and connect new E-A-2 7.5 hp motor with

3 #12 and 1 #12 ground in 3/4 in conduit.

High-rise Office Building, Mail Room

General Findings

The walls, ceilings and doors are not airtight and cannot contain a release within the room.

It will not be possible to install a dedicated new air handling unit in Mechanical Room #2 due to 

congestion in the Mechanical Room and ceiling space above the Mail Room. In addition, a new

outside air duct would need to be installed from the present unit's outside air intake to the top of

the existing architectural louver located above a Wing D entrance door. This duct modification

will raise the outside air intake to around 30 ft (roof level) from the ground. Therefore, since a

new dedicated unit cannot be installed, the fallback position is to upgrade the filtering system of

the existing AHU.

The existing exhaust fan E-B-2b dedicated to the Mail Room will need to be fitted with a new

filter bank with one of the two filter options (2 or 3) to prevent spreading hazardous materials

from the Mail Room to the outdoors during an emergency.

Installation of Filtration Level I filters, as described above, is not recommended because it will

not provide the quality of protection required for the Mail Room.

During a previous expansion and renovation of the Mail Room, a corridor between the room and 

the loading dock became part of the Mail Room, the air registers connected to the exhaust duct

from the exhaust fan E-13-1A were removed, and the duct was abandoned in place. Presently,
152

the air supplied to the Mail Room is exfiltrated through two transfer grilles to the adjacent

corridors at the east and west side of the room.

Recommended Retrofits

PHYSICAL SEPARATION

Seal room envelope; walls, ceilings, doors and slabs.

HVAC ISOLATION

Maintain the Mail Room at negative pressure all the time during normal and emergency 

operation by adjusting the supply and return airflows.

UPGRADE TO FILTRATION LEVEL 2 

Upgrade ACU-B1 with Filtration Level 2 system consisting of 4 in pre-filter, 85 % intermediate

filter, and 99.97 % HEPA filter. Remove the existing filter bank assembly to achieve this level of

filtration. Install a new field fabricated, build up bank of HEPA-rated frames within the existing

AHU with new safing on all four sides. The frames will have HEPA clamping mechanisms to 

achieve 99.97 % seal. Safings will consist of 18/20 gauge galvanized steel. Screw in place and

seal with an appropriate sealant the frame and safing. To achieve the maximum amount of filter

area the nominal frame size will be 24 in x 24 in and 12 in x 24 in as required.

Replace the existing 25 hp fan motor with a new 40 hp motor to overcome the additional static

pressure. Remove from MCC-B1 the combination starter/disconnect switch for fan S-B-1 and 

associated feeder. Install in-place combination starter size 3 and 100 A disconnect switch and 

connect new 40 hp motor with 3 #3 and I #8 ground in 1 1/4 in conduit.

Equip existing exhaust fan E-B-2b with Filtration Level 2 system consisting of 4 in pre-filter,

85 % intermediate filter, and 99.97 % HEPA filter in a filter section.

Remove MCC-B1 combination starter/disconnect switch for fan E-B-1 b and associated feeder.

Install in-place combination starter size 0 and 15A disconnect switch and connect new 2 hp 

motor with 3 #12 and 1 # 12 grounds in 3/4 in conduit.

Replace the existing 1 hp fan motor with a 2 hp motor to meet the additional static pressure drop

associated with the filter.

The pre-filter should be changed four times per year, one final filter change per year, and one

HEPA filter change per year.

UPGRADE TO FILTRATION LEVEL 3

Upgrade ACU-B1 with Filtration Level 3 system consisting of 4 in pre-filter, 85 % intermediate

filter, 99.97 % HEPA filter, 99.99 % gas phase filter, and 2 in post filter. Remove the existing 

filter bank assembly to achieve this Level of filtration. The filter bank for the gas phase will

include ASZM-TEDA military grade carbon designed for chemical agents and be designed to 

provide approximately 0.10 s of residence time. Remove the existing filter bank assembly to 

achieve this level of filtration. Install two new field fabricated, build up banks of HEPA rated 

frames within the existing AHU with new safing on all four sides. The frames will be 14 gauge

stainless steel with welded corners, welded, and ground filter seal surface. The frames will have

HEPA clamping mechanisms to achieve 99.97 % seal. Safings will consist of 18/16 gauge

stainless steel. Weld in place the frames and safing, mechanically fasten, and seal them to the

plenum with appropriate sealant. To achieve the maximum amount of filter area the nominal

frame size will be 24 in x 24 in and 12 in x 24 in as required to achieve the maximum of filter

area.
153

Replace the existing 25 hp fan motor with a new 40 hp motor to overcome the additional static

pressure. Remove in MCC-B1 the combination starter/disconnect switch for fan S-B-1 and

associated feeder. Install in-place combination starter size 3 and 100A disconnect switch and 

connect new 40 hp motor with 3 #3 and 1 #8 ground 1 1/4 in conduit.

