United States EPA-600/R-00-094
Environmental Protection
A9encv October 2000
&EPA Research and
Development
SIMULATION TOOL KIT FOR
INDOOR AIR QUALITY AND
INHALATION EXPOSURE (IAQX)
VERSION 1.0
USER'S GUIDE
Prepared for
National Risk Management Research Laboratory
Prepared by
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
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FOREWORD
The U. S. Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources, protection of water quality in public water
systems; remediation of contaminated sites and-groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
EPA REVIEW NOTICE
This report has been peer and administratively reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161.
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EPA-600/R-00-094
October 2000
Simulation Tool Kit for
Indoor Air Quality and Inhalation Exposure (IAQX)
Version 1.0
User's Guide
Prepared by
Zhishi Guo
United States Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Air Pollution Prevention & Control Division
Indoor Environment Management Branch
Research Triangle Park, NC 27711
Prepared for
United States Environmental Protection Agency
Office of Research and Development
Washington, DC 20460
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DISCLAIMER
This software was developed by the U.S. Environmental Protection Agency for its own
use and for specific applications. The Agency makes no warranties, either expressed or implied,
regarding this computer software package, its merchantability, or its fitness for any particular
purpose, and accepts no responsibility for its use. Mention of trade names and commercial
products does not constitute endorsement or recommendation for use.
ABSTRACT
A Microsoft Windows-based indoor air quality (IAQ) simulation software package is
presented. Named Simulation Tool Kit for Indoor Air Quality and Inhalation Exposure., or
IAQX for short, this package complements and supplements existing IAQ simulation programs
and is designed mainly for advanced users. IAQX version 1.0 consists of five stand-alone
simulation programs. A general-purpose simulation program performs multi-zone, multi-
pollutant simulations and allows gas-phase chemical reactions. The other four programs
implement fundamentally based models, which are often excluded in the existing IAQ simulation
programs. In addition to performing conventional IAQ simulations, which compute the time-
concentration profile and inhalation exposure, IAQX can estimate the adequate ventilation rate
when certain air quality criteria are provided by the user, a unique feature useful for product
stewardship and risk management. IAQX will be developed in a cumulative manner and more
special-purpose simulation programs will be added to the package in the future.
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TABLE OF CONTENTS
DISCLAIMER -ii-
ABSTRACT -ii-
LIST OF FIGURES -vi-
LIST OF TABLES -viii-
CHAPTER ONE. INTRODUCTION -1-
1.1 WhatlsIAQX? -1-
1.2 What's In IAQX? -2-
1.3 Basic Framework -3-
1.4 About This Guide -4-
CHAPTER TWO. GETTING STARTED -6-
2.1 System Requirements -6-
2.2 Install IAQX -6-
2.3 Uninstall IAQX -6-
2.4 User-Interface Design -6-
2.5 How to Start and Exit an IAQX Program -7-
2.6 The Four-Step Procedure for a Simulation -8-
2.7 Storage of IAQ Models -8-
2.8 On-line Help -8-
2.9 Contacting the Developer -9-
CHAPTER THREE. THE GENERAL-PURPOSE SIMULATION PROGRAM (GPS.EXE) -10-
3.1 Program Description -10-
3.2 A Brief Tour of the Program -10-
3.2.1 Start the Program -11-
3.2.2 Define the IAQ Model -11-
3.2.3 Compile the Model -15-
3.2.4 Make the Simulation -16-
3.2.5 Examine the Results -16-
3.2.6 Calculate Inhalation Exposure -16-
3.2.7 Calculate the Adequate Ventilation Rate -16-
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3.2.8 Save Your IAQ Model -18-
3.3 More About the GPS Program -18-
3.3.1. Define the Ventilation Rate -18-
3.3.2 Add Pages -23-
3.3.3 Source Models -24-
3.3.4 Sink Models -25-
3.3.5 Models for Air Cleaners -26-
3.3.6 Chemical Reactions -26-
3.3.7 Defining the HVAC System -28-
3.3.8 Time-Varying Sources -29-
3.3.9 Non-Zero Initial Concentrations -29-
CHAPTER FOUR. MODELS FOR VOC EMISSIONS FROM SOLVENT-BASED
INDOOR COATING PRODUCTS (VBX.EXE) -31-
4.1 Model Description -31-
4.1.1 Overview -31-
4.1.2 The VB Model for TVOCs -32-
4.1.3 The VBX Model for Individual VOCs -32-
4.1.4 The First-Order Decay Model for Individual VOCs -33-
