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NAT L INST. OF STAND & TECH 35-3150

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I I 1 uuor Air Quality Modeling

Workshop Report

Preston E. McNali

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Physics Division

Gaithersburg, MD 20893

April 1985

Issued May 1 985

Prepared for Environmental Protection Agency (MD-75) “ QC cnmentai Monitoring Systems Laboratory

2Q 0

arch Triangle Park, NC 27711

. U56

85-3150

1985

RATIONAL BUREAU

OF STAND

LIBRARY NBSIR 85-3150

i •* INDOOR AIR QUALITY MODELING

WORKSHOP REPORT

Preston E. McNall

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Physics Division

Gaithersburg, MD 20899

April 1985

Issued May 1 985

Prepared for Environmental Protection Agency (MD-75)

Environmental Monitoring Systems Laboratory

Research Triangle Park, NC 2771

1

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
'
INDOOR AIR QUALITY MODELING WORKSHOP REPORT

Preston E. McNall

ABSTRACT

Comprehensive modeling of emission, absorption, movement and controls of

indoor air contaminants is essential for developing national policy for IAQ

assessment and controls. This report describes several topics discussed in

the workshop on indoor air quality, which was held on February 11, 1985 at

the National Bureau of Standards. Researchers on IAQ modeling were invited

to state their current activities, identify research needs and recommend

specific parameters and contaminants to be included in the models. The

input thus obtained in this workshop will be incorporated into an advanced

simulation model for IAQ, to be developed by NBS under a contract with EPA.

KEY WORDS:

absorption; air circulation; contaminants; emission; indoor air quality;

simulation models

ii

IAQ Modelling Workshop Report

February 11, 1985

at the National Bureau of Standards

The National Bureau of Standards, Center for Building Technology has a project funded by the Environmental Protection Agency IAG DW1 3931 103—01 —0

,

for the purpose of establishing a framework for an extensive IAQ model to

predict the levels of indoor pollutants under various conditions. In order

to receive the available technical inputs, an invited workshop was held.

Each of the participants was asked to state briefly what he is currently

doing in the modeling area, and to contribute one or more recent

publications

.

While all of the experts involved in indoor air quality modelling research

could not attend, those who did were familiar enough with prior work so

that all important facets of the problem were covered. Other modellers who

may have specific inputs were identified, and other information will be

obtained by literature search or personal contact.

The meeting attendance and a list of the recent publications are appended

to this report.

The meeting began with a welcome by Dr, Preston McNall and introduction of

the attendees. Also attached is a list of handouts brought by the

participants

.

Dr. Mage of EPA stated that a good comprehensive model is needed to:

1. Evaluate the effectiveness of various IAQ control options, such as ventilation, purification and the use of heat exchangers in terms of

energy conservation, indoor thermal comfort, material degradation and

cost/benefit analysis.

2. Evaluate the value of various test data collected for emission rate,

sink strength and diffusion rate.

3. Coordinate research programs by identifying key parameters to be

studied

.

4. Evaluate the requirements for testing instruments, e.g., the right

instrument time constant to measure a given parameter, when to

measure, how often, etc.

5. Check the measured contaminant concentration data with respect to air

flow patterns and the temperature stratification around the

instruments

.

6. Be able to create a scenario whereby different people using different

models can yield consistent answers.

1
7. Predict microenvironmental distribution of pollutant concentration,

which will dictate the sizes of space and time increments for

experimental measurements.

8. Determine the value of data collected for other purposes for model

validation.

9. Be able to evaluate unpublished and/or obscure data sets.

10. Be able to lead to the establishment of standards.

11. Be used for the risk assessment for various pollutants by being able

to predict their peak exposures which may occur in a short time period

in a microenvironment. (The model must be able to predict

microenvironmental pollutant concentration distribution.)

