Simulations of Indoor Air Quality and

Ventilation Impacts of Demand

Controlled Ventilation in Commercial

and Institutional Buildings

Andrew Persily

Amy Musser

Steven Emmerich

Michael Taylor

NISTIR 7042
NISTIR 7042

August 2003

U.S. Department of Commerce

Donald L. Evans, Secretary

Technology Administration

Phillip J. Bond, Undersecretary of Commerce for Technology

National Institute of Standards and Technology

Arden L. Bement, Jr., Director

Simulations of Indoor Air Quality and

Ventilation Impacts of Demand

Controlled Ventilation in Commercial

and Institutional Buildings

Andrew Persily

Building and Fire Research Laboratory

Amy Musser

University of Nebraska

Steve Emmerich

Building and Fire Research Laboratory

Michael Taylor

University of Nebraska

Prepared for:

Architectural Energy Corporation

Boulder, Colorado
i

ABSTRACT

Carbon-dioxide (CO2) based demand controlled ventilation (DCV) offers the potential for more

energy efficient building ventilation compared with constant ventilation rates based on design

occupancy levels. A number of questions related to CO2-based DCV have been raised

concerning the indoor air quality impacts, primarily with respect to contaminants with source

strengths that are not dependent on the number of occupants. In addition, questions exist

regarding potential energy efficiency benefits, optimal control strategies for different building

types, and sensor performance and deployment. In order to obtain some insight into the issue of

IAQ impacts of CO2-based DCV, a simulation study was performed in six commercial and

institutional building spaces using the multizone airflow and IAQ model CONTAMW. These

simulations compared seven different ventilation strategies, four of which used CO2 DCV. The

simulations, performed for six U.S. cities, were used to compare ventilation rates, indoor CO2

levels, indoor concentrations of a generic volatile organic compound (VOC) as an indicator of

non-occupant contaminant sources, and energy impacts. The results indicate that these impacts

are dependent on the details of the spaces including occupancy patterns, design ventilation rate

and ventilation system operating schedule, as well as the specific assumptions used in the

analysis including contaminant source strengths and system-off infiltration rates. For the cases

studied, the application of CO2 DCV resulted in significant decreases in ventilation rates and

energy loads accompanied by increased indoor CO2 and VOC concentrations. The increases in

CO2 were not particularly large, in the range of 180 mg/m3 (100 ppm(v)). The indoor VOC levels

increased by a factor of two to three, but the absolute concentrations were still relatively low

based on the assumed emission rates. The annual energy load reductions were significant in most

of the cases, ranging from 10 % to 80 % depending on the space type, climate, occupancy

schedule, and ventilation strategy.

Keywords: carbon dioxide, control, energy efficiency, indoor air quality, modeling, simulation,

ventilation, volatile organic compounds

Disclaimer

This report was prepared as a result of work sponsored by the California Energy Commission

(Commission). It does not necessarily represent the views of the Commission, its employees, or the

State of California. The Commission, the State of California, its employees, contractors, and

subcontractors make no warranty, express or implied, and assume no legal liability for the

information in this report; nor does any party represent that the use of this information will not

infringe upon privately owned rights. This report has not been approved or disapproved by the

Commission nor has the Commission passed upon the accuracy or adequacy of the information in

this report.
iii

TABLE OF CONTENTS

Abstract i

1. INTRODUCTION AND BACKGROUND 1

2. DESCRIPTION OF ANALYSIS 4

2.1 Study Spaces 4

2.2 Ventilation Rates and Control Approaches 7

2.3 Airflow and Contaminant Analysis 11

2.4 Energy Analysis 11

3. RESULTS 14

3.1 Ventilation Rates 14

3.2 Carbon Dioxide Concentrations 21

3.3 VOC Concentrations 26

3.4 Energy Loads 32

4. DISCUSSION 34

5. ACKNOWLEDGEMENTS 37

6. REFERENCES 37

Appendix A: Details of Energy Simulation Results 39

Appendix B: PIER RFP Issues 46
1

1. INTRODUCTION AND BACKGROUND

Commercial building ventilation systems are designed, installed and operated to heat and cool

occupied spaces to achieve thermal comfort and to provide outdoor air to the occupants. Outdoor

air ventilation is provided to buildings primarily to dilute contaminants that are generated by

building occupants and their activities and by building materials and furnishings. The rate at

which outdoor air is brought into a building by its ventilation system is determined during the

building design based on requirements of applicable building codes and standards. For example,

ASHRAE Standard 62-2001 (ASHRAE 2001a) and California Energy Efficiency Standards, socalled Title 24, (CEC 2001) contain minimum ventilation requirements for a number of different

occupancy types in units of L/s (cfm) per person and in L/s per m2 of floor area (cfm/ft2).

Determining design outdoor air ventilation rates for commercial buildings using Standard 62-

2001 or Title 24 is a relatively straightforward process. For each space served by a given

ventilation system, one determines the expected or design number of occupants for space types

with ventilation requirements in units of L/s (cfm) per person. In spaces with requirements in

units of L/s-m2 (cfm/ft2), one determines the floor area. Based on the ventilation requirements

contained in the standard, these values (number of people and floor area) are used to determine

the L/s (cfm) of outdoor air required by that space under full occupancy. Standard 62-2001 also

requires that these rates be adjusted to account for ventilation effectiveness (degree of ventilation

air mixing in the space). Also, if the spaces are served by a system that recirculates air from

multiple spaces and redistributes it along with “new” outdoor air, Standard 62-2001 requires the

use of the so-called “multiple spaces” approach to determine the outdoor air intake rate. If no

such recirculation occurs, then the outdoor air intake rate is equal to the sum of the outdoor air

requirements for all the spaces served by the system, after adjusting for ventilation effectiveness.

ASHRAE Standard 62-2001 also allows for a reduction in the design occupancy under

conditions of intermittent occupancy. Basically, the standard allows one to use the average

occupancy instead of the design occupancy for spaces where the design occupancy is based on a

peak lasting 3 h or less. However, one is not permitted to reduce the design occupancy by any

more than 50 %. The average occupancy is then multiplied by the per person ventilation

requirement for the space to determine the design outdoor air intake rate. Note that this reduction

cannot also be employed when demand controlled ventilation is also used.

Demand controlled ventilation (DCV) is a ventilation rate control strategy to address the concern

that when a space is occupied at less than its design occupancy, unnecessary energy consumption

can result if the space is ventilated at the design minimum rate rather than the ventilation rate

based on the actual occupancy. Furthermore, early during a given day of building occupancy,

contaminants generated by people and their activities will not yet have reached their ultimate

levels based on the transient nature of contaminant buildup. As a result, it is sometimes possible

to delay or lag the onset of the design ventilation rate to take credit for this transient effect. A

number of approaches have been proposed to account for actual occupancy levels and to provide

the ventilation rate corresponding to actual rather than design occupancy. These include timebased scheduling when occupancy patterns are predictable, occupancy sensors to determine

when people have entered a space (though not necessarily how many), and carbon dioxide (CO2)

sensing and control as a means of estimating the number of people in a space or the strength of

occupant-related contaminant sources.

Controlling outdoor air intake rates using CO2 DCV offers the possibility of reducing the energy

penalty of over-ventilation during periods of low occupancy, while still ensuring adequate levels

of outdoor air ventilation. As discussed later in this report, depending on climate and occupancy
2

patterns, CO2 DCV may provide significant energy savings in commercial and institutional

buildings. While a number of studies have suggested the extent of such savings via field studies

and computer simulations, additional work is needed to better define the magnitude of energy

savings possible and the dependence of these savings on climate, building and system type,

control approach, and occupancy patterns. In addition, important issues remain to be resolved in

the application of CO2 DCV including how best to apply the approach, which in turn includes

issues such as which control algorithm to use in a given building, sensor location, sensor

maintenance and calibration, and the amount of baseline ventilation required to control

contaminant sources that don’t depend on the number of occupants.

An earlier report presented a state-of-the-art review of CO2 DCV technology and its application

in commercial and institutional buildings (Emmerich and Persily 2001). That report presented

discussions of CO2 generation rates by people, the relationship of indoor CO2 to building

ventilation rates, and the basic concept of controlling ventilation based on indoor CO2 levels. It

also contained a literature review of previous research on CO2 DCV, including field

demonstration projects, computer simulation studies, studies of sensor performance and location,

and discussions of the application of the approach. This earlier report and other discussions of

CO2 DCV identified indoor air quality impacts as an important issue in the application and

performance of these systems. The key indoor air quality concern relates to contaminants that are

generated in a building at a rate that does not depend on the number of occupants. For example,

building materials and furnishings emit contaminants at an approximately constant rate

independent of the occupancy level, including when the building is empty. Questions have been

raised as to how well these contaminants will be controlled by a DCV system when the

occupancy level is low. Some have proposed maintaining a minimum outdoor air ventilation rate

at all times to control these contaminants, with the minimum based on a specific outdoor air

intake rate per unit floor area expressed in L/s•m2 (cfm/ft2) (CEC 2001) or as a fraction of the

design outdoor air intake rate, for example 25 % (Schell et al. 1998).

ASHRAE Standard 62-2001 allows for the outdoor air intake rate to be adjusted based on

variations in occupancy (as noted earlier in the discussion of the intermittent occupancy

approach), but regardless of the approach used to make these adjustments the system must still

provide the required outdoor air ventilation rate per person. The standard does not explicitly

discuss CO2-based DCV in terms of sensor location, minimum outdoor airflow rates or other

details. However, a number of official interpretations to the standard issued by ASHRAE make it

clear that these approaches can comply with the standard if properly implemented. Title 24 also

allows the use of demand controlled ventilation. If fact, it is required in spaces with high

occupant densities as an energy efficiency measure.

As noted above, the outdoor air ventilation requirements in ASHRAE Standard 62-2001 are

largely expressed as airflow rates per person in L/s•person (cfm/person). In some spaces, for

example corridors and retail spaces, they are expressed in L/s•m2 (cfm/ft2) of floor area. The per

person requirements are intended to address contaminants emitted by the occupants themselves

as well as by the space they occupy, including building materials, furnishings and equipment. In

developing the ventilation requirements per person, there is an implicit assumption as to the

number of occupants per unit floor area in order to handle these non-occupant contaminants. If

the space being designed has a different occupant density, it may receive more or less outdoor air

than needed to handle the floor-area contaminants. In order to address that concern, a revision of

the Ventilation Rate Procedure in ASHRAE Standard 62 has been developed that contains per

person and per floor area outdoor air requirements for all spaces (Persily 2001). Under the

revision, referred to as addendum 62n, one multiplies the number of people in a space by a per
3

person ventilation requirement Rp and multiplies the floor area of the space by a per floor area

requirement Ra. These two products are then added together to determine the outdoor air

requirement in the occupied zone of the space. Further adjustments are required to account for

mixing in the space and system effects in recirculating systems serving multiple spaces. This socalled additive approach has the advantage of addressing the concern about non-occupant

contaminant sources and the provision of ventilation to handle these sources when occupancy is

low or zero. It could also make the application of CO2 DCV more challenging compared with

ventilation requirements expressed solely in terms of per person rates, but control algorithms

have been developed to implement CO2 DCV for so-called “additive” ventilation requirements

(Sowa 2002).

Resolving all the issues related to the application of CO2 DCV in commercial buildings,

including the energy and IAQ impacts, will require field testing and application experience, as

well as simulation studies. A number of modeling studies have looked at energy impacts of CO2

DCV strategies in different building types and different climates (e.g., Brandemuehl and Braun

1999). Other simulation studies have focused on the indoor air quality implications of CO2 DCV

(e.g., Carpenter 1996, Emmerich et al. 1994, Enermodal 1995). The study described in this paper

employs an airflow and contaminant dispersal model to investigate the issue of how CO2 DCV

and other ventilation strategies impact indoor air quality and ventilation. In particular, the

simulations are focused on how CO2 DCV impacts the control of non-occupant contaminants, in

this case a generic volatile organic compound (VOC), generated at a constant rate to represent

contaminants emitted by building materials and furnishings.

These simulations are performed using the airflow and indoor air quality model CONTAMW

(Dols and Walton 2002) for six commercial and institutional building spaces. The results are

then used to compare ventilation rates, contaminant concentrations and energy associated with

ventilation for seven ventilation strategies: constant ventilation volumes specified in ASHRAE

Standard 62-2001 and addendum 62n, a theoretical demand control strategy that perfectly tracks

occupancy, and four CO2 DCV strategies with different maximum and minimum flow rates,

including one based on California’s Title 24 requirements.
4

2. DESCRIPTION OF ANALYSIS

The simulations in this study were performed using the multizone network airflow and

contaminant dispersal model CONTAMW (Dols and Walton 2002). This model allows one to

represent a building as a collection of interconnected zones and then calculates airflow rates

induced by weather and ventilation system operation based on air leakage characteristics of the

boundaries between zones and pressures and on ventilation system airflows. The user can also

enter contaminant source strengths to calculate concentrations over time based on the calculated

airflow rates and other mass transport mechanisms (e.g. filtration, deposition, chemical reaction).

The latest version of CONTAMW can simulate the performance of controls, in which an airflow

rate, fan or damper is controlled based on the contaminant concentration, temperature or pressure

in a zone. The simulations described in this report employed this new capability in simple

models of the six study spaces as a means of simulating CO2 DCV.

2.1 Study Spaces

Building models were created in CONTAMW for six different space types. Four of these were

generic spaces devised for the purposes of this study: office, conference room, lecture hall and

classroom. The two other spaces were based on actual buildings being monitored as part of a

larger study on CO2 DCV being conducted as part of the same CEC-sponsored program that

supported this work: portable classroom and playroom in a fast food restaurant. Table 1

summarizes the characteristics of the six spaces including floor area, ceiling height and design

occupancy. For the first four spaces, the design occupancy is based on the default values given in

ASHRAE Standard 62-2001 (ASHRAE 2001a). Actual dimensions of the two monitored spaces

were used to construct models of the portable classroom and fast food playroom, and the

occupancies were estimated based on available design information.