Equip the fan with Filtration Level 3 system consisting of 4 in pre-filter, 85 % intermediate filter,

99.97 % HEPA filter, 99.9 9% gas phase filter, and 2 in post filter.

Replace the existing fan and the 1 hp motor with a new fan with a 2 hp motor to meet the

additional static pressure drop. Remove in MCC-B1 the combination starter/disconnect switch 

for fan E-B-1b and associated feeder. Install in place combination starter size 0 and 15 A

disconnect switch and connect new 2 hp motor with 3 #12 and 1 #12 in 3/4 in conduit.

The pre-filter should be changed four times per year, one final filter change per year, and one

HEPA filter change per year for more efficient and energy saving operation.

One-story office building

General Findings

The one-story office building is a modular type building composed of 24 trailers attached 

together. The building is heated, ventilated, and air conditioned by 28 rooftop heat pumps. The

space where the supply fan and the motor are located in the heat pumps is tight and will not

permit the replacement of the installed fan with a larger supply fan and motor to handle

additional static pressure that will be able to support more efficient particle and gaseous removal

filters. Neither is there enough space to install additional filters inside the heat pumps. In

addition, the units have air economizer systems that supply 100 % outside air while in this mode

of operation and will require the selection of the filters to handle the larger airflow.

Recommended Retrofits

The provision of better outside air filtration to the heat pumps will require the installation of one

or two outside air supply fan on the roof with filter banks for each of the three filter options

indicated above for the high-rise office building and running a supply duct from the fan to each 

unit. There are 28 rooftop heat pump units on the roof (approximately one per trailer) supplying

1600 cfm each with approximately 160 cfm minimum outside air each during normal operation 

and 1600 cfm during air economizer operation. The outside air introduced by each unit, which is

not exhausted through toilet exhaust and exfiltration, is exhausted by means of a barometric

damper in each unit. During an emergency, each unit's fan should supply 1600 cfm outside air

each for a total of 44 800 cfm. About 35 840 cfm should be exhausted and 8900 cfm should 

remain in the building to maintain around 20 % positive pressure during emergencies. The

outside air intake filters will require a casing of 10 ft H x 10 ft W and 24 in in depth (or similar

dimensions) for Option No. 2 and 10 ft H x 10 ft W and 52 in depth (or similar dimensions) for

Option No. 3. To achieve the maximum amount of filter area the nominal frame size will be

24 in x 24 in and 12 in x 24 in as required.

The supply fan alone will weigh approximately 3400 lbs plus the weight of the filter banks and 

the ductwork. The building's roof will not be able to support all this weight unless additional

structural reinforcement is provided. Another option is to install two fans with the filters and

ductwork, but still will require additional structural reinforcement.

Instead of installing the fan(s) and filter bank(s) on the roof, they can be installed on an elevated 

platform at the same height as the roof and adjacent to the east side of the building and from
154

there the ductwork run to each heat pump.

Variable frequency drive(s) should be provided to modulate the outside air fan(s) to supply the

minimum outside air during normal operation and 100 % air during emergency operation.

The 28 rooftop heat pumps are powered from HVAC panels PA-7 and PA-8 and both panels are

full with each containing circuits for 14 heat pumps. The proposed installation of two outside air

fans shall instead be powered each from the main panels PA-1 and PA-2.

Upgraded filtration should be provided as indicated below.

The protection needed against release of biological or chemical attack will require the

installation of quick shut-off switch to be located at reception desk.

SEALING BUILDING ENVELOPE

To enhance the airtightness of the structure, it is recommended to patch roof leaks, seal around 

exterior windows, provide exterior doors with gasket hardware to close gaps between door

leaves, replace exterior door thresholds with others designed to form a seal at the base of doors,

and seal around pipe and conduit floor penetrations within the building's crawl space.

INSTALL SHUT-OFF SWITCH

The protection needed against outdoor releases requires the installation of quick shut-off

switches to stop the rooftop heat pumps. This switch is to be located at the reception desk.

UPGRADE TO FILTRATION LEVEL 1

Installation of Filtration Level 1 filters is not recommended because it will not provide the

quality of protection required. However, the existing filtration could be improved by replacing 

the existing MERV 4 filters with 1 in thick MERV 11 filters. The MERV 11 filters will not

affect the system static pressure.

UPGRADE TO FILTRATION LEVEL 2

Provide two outside air supply fans on two steel platforms, supported by steel legs on footings

and with metal grating, adjacent to the east side of the building and at the same height of the

roof. Provide with each fan a 7 ft H x 8 ft W filter bank, with Filtration Level 2 as described for

the high-rise office building. Connect the new fans to the filter banks and to their respective heat

pump units with ductwork to each unit's air intake. Provide variable frequency drives for each 

fan to modulate the outside air to each unit during normal operation and during emergency 

operation. Provide automatic controls with a static pressure sensor in each fan supply duct to 

control the respective fan. Interlock the exhaust fans controls with the existing heat pumps

controls.