Dr. Moshandreas of IITRI recently completed a study on source/sink

strengths of the combustion products of furnaces, ranges, stoves, gas

heaters, kerosene heaters, gas dryers, and cigarettes. His laboratory is

engaged in testing proprietary pollutant control methods. He also studied

"sick building" problems and is developing an expert system to assist local

authorities for developing counter measures.

His model is based upon a mass balance method and incorporates a Monte

Carlo technique to account for a "surprising" user patterns for gas

appliances, which are reflected in NO 2 emission rates and personal

exposures. (People spend very little time standing at a gas range.) Dr.

Grot mentioned that the Twin River data may be useful for comparing the

user pattern.

Dr. Matthews or ORNL talked about his emission rate model for formaldehyde

as a function of room temperature, humidity and room concentration that

includes the effect of a permeation barrier. This model has been

established using test cell data. He also used the model for field

validation of ORNL's unoccupied house data and obtained good agreements.

The model assumes that the formaldehyde transfer between a material and the room air obeys Pick’s diffusion laws and is time independent.

Mr. Janssen of Honeywell is working on a ventilation efficiency model using

recirculation rate and short circuit factor of room supply air. These two

factors can be related to the Kusuda mixing factor and Sundberg’s

ventilation efficiency factor reported previously. He is currently

conducting ventilation control experiments using the C02 control in a test

house under a Bonneville Power Administration contract. A small Japanesemade C0 2 sensor is used to activate an outdoor air damper when the C02

level exceeds the set point. He is also testing a simple exhaust fan

control scheme using indoor-outdoor temperature difference and wind speed

as sensors. The latter has the possibility of being very cost effective.

Dr. Moschandreas commented that Janssen's research is appropriate for non- residential buildings where the mixing of supply air is critical. For the

residential application, however, he found that the mixing factor is near

unity as long as one is addressing the long time phenomena. Mr. Janssen

asserted that even for the steady state imperfect mixing occurs. Dr. Mage

is interested in residential applications where the short time mixing is

important

.

2
Dr. Grot of NBS talked about his current formaldehyde measurement research

for CPSC to validate Matthews’ ORNL model. His measured data is getting

good agreements with a single cell model using the ORNL emission model.

Dr. Mage mentioned the need for the model to include simulation of the

effect of air velocity in addition to temperature and humidity, citing an example that the use of a heat exchanger may create drafts undesirable for

thermal comfort. Janssen concurred that an air-to-air heat exchanger used

at the Bonneville Power Administration test building did produce

undesirable drafts as well as noise.

Dr. Ryan of the Harvard School of Public Health talked about the exposure

assessment program of a GRI contract research at Harvard and epidemo logical

studies developing the human exposure data needed for this model. He has a microcomputer program for the model developed for two compartments based

upon the mass balance principle. For some pollutants he uses empirical

data relating the indoor concentration of pollutant to outdoor

concentration in relation to air infiltration and emission rate. He also

used a Monte Carlo type analysis for simulating the usage pattern of doors

between compartments.

Dr. Nagda of Geomet showed his mass balance model that includes, among

other things, mixing factor and decay rate. The mixing factor was

determined by comparing the measured concentration of CO with the predicted

values based upon the air infiltration data obtained from the SFg decay

method. He found that the mixing factor is usually around unity when the

gas range exhaust fan is not in use. It is approximately 10 when the range

fan is in operation indicating a strong localized removal of the

contaminant. Using this mixing factor he was able to obtain a good

agreement between calculated and observed concentrations of CO. His

current research is with multizone modeling and stratification, the

effects of sources and N02 decay rate.

Dr. Davidson of Carnegie-Mel Ion University is testing three experimental

homes whose air leakage rates vary from 2 h

- "' to 0.1 h" "* . Emission rates

from stoves and gas driers are measured. Intercompartmental air movement

is also measured. Single compartment and multi-compartment models were

developed and compared with experimental results. Agreement between test

results and models depended upon the type of weather. Agreement was good

when the mixing factor was near unity and became worse when mixing factors

became different from unity. The worst agreement occurred when mixing was poor. Temperature and humidity had a large influence on N0 2 decay rate.