Space type

Floor area

m2 (ft2)

Ceiling

height

m (ft)

Design

occupancy

# of people

Occupant density

#/100 m2

(#/1000 ft2)

Ventilation

system

operating time

Office 1000 (10760) 3.0 (9.8) 70 7.0 (6.5) 0600-1900

Conference Room 100 (1076) 3.0 (9.8) 50 50.0 (46.5) 0600-1800

Lecture Hall 100 (1076) 6.0 (19.7) 150 150.0 (139.4) 0800-2100

Classroom 100 (1076) 3.0 (9.8) 35 35.0 (32.5) 0600-1800

Portable classroom 89 (958) 2.6 (8.5) 20 22.5 (20.9) 0700-1700

Fast food restaurant 125 (1346) 5.4 (17.7) 70 56.0 (52.0) 0600-2400

Table 1 Space Characteristics

Each space was modeled as a single zone with a ventilation system that provides outdoor air at a

rate determined by the control strategy of interest, as outlined below. Details of the ventilation

system equipment were not considered in this study, though they can be important; only the

outdoor air intake rate is accounted for in the modeled ventilation systems. The systems are

assumed to operate during the times indicated in the last column of Table 1 and to be off at night

and during unoccupied periods over the weekends. A constant infiltration rate of 0.1 air changes

per hour is assumed to exist in each space at all times, including when the ventilation system is

operating. This value was chosen to represent a low infiltration condition that might exist under

low wind speeds and moderate outdoor temperatures and result in significant buildup of

contaminants before the system is activated.
5

Occupancy profiles

Weekly occupancy schedules for each space are shown in Figure 1. Schedules for the four

generic spaces (1a through 1d) were selected to represent realistic usage and to include scenarios

that were significantly different from one another in order to test of each control scheme. The

Office and Classroom tend to experience long periods at close to their design occupancies.

Occupancy changes in the morning and evening are more gradual for the Office, where workers

tend to arrive and depart at different times. The Classroom is more densely occupied than the

Office, and operates on a more rigid schedule, with the students arriving, departing, and taking

lunch at the same time. However, it was assumed that a teacher would arrive early and stay later

than the students. In contrast, the Lecture Hall and Conference Room are intermittently occupied.

The Lecture Hall schedule is the busier of the two, with more occupied hours in the day, and

usually with 50 % or more of the design capacity when the room was occupied. The Conference

Room is modeled with two occupancy profiles, with a busier schedule specified for Mondays

and Wednesdays. All four of these spaces are assumed to be unoccupied on weekends, and all

occupants for these spaces are specified as adults.

The Portable Classroom was modeled with two adults and eighteen children. The occupancy

profile specified for the Classroom is also used here for the children, with different CO2

generation rates for the adults and children based on body size. The occupancy profiles used for

the Fast Food Restaurant simulations are based on actual occupancy data collected in the

monitored restaurant. These data were used to develop an occupancy schedule between 0600 to

2400 seven days a week, with different schedules for weekdays and weekends.
6

(a) Office (b) Conference Room

 (c) Lecture Hall (d) Classroom

(e) Portable Classroom (f) Fast food restaurant

Figure 1 Occupancy Schedules

0%

20%

40%

60%

80%

100%

0:00 6:00 12:00 18:00 0:00

Time 

Occupancy %

Adults

Children

0%

20%

40%

60%

80%

100%

0:00 6:00 12:00 18:00 0:00

Time 

Occupancy %

0%

20%

40%

60%

80%

100%

0:00 6:00 12:00 18:00 0:00

Time 

Occupancy %

0%

20%

40%

60%

80%

100%

0:00 6:00 12:00 18:00 0:00

Time

Occupancy %

Weekend

Weekday

0%

20%

40%

60%

80%

100%

0:00 6:00 12:00 18:00 0:00

Time

Occupancy %

Mon., Wed.

Tue., Thur., Fri.

0%

20%

40%

60%

80%

100%

0:00 6:00 12:00 18:00 0:00

Time 

Occupancy %
7

Contaminant generation rates

The simulations accounted for two contaminants, occupant-generated carbon dioxide (CO2) and

a generic volatile organic compound (VOC) intended to represent contaminants from building

materials and furnishings. While VOC emissions in buildings are far more complex than the

simple approach used here (Levin 1995, Wolkoff 1995), the objective in including VOCs in

these simulations was to capture the impact of DCV systems on non-occupant sources that are

relatively constant over and time by including a source strength related to the floor area of the

space.

In these simulations, CO2 was generated by adults at a rate of 0.3 L/min•person, which

corresponds to an activity level consistent with office work (ASHRAE 2001b). In the Portable

Classroom, children were assumed to generate CO2 at a rate of 0.18 L/min•person, a value based

on the body size of a ten year old child. Carbon dioxide generation in the Fast Food Restaurant

playroom was modeled as 0.3 L/min•person, a value appropriate for both sedentary adults and

small school children at an activity level of 2.5 met (ASTM 2002, EPA 1999). The emission rate

for the generic VOC was assumed to be constant at a rate of 0.25 mg/h per m2 of floor area

during unoccupied periods and 0.50 mg/h•m2 during occupancy. These values are based on

limited field measurements of VOC emission rates (Levin 1995). Although actual contaminant

generation rates may differ significantly for different building types, there is not sufficient data

available to justify varying these rates in this study. Sorption and re-emission of VOCs from

surfaces were not modeled in these simulations, and the outdoor concentrations of CO2 and VOC

were assumed to equal 720 mg/m3 (400 ppm(v)) and 0 mg/m3 respectively over the entire

simulation period.

2.2 Ventilation Rates and Control Approaches

The ventilation rates in the spaces were based on ASHRAE Standard 62-2001, the revision to

those rates described earlier (Addendum 62n), and the requirements in California’s Title 24

(CEC 2001). Table 2 presents the outdoor air requirements for each space based on 62-2001,

addendum 62n, and Title 24. For Standard 62-2001, the outdoor air requirements are presented in

L/s•person (cfm/person) followed by the outdoor air intake requirement for the space based on

the number of occupants (see Table 1). These outdoor air intake rates for each space are

presented in L/s (cfm) and in L/s•m2 (cfm/ft2) of floor area. For addendum 62n, the outdoor air

requirements are presented as both the people and area rate, which are then combined based on

the number of occupants and the floor area of the space given in Table 1. Title 24 requires

7.1 L/s (15 cfm) per person based on the larger of the actual design occupancy or 50% of the

exiting density specified by the Uniform Building Code (UBC), with a minimum ventilation rate

of 0.76 L/s•m2 (0.15 cfm/ft2). Under Title 24, carbon dioxide DCV cannot be used in the Office,

since the 0.76 L/s•m2 (0.15 cfm/ft2) minimum is larger than 7.1 L/s (15 cfm) for the assumed

occupant density. Therefore the outdoor air intake for the Office is based on the floor area rather

than the number of people. Also, the assumed occupancy for the Portable Classroom (20 people)

is less than 50% of the UBC exiting density, so the maximum flow rate for that case is based on

24 occupants. Note that since the simulations were originally performed using IP units, the

ventilation requirements in Table 2 are correct for IP units. The SI values are converted from the

IP values, resulting in slight differences relative to the SI values contained in Standard 62-2001,

Addendum 62n and Title 24.

For each space type, Table 2 also contains the steady-state CO2 and VOC concentrations

corresponding to the design outdoor air intake rate based on the assumed VOC and CO2

generation rates. Note that for the Standard 62-2001 ventilation rates, the steady-state CO2
8

concentrations range from about 1500 mg/m3 (900 ppm(v)) to 1900 mg/m3 (1100 ppm(v)),

except in the two cases employing the intermittent occupancy provision of the standard. The

VOC concentrations vary more widely, over a range of twenty to one, with the variation due

primarily to the variation in the floor area per occupant among the spaces. The VOC levels are

all range from less than 0.1 mg/m3 to 0.2 mg/m3, with the lowest concentrations in the more

densely occupied spaces. Note that these concentrations are on the low end of those reported

from field measurements in commercial buildings, which are in this range and even higher in

non-problem buildings (Anderson et al. 1997, Brown et al. 1994, Daisey et al. 1994, Hadwen et

al. 1997, Wolkoff 1995). Note that the concentrations in Table 2 are all steady-state values, i.e.,

the values that would eventually exist if the emission rate and ventilation rate were maintained

long enough for steady-state conditions to be achieved. However, depending on the occupancy

and ventilation schedules, steady-state conditions will not necessarily occur in these spaces.

The outdoor air ventilation rates for the six spaces based on Addendum 62n tend to be lower than

those based on 62-2001, particularly in the more densely occupied spaces (Conference Room,

Lecture Hall and Restaurant). In fact, part of the reason for the changes in this addendum was the

concern that the existing rates in the standard were larger than necessary in densely occupied

spaces due to “overcounting” of emissions from floor area-related contaminants. The ventilation

rate in the Portable Classroom is slightly higher under 62n based on it having a lower occupancy

density than assumed in Standard 62-2001. The lower ventilation rates under the addendum

generally result in higher steady-state CO2 levels, particularly in the densely occupied spaces.

Most of the values are still in the range of 1800 mg/m3 (1000 ppm(v)), but the two most densely

occupied spaces (Conference Room and Lecture Hall) are closer to 3600 mg/m3 (2000 ppm(v)).

The VOC levels for the 62n rates are generally higher than those based on 62-2001, with the

largest increases again seen in the densely occupied spaces. However, the VOC levels are still

range from less than 0.1 mg/m3 to 0.3 mg/m3, again on the low end of concentrations measured

in the field. Again, these are all steady-state concentrations, which may not necessarily occur in

these spaces given the occupancy schedules. Also, these steady-state VOC concentrations are

based on the ventilation rates and source strengths assumed to exist during occupied periods and

neglect any impacts of higher concentrations that might occur overnight when the system is off.

For Title 24 the steady-state CO2 levels are all approximately 2000 mg/m3 (1100 ppm(v)), with

lower levels in the Office and the Portable Classroom. In the office, the lower concentration

results from its ventilation requirement under CO2 DCV being based on 0.76 L/s•m2

(0.15 cfm/ft2), which is higher than 7.1 L/s (15 cfm) per person. The Portable Classroom outdoor

air intake rate is based on 24 occupants rather than the actual 20 occupants based on the Title 24

requirement to assume no less than 50 % of the UBC exiting density. The steady-state VOC

concentrations are similar to those seen for Standard 62-2001 and Addendum 62n.
9

Standard 62-2001

Outdoor air intake

Steady-state

concentration

Space type

Outdoor air requirement

L/s (cfm) per person L/s (cfm)

L/s•m2

(cfm/ft2)

CO2 mg/m3

(ppm(v))

VOC

mg/m3

Office 9.4 (20) 661 (1400) 0.7 (0.13) 1674 (930) 0.21

Conference Room 9.4 (20) 472 (1000) 4.7 (0.93) 1674 (930) 0.03

Lecture Hall 7.1 (15) 1062 (2250) 10.6 (2.09) 1991 (1106) 0.01

Classroom 7.1 (15) 248 (525) 2.5 (0.49) 1991 (1106) 0.06

Portable classroom 7.1 (15) 142 (300) 1.6 (0.31) 1532 (851) 0.09

Fast food restaurant 9.4 (20) 661(1400) 5.3 (1.04) 1674 (930) 0.03

Conference room* 9.4 (20) 236 (500) 2.4 (0.47) 2626 (1459) 0.06

Lecture Hall* 7.1 (15) 531 (1125) 5.3 (1.05) 3262 (1812) 0.03

* Under intermittent occupancy provision of Standard 62-2001

Addendum 62n

Outdoor air intake

Steady-state

concentration

Space type

Outdoor air requirement

L/s (cfm) per person/

L/s•m2 (cfm/ft2) L/s (cfm)

L/s•m2

(cfm/ft2)

CO2 mg/m3

(ppm(v))

VOC

mg/m3

Office 2.4/0.3 (5.0/0.06) 470 (996) 0.5 (0.09) 2061 (1145) 0.30

Conference Room 2.4/0.3 (5.0/0.06) 149 (315) 1.5 (0.29) 3740 (2078) 0.09

Lecture Hall 3.5/0.3 (7.5/0.06) 562 (1190) 5.6 (1.11) 3123 (1735) 0.03

Classroom 4.7/0.6 (10/0.12) 226 (479) 2.2 (0.44) 2113 (1174) 0.06

Portable classroom 4.7/0.6 (10/0.12) 149 (315) 1.7 (0.33) 1494 (830) 0.08

Fast food restaurant 3.5/0.9 (7.5/0.18) 362 (767) 2.9 (0.57) 2461 (1367) 0.05

Title 24

Outdoor air intake

Steady-state

concentration

Space type Outdoor air requirement L/s (cfm)

L/s•m2

(cfm/ft2)

CO2 mg/m3

(ppm(v))

VOC

mg/m3

Office 0.76 L/s•m2 (0.15 cfm/ft2) 762 (1614) 0.75 (0.15) 1546 (859) 0.18

Conference Room 7.1 L/s (15 cfm) per person 354 (750) 3.5 (0.70) 1991 (1106) 0.04

Lecture Hall 7.1 L/s (15 cfm) per person 1062 (2250) 10.6 (2.09) 1991 (1106) 0.01

Classroom 7.1 L/s (15 cfm) per person 248 (525) 2.5 (0.49) 1991 (1106) 0.06

Portable classroom 7.1 L/s (15 cfm) per person 170 (360) 1.9 (0.38) 1399 (777) 0.07

Fast food restaurant 7.1 L/s (15 cfm) per person 495 (1050) 4.0 (0.78) 1991 (1106) 0.04

Table 2 Design Ventilation Rates and Steady-State Contaminant Levels during Occupancy

Seven ventilation control scenarios were simulated in the six spaces, with one additional scenario

applied to two of them. The first three scenarios, based on ASHRAE Standard 62, serve as

reference cases for comparing the DCV options. They are:

62/2001: Constant outdoor air intake rates based on ASHRAE Standard 62-2001 and the

design occupancy values in Table 1.

62tracking: Outdoor air intake rates that track occupancy (as depicted in Figure 1) perfectly

using the ASHRAE Standard 62-2001 rates, i.e., the intake rate always equals the number of

occupants times the per person ventilation requirement.

62/Int: Outdoor air intake rate based on 50 % of peak occupancy using the intermittent

occupancy approach in the standard (only applied to the Conference Room and Lecture Hall).
10

Two cases employing CO2 DCV using the Standard 62-2001 rates were also studied:

C-ZeroMin: Maximum ventilation rate based on ASHRAE Standard 62-2001; minimum

ventilation rate equal to zero.

C-25%Min: Maximum ventilation rate based on ASHRAE Standard 62-2001; minimum

ventilation rate equal to 25 % of the maximum.