Provide a 20 hp motor with each outside air supply fan. Install in main panel PA-1 and PA-2

each a 3 pole, 50 A circuit breaker for each of the proposed supply fans. Install combination 

variable frequency drive, disconnect switch at each supply fan location, and connect the 20 hp 

motors with 3 # 8 and 1 # 10 ground in 1 in conduit.

UPGRADE TO FILTRATION LEVEL 3

Provide two outside air supply fans on two platforms adjacent to the east side of the building at

roof height. Provide each fan with a 3.5 ft x 4 ft filter bank with Filtration Level 3 as described 

above. Connect the new fans to the filter banks and to their respective heat pump units with

ductwork to each unit's air intake. Provide variable frequency drive for each fan to modulate the

outside air to each unit during normal operation and during emergency operation. Provide

automatic controls with a static pressure sensor in each fan supply duct to control the respective
155

fan. Interlock the exhaust fans controls with the existing heat pumps controls.

Provide a 25 hp motor with each of the two outside air supply fan. Install in main panel PA-I and 

PA-2 each a 3 pole, 70 A circuit breaker for each of the proposed supply fans. Install

combination variable frequency drive, disconnect switch at each supply fan location, and connect

the 25 hp motors with 3 # 6 and I # 8 ground in 1 1/4 in conduit.
156
157

Appendix C Case Study Retrofit Costs Per Unit of Floor Area

The cost data presented in this appendix are based on a critical analysis of the contractorprovided estimates for initial capital costs (i.e., first costs) and annual-recurring costs for filter

replacement for a variety of chembio retrofit strategies in the two case study buildings.

1 This

appendix presents a fairly detailed classification of cost data, in which major cost items (e.g.,

HVAC Upgrade) are broken down into their constituent cost items (e.g., Remove Existing Filter

Bank).

The cost data are presented as a series of tables. The tables are organized around four retrofit

categories in the two case study buildings: (1) High-rise office building; (2) Lobby in the highrise office building; (3) Mail room in the high-rise office building; and (4) Low-rise office

building. Within each category, the tables are organized around the three levels of filtration 

considered as well as the non-filtration retrofits. The three filtration levels are as follows: Level

1, minimal protection from biological agents and no protection from chemical agents; Level 2,

enhanced protection from biological agents and no protection from chemical agents; and, Level

3, enhanced protection from biological agents and enhanced protection from chemical agents.

Tables C.1 through C.3 present initial capital costs in the high-rise office building for Filtration

Levels 1 through 3 respectively. Table C.4 covers annual-recurring costs for the filter

replacements for the high-rise office building. Table C.5 covers initial capital costs for the highrise office building for five non-filtration retrofits, i.e., envelope sealing, moving the outdoor air

intake, installing quick shut-off/purge switches, shelter-in-place, and system testing and 

balancing. Tables C.6 and C.7 cover initial capital costs for the Lobby in the high-rise office

building for Filtration Levels 2 and 3. Table C.8 covers initial capital costs for the two nonfiltration retrofits of the lobby, i.e., installing interior partitions between the lobby and the rest of

the first floor, and raising the outdoor air intake serving the lobby. Tables C.9 and C.10 cover

initial capital costs for Filtration Levels 2 and 3 in the mail room in the high-rise office building.

Table C.11 covers initial capital costs for sealing the mail room partitions from the rest of the

basement. Tables C.12 through C.14 cover initial capital costs for Filtration Levels 1 through 3

in the low-rise office building. Table C.15 covers initial capital costs for sealing the envelope of

the low-rise office building. Note that the sums of the constituent cost items in the tables may not

add to the dollar amount for the major cost items due to independent rounding.

With the exception of Table C.4, which deals with annual recurring costs for filter replacement

rather than initial capital costs, each table has four columns: (1) Cost Item; (2) Total Cost; (3)

Cost per Square Foot ($/ft

2

); and (4) Cost per Square Meter ($/m

2

). The entries under the Cost

Item column record the major cost items in boldface font (e.g., HVAC Upgrade); each 

constituent cost item is indented and printed in regular font. The values under the Total Cost

column record the overall cost for the major cost item in boldface font. The constituent cost

items are printed in regular font; their sum is equal to the dollar amount for the major cost item.

Columns 3 and 4 are patterned after Column 2. The per unit cost for each major cost item is

shown in boldface font and the per unit costs for each constituent cost item are shown in regular

font. Note that the sums of per unit costs of the constituent cost items may not add to the dollar

amount for the major cost item due to independent rounding.