When stoves were turned off, N02 decayed rapidly. The decay was assumed to

be caused by surface absorption, because the infiltration rate showed only

a small effect on decay. He attempted to find re-emission phenomena by

observing the N02 decay curve, which is expected to deviate from the simple

exponential decay if there is re-emission. He was unable to find the re- emission which was similar to the experiences of Moschandreas and Ryan.

Mr. Walton of NBS presented time profiles of contaminant concentration

calculated by his multi-compartment Thermal Analysis Research Program

(TARP) model. He showed the increase and decay of contaminant

concentration in various rooms in a house when the contaminant generation

was suddenly started in the kitchen, continued with a constant rate for a while and abruptly turned off. Although the concentration levels are very

3
different among the rooms during the emission stage, the curves for the

different rooms seem to merge rapidly as soon as the source was turned off.

Grimsrud and Nagda indicated that they observed similar phenomena in their

test houses.

Dr. Persily of NBS briefly talked about his work on air leakage

measurements for large buildings, indicating its strong dependence on outdoor temperature mainly because of ventilation control schemes employed

by building mechanical systems.

Dr. Grimsrud of LBL discussed LBL activities on radon measurements and

modeling. He indicated that radon levels varied by a factor of ten even

when environmental conditions and air change rates were identical and

concluded that radon concentration is source-dominated rather than the air

leakage controlled. His associates at LBL developed a model to determine

radon migration through soils and are studying the mechanisms of the radon

entry into buildings by a pressure balance principle. He then talked about

experimental measurements of radon at sump pumps located in basements.

Water levels in the sump showed a strong correlation with house radon

levels because the high water level in the sump effectively eliminated soil

emission. He showed an interesting graph depicting lack of correlation of

measured radon levels with infiltration rates. The experimental trend can better be explained if the pressure-induced flow is assumed such that the

radon emission rate is proportional to the air infiltration rate, which is

a function of pressure difference between in and outdoors. This pressuredriven flow concept could also explain the results reported by others. He

indicated that radon levels in soil were near 1000 Pc/L while in the air

around the sump they were 500 Pc/L. The pressure differential that is

considered to influence the radon entry was in the neighborhood of 3.5 Pa.

The meeting was concluded using a list of parameters, contaminants and the

algorithms to be used in the model. After much discussion it was concluded

that the parameters to be used in a comprehensive IAQ model are:

o Forced ventilation

o Infiltration (uncontrolled leakage)

o Natural ventilation (through purposeful openings, such as windows)

o Micro-air movement within a space (including movement around a point

contaminant source such as a gas range). In this case, the ability to

model in small enough time units and grid sizes needs serious

consideration.

o Another important element of the micro-movement is the ability to

handle ventilation efficacy (defined as the ability of the ventilation

to mix, or remove at the source, the contaminants).

o Micro-air movement (room-to-room) (both horizontal and vertical

compartments should be included).

o Building architectural descriptions as they affect pollutants

- Geometry, openings, etc.

4
- Exposures to the weather.

- Ground contact.

o Weather conditions

- Outdoor micro-climate (effects of local pollution, temperature,

wind, etc.) effected by landscaping, etc.

- Correlation with weather bureau data.

o Indoor environment (temperature, humidity and other comfort

variables)

.

o HVAC systems, including humidifiers and dehumifiers as they affect

pollution levels.

o Pollution removal mechanisms (other than dilution, ventilation).

- Air treatment devices - point sinks, area sinks.

- Settling, deposition, absorption, re-emission and pollution capacity

of certain materials.

o Sources

- People, machines and people’s activities.

- Building materials.

- Consumer products.

- Outdoor air.

- Water supply

o Source strength variations - time, temperature, RH, etc.

- Point sources.

- Area sources.

- Effects permeation barriers.

- Volume source (as in radon daughters).