In addition, two cases were studied based on the revision of the Ventilation Rate Procedure in the

standard, so-called addendum 62n:

62n: Constant outdoor air intake rates based on addendum 62n and the design occupancy

values from Table 1.

C-62nAreaMin: CO2 DCV control with the maximum ventilation rate based on the design

occupancy and the requirements in addendum 62n; minimum ventilation rate equal to the

“area” requirement times the floor area of the space.

Finally, one case followed the requirements of California’s Title 24:

C-T24: CO2 DCV control with the maximum ventilation rate based on the requirement for

7.1!L/s (15 cfm) person in these spaces, using the larger of the design occupancy or 50 % of the

UBC exiting density. The minimum ventilation rate is based on 0.76 L/s•m2 (0.15 cfm/ft2). In

the case of the office, the ventilation rate is constant at this minimum level because the per

person requirement results in a ventilation rate that is lower than this value.

For the reference cases and the 62n case, it was not necessary to model outdoor air intake

controls. In the simulations, the ventilation system was simply scheduled to turn on and off per

the operating schedules described earlier. In the case of 62tracking, in which the outdoor air

intake rate was “controlled” to track occupancy perfectly, the fan was set to follow the same

schedule as the occupancy. For the cases in which CO2 control was implemented, the control

simulation capabilities of CONTAMW were employed. A proportional control algorithm based

on previously published descriptions was used (Schell, et al. 1998, Schell and Int-Hout 2001).

The proportional controllers were specified to modulate the ventilation rate between the

minimum and maximum rates with a linear response to CO2 concentration based on the output O

described below. The lower limit of this range was selected to be 90 mg/m3 (50 ppm(v)) higher

than the outdoor level, and the upper CO2 limit was set at the equilibrium concentration

corresponding to the design occupancy and design ventilation rate under steady conditions Ceq.

For the Title 24 case, the upper CO2 limit was set to 1440 mg/m3 (800 ppm(v)) for all cases, with

constant flow at the maximum ventilation rate delivered at all concentrations above this level.

The CONTAMW proportional control algorithm calculates the output O according to the

following relationship,

O = I x Kp (1)

where I is the controller input and Kp is a constant. In this control strategy the controller input is

the indoor CO2 concentration minus 810 mg/m3 (450 ppm(v)), and Kp defined as,

Kp = 1 / [Ceq – 450 ppm(v)] (2)

Other control algorithms have been proposed and employed for CO2 DCV, such as proportionalintegral control.
11

2.3 Airflow and contaminant analysis

Each of the cases was simulated in the six spaces for a period of 7 days. The simulations were

performed using a 5 min time step and yielded a CO2 and VOC concentration at each time step.

In the case of the DCV systems, the simulations also yielded a ventilation rate. These ventilation

data were analyzed to yield the average ventilation rate during the occupancy period. The CO2

concentration data were analyzed to yield the average concentration over the occupancy period

and the peak hourly average during occupancy. The VOC data were also analyzed to determine

the average concentration during occupancy, plus the peak concentration. Plots of CO2 and VOC

concentrations during the simulation period are presented in the results section.

2.4 Energy analysis

In order to compare the energy consumption associated with the different ventilation control

cases, a simplified approach was used to estimate the heating and cooling loads associated with

conditioning the ventilation air to the indoor conditions based on the sensible and latent heat

capacity of the outdoor air relative to the indoor air. Therefore, the energy analysis accounts for

only the load due to ventilation air, and not the energy required to meet that load, which depends

on the type of system used to meet that load. Economizer operation is, however, taken into

account by not including any cooling energy consumed when operating in this mode. Also, no

energy consumption is assessed when the outdoor air temperature is between the heating balance

point and the space temperature

Determination of heating balance point temperature

The balance point temperature was estimated using a simplified steady-state energy balance in

which the heat transferred out of the structure equals the heat transferred in via airflows and

internal gains:

 (SUA + QCp) To + q = (SUA + QCp) Ti (3)

where,

SUA = building envelope thermal conductance

Q = mass flow rate of ventilation air

Cp = specific heat of air

To = outdoor temperature

Ti = indoor temperature

q = internal heat gains

The heating balance point temperature is the outdoor temperature at which internal heat gains are

equal to the heat loss rate at a given ventilation rate and indoor temperature, Ti. Heating is

required below this temperature, and internal gains maintain the building at the heating setpoint

above this temperature. The heating balance point, Thbp, can be defined as:

Thbp = Ti – q / (SUA + QCp) (4)

The thermal conductance term (SUA) is often much smaller than the ventilation flow term in

equation (4) for commercial buildings, and is sometimes neglected. However, since some of the

airflow control strategies allowed the airflow to occasionally go to zero, it was maintained for

this analysis. However, the accuracy of the thermal conductance term is not critical, since the

QCp term is usually much larger than the UA term. The value of SUA was estimated based on
12

ASHRAE Standard 90.1 envelope requirements (ANSI/ASHRAE/IESNA 1999). During the few

times when the ventilation flow rate does approach zero, the heating balance point is so low that

it was not reached in any of the climates investigated.

Table 3 shows the internal heat gain used for each space, which were estimated using data

published for nonresidential cooling and heating load calculations by ASHRAE (2001b).

Occupant heat gains were based on the average modeled occupancy during the occupied period

and assumed occupant activity levels. Heat gain from lighting was estimated using the installed

lighting load from ASHRAE Standard 90.1 (ANSI/ASHRAE/IESNA 1999), adjusted for usage

and allowance factors. Heat gain from 80 computers was included for the office.

Occupants Lighting Computers Total

Space W/m2 W/m2 W/m2 W/m2

Office 4.9 12.1 10.0 27.0

Conference Room 9.8 6.4 0.0 16.2

Lecture Hall 42.0 9.3 0.0 51.3

Classroom 16.1 9.3 0.0 25.4

Portable Classroom 7.8 9.3 0.0 17.1

Fast Food Restaurant 17.3 20.1 0.0 37.3

Table 3 Internal Heat Gains Used to Estimate Balance Point

The weekly CONTAM simulations, repeated for an entire year, were used to determine the

ventilation mass flow rate in equation (4). And because the heating balance point depends on this

flow rate, it was calculated individually for each hour of the year.

Heating load

Based on the estimated heating balance point temperature, the heating load associated with

ventilation was calculated for each hour in which the outdoor temperature was below the heating

balance point using the relationship:

qheating = QCp (Ti – To) (5)

where,

qheating = heating load

Q = mass flow rate of ventilation air

Cp = specific heat of air

To = outdoor temperature

Ti = indoor temperature (assumed 22 oC year round)

Cooling load

When the outdoor temperature is greater than the indoor temperature, the additional sensible

cooling load qcooling associated with the ventilation air can be calculated from the relationship:

qcooling = QCp (To – Ti) (6)

Whether or not a latent cooling load exists depends, to some extent, on the latent loads as well as

the degree of humidity control that can be achieved by the means of thermal conditioning in the

space. For this simplified model, it was assumed that the thermal control strategy was capable of

maintaining a maximum indoor relative humidity of 60 %. Therefore, when the outdoor humidity

ratio exceeds this humidity ratio upper limit, a latent load associated with ventilation is assessed:

qlatent = Q hfg (Wo – Wlimit) (7)
13

where,

qlatent = latent cooling load

Q = mass flow rate of ventilation air

hfg = latent heat capacity of moist air

Wo = outdoor humidity ratio

Wlimit = indoor humidity ratio (defined at 60 % relative humidity at 22 oC)

The energy calculations assume that each space operates with a return air temperature

economizer that uses outdoor air for cooling. Under this strategy the system provides 100 %

outdoor air when the outdoor dry bulb temperature is between the supply air temperature and the

indoor temperature. Some mechanical cooling will be required under these conditions, but it will

be less than would be needed if indoor air was recirculated. When the outdoor temperature is

above the heating balance point but below the system supply temperature, the economizer

strategy mixes return air with a volume of outdoor air greater than that needed for ventilation,

and neither cooling nor heating is required. In both of these cases, thermal conditioning and

control, not the ventilation control strategy, dictate the amount of outdoor air supplied to the

spaces. Since our approach is intended to determine the heating and cooling loads associated

with ventilation, cooling energy consumed in this mode is not included in the reported values.

The heating, cooling, and latent loads associated with ventilation were calculated for every hour

during which the ventilation system was assumed to be operating. These were then summed for

each case over an entire year of weather data for the six cities identified below.

Climates analyzed

Based on the methodology outlined above, the energy consumption was estimated for four

California climates (Bakersfield, Los Angeles, Sacramento, and San Francisco) selected to cover

a range of coastal and inland climates. As points of reference, Miami (hot and humid) and

Minneapolis (cold) were also analyzed. These energy estimates employed TMY2 weather data

(Marion and Urban 1995), except for Sacramento and Miami for which WYEC data (ASHRAE

1997) was used. Table 3 summarizes the weather data for these six climates.

City Heating degree days °C (°F) Cooling degree days °C (°F)

Bakersfield 1213 (2183) 1210 (2178)

Los Angeles 1010 (1816) 341 (614)

Sacramento 1579 (2842) 643 (1157)

San Francisco 1690 (3042) 60 (108)

Miami 114 (205) 2243 (4037)

Minneapolis 4532 (8158) 325 (585)

Table 4 Summary of Six Climates Analyzed (Knapp et al. 1980)
14

3. RESULTS

This section presents the results of the simulations for the six space types, seven ventilation

control approaches and six climates. These results are presented separately for the ventilation

rates, CO2 and VOC contaminant concentrations, and energy loads.

3.1 Ventilation Rates

The ventilation rates for the different space types and control strategies are summarized in Table

5. Note that these rates are inputs to the contaminant simulations for three of the cases (62/2001,

62 tracking and 62n), as well as 62/Int when relevant, but are calculated during the simulations

for the four DCV cases (C-ZeroMin, C-25%Min, C-62nMinArea and C-T24). Also note that the

intermittent occupancy case is only applied to the Conference Room and Lecture Hall. Also,

while the Title 24 case is thought of as DCV, in the case of the Office it is in fact a constant

ventilation rate based on the minimum outdoor air requirement of 0.76 L/s•m2 (0.15 cfm/ft2).

For each space and control strategy, Table 5 contains the average, minimum and maximum

outdoor air intake during occupancy in units of airflow rate per person L/s•person (cfm/person).

Also, in the first column, the table presents the per person design value for outdoor air intake for

Standard 62-2001, addendum 62n and Title 24. The calculations were initially performed in IP

units and converted to SI units. Therefore, some of the SI values are slightly different from those

that appear in Standard 62, addendum 62n and Title 24. The last column of the table contains the

minimum and maximum per person outdoor air intake during periods of time when the space is

at its maximum occupancy level. For some spaces (e.g., Office) the space is at maximum

occupancy for many hours, while for other spaces (e.g., Fast Food) maximum occupancy occurs

for only short periods of time. Note that the Conference Room is never at its design occupancy of

50 people, but rather has a maximum occupancy of 40.

The maximum rates during occupancy in Table 5, for all but the 62tracking case, are well above

the relevant requirements of Standard 62, 62n or Title24. This is particularly true for cases

62/2001 and 62n in which the design outdoor air intake is in effect whenever the system

operates, which results in high per person rates when the occupancy is low. For the 62tracking

case, the averages, minimums and maximums are all equal to the Standard 62 requirement as

expected, except in the Portable Classroom because the 62tracking case is actually based on the

CO2 generation rates of the occupants. (Since different CO2 generation rates are used for the

adults and children in that space, there is some variation in the per person rates based on whether

the space is occupied by only the adults or by the whole class.) The minimum per person rate for

the case of C-ZeroMin is always zero, since the intake is at its minimum position (zero intake)

until the CO2 levels build-up after the space has been occupied for some time. The other CO2

DCV cases also have minimum per person rates below the rate required by the standard, as the

indoor CO2 levels are too low at the start of occupancy for the CO2 controls to induce outdoor air

intake. However, these low rates are temporary and not unexpected.

Figures 2 through 7 are plots of the total ventilation rates, including infiltration, for each of the

spaces and ventilation control approaches over a period of one or two days. The one-day plots all

contain data for a Friday, to capture the impact of any CO2 buildup over the week in cases where

the assumed infiltration rate of 0.1 h-1 is not sufficient to bring the indoor CO2 level down to the

outdoor level overnight. For the CO2 control cases, this residual CO2 leads to a low level of

ventilation early in the morning. For the spaces with occupancy patterns that vary by day of the

week, two days are presented in the corresponding figure. Specifically, Figure 3 presents the

ventilation rates for Wednesday and Thursday in the Conference Room, and Figure 6 presents
15

Friday and Saturday for the Fast Food Restaurant. In all the figures, the 62-2001 and 62n cases

are horizontal lines indicating constant ventilation rates when the system operates. The Title 24

case C-T24 results in a constant intake rate for the office space as discussed earlier. The

intermittent occupancy cases (62-Int) in the Conference Room and the Lecture Hall, Figures 3

and 4 respectively, also exhibit constant ventilation rates. The 62tracking case appears as a solid

black line in all the figures, with the ventilation rate corresponding to the occupancy schedule of

the given space. The four control cases (C-ZeroMin, C25%Min, C-62nAreaMin and C-T24)

exhibit more variation as the controls respond to the indoor CO2 level. They generally start each

day low relative to the constant ventilation rate cases, with the ventilation rates increasing as the

indoor CO2 levels increase.

Referring to Table 5, the results for the Office exhibit a number of trends that are also reflected

in most of the other spaces. The average per-person outdoor air intake rate is the second highest

for the 62/2001 case in which the intake rate is always equal to 9.4 L/s (20 cfm) times the

maximum number of occupants. Under low occupancy, the constant intake rate is divided by a

relatively small number of people, yielding per person ventilation rates with a maximum value of

94 L/s (200 cfm). The lowest average intake rate is for 62tracking, in which the system always

brings in 9.4 L/s (20 cfm) per person times the number of people in the space. The 62n rate is

also constant during system operation, but at a lower value than 62/2001, resulting in a lower

average ventilation rate but still yielding high maximum values when occupancy is low. The CT24 case has the highest rates in the Office based on the minimum requirement. Other than

62tracking, all the ventilation strategies have high per person intake rates at low occupancy

relative to the design values. The control approaches based on the Standard 62 rates (C-ZeroMin

and C-25%Min) both have average ventilation rates higher than 62tracking. Therefore, while

these CO2 control strategies may have lower ventilation rates during periods of the day, overall

they provide more ventilation air than a “perfect” control system, presumably a desirable and

conservative outcome from an indoor air quality perspective.