Table C.4, which covers annual filter replacement costs for the high-rise office building, is

broken into two parts. Part A reports annual costs per air-handling unit (AHU). There are six

 1 Note that the cost estimates are for purposes of illustration only—actual renovations of different buildings will face

different costs and different risk profiles.
158

AHUs in the high-rise office building. Part B reports annual costs per unit of floor area. Part A of

Table C.4 has nine columns. The first two columns designate the system and type of filter. Table

C.4 makes reference to four systems: (1) As Is; (2) Filtration Level 1; (3) Filtration Level 2; and

(4) Filtration Level 3. Filters are designated by their MERV (Minimum Efficiency Reporting

Value) rating, as HEPA (High Efficiency Particulate Air), or as Gas Phase ACS (Air-Cleaning 

System). Columns 3 through 7 record the information needed to calculate the cost per change per

AHU. Column 8 records the number of changes per year for each type of filter. Column 9 

records the annual cost per AHU for each system and type of filter. Part B of Table C.4 has four

columns: (1) Cost Item; (2) Total Annual Cost; (3) Cost per Square Foot ($/ft

2

); and (4) Cost per

Square Meter ($/m

2

). The entries under the Cost Item column record the system in boldface font;

each constituent cost item (i.e., type of filter) is indented and printed in regular font. The values

under the Total Annual Cost column record the overall cost for the system in boldface font. The

constituent cost items are printed in regular font; their sum is equal to the dollar amount for the

system. Columns 3 and 4 are patterned after Column 2. The annual cost per unit for each system

is shown in boldface font and the annual cost per unit for each constituent cost item is shown in 

regular font. Note that the sums of the annual costs per unit of the constituent cost items may not