4.1.5 Estimation of the Total Vapor Pressure and Average Molecular Weight for
TVOCs Based on the VOC Contents in the Product -33-
4.1.6 Model for Estimating Gas-Phase Mass Transfer Coefficient -34-
4.2 A Brief Tour of the Program -34-
4.3 More About the VBX Program -41-
4.3.1 What If a VOC Does Not Exist in the VOC Database? -41-
4.3.2 About the MSDS Option -41-
4.3.3 Adding Sink Models -43-
CHAPTER FIVE. MODELS FOR SMALL-SCALE SOLVENT SPILLS (SPILL.EXE) . . . -45-
5.1 Model Description -45-
5.1.1 Model for Single-Component Solvent -45-
5.1.2 Model for Solvent Mixture Whose Exact Composition Is Known -45-
5.1.3 Model for Petroleum-Based Solvent -46-
5.1.4 Estimation of the Spill Area -47-
5.2 A Brief Tour of the Program -47-
5.3 More About the SPILL Program -50-
5.3.1 Adding Sink Models -50-
5.3.2 Comparison of the Two Methods for Estimating the Gas-Phase Mass
Transfer Coefficient -50-
5.3.3 Dealing with the Temperature Drop -51-
5.3.4 About the Short Circuiting Factor -52-
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CHAPTER SIX. A MODEL FOR VOC EMISSIONS FROM DIFFUSION-CONTROLLED
HOMOGENEOUS SLABS (SLAB.EXE) -53-
6.1 Model Description -53-
6.2 A Brief Tour of the Program -55-
6.3 More About the SLAB Program -56-
6.3.1 Model Parameters for New Carpet Backing -56-
6.3.2 Dealing with Zero Ventilation Rate -56-
6.3.3 Source Reduction Simulation Mode -56-
CHAPTER SEVEN. A MODEL FOR INDOOR PARTICULATE MATTER (PM.EXE) . . -58-
7.1 Model Description -58-
7.2 A Brief Tour of the Program -59-
7.3 More About the PM Program -63-
7.3.1 Calculation of PM Deposition Rate -63-
7.3.2 PM Source Types -64-
7.3.3 Adding Pages -65-
7.3.4 HVAC Filters, Interzone Filters, and Free-Standing Filters -65-
CHAPTER EIGHT. INSIDE IAQX -67-
8.1 Programming Language -67-
8.2 Method for Numeric Integration -67-
8.3 Algorithm for Application-Phase Simulation -67-
8.4 Algorithm for Estimating Adequate Ventilation Rate (AVR) -69-
8.5 Handling of Time-varying Parameters -69-
ACKNOWLEDGMENTS -71-
REFERENCES -72-
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LIST OF FIGURES
Figure 2.1 The user interface of the GPS program -7-
Figure 3.1 The main window of the GPS program -12-
Figure 3.2 The layout of the Sources page of the GPS program -13-
Figure 3.3 Layout of the model entry dialog box of the GPS program -14-
Figure 3.4 The GPS' Sources page after adding a source model -15-
Figure 3.5 GPS dialog box for estimating the adequate ventilation rate -18-
Figure 3.6 Constant ventilation mode in the GPS program -19-
Figure 3.7 Cyclic ventilation mode in the GPS program -20-
Figure 3.8 Concentration profile generated by a constant source under
the cyclic ventilation mode -21-
Figure 3.9 Comparison between the two time-varying flow modes -23-
Figure 3.10 Diagrammatic description of the air handling system -28-
Figure 3.11 The layout of the Input Data page of the GPS program -29-
Figure 3.12 Layout of the Conditions page of the GPS program -30-
Figure 4.1 The main window of the VBX program (showing the Building page) -35-
Figure 4.2 Layout of the Ventilation page of the VBX program: -36-
Figure 4.3 Layout of the VOC Contents page of the VBX program -37-
Figure 4.4 Dialog window for the built-in database of the VBX program -39-
Figure 4.5 Layout of the VOC Contents page of the VBX program -40-
Figure 4.6 Layout of the Source page ofthe VBX program -41-
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Figure 4.7 Layout of the VOC Contents page when the MSDS option is selected -42-
Figure 4.8 Defining the application-phase simulation in the Conditions page -43-
Figure 4.9 Layout of the Sink page of the VBX program -44-
Figure 5.1 Layout of the Solvent page of the SPILL program -48-
Figure 5.2 Layout of the Source page of the SPILL program -49-
Figure 5.3 Comparison of the gas-phase mass transfer coefficient for decane estimated
by the two methods -51-
Figure 6.1 The main window of the SLAB program -55-
Figure 6.2 The SLAB dialog box for the Source Reduction simulation mode -57-
Figure 7.1 Layout of the Building page of the PM program -59-
Figure 7.2 Layout of thePM Properties page of the PM program -60-
Figure 7.3 Layout of the Outdoor Sources page of the PM program -61-
Figure 7.4 Layout of the Indoor Sources page of the PM program -62-
Figure 7.5 Layout of the Conditions page of the PM program -63-
Figure 7.6 Possible filter positions in three-zone (zone 1, zone 2, and HVAC) configuration. -66-
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LIST OF TABLES