The most important pollutants to be treated by the IAQ model and the

available algorithms should be:

o Radon

- Source strength (temperature and pressure) (no algorithm exists).

- Decay and daughter formation (algorithm can be worked out).

- Daughter removal and decay (Jonnason has algorithms) (attached and

unattached daughters).

- Distribution in spaces (ventilation algorithms needed)

.

o Formaldehyde

- Source strength (area, temperature, humidity, space, concentration,

time history, material conditioning) (algorithms are well along).

- Distribition in the space.

- Decay, absorption, desorption (models not yet developed).

- Water as a sink (needs modelling).

o NO2 and NO

- Source strength (usage pattern and activities) (models well along)

.

- Distribution in space.

- Decay and chemical reaction (model needed)

.

5
o Tobacco smoke (sidestream only)

- Source strengths (models need more work on gaseous constituants)

.

- Decay mechanism (better model needed).

- Distribution in space.

o Particulates (other than tobacco smoke, includes biomaterials and

allergens)

.

- Source strengths (models needed)

.

- Decay, agglomeration, settling, deposition, chemical reactions, size

and shape of resuspension (some models exist, more are needed).

- Distribution in the space.

- Outdoor sources, geographical location (some models exist),

o C02 - Source strengths (people, combustion) (good models exist).

- Distribution in space.

- Absorption and desorption (some models exist),

o CO

- Source strength (good models exist).

- Distribution in space (good models exist).

o H

2 0 (not a pollutant, but its effects on pollutants needs

consideration) (H20 models are good, but the effects on pollutants are

not well modelled).

The following pollutants were considered to be important, but could not be

modelled with current knowledge, due to the complexity and number of

individual pollutants.

o Volatile Organic Compounds (VOC) (other than tobacco smoke).

- Source strengths

.

- Distribution in space.

- Decay, absorption and chemical reactions.

- Human activity and consumer products.

- Architectural materials.

o S02 - Source strengths (combustion of impure kerosene, coal and wood).

- Distribution in space.

o Pesticides

- Source strengths (no models).

- Distribution in space.

- Removal (cleaning, mopping, etc.).

The following pollutants were not to be considered, since they are too

complex, and no models exist, even though some are important.

o Asbestos (is being handled as a separate problem).

o Micro-organisms and allergens.

o Ozone

6
Dr. Moschandreas questioned the value of multi-nodal models contending that

his model is based on the single node analysis and appears to be adequate.

Mage again stressed the importance of multi-nodal models that account for

stratification and local high concentration of contaminants occuring in

short time intervals.

Dr. Matthew asked; "Are we developing a model applicable to all the

pollutants or different models for different pollutants?" Certain

pollutants do not require a complex model, while others do. He suggested a series of models for different mechanisms, such as source models,

ventilation models, mixing models and feedback models. Responding to

Silberstein's question, Matthew explained a fact that the emission rate of

a contaminant may be dependent upon its own concentration and he was

assured that the feedback is usually included in the general mass balance

model

.

Responding to Nagda's question on the f loor-to-f loor migration calculation,

Walton indicated that the TARP model already includes that. Mage stressed

the importance of micro environmental models to be able to simulate the

performance of small personal monitor; where readings at the breathing zone may be dependent upon the size and shape of the wearers.

Other points raised during the discussion were:

1. Absorption and re-emission should be time dependent functions.

2. Pollutant storage in the sources and air should be considered.

3. The radon model requires different treatments for attached and

unattached fractions.

Dr. Moschandreas cited a recent paper by Jonnesson dealing with this

subject

.

It is difficult to measure the source strength of radon and no good model

exists to determine the source strength, although the models are

sufficiently good for simulating radon decay and daughter formation.

Radon emission rate from water is well known according to Grimsrud. David

Harrje of Princeton University is believed to have good data on this

subject

.

4. Is the Pick's law adequate for permeation barrier models?

5. Is the measurement accuracy good enough to see the effects of air

speed over the contaminant emitting surface?