add to the annual cost per unit for the system due to independent rounding.
159

Table C.1 Cost for Level 1 Filtration for the High-Rise Office Building

Cost Per Unit Floor Area Cost Item

Total Cost 

($) $/ft

2 $/m2

HVAC Upgrade 71 354 0.59 6.40

Remove Existing Filter Bank 3640 0.03 0.33

Upgrade Air Handling Unit w/ One Bank MERV 11

Frames, Clips and Filters

1843 0.02 0.17

Safing, Stiffener Bars and Welding 2070 0.02 0.19

Electric Motor 25 hp w/ Belts and Pulley 8467 0.07 0.76

Electric Motor 40 hp w/ Belts and Pulley 11 773 0.10 1.06

Electric Motor 50 hp w/ Belts and Pulley 6643 0.06 0.60

Centrifugal Fan 40 hp 21 303 0.18 1.91

Miscellaneous 8504 0.07 0.76

Balance Air Handling Unit 3848 0.03 0.35

Mobilization and Demobilization 1600 0.01 0.14

Clean-Up 1664 0.01 0.15
160

Table C.2 Cost for Level 2 Filtration for the High-Rise Office Building

Cost Per Unit Floor Area Cost Item

Total Cost 

($) $/ft

2 $/m2

HVAC Upgrade 209 445 1.75 18.79

Remove Existing Filter Bank 3640 0.03 0.33

Remove Electric Motor & Assembly Wiring 3952 0.03 0.35

Remove Centrifugal Fan 520 0.00* 0.05

Upgrade the Air Handling Unit w/ One Bank of HEPA

Rated Galvanized Steel, Frames, Clips and Filters

135 465 1.13 12.15

Safing, Stiffener Bars and Welding 2070 0.02 0.19

Electric Motor 25 hp w/ Belts and Pulley 8467 0.07 0.76

Electric Motor 40 hp w/ Belts and Pulley 11 773 0.10 1.06

Electric Motor 50 hp w/ Belts and Pulley 6643 0.06 0.60

Centrifugal Fan 40 hp 21 303 0.18 1.91

Miscellaneous 8501 0.07 0.76

Balance Air Handling Unit 3848 0.03 0.35

Clean-Up 1600 0.01 0.14

Mobilization and Demobilization 1664 0.01 0.15

Electrical Modifications 86 415 0.72 7.75

Remove Miscellaneous (Wire, Conduit and Switches) 3921 0.03 0.35

SWBD C/B – 600 A, 3P 5883 0.05 0.53

Wire Miscellaneous 24 246 0.20 2.17

Conduit: 3 in EMT 22 271 0.19 2.00

Combination Starter Size 2/Switch 6864 0.06 0.62

Combination Starter Size 3/Switch 15 692 0.13 1.41

Conduit: 1 in EMT 978 0.01 0.09

Conduit: 1 1/4 in EMT 2182 0.02 0.20

Disc. Switch 60 A, 3P 1055 0.01 0.09

Disc. Switch 100 A, 3P 2217 0.02 0.20

Disc. Switch 200 A, 3P 1107 0.01 0.10

* Entries recorded as 0.00 indicate values less than $0.01.
161

Table C.3 Cost for Level 3 Filtration for the High-Rise Office Building

Cost Per Unit Floor Area Cost Item

Total Cost 

($) $/ft

2 $/m2

HVAC Upgrade 1 025 156 8.54 91.96

Remove Existing Filter Bank 3640 0.03 0.33

Remove Electric Motor & Assembly Wiring 3952 0.03 0.35

Remove Centrifugal Fan 1560 0.01 0.14

Upgrade the Air Handling Unit w/ One Bank of HEPA

Rated Galvanized Steel, Frames, Clips and Filters

843 564 7.03 75.67

Safing, Stiffener Bars and Welding 6493 0.05 0.58

Electric Motor 30 hp w/ Belts and Pulley 6351 0.05 0.57

Electric Motor 50 hp w/ Belts and Pulley 8868 0.07 0.80

Electric Motor 75 hp w/ Belts and Pulley 13 286 0.11 1.19

Centrifugal Fan 40 hp 21 303 0.18 1.91

Centrifugal Fan 50 hp 68 933 0.57 6.18

Miscellaneous 39 215 0.33 3.52

Balance Air Handling Unit 3848 0.03 0.35

Clean-Up 1600 0.01 0.14

Mobilization and Demobilization 2544 0.02 0.23

Electrical Modifications 91 617 0.76 8.22

Remove Miscellaneous (Wire, Conduit and Switches) 3957 0.03 0.35

SWBD C/B – 600 A, 3P 5883 0.05 0.53

Wire Miscellaneous 24 996 0.21 2.24

Conduit: 3 in EMT 22 271 0.19 2.00

Combination Starter Size 3/Switch 19 615 0.16 1.76

Combination Starter Size 4/Switch 5435 0.05 0.49

Conduit: 1 in EMT 414 0.00* 0.04

Conduit: 1 1/4 in EMT 2327 0.02 0.21

Conduit: 2 in EMT 813 0.01 0.07

Disc. Switch 100 A, 3P 1478 0.01 0.13

Disc. Switch 20 0A, 3P 4428 0.04 0.40

* Entries recorded as 0.00 indicate values less than $0.01.
162

Table C.4 Summary of Annual Filter Replacement Costs for the High-Rise Office Building

Part A Annual Costs per Air-Handling Unit

Cost Per Change Per AHU (costs in $) System Material

Unit Cost Units Material Cost Labor Cost Total

Changes/Year

Annual Cost 

Per AHU ($)

As Is MERV 6 5 20 100 20 120 4 480

TOTAL 480

Level 1 MERV 11 8 20 160 32 192 1 192

TOTAL 192

MERV 8 5 20 100 20 120 1 120

Level 2 MERV 13 125 20 2500 500 3000 0.33 1000

HEPA 300 20 6000 1200 7200 0.33 2400

TOTAL 3520

MERV 8 5 20 100 20 120 1 120

MERV 13 125 20 2500 500 3000 0.33 1000

HEPA 300 20 6000 1200 7200 0.33 2400

GPAC 4,500 20 90 000 18 000 108 000 0.2 21 600

Level 3

MERV 11 8 20 160 32 192 2 384

TOTAL 25 504

NOTE: Costs are per AHU and there are six AHUs in the building.
163

Table C.4 Summary of Filter Replacement Costs for High-Rise Office Building (Continued)