Figure 2 is a plot of the total outdoor air ventilation rate (intake plus infiltration) for a single day

in the Office. Note that the two CO2 control strategies using the Standard 62 rates, C-25%Min

and C-ZeroMin, track the idealized case of 62tracking fairly well, with some “underventilation”

early in the day and some “overventilation” after occupancy has peaked and towards the end of

the day. However, one could argue that one would desire overventilation at these times to “flush

out” residual contaminants and that one could tolerate some underventilation early in the day

before contaminants have built up. However, overventilation late in the workday can have an

energy penalty in hot weather. The use of the terms underventilation and overventilation are only

relative to the rates required by the standard or addendum (design values). The C-25%Min case

is more conservative, in that it starts the day with higher ventilation rates relative to the

62tracking and 62-ZeroMin cases. The C-62nAreaMin case is even more conservative in the

early part of the day, based on its higher minimum ventilation rate, but it does not provide as

much ventilation later in the day as the other DCV cases.
16

Outdoor Air Intake Rate (neglecting infiltration) L/s•person (cfm/person)

Design During Occupancy

value Average Minimum Maximum

Min/Max at

maximum occupancy

Office

62/2001 9.4 (20.0) 24.0 (50.9) 9.4 (20.0) 94.0 (200.0) 9.4/9.4 (20.0/20.0)

62tracking -- 9.4 (20.0) 9.4 (20.0) 9.4 (20.0) 9.4/9.4 (20.0/20.0)

C-ZeroMin -- 12.1 (25.7) 0 (0) 65.0 (137.8) 6.1/8.9 (12.9/18.8)

C-25%Min -- 14.7 (31.2) 5.0 (10.5) 70.9 (150.3) 6.6/9.0 (13.9/19.0)

62n 6.8 (14.4) 16.3 (34.6) 6.4 (13.6) 64.1 (135.7) 6.4/6.4 (13.6/13.6)

C-62nAreaMin -- 13.2 (27.9) 5.1 (10.7) 56.9 (120.6) 5.1/6.2 (10.7/13.1)

C-T24 10.8 (23.1) 27.8 (58.8) 10.9 (23.1) 108.9 (230.8) 10.9/10.9 (23.1/23.1)

Conference Room

62/2001 9.4 (20.0) 49.4 (104.7) 11.8 (25.0) 188.9 (400.1) 11.8/11.8 (25.0/25.0)

62tracking -- 9.4 (20.0) 9.4 (20.0) 9.4 (20.0) 9.4/9.4 (20.0/20.0)

62/Int -- 24.7 (52.4) 5.9 (12.5) 94 (200.0) 5.9/5.9 (12.5/12.5)

C-ZeroMin -- 13.2 (28.0) 0 (0) 26.3 (55.8) 2.0/10.4 (4.2/22.1)

C-25%Min -- 19.7 (41.7) 3.7 (7.9) 53.4 (113.1) 3.7/10.6 (7.9/22.5)

62n 3.9 (8.2) 15.3 (32.5) 3.7 (7.8) 58.5 (124.0) 3.7/3.7 (7.8/7.8)

C-62nAreaMin -- 5.2 (11.0) 1.4 (3.0) 13.4 (28.3) 1.6/3.1 (3.4/6.5)

C-T24 7.1 (15.0) 17.0(36.0) 3.1 (6.6) 42.7 (90.5) 3.2/8.9 (6.8/18.8)

Lecture Hall

62/2001 7.1 (15.0) 14.7 (31.1) 7.1 (15.0) 35.4 (75.0) 7.1/7.1 (15/15)

62tracking -- 7.1 (15.0) 7.1 (15.0) 7.1 (15.0) 7.1/7.1 (15/15)

62/Int -- 7.4 (15.6) 3.5 (7.5) 17.7 (37.5) 3.5/3.5 (7.5/7.5)

C-ZeroMin -- 10.1 (21.4) 0 (0) 31.6 (67.0) 0.8/7.1 (1.8/15.0)

C-25%Min -- 10.8 (22.9) 2.0 (4.3) 32.1 (68.1) 2.0/7.1 (4.3/15.0)

62n 3.8 (8.0) 7.8 (16.6) 3.8 (8.0) 18.9(40.0) 3.8/3.8 (8.0/8.0)

C-62nAreaMin -- 5.3 (11.2) 0.3 (0.7) 16.5 (35.0) 0.9/3.8 (1.9/8.0)

C-T24 7.1 (15.0) 12.8 (27.1) 0.8 (1.8) 35.4 (75.0) 1.3/7.1 (2.7/15.0)

Classroom

62/2001 7.1 (15.0) 35.9 (76.1) 7.0 (14.9) 140.3 (297.2) 7.0/7.0 (14.9/14.9)

62tracking 7.0 (14.9) 7.0 (14.9) 7.0 (14.9) 7.0/7.0 (14.9/14.9)

C-ZeroMin 12.1 (25.6) 0 (0) 71.4 (151.2) 0.2/6.9 (0.4/14.7)

C-25%Min 17.1 (36.3) 1.8 (3.8) 84.9 (179.8) 1.8/6.9 (3.8/14.7)

62n 6.7 (14.2) 32.1 (68.1) 6.3 (13.3) 125.6 (266.1) 6.3/6.3 (13.3/13.3)

C-62nAreaMin 15.6 (33.0) 1.6 (3.4) 77.9 (165.0) 1.6/6.2 (3.4/13.1)

C-T24 7.1 (15.0) 20.2 (42.7) 2.2 (4.6) 111.6 (236.5) 2.2/7.0 (4.6/14.9)

Portable Classroom

62/2001 7.1 (15.0) 21.2 (44.9) 7.0 (14.9) 70.1 (148.6) 7.0/7.0 (14.9/14.9)

62tracking 7.9 (16.7) 7.0 (14.9) 10.9 (23.1) 7.0/7.0 (14.9/14.9)

C-ZeroMin 9.7 (20.6) 0 (0) 43.2 (91.6) 0.5/6.9 (1.0/14.6)

C-25%Min 12.0 (25.4) 1.9 (4.1) 48.4 (102.5) 1.9/6.9 (4.1/14.6)

62n 7.7 (16.2) 21.7 (45.9) 7.2 (15.2) 71.7 (152.1) 7.2/7.2 (15.2/15.2)

C-62nAreaMin 13.3 (28.1) 2.6 (5.6) 51.6 (109.4) 2.6/7.1 (5.6/15.0)

C-T24 8.5 (18.0) 16.0 (33.9) 3.6 (7.6) 60.4 (127.9) 3.6/8.4 (7.6/17.7)

Fast Food

62/2001 9.4 (20.0) 65.2 (138.1) 9.4 (20.0) 944.0 (2000.0) 9.4/9.4 (20.0/20.0)

62tracking 9.4 (20.0) 9.4 (20.0) 9.4 (20.0) 9.4/9.4 (20.0/20.0)

C-ZeroMin 16.4 (34.8) 0 (0) 87.0 (184.4) 9.2/9.3 (19.5/19.8)

C-25%Min 26.2 (55.5) 9.0 (19.0) 236.1 (500.1) 9.2/9.3 (19.5/19.8)

62n 5.1 (10.8) 35.3 (74.7) 5.1 (10.8) 510.7 (1082.0) 5.1/5.1 (10.8/10.8)

C-62nAreaMin 15.9 (33.6) 4.5 (9.6) 151.8 (321.6) 4.8/5.0 (10.1/10.5)

C-T24 7.1 (15.0) 21.5 (45.5) 7.1 (15.0) 136.2 (288.5) 7.1/7.1 (15.0/15.0)

Table 5 Summary of Ventilation Rates
17

The Conference Room ventilation results are also presented in Table 5, with the additional case

of 62/Int, which implements the intermittent occupancy provision of Standard 62-2001. The

highest average intake rate is for 62/2001. Note that the conference room is never occupied at its

design value of 50 occupants; the maximum is 40 in these simulations, and this value only occurs

for a few hours on Mondays and Wednesdays. Based on the lower and more variable occupancy

pattern relative to the Office, the maximum ventilation rates for the CO2 control approaches are

not as high relative to 62-2001 as in the Office. In the Office control cases, the ventilation rates

continue to increase over several hours of high occupancy. However, in the Conference Room

the occupancy drops before the CO2 levels get as high, and the ventilation rates are lower on

average. Figure 3 presents the Conference Room ventilation rates for Wednesday and Thursday

of the simulation period. The most significant difference from the Office results in Figure 2 is

seen for the CO2 control cases that “overshoot” the 62tracking case. This “overshooting” occurs

during the short periods of elevated occupancy because these peak occupancy levels are below

the design value and the maximum ventilation rate in the CO2 control algorithm is based on the

design occupancy. The Conference Room in fact never achieves the design occupancy, and

therefore this overshoot occurs for all the occupancy peaks.

The Lecture Hall results in Table 5 are similar to those for the Conference Room except all the

rates are lower given the lower design ventilation rates. Also, the Lecture Hall does attain its

design occupancy level, even if only briefly. The Lecture Hall ventilation rates are plotted in

Figure 4 and also exhibit the “overshoot” relative to the 62tracking case that is seen in the

Conference Room. However, the occupancy peak that occurs after lunch is at the design

occupancy level and therefore no overshoot is seen here.

The results for the Classroom and Portable Classroom are similar, with some differences seen

due to the lower occupancy density and lower average CO2 generation rate in the Portable

Classroom. These differences generally result in lower per person ventilation rates. The

ventilation rates plotted in Figures 5 and 6 for the two spaces exhibit very similar patterns, with

the values lower in the Portable Classroom. Note that the C-T24 case has the highest ventilation

rates of the control cases in both classrooms, notably so in the Portable Classroom.

The Fast Food Restaurant has an extremely variable occupancy pattern in which the design

occupancy pattern is only achieved briefly once during each day. Therefore, the ratio of the

average and maximum per person ventilation rates to the design value for the 62/2001 and 62n

case are highest for this space. The ventilation rates for Friday and Saturday in this space are

plotted in Figure 7.
18

Figure 2 Office Ventilation Rates during Weekday (Friday)

Figure 3 Conference Room Ventilation Rates during Week (Wednesday and Thursday)

0

500

1000

1500

2000

0:00 6:00 12:00 18:00 0:00

Time

Ventilation rate (cfm)

0

200

400

600

800

Ventilation rate (L/s)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24

0

250

500

750

1000

1250

0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time

Ventilation rate (cfm)

0

100

200

300

400

500

Ventilation rate (L/s)

62-2001 62n 62-Int 62tracking

C-25%Min C-ZeroMin C-62nAreaMin C-T24
19

 Figure 4 Lecture Hall Ventilation Rates during Week (Friday)

Figure 5 Classroom Ventilation Rates during Week (Friday)

0

500

1000

1500

2000

2500

0:00 6:00 12:00 18:00 0:00

Time

Ventilation rate (cfm)

0

200

400

600

800

1000

Ventilation rate (L/s)

62-2001 62n 62-Int 62tracking

C-25%Min C-ZeroMin C-62nAreaMin C-T24

4

0

150

300

450

600

0:00 6:00 12:00 18:00 0:00

Time

Ventilation rate (cfm)

0

50

100

150

200

250

Ventilation rate (L/s)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24
20

Figure 6 Portable Classroom Ventilation Rates during Week (Friday)

Figure 7 Fast Food Restaurant Ventilation Rates over Friday and Saturday

0

100

200

300

400

0:00 6:00 12:00 18:00 0:00

Time

Ventilation rate (cfm)

0

50

100

150

Ventilation rate (L/s)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24

0

250

500

750

1000

1250

1500

0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time

Ventilation rate (cfm)

0

100

200

300

400

500

600

700

Ventilation rate (L/s)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24
21

3.2 Carbon Dioxide Concentration

Table 6 summarizes the indoor CO2 concentrations for the ventilation strategies and spaces in

terms of the average and maximum concentration during occupancy. The first column of the

table also presents the steady-state CO2 concentration for the 62/2001, 62n and Title 24 cases, as

well as the 62/Int case when relevant, based on the values in Table 2.

In all spaces, the average and maximum CO2 concentrations are lower for the 62/2001 cases than

for the other cases, except for C-T24 in the Office. This result is expected due to 62/2001 having

the highest ventilation rates compared to the 62tracking and the CO2 control cases. And while

62tracking and the CO2 control cases have higher average and maximum CO2 concentrations

relative to the 62/2001 case, they are almost always within about 200 mg/m3 (about 100 parts per

million by volume (ppm(v))) of the 62/2001 values. Also, the CO2 control cases almost always

have average and maximum concentrations below the idealized 62tracking case, which indicates

good control of occupant-generated contaminants. In all cases the maximum CO2 concentration

during occupancy is less than the steady-state concentration based on the design value in the first

column. These differences are generally on the order of 200 mg/m3 (roughly 100 ppm(v)) except

for the Conference Room where the design occupancy is never achieved. The 62/Int case,

applicable to only the Conference Room and Lecture Hall, has higher CO2 concentrations than

the other 62-based cases as expected. However, the average concentrations during occupancy are

still only about 200 mg/m3 (roughly 100 ppm(v)) above the 62tracking case.

Figures 8 through 13 present the CO2 concentrations in each of the spaces over one day (two

days in selected cases) for the different ventilation strategies. The CO2 concentrations in the

Office in Figure 3 are fairly similar for the six different ventilation strategies. The 62tracking

case is higher during unoccupied periods as the ventilation rate during those periods includes

only infiltration, and therefore the post-occupancy CO2 concentration is elevated relative to the

other strategies. This residual concentration builds up during the week, and the biggest

differences are seen in this plot for Friday. The two 62n cases, 62n and C-62nAreaMin, have

higher concentrations than the other cases during occupancy based on the lower design

ventilation rates. The Title 24 DCV case has the lowest CO2 levels in the Office as expected

since it has the highest, and in fact constant, ventilation rates during occupancy. In the other

spaces, the 62-2001 case has the lowest CO2 levels due its having the highest ventilation rates.