6. Effect of conditioning specimens ... the past history of building

products containing formaldehyde as well as the temperature and

humidity affect their present source emission rate.

7. Volatile organic compounds (VOC) need categorization because there are so many of them involved. They are generated by various household

activities, such as cleaning, hair spraying and furniture polishing.

7
Yet we know little about any of these contaminants; some are very

transitory some vary with occupants’ activities, some are

internal ly generated. A suggested classification is to categorize

them by whether or not they are due to combustion. Measurements for

combustion-based contaminants showed emission rates to vary by a factor of 2 even under supposedly similar conditions.

Outside contaminants from automobile exhaust and gasoline spills

originating in attached garages were mentioned as a potential problem.

8. Tobacco smoke: Although it is believed that we know much about the

source strength of tobacco smoke, its gaseous source characteristics

are not well understood. It is believed to contain over 2000

compounds including formaldehyde (later someone mentioned over 30,000

compounds referring to a National Cancer Institute study). If five

measurements were taken, five different answers would result.

The modellers are interested in the passive smoking aspects.

Moschandreas is conducting a passive smoking study. His study

revealed that smokers indicated that they smoked fewer cigarettes than

they actually did by count, while non-smokers indicated more were

smoked than actual.

9. Mulligan mentioned that some contaminants sources are interactive.

Some are source-specific contaminants and some sources are connected

to many other contaminants.

10. Particulate sources are not well defined: There are many factors to

be considered, such as outdoor sources, vacuum cleaners, humidity

effects, air motion, solid surface friction, and geographic elements.

11. When considering C02 emission, oxygen depletion becomes important for

unvented combustion appliances in a small enclosure.

12. CO is a "beautiful” pollutant to study, because it is easy to measure

and non-reacting.

A list of recent publications handed out follows.

8
LIST OF PUBLICATIONS

"Estimated Distributions of Personal Exposure to Respirable Particles", by

Richard Letz, P. Barry Ryan, and John D. Spengler. Department of

Environmental Science and Physiology, Harvard School of Public Health.

"The Effects of Kerosene Heaters on Indoor Pollutant Concentrations: A

Monitoring and Modeling Study," by P. Barry Ryan, John D. Spengler and

Richard Letz.

"A Computer Algorithm for Estimating Infiltration and Inter-Room Air

Flows," by George N. Walton.

"Formaldehyde Emissions from Combustion Sources and Solid Formaldehyde

Resin Containing Products: Potential Impact on Indoor Formaldehyde

Concentrations and Possible Corrective Measure," by T. G. Matthews, T. J. Reed, B. J. Tromberg, C. R. Daffron, and A. R. Hawthorne. Sponsored by

CPSC. Preprint: Proceedings of the ASHRAE Symposium, "Management of

Atmospheres in Tightly Enclosed Space," Santa Barbara, 10/83.

"Ventilation Stratification and Air Mixing," by John E. Janssen, Honeywell,

Inc., St. Paul, MN, USA.

"Environmental Dependence of Formaldehyde Emissions from Pressed Wood

Products: Experimental Studies and Modeling," by T. F. Matthews, T. J.

Reed, C, R. Daffron, and A. R. Hawthorne, Measurement Applications Group,

Health and Safety Research Division, Oak Ridge National Laboratory.

Sponsored by CPSC. Proceedings: 1 8th International Washington State

University, Particleboard/Composite Materials Symposium.

"Radon Transport Into a Single-Family House with a Basement," by W. W.

Nararoff, H. Feustel, A. V. Nero, K. L. Revzan, D. T. Grimsrud, M. A.

Essling, and R. E. Toohey. To be submitted to Atmospheric Environment

January 1984.

Geomet Report Number ERF-1461, August 1984, "Energy Use, Infiltration, and

Indoor Air quality in Tight, Well-Insulated Residences", by Niren L. Nagda,

Ph.D., Michael D. Koontz, M.S., and Harry E. Rector, B.S. Prepared for

Energy Analysis and Environment Division and Energy Management and

Utilization Division, Electric Power Research Institute, Inc.