Part B Annual Cost Per Unit of Floor Area

Cost Per Unit Floor Area Cost Item

Total Annual Cost

($) $/ft

2 $/m2

System As Is 2880 0.02 0.26

MERV 6 2880 0.02 0.26

System Level 1 1152 0.01 0.10

MERV 11 1152 0.01 0.10

System Level 2 21 120 0.18 1.89

MERV 8 720 0.01 0.06

MERV 13 6000 0.05 0.54

HEPA 14 400 0.12 1.29

System Level 3 153 024 1.28 13.12

MERV 8 720 0.01 0.06

MERV 13 6000 0.05 0.54

HEPA 14 400 0.12 1.29

GPAC 129 600 1.08 11.63

MERV 11 2304 0.02 0.21
164

Table C.5 Cost for Non-filtration Retrofits for the High-Rise Office Building

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

Sealing the Envelope 625 326 5.21 56.09

Seal Exterior Windows and Openings 352 285 2.94 31.60

Swing Staging Equipment 214 611 1.79 19.25

Scaffolding 54 858 0.46 4.92

Seal Doors and Thresholds 3573 0.03 0.32

Move Outside Air Intake to Roof 225 261 1.88 20.21

Swing Staging Equipment 7495 0.06 0.67

Scaffolding 10 363 0.09 0.93

Duct Support 11 899 0.10 1.07

Painting 11 258 0.09 1.01

Remove Louver - 8 ft x 4 ft 208 0.00* 0.02

Bird Screen 2804 0.02 0.25

Ductwork 178 256 1.49 15.99

Clamps, Anchors 2978 0.02 0.27

Shelter-In-Place (covers six shelters in building) 93 812 0.78 8.42

Seal Doors and Thresholds 5359 0.04 0.48

Miscellaneous sealing (Registers, Windows,

Fixtures, Plates) 4990 0.04 0.45

Seal Ceiling Slab Openings 22 318 0.19 2.00

Supply Damper Incl. Elect. Motor - 10 in Dia 3706 0.03 0.33

Return Damper Incl. Elect. Motor - 16 in x 8 in 3438 0.03 0.31

Stand Alone Filtration/Air Cleaning Units 54 000 0.45 4.84

Quick Shut-Off and Purge 20 949 0.17 1.88

System Testing, Adjusting and Balancing 75 000 0.63 6.73

* Entries recorded as 0.00 indicate values less than $0.01.
165

Table C.6 Cost for Level 2 Filtration for the Office Building Lobby

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

HVAC Upgrade $14 112 40.60 437.27

Ductwork 1407 0.40 4.33

Caps 139 0.04 0.43

Air Handling Unit - ACU-A2 w/ Coils 8529 2.44 26.24

Ductwork 23 225 6.64 71.46

Duct Insulation - Fiberglass Board Type 3 Lb Density - 1

1/2 in Thick 15 693 4.48 48.29

Louver 48 in x 48 in with Wall Opening 279 0.08 0.86

Duct - Flex. Connector 235 0.07 0.72

2 in Dia. Piping - Sch. 40 1409 0.40 4.34

Reducer 6 in x 2 in 464 0.13 1.43

2 in Dia. Piping Hook-up 5168 1.48 15.90

2 in Dia. Elbow 786 0.22 2.42

2 in Dia. Piping Fiberglass Insulation -1 1/2 in Thick 382 0.11 1.18

2 in Dia. Piping - Sch. 40 1409 0.40 4.34

Demobilization 800 0.23 2.46

Reducer 3 in x 2 in 317 0.09 0.97

2 in Dia. Piping Hook-up 5168 1.48 15.90

2 in Dia. Elbow 786 0.22 2.42

2 in Dia. Piping Fiberglass Insulation - 1 1/2 in Thick 382 0.11 1.18

Concrete Pad 394 0.11 1.21

Louver 0/A Air 595 0.17 1.83

Balancing Air Handling Unit 494 0.14 1.52

Controls 16 698 4.77 51.38

Piping 1409 0.40 4.34

Valve Tag (Brass - 2 in Dia.) 464 0.13 1.43

Upgrade the Air Handling Unit w/ One (1) Bank of HEPA

Rated Galvanized Steel, Frames, Clips and Filters

13 631 3.89 41.94

Clean-Up 624 0.18 1.92

Housing 1932 0.55 5.94

Exhaust Fan E-A2 5819 1.66 17.90

Exhaust Fan E-A2B 4266 1.22 13.12

HEPA Solution Budget Double Wall Insulated 2645 0.76 8.14

Remove & Relocate Existing Piping, Ductwork, Electrical

Conduit & Wire and Additional Material 24 998 7.14 76.92

Mobilization and Demobilization 1567 0.45 4.82

Electrical Modifications 9432 2.69 29.02

Remove Miscellaneous (Wire, Conduit, Switches) 254 0.07 0.78

Combination Starter Size 1/Switch 5354 1.53 16.47

Wire: #12 THHN 1349 0.39 4.15

Conduit: 3/4 in EMT 1050 0.30 3.23

Disc. Switch, 30 A, 3P 1425 0.41 4.38
166

Table C.7 Cost for Level 3 Filtration for the Office Building Lobby

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

HVAC Upgrade 199 609 57.03 614.18

Ductwork 1407 0.40 4.33

Caps 139 0.04 0.43

Air Handling Unit - ACU-A2 w/ Coils 8529 2.44 26.24

Ductwork 27 194 7.77 83.67

Duct Insulation - Fiberglass Board Type, 3 Lb Density - 1

1/2 in Thick 19 653 5.62 60.47

Louver 48 in x 48 in with Wall Opening 279 0.08 0.86

Duct - Flex. Connector 235 0.07 0.72

2 in Dia. Piping - Sch. 40 1409 0.40 4.34

Reducer 6 in x 2 in 464 0.13 1.43

2 in Dia. Piping Hook-up 5168 1.48 15.90

2 in Dia. Elbow 786 0.22 2.42

2 in Dia. Piping Fiberglass Insulation -1 1/2 in Thick 382 0.11 1.18

2 in Dia. Piping - Sch. 40 1409 0.40 4.34

Reducer 3 in x 2 in 317 0.09 0.97

2 in Dia. Piping Hook-up 5168 1.48 15.90

2 in Dia. Elbow 786 0.22 2.42

2 in Dia. Piping Fiberglass Insulation - 1 1/2 in Thick 382 0.11 1.18