There is more variation in CO2 levels among the ventilation strategies for the Conference Room

as seen in Figure 9. The two 62n-based cases, 62n and C-62nAreaMin, have lower per person

ventilation rates relative to Standard 62, and therefore the CO2 concentrations are significantly

higher. The 62tracking case again has elevated concentrations during unoccupied periods based

on only infiltration occurring during these times. The Lecture Hall in Figure 10 shows the same

features as the Conference Room, higher concentrations for the 62n-based cases and elevated

concentrations for 62tracking during unoccupied periods. The different ventilation strategies

have fairly similar CO2 concentrations in the two classroom cases (Figures 11 and 12). Finally,

the Fast Food Restaurant in Figure 13 also exhibits elevated concentrations for the 62n-based

cases and elevated concentrations for 62tracking.

From the concentrations in Table 6 and the figures, one sees that the CO2 control cases result in

CO2 concentrations that are not very different from those in the cases without CO2 control. While

the CO2 control cases have higher concentrations, the differences are generally on the order of

200 mg/m3 (100 ppm(v)).
22

Indoor CO2 concentrations during occupancy

Average

mg/m3 (ppm(v))

Maximum

 mg/m3 (ppm(v))

Office

62/2001 (1674 mg/m3, 930 ppm(v))* 1305 725 1555 864

62tracking 1427 793 1571 873

C-ZeroMin 1413 785 1620 900

C-25%Min 1393 774 1613 896

62n (2061 mg/m3, 1145 ppm(v))* 1512 840 1854 1030

C-62nAreaMin 1573 874 1908 1060

C-T24 (1546 mg/m3, 859 ppm(v))* 1231 684 1447 804

Conference Room

62/2001 (1674 mg/m3, 930 ppm(v))* 1037 576 1471 817

62tracking 1467 815 1661 923

62/Int (2626 mg/m3, 1459 ppm(v))* 1291 717 2106 1170

C-ZeroMin 1244 691 1575 875

C-25%Min 1183 657 1561 867

62n (3740 mg/m3, 2078 ppm(v))* 1553 863 2736 1520

C-62nAreaMin 1962 1090 3240 1800

C-T24 (1991 mg/m3, 1106 ppm(v))* 1202 668 1694 941

Lecture Hall

62/2001 (1991 mg/m3, 1106 ppm(v))* 1436 798 1980 1100

62tracking 1926 1070 1980 1100

62/Int (3262 mg/m3, 1812 ppm(v))* 2032 1129 3078 1710

C-ZeroMin 1606 892 1980 1100

C-25%Min 1568 871 1980 1100

62n (3123 mg/m3, 1735 ppm(v))* 1962 1090 2952 1640

C-62nAreaMin 2299 1277 3024 1680

C-T24 (1991 mg/m3, 1106 ppm(v))* 1469 816 1962 1090

Classroom

62/2001 (1991 mg/m3, 1106 ppm(v))* 1559 866 1962 1090

62tracking 1827 1015 1962 1090

C-ZeroMin 1688 938 1980 1100

C-25%Min 1656 920 1980 1100

62n (2113 mg/m3, 1174 ppm(v))* 1647 915 2088 1160

C-62nAreaMin 1760 978 2124 1180

C-T24 (1991 mg/m3, 1106 ppm(v))* 1573 874 1944 1080

Portable Classroom

62/2001 (1532 mg/m3, 851 ppm(v))* 1262 701 1496 831

62tracking 1418 788 1505 836

C-ZeroMin 1352 751 1519 844

C-25%Min 1332 740 1517 843

62n (1494 mg/m3, 830 ppm(v))* 1251 695 1480 822

C-62nAreaMin 1310 728 1499 833

C-T24 (1399 mg/m3, 777 ppm(v))* 1222 679 1384 769

Fast Food Restaurant

62/2001 (1674 mg/m3, 930 ppm(v))* 1132 629 1640 911

62tracking 1566 870 1656 920

C-ZeroMin 1314 730 1667 926

C-25%Min 1246 692 1636 909

62n (2461 mg/m3, 1367 ppm(v))* 1463 813 2322 1290

C-62nAreaMin 1687 937 2412 1340

C-T24 (1991 mg/m3, 1106 ppm(v))* 1318 732 1908 1060

* Steady-state CO2 concentration based on the design ventilation rate from Table 2.

Table 6 Summary of Carbon Dioxide Concentrations
23

Figure 8 Office CO2 Concentrations during Weekday (Friday)

Figure 9 Conference Room CO2 Concentrations during Week (Wednesday and Thursday)

0

200

400

600

800

1000

1200

0:00 6:00 12:00 18:00 0:00

Time

Carbon dioxide concentration (ppm(v))

0

250

500

750

1000

1250

1500

1750

2000

Concentration (

mg/m3

)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24

0

500

1000

1500

2000

0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time

Carbon dioxide concentration (ppm(v))

0

500

1000

1500

2000

2500

3000

3500

Concentration (mg/m3

)

62-2001 62n 62-Int 62tracking

C-25%Min C-ZeroMin C-62nAreaMin C-T24
24

Figure 10 Lecture Hall CO2 Concentrations during Week (Friday)

Figure 11 Classroom CO2 Concentrations during Week (Friday)

0

250

500

750

1000

1250

1500

1750

0:00 6:00 12:00 18:00 0:00

Time

Carbon dioxide concentration (ppm(v))

0

500

1000

1500

2000

2500

3000

Concentration (mg/m3

)

62-2001 62n 62-Int 62tracking

C-25%Min C-ZeroMin C-62nAreaMin C-T24

0

200

400

600

800

1000

1200

0:00 6:00 12:00 18:00 0:00

Time

Carbon dioxide concentration (ppm(v))

0

500

1000

1500

2000

Concentration (mg/m3

)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24
25

Figure 12 Portable Classroom CO2 Concentrations during Week (Friday)

Figure 13 Fast Food Restaurant CO2 Concentrations over Friday and Saturday

0

250

500

750

1000

1250

1500

0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time

Carbon dioxide concentration (ppm(v))

0

500

1000

1500

2000

2500

Concentration (mg/m3)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24

0

200

400

600

800

1000

0:00 6:00 12:00 18:00 0:00

Time

Carbon dioxide concentration (ppm(v))

0

250

500

750

1000

1250

1500

1750

Concentration (mg/m3

)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24
26

3.3 VOC Concentration

Table 7 summarizes the indoor VOC concentrations for the ventilation strategies in each of the

spaces in terms of the average and maximum concentrations during occupancy. The first column

of the table also presents the steady-state VOC concentration for the various cases based on the

design ventilation rates from Table 2. Figures 14 through 19 present the VOC concentrations in

each of the spaces over one day (two in selected cases). Note that the averages in Table 7 are less

than 0.4 mg/m3 in all cases and less than 0.1 mg/m3 in most cases. While these concentrations are

on the low end of those measured in the field, they are dependent on the assumed source

strengths during occupied and unoccupied periods and on the assumed infiltration rate during the

unoccupied periods. The maximum concentrations are closer to, and in several cases above,

1 mg/m3 as a result of increases in concentration over unoccupied periods as discussed below.

In all spaces, the average and maximum VOC concentrations are lower for the 62/2001case than

for the other cases, except C-T24 in the Office, as expected. And while the 62tracking and CO2

control cases have higher average concentrations than the 62/2001 case, these averages are

generally only two to three times higher and always below 0.4 mg/m3. Also, the CO2 control

cases almost always have average concentrations that are close to or even below the 62tracking

case. If one is willing to assume that 62tracking, which is clearly in compliance with the

standard, provides adequate control of building-related contaminants, then the CO2 DCV cases

also control these contaminants on average. The 62n-based CO2 control case (C-62nAreaMin)

also has an average VOC concentration that is generally within a factor of two of the 62n case,

again indicating reasonable control of building-related contaminants. The only exception is in the

Conference Room where the initial VOC concentration for C-62nAreaMin is elevated at the start

of the day. It is worth noting that the average VOC level in non-office spaces with CO2 control is

almost always lower than the VOC level in the Office with the Standard 62-2001 ventilation rate.

Therefore, if the VOC level in the Office based on Standard 62 is acceptable, then the level in the

other spaces is also acceptable. Of course, this conclusion is based on the same VOC emission

rates per unit floor area in all the spaces, which may not always be a good assumption.

The maximum VOC concentrations during occupancy are generally greater than the steady-state

VOC concentrations from Table 2 by a factor of two or three, but in some cases by more than an

order of magnitude. These maximum concentrations are so much higher due to the increase in

VOC concentrations over unoccupied periods when the spaces have an infiltration rate of only

0.1 h-1. Note that the steady-state concentrations are based on the design ventilation rates and are

not impacted by the elevated initial concentrations that may exist early in the morning. The

maximum concentrations are strongly dependent on the unoccupied infiltration rate and the

relative values of the source strength during occupied and unoccupied periods, and therefore the

relative values of the different cases are more informative than the absolute values. The highest

maximum concentrations are seen for 62tracking or the CO2 control cases where there is very

little ventilation in the early part of occupancy. The maximum concentrations confirm the

observation above that if the 62tracking case is considered to control IAQ acceptably then the

DCV cases should also be considered acceptable as the maximum concentrations for the DCV

cases are near or below the 62tracking cases in all situations.

Figure 14 presents the VOC concentrations in the Office space. The patterns are similar for the

different ventilation cases with the exception of the elevated concentrations early in the day for

62tracking and C-ZeroMin, where the VOC source increases as soon as the system comes on but

the ventilation rate does not increase until later in the morning. A slight increase in concentration

is seen at mid-day for the 62tracking and the CO2 control cases when the ventilation rate is
27

reduced in response to the lower occupancy. After the system is turned off at 1900, the VOC

concentration increases steadily and reaches its maximum value just before the system comes

back on the next morning. Figures 15 and 16 shows similar trends for the Conference Room and

Lecture Hall, with dramatic increases in concentration at system startup for 62tracking and CZeroMin. Once the ventilation rates increase, the concentrations reduce by a factor of 5 to 10.

The increases in VOC concentrations during periods of low occupancy are more evident in these

spaces than in the Office. The two classrooms show similar results in Figures 17 and 18, as does

the Fast Rood Restaurant in Figure 19.

The average and maximum VOC concentrations in Table 7 are both heavily influenced by the

elevated concentrations at the start of occupancy. The figures reveal that once the early morning

transients die out, the differences between the various ventilation strategies become less

significant. Looking at the concentrations in the late afternoon, the ratio of maximum to

minimum VOC concentrations for the various cases, neglecting the idealized 62tracking case, is

about 1.5 in the Office, at most 3 or 4 in the Conference Room, Lecture Hall and classrooms, and

around 2 in the fast food restaurant.
28

Indoor VOC concentrations during

occupancy (mg/m3)

Average Maximum

Office

62/2001 (0.21 mg/m3)* 0.22 0.58

62tracking 0.34 0.89

C-ZeroMin 0.37 0.96

C-25%Min 0.32 0.80

62n (0.03 mg/m3)* 0.31 0.67

C-62nAreaMin 0.35 0.74

C-T24 (0.18 mg/m3)* 0.19 0.55

Conference Room

62/2001 (0.03 mg/m3)* 0.03 0.03

62tracking 0.30 0.90

62/Int (0.06 mg/m3)* 0.06 0.06

C-ZeroMin 0.22 1.06

C-25%Min 0.07 0.12

62n (0.09 mg/m3)* 0.09 0.09

C-62nAreaMin 0.25 0.50

C-T24 (0.04 mg/m3)* 0.09 0.20

Lecture Hall

62/2001 (0.01 mg/m3)* 0.02 0.28

62tracking 0.04 0.32

62/Int (0.03 mg/m3)* 0.04 0.34

C-ZeroMin 0.03 0.42

C-25%Min 0.03 0.37

62n (0.03 mg/m3)* 0.03 0.33

C-62nAreaMin 0.06 0.42

C-T24 (0.01 mg/m3)* 0.03 0.41

Classroom

62/2001 (0.06 mg/m3)* 0.06 0.06

62tracking 0.18 0.99

C-ZeroMin 0.19 1.03

C-25%Min 0.10 0.31

62n (0.06 mg/m3)* 0.06 0.07

C-62nAreaMin 0.11 0.35

C-T24 (0.06 mg/m3)* 0.08 0.26

Portable Classroom

62/2001 (0.09 mg/m3)* 0.09 0.18

62tracking 0.22 1.04

C-ZeroMin 0.24 1.10

C-25%Min 0.17 0.64

62n (0.08 mg/m3)* 0.09 0.17

C-62nAreaMin 0.15 0.52

C-T24 (0.07 mg/m3)* 0.12 0.41

Fast Food

62/2001 (0.03 mg/m3)* 0.03 0.06

62tracking 0.10 0.36

C-ZeroMin 0.07 0.31

C-25%Min 0.05 0.18

62n (0.05 mg/m3)* 0.05 0.11

C-62nAreaMin 0.08 0.20

C-T24 (0.04 mg/m3)* 0.06 0.21

* Steady-state VOC concentration based on the design ventilation rate from Table 2.

Table 7 Summary of VOC Concentrations
29

Figure 14 Office VOC Concentrations during Weekday (Friday)

 Figure 15 Conference Room VOC Concentrations during Week (Wednesday and Thursday)

0.00

0.20

0.40

0.60

0.80

1.00

0:00 6:00 12:00 18:00 0:00

Time

VOC concentration (mg/m3

)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24

0.00

0.20

0.40

0.60

0.80

1.00

0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time

VOC concentration (mg/m3

)

62-2001 62n 62-Int 62tracking

C-25%Min C-ZeroMin C-62nAreaMin C-T24
30

Figure 16 Lecture Hall VOC Concentrations during Week (Friday)

Figure 17 Classroom VOC Concentrations during Week (Friday)

0.00

0.10

0.20

0.30

0.40

0.50

0:00 6:00 12:00 18:00 0:00

Time

VOC concentration (mg/m3

)

62-2001 62n 62-Int 62tracking

C-25%Min C-ZeroMin C-62nAreaMin C-T24

0.00

0.20

0.40

0.60

0.80

1.00

0:00 6:00 12:00 18:00 0:00

Time

VOC concentration (mg/m3

)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24
31

Figure 18 Portable Classroom VOC Concentrations during Week (Friday)

Figure 19 Fast Food Restaurant VOC Concentrations over Friday and Saturday

0.00

0.25

0.50

0.75

1.00

0:00 6:00 12:00 18:00 0:00

Time

VOC concentration (mg/m3

)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24

0.00

0.10

0.20

0.30

0.40

0.50

0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time

VOC concentration (mg/m3

)

62-2001 62n 62tracking C-25%Min

C-ZeroMin C-62nAreaMin C-T24
32

3.4 Energy Loads

Table 8 summarizes the estimated energy loads associated with ventilation for each of the

spaces. For each city, this table presents the annual energy load associated with ventilation for

each ventilation strategy in units of MJ/m2 to account for differences in the sizes of the spaces.