9
Attendance Record for the Meeting on IAQ Modeling

February 11, 1985

Cliff Davidson

David Grimsrud

Richard Grot

John Janssen

James J. Keenan

Tamami Kusuda

Brian Leaderer*

David Mage

Thomas Matthews

P. E. McNall

D. J. Moschandreas

J. L. Mulligan

Niren Nagda

Room B221 of Building 226

National Bureau of Standards

Dept, of Civil Engineering

Carnegie-Mellon University

Pittsburgh, PA 15213

Lawrence Berkeley Labartory

90/058

Berkeley, CA 94720

National Bureau of Standards

Building 226 , Room B114

Gaithersburg, MD 20899

Honeywell, Inc., TSC

1700 W. Highway 36

St. Paul, MN 55113

CPC ESES

Washington, DC 20207

National Bureau of Standards

Building 226, Room B218

Gaithersburg, MD 20899

John B. Pierce Foundation

290 Congress Avenue

New Haven, CT 06519

U.S. EPA

EMSL/RTP MAD/MD-56

412-578-2951

415-486-6591

301-921-3501

612-638-5985

301-492-6508

301-921-3637

203-562-9901

919-541-3184

Oak Ridge National Laboratory

Building 4500 South

Oak Ridge, TN 37831

National Bureau of Standards

Building 226 , Room B226

Gaithersburg, MD 20899

IIT Research Institute

Chicago, IL 60616

CPSC ESES

Washington, DC 20204

Geomet

20251 Century Blvd.

Germantown, MD 20874

615-574-6248

301-921-3447

312-567-4310

301-492=6508

301-428-9898

1 0
Andrew Persily National Bureau of Standards 301 - 921-2330

Building 226 , Room B114

Gaithersburg, MB 20899

P. Barry Ryan Harvard School of Public Health 617-732-1431

677 Huntington Avenue

Boston, MA 02115

Samuel Silberstein National Bureau of Standards

Building 226, Room B114

Gaithersburg, MD 20899

Kevin Teichman Dept, of Energy

Washington, DC

301-921-2758

202-252-9187

George Walton National Bureau of Standards 301-921-3633

Building 226 , Room B114

Gaithersburg, MD 20899

•Brian Leaderer's inputs were received later in the evening of Febraury 11,

due to a travel delay.

'0«M NBS-1 14A REV 1 1 84)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See i nstruction s)

1. PUBLICATION OR

REPORT NO.

NBSIR 85-3150

2. Performing Organ. Report No 3. Publ ication Date

May 1985

4. TITLE AND SUBTITLE

Indoor Air Quality Modeling Workshop Report

5. AUTHOR(S)

Preston E. McNall

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State. ZIP)

Environmental Protection Agency

Research Triangle Park

North Carolina

io. supplementary notes

_ Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. I f document includes a significant

bi bl iography or literature survey, mention it here)

Comprehensive modeling of emission, absorption, movement and controls of indoor

air contaminants is essential for developing national policy for IAQ assessment

and controls. This report describes several topics discussed in a workshop on indoor air quality, which was held on February 11, 1985 at the National Bureau

of Standards. Researchers on IAQ modeling were invited to state their current

activities, identify future research needs and recommend specific parameters and

contaminants to be included in the IAQ models. The input thus obtained in this

workshop will be incorporated in an advanced simulation model for IAQ, to be

developed by NBS under a contract with EPA.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate <e / absorption; air circulation; contaminants; emission; indoor air qualif;

simulation models

13. AVAILABILITY

j—X] Uni imited

| j For Official Distribution. Do Not Release to NTIS

T Order From Superintendent of Documents, U.S. Government Printing Office, Washington. DC

20402.

[_X\ Order From National Technical Information Service (NTIS), Springfield, VA 22l6 ;

14. NO. OF

PRINTE!

15. Pr