Concrete Pad 394 0.11 1.21

Louver 0/A Air 595 0.17 1.83

Balancing Air Handling Unit 494 0.14 1.52

Controls 16 698 4.77 51.38

Piping 1409 0.40 4.34

Valve Tag (Brass - 2 in Dia.) 464 0.13 1.43

Clean-Up 624 0.18 1.92

Housing 1932 0.55 5.94

Exhaust Fan E-A2 5819 1.66 17.90

Exhaust Fan E-A2C 4266 1.22 13.12

HEPA and Gas Filter Equipment 65 843 18.81 202.59

Remove & Relocate Existing Piping, Ductwork,

Electrical Conduit & Wire and Additional Material 24 998 7.14 76.92

Mobilization and Demobilization 2366 0.68 7.28

Electrical Modifications 9432 2.69 29.02

Remove Miscellaneous (Wire, Conduit, Switches) 254 0.07 0.78

Combination Starter Size 1/Switch 5354 1.53 16.47

Wire: #12 THHN 1349 0.39 4.15

Conduit: 3/4 in EMT 1050 0.30 3.23

Disc. Switch, 30 A, 3P 1425 0.41 4.38
167

Table C.8 Cost for Non-filtration Retrofits for the Office Building Lobby

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

Isolating the Lobby 64 067 18.30 197.13

Marble 23 508 6.72 72.33

Concrete Lintel 475 0.14 1.46

1/2 Tempered Glass 10 473 2.99 32.22

Metal Doors (Frames) Hdw 23 424 6.69 72.07

Seal Doors and Thresholds 3873 1.11 11.92

CMU 2314 0.66 7.12

Extend Outside Air Intake to Roof 23 773 6.79 73.15

Opening Wall 400 0.11 1.23

Bird Screen 140 0.04 0.43

Ductwork 11 842 3.38 36.44

Clamps, Anchors 496 0.14 1.53

Swing Staging Equipment 1458 0.42 4.49

Scaffolding 5073 1.45 15.61

Duct Support 2400 0.69 7.38

Painting 1964 0.56 6.04
168

Table C.9 Cost for Level 2 Filtration for the Office Building Mail Room

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

HVAC Upgrade 63 350 17.60 189.67

Remove Existing Filter Bank 607 0.17 1.82

Remove Electric Motor & Assembly Wiring 693 0.19 2.08

Upgrade the Air Handling Unit w/ One (1) Bank of HEPA

Rated Galvanized Steel, Frames, Clips and Filters

16 940 4.71 50.72

Safing, Stiffener Bars and Welding 345 0.10 1.03

Housing Filters 2400 0.67 7.19

Ductwork 6773 1.88 20.28

Duct Insul. - Fiberglass Board Type - Thick 1 1/2 in 5818 1.62 17.42

Electric Motor 2 hp 688 0.19 2.06

Electric Motor 40 hp w/ Belts and Pulley 5887 1.64 17.62

Exhaust Fan E-A2 4267 1.19 12.78

Exhaust Fan E-A2B 4267 1.19 12.78

Exhaust Fan Filters (3 Stage) 8907 2.47 26.67

Handling and Shipping 5% on Material 1708 0.47 5.11

Clean-Up 277 0.08 0.83

Sealant 223 0.06 0.67

Balancing Air Handling Unit 641 0.18 1.92

Exhaust Register 24 in x 12 in 654 0.18 1.96

Exhaust Registers 24 in x 12 in 654 0.18 1.96

Mobilization and Demobilization 1600 0.44 4.79

Electrical Modifications 8897 2.47 26.64

Remove Miscellaneous (Wire, Conduit, Switches) 667 0.19 2.00

Combination Starter Size 3/Switch 3923 1.09 11.75

Miscellaneous Wire 483 0.13 1.45

Conduit: 1 1/4 in EMT 388 0.11 1.16

Disc. Switch, 100 A, 3P 739 0.21 2.21

Combination Starter Size 0/Switch 1785 0.50 5.34

Conduit: 3/4 in EMT 438 0.12 1.31

Disc. Switch, 30 A, 3P 475 0.13 1.42
169

Table C.10 Cost for Level 3 Filtration for the Office Building Mail Room

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

HVAC Upgrade 156 118 42.85 461.87

Remove Existing Filter Bank 607 0.17 1.82

Remove Electric Motor & Ass. Wiring 693 0.19 2.08

Remove Exhaust Fan 260 0.07 0.78

Upgrade the Air Handling Unit w/ One (1) Bank of HEPA

Rated Galvanized Steel, Frames, Clips and Filters

81 592 22.66 244.29

Safing, Stiffener Bars and Welding 345 0.10 1.03

Housing Filters 3310 0.92 9.91

Ductwork 6773 1.88 20.28

Duct Insul. - Fiberglass Board Type - Thick 1 1/2 in 5818 1.62 17.42

Electric Motor 2 hp 688 0.19 2.06

Electric Motor 40 hp w/ Belts and Pulley 5887 1.64 17.62

Exhaust Fan E-A2 4267 1.19 12.78

Exhaust Fan E-A2C 4983 1.38 14.92

Exhaust Fan 2 hp 1852 0.51 5.54

Exhaust Fan Filters (5 Stage) 30 389 8.44 90.98

Handling and Shipping 5 % on Material 5081 1.41 15.21

Clean-Up 424 0.12 1.27

Sealant 254 0.07 0.76

Balancing Air Handling Unit 641 0.18 1.92

Exhaust Registers 24 in x 12 in 654 0.18 1.96

Mobilization and Demobilization 1600 0.44 4.79

Electrical Modifications 8897 2.47 26.64

Remove Miscellaneous (Wire, Conduit, Switches) 667 0.19 2.00

Combination Starter Size 3/Switch 3923 1.09 11.75

Wire Miscellaneous 483 0.13 1.45

Conduit: 1 1/4 in EMT 388 0.11 1.16

Disc. Switch, 100 A, 3P 739 0.21 2.21

Combination Starter Size 0/Switch 1785 0.50 5.34

Conduit: 3/4 in EMT 438 0.12 1.31

Disc. Switch, 30 A, 3P 475 0.13 1.42
170

Table C.11 Cost Per Unit of Floor Area for the Air Sealing Retrofit of the Mail Room