Appendix A contains more details on the energy loads, including the heating, sensible cooling

and latent cooling for each case. In general, the CO2 control cases use less energy than the

constant ventilation rate cases, and the 62n case uses less than 62/2001 except in the Portable

Classroom where the 62n ventilation rate is higher. The magnitude of these reductions in a

particular city and space combination is a fairly complex function of climate (relative amounts of

heating and cooling), ventilation rate per unit floor area as shown in Table 2 (which also impacts

the heating load via the balance point), internal heat loads shown in Table 3 (which also impacts

balance point) and occupancy patterns.

In the Office space, 62tracking and the two 62-based CO2 control cases have energy loads that

are roughly 20 % lower than the straight 62-2001 case. (The loads in San Francisco are so low in

the Office space that the reductions are not discussed.) Compared to 62/2001, the addendum 62n

rates decrease the ventilation-induced energy load by 30 % to 60 % depending on the city, with

the largest reduction in the heating-dominated Minneapolis climate. Implementing CO2 control

under 62n leads to further variable reductions in the energy loads among the different cities,

ranging from around 10 % to 30 %. For the Office space, the biggest reductions in energy under

CO2 control occur in Minneapolis, which is a heating dominated climate. These reductions are

larger under heating due to the combined impact of lower ventilation rates under CO2 control and

decreased balance point temperatures due to these lower rates. Another reason for larger

reductions under heating is that the ventilation rates tend to be lower early in the day when the

outdoor temperature is lower. The energy load increases in the Office under C-T24, but as noted

earlier that is not really a DCV case in the Office and in fact has a higher ventilation rate than

required by Standard 62-2001.

The reductions in energy load for the CO2 control cases, including C-T24, are much larger in the

Conference Room and Lecture Hall given the higher design ventilation rates per unit floor area

and impact of these rates on balance point temperature. The reduction in energy load from the

62/2001 to 62n cases is also much larger than in the Office, more than 50 % in all cases and as

high as 80 %. Implementing CO2 control under 62n leads to further reductions in energy load.

The results for the classrooms are similar in relative magnitude to the changes seen in the other

cases, with the exception of the difference between 62n and 62/2001. As noted earlier, the

ventilation rate under 62n in the Portable Classroom is actually higher than under 62/2001,

leading to a slight increase in the energy load. Otherwise, implementing CO2 control under

Standard 62, Title 24 or 62n results in energy reductions from around 30 % to 50 % depending

on the city. Implementing CO2 control under Standard 62 or Title 24 in the Fast Food Restaurant

reduces the energy load by around 40 % to as high as 75 %, again depending on the city. The

lower rates under addendum 62n reduce the energy load by around 50 % relative to 62/2001,

with an 86 % reduction in Los Angeles due to a greater relative reduction in the heating load

compared to the other cities.

The energy reductions for C-62nAreaMin relative to 62/2001 are as high as 80 % to 90 % in

many cases based on the lower rates in addendum 62n. Also, the percent reductions in the spaces

studies are much greater in the mild climates than the more extreme climates.
33

Annual Energy Load due to Ventilation (MJ/m2)

Bakersfield

Los

Angeles Sacramento

San

Francisco Miami Minneapolis

Office

62/2001 30 6 18 1 117 63

62tracking 24 5 15 1 85 34

C-ZeroMin 26 5 17 1 87 35

C-25%Min 27 5 17 1 93 37

62n 20 4 12 1 79 18

C-62nAreaMin 19 4 12 1 71 13

C-Title24 35 7 21 1 135 94

Conference Room

62/2001 357 173 348 298 670 727

62tracking 71 25 66 44 147 148

62/Int 169 63 162 127 332 356

C-ZeroMin 111 41 104 73 228 233

C-25%Min 151 56 145 106 303 320

62n 93 22 89 53 205 213

C-62nAreaMin 30 4 22 4 87 71

C-Title24 129 48 122 85 248 280

Lecture Hall

62/2001 1049 528 1010 931 1943 2168

62tracking 383 142 362 292 790 841

62/Int 464 127 437 322 962 1041

C-ZeroMin 568 219 537 428 1143 1231

C-25%Min 645 248 614 502 1278 1395

62n 508 157 479 372 1025 1117

C-62nAreaMin 242 40 215 95 620 618

C-Title24 714 302 687 585 140 1521

Classroom

62/2001 197 56 194 132 406 446

62tracking 81 16 74 34 203 202

C-ZeroMin 97 19 87 43 236 228

C-25%Min 105 21 93 45 271 264

62n 168 43 166 105 364 397

C-62nAreaMin 88 16 80 33 242 230

C-Title24 119 23 108 53 300 303

Portable Classroom

62/2001 108 36 106 79 219 236

62tracking 62 17 57 35 135 138

C-ZeroMin 64 17 61 37 143 146

C-25%Min 71 17 65 40 157 163

62n 110 38 109 81 222 240

C-62nAreaMin 76 17 72 44 166 175

C-Title24 94 27 92 63 199 212

Fast Food

62/2001 1021 514 1041 1018 1875 2171

62tracking 362 94 326 229 833 847

C-ZeroMin 516 158 489 381 1109 1204

C-25%Min 574 180 550 442 1228 1357

62n 435 74 421 254 995 1106

C-62nAreaMin 222 29 174 50 679 672

C-Title24 490 125 465 345 1090 1178

Table 8 Summary of Energy Loads
34

4. DISCUSSION

The objective of this study was to examine the ventilation, indoor air quality and energy impacts

of CO2 demand controlled ventilation in a number of different space types and climates based on

the project goal of developing application guidance for potential users of CO2 DCV. The results

indicate that these impacts are dependent on the details of the spaces including occupancy

patterns, ventilation rate requirements and ventilation system operating schedule as well as the

assumptions used in the analysis, including contaminant source strengths and system-off

infiltration rates. The results and conclusions presented in this report are therefore specific to the

cases studied; however, some general conclusions can be reasonably made and the methodology

can be extended to other cases and even used in the design process as discussed below.

In terms of the ventilation rates, the simulations results yield the expected result that basing

design ventilation rates on design occupancy levels results in “overventilation” for potentially

many hours depending on the occupancy schedule. While ventilating at the design rate, even

under low occupancy, may have indoor air quality benefits in terms of better dilution of indoor

contaminant sources, there is an energy penalty. The CO2 control cases help avoid such periods

of overventilation, but generally result in relatively low ventilation rates early in the day when

occupancy is low. These low rates result in contaminant buildup, particularly of those

contaminants associated with the building, including potential exposure to contaminants that may

have built up overnight when the system was off. The extent of such contaminant buildup is

highly dependent on the source strengths in the unoccupied building, for which only very limited

data is available, and fan off infiltration rates, which are highly building specific and weather

dependent. Therefore it is very hard to generalize about early occupancy exposure, other than

stating that CO2 control strategies with a nonzero base ventilation rate, such as C-25%Min, C62nAreaMin and C-T24, will help to temper such exposure. Pre-occupancy “flush out” strategies

(a requirement of Title 24, but not Standard 62-2001) may also be helpful in lessening such

exposure, but need to be considered for the given space and climate, as early morning ventilation

can have energy implications that depend on temperature and humidity variations over the day.

As expected, the 62n rates are significantly lower than the 62/2001 rates for all but the two

classroom spaces. While this reduction has generated some questions based on potential IAQ

concerns, the CO2 and VOC simulations provide some insight into this question.

While CO2 is not a contaminant of concern at typical indoor levels, it has become viewed as an

indicator of occupant-generated contaminants and is useful in this respect if the limitations are

understood. In particular, it provides information on the acceptability of the space in terms of

odor from human bioeffluents and perhaps the level of other occupant generated contaminants,

but is not a comprehensive indicator of overall indoor air quality. Many have come to view an

indoor CO2 concentration of 1800 mg/m3 (1000 ppm(v)) as a threshold separating good and bad

indoor air quality, but in reality 1800 mg/m3 (1000 ppm(v)) CO2 has no significance from a

health or comfort perspective (ASTM 2002) and is only of interest based on it being the expected

steady-state concentration at ventilation rates of about 8 L/s (17 cfm) per person and an outdoor

concentration of 540 mg/m3 (300 ppm(v)). Nonetheless, the average and maximum indoor CO2

concentrations serve as metrics for comparing the different cases.

As expected, ventilating at the Standard 62-2001 rate whenever the system is operating results in

the lowest CO2 concentrations, except for the offices where Title 24 results in lower

concentrations. However, the CO2 control cases increase the average and maximum CO2

concentrations during occupancy by only about 180 mg/m3 (100 ppm(v)). In terms of the impact

on bioeffluent perception, 180 mg/m3 (100 ppm(v)) is not very significant. Specifically, based on
35

the relationship between percent of occupants dissatisfied with human bioeffluents and CO2

concentration (ECA 1992), a change of 180 mg/m3 (100 ppm(v)) corresponds to an increase in

the percent dissatisfied of only about 2 %.

The use of ventilation rates based on addendum 62n resulted in more significant increases in

indoor CO2 levels. The average concentrations increased from 180 mg/m3 (100 ppm(v)) or less

to about 540 mg/m3 (300 ppm(v)) in the Conference Room. The increases in the maximum

concentration were larger, up to 900 mg/m3 (500 ppm(v)) in the Lecture Hall and 1260 mg/m3

(700 ppm(v)) in the Conference Room. These increases in the maximum concentrations are more

significant but still below any level of concern based on health (ASTM 2002). None of the

maximum concentrations exceeded 3060 mg/m3 (1700 ppm(v)), which corresponds to about

35 % dissatisfaction with odor from human bioeffluents on the part of unadapted visitors to a

space and about 12 % dissatisfaction on the part of adapted occupants (ECA 1992). The term

adapted refers to the fact that people become accustomed to body odors relatively quickly, in less

than a minute, and therefore express lower levels of dissatisfaction at the same level of body

odor (or CO2) than individuals who have not yet become adapted to these odors.

For some of the CO2 control scenarios, the indoor CO2 level built-up during the week, but this

was due to the value assumed for infiltration when the system was off. Note that while there is

not a great deal of data on commercial building infiltration rates, the value used in these

simulations is likely conservatively low for most building-climate combinations. In fact, a low

value was selected intentionally to highlight the impact of contaminant build-up during

unoccupied periods. The magnitude of the build-up depended on the details of the control

algorithm, but was rarely more than about 180 mg/m3 (100 ppm(v)).

Indoor VOC concentrations were calculated to assess the impact of CO2 control on non-occupant

generated contaminants, for example those emitted by building materials and furnishings. Based

on the assumed emission rates, which were not particularly low relative to the limited data from

field studies, the average indoor VOC levels during occupancy were always less than 0.4 mg/m3

and less than 0.1 mg/m3 in most cases. While the lack of definitiveness of the VOC emission rate

values limits the reliability of the predicted VOC levels in absolute terms, the relative

comparison between cases is far more reliable. Using the 62tracking case, which complies with

Standard 62-2001, as a baseline, all the other cases have average VOC concentrations that are

close to or below this idealized case. If one is willing to accept that 62tracking provides adequate

control of building-related contaminants, then the CO2 DCV cases also control these

contaminants on average. The CO2 control cases had higher VOC concentrations than the

reference cases based on Standard 62-2001 and addendum 62n, with the greatest increase in the

Conference Room based on its low occupancy early in the day. The average concentrations, and

more so the maximum concentrations, were heavily influenced by the build-up in concentration

during unoccupied hours, which in turn depend on the values, assumed for the fan-off infiltration

rate and VOC emission rate. As discussed earlier, these elevated concentrations early in the day

can be tempered by a nonzero minimum ventilation rate under CO2 control (as with C-25%Min,

C-62nAreaMin and C-Title24) or with an early morning flush-out. That latter strategy was not

evaluated as part of this project, but this simulation approach could be used to investigate its

potential benefits. Note that while the VOC results are dependent on the assumed emission rates,

they can be scaled up or down linearly for other emission rates as long as the two-to-one ratio of

occupied to unoccupied emission rate is maintained.

The annual energy load reductions due to the use of CO2 control were significant in most of the

cases, ranging from 10 % to 80 % depending on the space type, climate and ventilation strategy.

For the Office , the reductions are generally around 20 %, given the relatively stable occupancy
36

pattern in that space relative to some of the others. Spaces with more variability in occupancy,

such as the Conference Room and Lecture Hall, exhibit larger energy reductions. The energy

load reductions associated with the use of addendum 62n relative to the ventilation requirements

in Standard 62-2001 are as large as 30 % to 50 % in the spaces where the 62n rates are lower.

However, in the two classroom spaces, the 62n rates are similar to those based on Standard 62-

2001 and therefore no significant difference is seen. The most significant reductions are seen for

the 62n DCV case relative to the Standard 62 baseline case.

Taking a closer look at the California climates, these results indicate that CO2 DCV is not likely

to provide much energy benefit in offices in the milder climates (Los Angeles and San

Francisco) for the relatively stable occupancy patterns used in this study. However in the more

“severe” climates of Bakersfield and Sacramento, the savings in the Office were more

significant. The spaces with more variable occupancy (Conference Room, Lecture Hall and Fast

Food Restaurant) resulted in significant energy savings in all the climates studied. The energy

savings in the classroom spaces are strongly dependent on the system operating schedule versus

the occupancy schedule, and while significant load reductions were seen in this study,

application of CO2 DCV in classrooms may require more careful consideration.

This study has employed an approach to assessing ventilation, IAQ and energy impacts of

different ventilation strategies using the control simulation capabilities of the CONTAMW

program. As noted above, this methodology can be applied to other spaces, climates and

ventilation strategies to investigate a number of other issues of interest. In particular, the impacts

of different VOC source strengths in different spaces and variable emissions patterns over the

day would be of interest. Also, the impacts of occupancy levels both lower and greater than those

assumed in the design, which does occur in practice, would be worth considering.
37

5. ACKNOWLEDGEMENTS

This report was supported by the California Energy Commission through the Architectural

Energy Corporation. The authors acknowledge the contributions of Vern Smith of the

Architectural Energy Corporation and Steven Taylor of Taylor Engineering.

6. REFERENCES

Anderson, K, JV Bakke, O Bjørseth, C-G Bornehag, G Clausen, JK Hongslo, M Kjellman, S

Kjærgaard, F Levy, L Mølhave, S Skerfving and J Sundell. 1997. TVOC and Health in NonIndustrial Indoor Environments. Report from a Nordic Scientific Consensus Meeting at

Långholmen in Stockholm, 1996. Indoor Air, Vol 7:78-91.

ANSI/ASHRAE/IESNA. 1999. ANSI/ASHRAE/IESNA Standard 90.1-1999: Energy Standard

for Buildings Except Low-Rise Residential Buildings. American Society of Heating,

Refrigerating, and Air Conditioning Engineers and Illuminating Engineering Society of North

America.

ASHRAE. 1997. WYEC2: Weather Year for Energy Calculations 2. American Society of

Heating, Refrigerating and Air-Conditioning Engineers.

ASHRAE. 2001a. ANSI/ASHRAE Standard 62-2001, Ventilation for Acceptable Indoor Air

Quality. American Society of Heating, Refrigerating and Air-Conditioning Engineers.

ASHRAE 2001b. ASHRAE Handbook of Fundamentals. American Society of Heating,

Refrigerating, and Air Conditioning Engineers.

ASTM. 2002. D6245-98 (2002) Standard Guide for Using Indoor Carbon Dioxide

Concentrations to Evaluate Indoor Air Quality and Ventilation. American Society for Testing

and Materials.

Brandemuehl, MJ and JE Braun. 1999. The Impact of Demand-Controlled and Economizer

Ventilation Strategies on Energy Use in Buildings. ASHRAE Transactions 105 (2): 39-50.

Brown, S, MR Sim, MJ Abramson and CN Gray. 1994. Concentrations of Volatile Organic

Compounds in Indoor Air - A Review, p. 123-134. Indoor Air, Vol. 4.

Carpenter, SC. 1996. Energy and IAQ Impacts of CO2-Based Demand Controlled Ventilation.

ASHRAE Transactions, Vol. 102 (2): 1183-1197.

CEC. 2001. Energy Efficiency Standards for Residential and Nonresidential Buildings.

California Energy Commission, P400-01-024.

Daisey, JM, AT Hodgson, WJ Fisk, MJ Mendell, and J Ten Brinks. 1994. Volatile Organic

Compounds in Twelve California Office Buildings: Classes, Concentrations, and Sources, p.

3557-3562. In Atmospheric Environment. Vol. 28, No. 22.

Dols, WS and GN Walton. 2002. CONTAMW 2.0 User Manual. National Institute of Standards

and Technology, NISTIR 6921.

ECA (European Collaborative Action). 1992. Guidelines for Ventilation Requirements in

Buildings, Report No. 11, EUR1449EN. Luxembourg Office for Official Publications of the

European Communities.
38

Emmerich, SJ, JW Mitchell and WA Beckman. 1994. Demand-Controlled Ventilation in a MultiZone Office Building. Indoor Environment, Vol. 3: 331-340.

Emmerich, SJ and AK Persily. 2001. State-of-the-Art Review of CO2 Demand Controlled

Ventilation Technology and Application. National Institute of Standards and Technology,

NISTIR 6729.

Enermodal. 1995. An Evaluation of the Effect of CO2-Based Demand-Controlled Ventilation

Strategies on Energy Use and Occupant-Source Contaminant Concentrations. ASHRAE

Research Project 740-TRP. Enermodal Engineering Limited.

EPA. 1999. Exposure Factors Handbook. U.S. Environmental Protection Agency, EPA/600/C99/001.

Hadwen, GE, JF McCarthy, SE Womble, JR Girman and HS Brightman. 1997. Volatile Organic

Compound Concentrations in 41 Office Buildings in the Continental United States. In

Proceedings of Healthy Buildings/IAQ'97. Volume 2: 465-470.

Knapp, CL, TL Stoffel and SD Whitaker. 1980. Insolation Data Manual. Solar Energy Research

Institute, SERISP-755-789.

Levin, H. 1995. Emissions Testing Data and Indoor Air Quality. Second International

Conference on Indoor Air Quality, Ventilation and Energy Conservation in Buildings, 1: 465-

482.

Marion W and K Urban. 1995. User’s Manual for TMY2s, Typical Meteorological Years,

Derived from the 1961-1990 National Solar Radiation Data Base. National Renewable Energy

Laboratory, NREL/SP-463-7668, E95004064.

Persily, AK. 2001. Addendum 62n: Revising the Ventilation Rate Procedure. ASHRAE Journal

43 (9): 12-13.

Schell, MB, SC Turner and RO Shim. 1998. Application of CO2-Based Demand-Controlled

Ventilation Using ASHRAE Standard 62: Optimizing Energy Use and Ventilation. ASHRAE

Transactions 104 (2): 1213-1225.

Schell, MB and D Int-Hout. 2001. Demand Control Ventilation Using CO2. ASHRAE Journal 43

(2): 18-29.

Sowa J. 2002. CO2-Based Occupancy Detection for On-Line Demand Controlled Ventilation

Systems. Proceedings of Indoor Air 2002, Vol. 3: 334-339.

Wolkoff, P. 1995. Volatile Organic Compounds – Sources, Measurements, Emissions, and The

Impact on Indoor Air Quality. Indoor Air. Supplement No. 3/95.
39

Appendix A: Details of Energy Simulation Results

This appendix presents the energy simulation results for the six space types for each ventilation

control strategy in each city. The tables that follow break down the total energy presented in the

body of the report into heating energy and sensible and latent cooling. A separate table is

included for each of the six cities.
40

Heating

(MJ)

Sensible

cooling

(MJ)

Latent

cooling

(MJ)

Total

cooling

(MJ)

Total

heating &

cooling

(MJ)

Total

heating &

cooling

(MJ/m2)

Office

62/2001 0 29,800 200 30,000 30,000 30

62tracking 0 23,600 100 23,700 23,700 24

C-ZeroMin 0 25,600 100 25,700 25,700 26

C-25%Min 0 26,300 200 26,500 26,500 27

62n 0 20,200 100 20,300 20,300 20

C-62nAreaMin 0 19,000 100 19,100 19,100 19

C-Title24 0 34,400 200 34,600 34,600 35

Conference Room

62/2001 17,200 18,400 100 18,500 35,700 357

62tracking 2,400 4,700 0 4,700 7,100 71

62/Int 7,600 9,200 100 9,300 16,900 169

C-ZeroMin 3,900 7,200 0 7,200 11,100 111

C-25%Min 6,000 9,000 100 9,100 15,100 151

62n 3,600 5,700 0 5,700 9,300 93

C-62nAreaMin 300 2,700 0 2,700 3,000 30

C-Title24 4,700 8,200 0 8,200 12,900 129

Lecture Hall

62/2001 51,800 52,800 300 53,100 104,900 1049

62tracking 18,200 20,000 100 20,100 38,300 383

62/Int 19,800 26,400 200 26,600 46,400 464

C-ZeroMin 26,500 30,100 200 30,300 56,800 568

C-25%Min 30,300 34,000 200 34,200 64,500 645

62n 22,400 28,200 200 28,400 50,800 508

C-62nAreaMin 7,300 16,800 100 16,900 24,200 242

C-Title24 34,400 36,800 200 37,000 71,400 714

Classroom

62/2001 9,600 10,000 100 10,100 19,700 197

62tracking 2,600 5,400 0 5,500 8,100 81

C-ZeroMin 3,100 6,600 0 6,600 9,700 97

C-25%Min 3,200 7,300 0 7,300 10,500 105

62n 7,800 8,900 100 9,000 16,800 168

C-62nAreaMin 2,300 6,500 0 6,500 8,800 88

C-Title24 3,900 8,000 0 8,000 11,900 119

Portable Classroom

62/2001 4,700 4,900 0 4,900 9,600 108

62tracking 2,300 3,200 0 3,200 5,500 62

C-ZeroMin 2,200 3,500 0 3,500 5,700 64

C-25%Min 2,500 3,800 0 3,800 6,300 71

62n 4,800 5,000 0 5,000 9,800 110

C-62nAreaMin 2,800 4,000 0 4,000 6,800 76

C-Title24 3,700 4,700 0 4,700 8,400 94

Fast Food

62/2001 74,200 53,000 400 53,400 127,600 1021

62tracking 18,600 26,400 200 26,600 45,200 362

C-ZeroMin 29,400 34,900 200 35,100 64,500 516

C-25%Min 34,000 37,500 300 37,800 71,800 574

62n 25,600 28,600 200 28,800 54,400 435

C-62nAreaMin 6,600 20,900 200 21,100 27,700 222

C-Title24 27,500 33,500 200 33,700 61,200 490

Table A1 Detailed Energy Loads for Bakersfield
41

Heating

(MJ)

Sensible

cooling

(MJ)

Latent

cooling

(MJ)

Total

cooling

(MJ)

Total

heating &

cooling

(MJ)

Total

heating &

cooling

(MJ/m2)

Office

62/2001 0 2,700 3,100 5,800 5,800 6

62tracking 0 2,300 2,400 4,700 4,700 5

C-ZeroMin 0 2,300 2,300 4,600 4,600 5

C-25%Min 0 2,400 2,500 4,900 4,900 5

62n 0 1,800 2,100 3,900 3,900 4

C-62nAreaMin 0 1,700 1,900 3,600 3,600 4

C-Title24 0 3,100 3,600 6,700 6,700 7

Conference Room

62/2001 13,600 1,900 1,800 3,700 17,300 173

62tracking 1,700 400 400 800 2,500 25

62/Int 4,500 900 900 1,800 6,300 63

C-ZeroMin 2,900 600 600 1,200 4,100 41

C-25%Min 3,900 900 800 1,700 5,600 56

62n 1,000 600 600 1,200 2,200 22

C-62nAreaMin 0 200 200 400 400 4

C-Title24 3,300 800 700 1,500 4,800 48

Lecture Hall

62/2001 43,900 4,200 4,700 8,900 52,800 528

62tracking 10,200 2,000 2,000 4,000 14,200 142

62/Int 8,200 2,100 2,400 4,500 12,700 127

C-ZeroMin 16,100 2,800 3,000 5,800 21,900 219

C-25%Min 18,400 3,100 3,300 6,400 24,800 248

62n 10,900 2,300 2,500 4,800 15,700 157

C-62nAreaMin 900 1,500 1,600 3,100 4,000 40

C-Title24 23,200 3,400 3,600 7,000 30,200 302

Classroom

62/2001 3,500 1000 1,100 2,100 5,600 56

62tracking 400 600 600 1,200 1,600 16

C-ZeroMin 500 700 700 1,400 1,900 19

C-25%Min 600 700 800 1,500 2,100 21

62n 2,400 900 1000 1,900 4,300 43

C-62nAreaMin 200 700 700 1,400 1,600 16

C-Title24 700 800 800 1,600 2,300 23

Portable Classroom

62/2001 2,100 500 600 1,100 3,200 36

62tracking 700 400 400 800 1,500 17

C-ZeroMin 700 400 400 800 1,500 17

C-25%Min 700 400 400 800 1,500 17

62n 2,200 600 600 1,200 3,400 38

C-62nAreaMin 700 400 400 800 1,500 17

C-Title24 1,400 500 500 1,000 2,400 27

Fast Food

62/2001 55,100 4,100 5,100 9,200 64,300 514

62tracking 7,200 2,200 2,400 4,600 11,800 94

C-ZeroMin 13,900 2,800 3,100 5,900 19,800 158

C-25%Min 16,100 3.000 3,400 6,400 22,500 180

62n 4,200 2,200 2,800 5,000 9,200 74

C-62nAreaMin 100 1,600 1,900 3,500 3,600 29

C-Title24 10,000 2,600 3,000 5,600 15,600 125

Table A2 Detailed Energy Loads for Los Angeles
42

Heating

(MJ)

Sensible

cooling

(MJ)

Latent

cooling

(MJ)

Total

cooling

(MJ)

Total

heating &

cooling

(MJ)

Total

heating &

cooling

(MJ/m2)

Office

62/2001 0 18,100 100 18,200 18,200 18

62tracking 0 14,900 100 15,000 15,000 15

C-ZeroMin 0 16,400 100 16,500 16,500 17

C-25%Min 0 16,600 100 16,700 16,700 17

62n 0 12,200 100 12,300 12,300 12

C-62nAreaMin 0 11,700 100 11,800 11,800 12

C-Title24 0 20,800 100 20,900 20,900 21

Conference Room

62/2001 22,900 11,800 100 11,900 34,800 348

62tracking 3,600 3,000 0 3,000 6,600 66

62/Int 10,300 5,900 0 5,900 16,200 162

C-ZeroMin 5,700 4,700 0 4,700 10,400 104

C-25%Min 8,700 5,800 0 5,800 14,500 145

62n 5,200 3,700 0 3,700 8,900 89

C-62nAreaMin 500 1,700 0 1,700 2,200 22

C-Title24 6,900 5,300 0 5,300 12,200 122

Lecture Hall

62/2001 70,000 30,800 200 31,000 101,000 1010

62tracking 24,600 11,500 100 11,600 36,200 362

62/Int 28,200 15,400 100 15,500 43,700 437

C-ZeroMin 35,900 17,700 100 17,800 53,700 537

C-25%Min 41,300 20,000 100 20,100 61,400 614

62n 31,400 16,400 100 16,500 47,900 479

C-62nAreaMin 11,400 10,000 100 10,100 21,500 215

C-Title24 46,800 21,800 100 21,900 68,700 687

Classroom

62/2001 13,200 6,200 0 6,200 19,400 194

62tracking 3,900 3,500 0 3,500 7,400 74

C-ZeroMin 4,400 4,300 0 4,300 8,700 87

C-25%Min 4,700 4,600 0 4,600 9,300 93

62n 11,100 5,500 0 5,500 16,600 166

C-62nAreaMin 3,800 4,200 0 4,200 8,000 80

C-Title24 5,700 5,100 0 5,100 10,800 108

Portable Classroom

62/2001 6,300 3,100 0 3,100 9,400 106

62tracking 3,100 2,000 0 2,000 5,100 57

C-ZeroMin 3,100 2,300 0 2,300 5,400 61

C-25%Min 3,400 2,400 0 2,400 5,800 65

62n 6,500 3,100 0 3,200 9,700 109

C-62nAreaMin 3,900 2,500 0 2,500 6,400 72

C-Title24 5,200 3,000 0 3,000 8,200 92

Fast Food

62/2001 102,500 27,500 100 27,600 130,100 1041

62tracking 26,500 14,100 100 14,200 40,700 326

C-ZeroMin 42,400 18,600 100 18,700 61,100 489

C-25%Min 48,700 19,900 100 20,000 68,700 550

62n 37,700 14,800 100 14,900 52,600 421

C-62nAreaMin 10,600 11,100 100 11,200 21,800 174

C-Title24 40,200 17,800 100 17,900 58,100 465

Table A3 Detailed Energy Loads for Sacramento
43

Heating

(MJ)