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

Sealing the Envelope 29 086 8.08 87.08

Seal/Patch Corridor Walls 15 798 4.39 47.30

Replace/Install Thresholds 952 0.26 2.85

Seal Doors 1570 0.44 4.70

Seal/Patch Ceiling Slab 10 766 2.99 32.23

Table C.12 Cost for Level 1 Filtration for the Low-Rise Office Building

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

HVAC Upgrade 2099 0.12 1.30

Remove Filters 170 0.01 0.11

New Filters 956 0.06 0.59

Clean-Up 173 0.01 0.11

Mobilization 800 0.05 0.50

Electrical Modifications 11 792 0.68 7.31

Remove Panel CB – 400 A 213 0.01 0.13

MCB – 400 A w/ Shunt Trip, 480 V 9806 0.57 6.08

Emergency Mushroom Push Button 223 0.01 0.14

Wire: #12 THHN 346 0.02 0.21

Conduit: 3/4 in EMT 1203 0.07 0.75
171

Table C.13 Cost for Level 2 Filtration for the Low-Rise Office Building

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

HVAC Upgrade 193 734 11.17 120.18

One (1) Bank of HEPA Rated, Casing and Filters, Clips

and Filters

90 031 5.19 55.85

Steel Platform for Fans & Filters 26 877 1.55 16.67

Centrifugal Fan 20 hp 26 235 1.51 16.28

Ductwork 42 071 2.42 26.10

Clean-Up 624 0.04 0.39

Sealant 856 0.05 0.53

Balancing Air Handling Unit 6239 0.36 3.87

Mobilization 800 0.05 0.50

Electrical Modifications 69 550 4.01 43.15

Panel C/B: 70A - 3P - 480 V W/S Hunt Trip 1696 0.10 1.05

VFD/Switch, 25 hp, 4 BOV, NEMA 3R 46 370 2.67 28.77

Wire: #6 THHN 1634 0.09 1.01

Wire: #8 THHN 412 0.02 0.26

Conduit: 1 1/4 in RGS 7495 0.43 4.65

Remove Panel CB – 400 A 213 0.01 0.13

MCB – 400 A w/ Shunt Trip, 480 V 9806 0.57 6.08

Emergency Mushroom Push Button 223 0.01 0.14

Wire: #12 THHN 365 0.02 0.23

Conduit: 3/4 in EMT 1337 0.08 0.83
172

Table C.14 Cost for Level 3 Filtration for the Low-Rise Office Building

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

HVAC Upgrade 284 132 16.38 176.26

One (1) Bank of HEPA Rated, Casing and Filters, Clips

and Filters

172 189 9.92 106.82

Steel Platform for Fans & Filters 26 877 1.55 16.67

Ductwork 42 071 2.42 26.10

Centrifugal Fan 34 475 1.99 21.39

Clean-Up 624 0.04 0.39

Sealant 856 0.05 0.53

Balancing Air Handling Unit 6239 0.36 3.87

Mobilization 800 0.05 0.50

Electrical Modifications 69 550 4.01 43.15

Panel C/B: 70A - 3P - 480 V W/S Hunt Trip 1696 0.10 1.05

VFD/Switch, 25 hp, 4 BOV, NEMA 3R 46 370 2.67 28.77

Wire: #6 THHN 1634 0.09 1.01

Wire: #8 THHN 412 0.02 0.26

Conduit: 1 1/4 in RGS 7495 0.43 4.65

Remove Panel CB - 400A 213 0.01 0.13

MCB – 400 A w/ Shunt Trip, 480 V 9806 0.57 6.08

Emergency Mushroom Push Button 223 0.01 0.14

Wire: #12 THHN 365 0.02 0.23

Conduit: 3/4 in EMT 1337 0.08 0.83

Table C.15 Cost for Envelope Air Sealing of the Low-Rise Office Building

Cost Per Unit Floor Area

Cost Item

Total Cost

($) $/ft

2 $/m2

Seal Envelope 32 356 1.86 20.07

Seal Exterior Windows 7046 0.41 4.37

Seal Crawl Space Openings 17 332 1.00 10.75

Seal Doors and Thresholds 2680 0.15 1.66

Sheet Metal 2866 0.17 1.78

Patch Roof 2433 0.14 1.51