Sensible

cooling

(MJ)

Latent

cooling

(MJ)

Total

cooling

(MJ)

Total

heating &

cooling

(MJ)

Total

heating &

cooling

(MJ/m2)

Office

62/2001 0 1,200 0 1,200 1,200 1

62tracking 0 1,000 0 1,000 1,000 1

C-ZeroMin 0 1,100 0 1,100 1,100 1

C-25%Min 0 1,100 0 1,100 1,100 1

62n 0 800 0 800 800 1

C-62nAreaMin 0 800 0 800 800 1

C-Title24 0 1,400 0 1,400 1,400 1

Conference Room

62/2001 29,000 800 0 800 29,800 298

62tracking 4,200 200 0 200 4,400 44

62/Int 12,300 400 0 400 12,700 127

C-ZeroMin 7,000 300 0 300 7,300 73

C-25%Min 10,200 400 0 400 10,600 106

62n 5,000 300 0 300 5,300 53

C-62nAreaMin 300 100 0 100 400 4

C-Title24 8,200 300 0 300 8,500 85

Lecture Hall

62/2001 91,200 1,900 0 1,900 93,100 931

62tracking 28,300 900 0 900 29,200 292

62/Int 31,200 1,000 0 1,000 32,200 322

C-ZeroMin 41,600 1,200 0 1,200 42,800 428

C-25%Min 48,800 1,400 0 1,400 50,200 502

62n 36,200 1,000 0 1,000 37,200 372

C-62nAreaMin 8,800 700 0 700 9,500 95

C-Title24 57,000 1,500 0 1,500 58,500 585

Classroom

62/2001 12,800 400 0 400 13,200 132

62tracking 3,200 200 0 200 3,400 34

C-ZeroMin 4,100 300 0 300 4,400 44

C-25%Min 4,200 300 0 300 4,500 45

62n 10,100 400 0 400 10,500 105

C-62nAreaMin 3,000 300 0 300 3,300 33

C-Title24 4,900 400 0 400 5,300 53

Portable Classroom

62/2001 6,800 200 0 200 7,000 79

62tracking 3,000 100 0 100 3,100 35

C-ZeroMin 3,100 200 0 200 3,300 37

C-25%Min 3,400 200 0 200 3,600 40

62n 7,000 200 0 200 7,200 81

C-62nAreaMin 3,700 200 0 200 3,900 44

C-Title24 5,400 200 0 200 5,600 63

Fast Food

62/2001 125,500 1,800 0 1,800 127,300 1018

62tracking 27,600 1,000 0 1,000 28,600 229

C-ZeroMin 46,300 1,300 0 1,300 47,600 381

C-25%Min 53,800 1,400 0 1,400 55,200 442

62n 30,700 1,000 0 1,000 31,700 254

C-62nAreaMin 5,500 800 0 800 6,300 50

C-Title24 41,900 1,200 0 1,200 43,100 345

Table A4 Detailed Energy Loads for San Francisco
44

Heating

(MJ)

Sensible

cooling

(MJ)

Latent

cooling

(MJ)

Total

cooling

(MJ)

Total

heating &

cooling

(MJ)

Total

heating &

cooling

(MJ/m2)

Office

62/2001 0 37,500 79,200 116,700 116,700 117

62tracking 0 29,200 56,100 85,300 85,300 85

C-ZeroMin 0 30,400 56,900 87,300 87,300 87

C-25%Min 0 31,700 61,500 93,200 93,200 93

62n 0 25,500 53,800 79,300 79,300 79

C-62nAreaMin 0 23,300 47,300 70,600 70,600 71

C-Title24 0 43,300 91,400 134,700 134,700 135

Conference Room

62/2001 1,600 22,800 42,600 65,400 67,000 670

62tracking 100 5,200 9,400 14,600 14,700 147

62/Int 500 11,400 21,300 32,700 33,200 332

C-ZeroMin 200 8,100 14,500 22,600 22,800 228

C-25%Min 300 10,600 19,400 30,000 30,300 303

62n 200 7,100 13,200 20,300 20,500 205

C-62nAreaMin 0 3,100 5,600 8,700 8,700 87

C-Title24 200 9,400 17,200 24,600 24,800 248

Lecture Hall

62/2001 4,300 62,300 127,700 190,000 194,300 1943

62tracking 1,400 25,500 52,100 77,600 79,000 790

62/Int 1,200 31,200 63,800 95,000 96,200 962

C-ZeroMin 2,000 37,400 74,900 112,300 114,300 1143

C-25%Min 2,300 41,600 83,900 125,500 127,800 1278

62n 1,200 33,200 68,100 101,300 102,500 1025

C-62nAreaMin 300 20,600 41,100 61,700 62,000 620

C-Title24 2,800 45,500 91,400 136,900 139,700 140

Classroom

62/2001 700 12,900 27,000 39,900 40,600 406

62tracking 100 7,100 13,100 20,200 20,300 203

C-ZeroMin 200 8,300 15,100 23,400 23,600 236

C-25%Min 200 9,200 17,700 26,900 27,100 271

62n 600 11,600 24,200 35,800 36,400 364

C-62nAreaMin 100 8,300 15,800 24,100 24,200 242

C-Title24 200 10,200 19,600 29,800 30,000 300

Portable Classroom

62/2001 400 6,500 12,600 19,100 19,500 219

62tracking 100 4,200 7,700 11,900 12,000 135

C-ZeroMin 100 4,500 8,100 12,600 12,700 143

C-25%Min 100 4,900 9,000 13,900 14,000 157

62n 400 6,600 12,800 19,400 19,800 222

C-62nAreaMin 100 5,100 9,600 14,700 14,800 166

C-Title24 200 6,100 11,400 17,500 17,700 199

Fast Food

62/2001 7,200 65,200 162,000 227,200 234,400 1875

62tracking 1000 31,700 71,400 103,100 104,100 833

C-ZeroMin 1,700 41,600 95,300 136,900 138,600 1109

C-25%Min 2,100 45,200 106,200 151,400 153,500 1228

62n 1,500 35,300 87,600 122,900 124,400 995

C-62nAreaMin 200 25,200 59,500 84,700 84,900 679

C-Title24 1,600 40,300 94,300 134,600 136,200 1090

Table A5 Detailed Energy Loads for Miami
45

Heating

(MJ)

Sensible

cooling

(MJ)

Latent

cooling

(MJ)

Total

cooling

(MJ)

Total

heating &

cooling

(MJ)

Total

heating &

cooling

(MJ/m2)

Office

62/2001 47,100 7,300 8,500 15,800 62,900 63

62tracking 21,900 5,900 6,300 12,200 34,100 34

C-ZeroMin 22,300 6,400 6,600 13,000 45,300 45

C-25%Min 23,000 6,600 7,000 13,600 36,600 37

62n 7,600 5,000 5,800 10,800 18,400 18

C-62nAreaMin 2,700 4,700 5,200 9,900 12,600 13

C-Title24 75,300 8,400 9.800 18,200 93,500 94

Conference Room

62/2001 63,300 4,600 4,800 9,400 72,700 727

62tracking 12,600 1,100 1,100 2,200 14,800 148

62/Int 30,900 2,300 2,400 4,700 35,600 356

C-ZeroMin 20,000 1,700 1,600 3,300 23,300 233

C-25%Min 27,600 2,200 2,200 4,400 32,000 320

62n 18,400 1,400 1,500 2,900 21,300 213

C-62nAreaMin 5,900 600 600 1,200 7,100 71

C-Title24 24,100 2,000 1,900 3,900 28,000 280

Lecture Hall

62/2001 189,500 12,800 14,500 27,300 216,800 2168

62tracking 73,500 4,900 5,700 10,600 84,100 841

62/Int 90,400 6,400 7,300 13,700 104,100 1041

C-ZeroMin 107,300 7,400 8,400 15,800 123,100 1231

C-25%Min 121,800 8,300 9,400 17,700 139,500 1395

62n 97,100 6,800 7,700 14,600 111,700 1117

C-62nAreaMin 53,100 4,100 4,600 8,700 61,800 618

C-Title24 132,900 9,000 10,200 19,200 152,100 1521

Classroom

62/2001 39,300 2,400 2,900 5,300 44,600 446

62tracking 17,300 1,400 1,500 2,900 20,200 202

C-ZeroMin 19,400 1,700 1,700 3,400 22,800 228

C-25%Min 22,700 1,800 1,900 3,700 26,400 264

62n 34,900 2,200 2,600 4,800 39,700 397

C-62nAreaMin 19,700 1,600 1,700 3,300 23,000 230

C-Title24 26,100 2,000 2,200 4,200 30,300 303

Portable Classroom

62/2001 18,400 1,200 1,400 2,600 21,000 236

62tracking 10,700 800 800 1,600 12,300 138

C-ZeroMin 11,200 900 900 1,800 13,000 146

C-25%Min 12,500 1,000 1000 2,000 14,500 163

62n 18,800 1,200 1,400 2,600 21,400 240

C-62nAreaMin 13,500 1,000 1,100 2,100 15,600 175

C-Title24 16,400 1,200 1,300 2,500 18,900 212

Fast Food

62/2001 241,200 12,100 18,100 30,200 271,400 2171

62tracking 91,400 6,200 8,300 14,500 105,900 847

C-ZeroMin 131,400 8,100 11,000 19,100 150,500 1204

C-25%Min 148,800 8,700 12,100 20,800 169,600 1357

62n 121,900 6,500 9,800 16,300 138,200 1106

C-62nAreaMin 72,400 4,800 6,800 11,600 84,000 672

C-Title24 128,700 7,800 10,800 18,600 147,300 1178

Table A6 Detailed Energy Loads for Minneapolis
46

Appendix B: PIER RFP Issues

The California Energy Commission (CEC) Public Interest Energy Research (PIER) Request for

Proposals (RFP) for the Buildings Energy Efficiency Program Area identified four broad issues

of key concern to the CEC. These four issues identify energy problems facing buildings in

California and present opportunities to have a significant positive impact. This appendix will

discuss the relationship of the application of CO2-based DCV systems in small non-residential

buildings to the four key issues based on information in this report.

Issue #1 Energy consumption is rapidly increasing in hotter, inland areas as new building

construction increases in these areas.

Obviously, the primary intent of CO2-based DCV systems are to reduce energy consumed to cool

or heat ventilation air in buildings and, as demonstrated in this report, they are capable of

achieving such reductions for many building types in a variety of climates. These results indicate

that CO2 DCV systems can reduce cooling energy consumption in the hotter, inland areas of

California in many occupancies. As application of CO2 DCV in new construction is considered,

some thought will need to be given to the possibility that these newer buildings may have low

infiltration rates during unoccupied periods and some strategy may be needed to address

contaminant buildup when the system is off.

Issue #2 Development of energy efficient products and services needs to adequately consider

non-energy benefits, such as comfort, productivity, durability, and decreased maintenance.

Since CO2-based DCV systems directly affect ventilation rates provided in buildings, there is the

potential to have a significant impact on building occupant comfort and productivity. That

impact could be either positive or negative depending on the DCV system design, installation,

operation and maintenance. CO2-based DCV systems can have a positive impact on IAQ that is

not commonly considered. Frequently, building zones are occupied by more people than the

ventilation system design criteria. At such times, a DCV system will result in improved IAQ by

increasing the ventilation supplied to the space. Additionally, ventilation systems may operate

with lower ventilation effectiveness than the design criteria. Again, a DCV system can increase

ventilation rates in such situations. While it is not possible to estimate potential impacts on

productivity for any given building, Fisk and Rosenfeld (1997) have estimated that nationwide

impacts of better indoor environments are in the billions of dollars.

Since DCV systems adjust ventilation rates based on measured concentrations of CO2 generated

by building occupants, they do not directly guarantee satisfactory indoor air quality (IAQ) due to

the presence of non-occupant generated contaminants. This results in a concern by some that

DCV could result in poor IAQ that would negatively impact comfort and productivity. Certain

steps need to be taken to avoid the occurrence of such a negative impact. The most fundamental

step is to implement the same good IAQ practices that should be applied to all commercial

buildings. This includes such practices as reducing contaminant sources, properly installing and

maintaining equipment, etc. Additional steps that should be taken for DCV systems include

appropriate selection of control algorithms and setpoints, thoughtful consideration of expected

contaminant sources, establishing needed minimum base and/or purge ventilation rates and

schedules, and proper maintenance and calibration of CO2 sensors.

Finally, the impacts of DCV systems on comfort and productivity have not been thoroughly

studied. Since this is an important issue, more research in this area is needed.

Issue #3 Building design, construction, and operation of energy-related features can affect

public health and safety.
47

The discussion above addressing Issue #2 applies equally to public health. CO2-based DCV

systems could have either a negative or positive impact on public health and care needs to be

taken in their application. Specifically for moisture issues, DCV can have a very positive impact

in lessening the moisture load in non-residential buildings in humid climates. Since most of the

moisture load for many non-residential buildings is brought into a building through ventilation,

reducing excess ventilation during times of reduced building occupancy can reduce this

moisture load. This reduction in moisture load can save energy and money by eliminating the

need for special equipment.

Issue #4 Investments in energy efficiency can affect building and housing affordability and value,

and the state’s economy.

As discussed in response to Issue #1, CO2-based DCV systems can reduce building heating and

cooling energy use and, therefore, reduce operating costs to improve building affordability and

value. However, these potential savings will vary widely depending on building type, climate,

occupancy density and patterns, other HVAC equipment used, and other factors. While

knowledge of these important parameters is growing, more work is needed to identify the best

opportunities for energy savings. No impacts are expected on the energy-related costs of

construction.

Fisk, W.J. and A.H. Rosenfeld. Estimates of Improved Productivity and Health from Better

Indoor Environments (1997) Indoor Air 1997; 7:158-172.