Table 1.1 Programs included in IAQX version 1 -2-
Table 1.2 Candidate simulation programs for future inclusion in IAQX -3-
Table 2.1 Default file extensions for IAQX programs -8-
Table 3.1 Main features of the GPS program -10-
Table 3.2 Time-varying ventilation mode in the time/flow format (one zone) -22-
Table 3.3 Time-varying ventilation mode in the duration/flow format (one zone) -22-
Table 3.4 Source models available in the GPS program -25-
Table 3.5 Sink models available in the GPS program -26-
Table 3.6 Air cleaner/filter models available in the GPS program -26-
Table 4.1 User input required by the VBX program -32-
Table 4.2 Differences between the two VOC data options -38-
Table 7.1 An example data input for the on/off source type -65-
Table 7.2 An example data input for the time-varying source type -65-
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CHAPTER ONE
INTRODUCTION
1.1 What Is IAQX?
IAQX is short for Simulation Tool Kit for Indoor Air Quality and Inhalation Exposure. It
is a Microsoft Windows-based indoor air quality (IAQ) simulation package consisting of a
general-purpose simulation program and a series of stand-alone, special-purpose programs.
Estimation of inhalation exposure to indoor air pollutants is an essential part of multi-
pathw ay expo sure a ssess ment s ince m ost pe ople s pend a large p ortio n of th eir ti me ind oors. In
the past two decades, a series of IAQ simulation programs have been developed. Insightful
reviews of major software packages are given by Austin, et al. (1992) and Rector and Koontz
(1993). More recent developments include several Microsoft Windows-based IAQ simulation
programs such as RISK (Sparks, 1996), MEDB-IAQ (Zhang, et al., 1999), MCCEM (Koontz and
Wilkes, 1999), and CONTAMW (Dols, et al., 2000). In-depth theoretical discussions on the
framework of IAQ modeling and simulation have also been reported (Axley, 1995; Van Loy, et
al., 1998).
IAQX is not intended to replace the existing IAQ simulation packages. Instead, it
complements and supplements them by focusing on fundamentally based models. In recent
years, modeling of indoor pollutant sources and sinks has gradually shifted from simple,
empirical models to more complex, mass transfer models. While the latter have demonstrated
improved accuracy, validity, and scalability, their usefulness has somewhat been overshadowed
by their increased complexity. Potential users are often scared away at the sight of unfamiliar
equations and tedious calculations. To a large extent, the newer models are excluded in the
existing IAQ simulation packages. IAQX attempts to resolve this problem by shielding users
from mathematical details, allowing them to concentrate on IAQ related issues. IAQX puts
relatively simple mass transfer models in the general-purpose simulation program; more complex
models are implemented as stand-alone, special-purpose simulation programs.
In addition to performing the conventional IAQ simulations, which calculate the
pollutant concentration and/or personal exposure as a function of time, IAQX can estimate the
adequate ventilation rate when certain air quality criteria need to be satisfied. This unique feature
is useful for product stewardship and risk management.
IAQX is designed mainly for advanced users, those who are directly involved in exposure
estimation, pollution control, risk assessment, and risk management. Users are encouraged to
look into other available IAQ simulation programs to find ones that are most suitable to their
specific needs.
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1.2 What's In IAQX?
IAQX version 1 consists of five stand-alone programs: one is for general-purpose
simulation, and four are for special-purpose simulation (see Table 1.1). This software package
will be developed in a cumulative manner. More special-purpose programs will be added in the
future. Table 1.2 lists five programs that are currently under consideration for future inclusion in
IAQX.
Table 1.1 Programs included in IAQX version 1.
No.
1
2
O
4
5
Program
GPS.EXE
VBX.EXE
SPILL.EXE
SLAB .EXE
PM.EXE
Purpose
A general-purpose simulation
program
Models for predicting VOC
emissions from solvent-based indoor
coating materials based on product
formulation
Models for indoor solvent spills
A model for VOC emissions from
diffusion-controlled homogeneous
slabs such as new carpet backing
A model for indoor parti culate
matter
Reference
Guo (1996)
Guo, etal. (1999)
Reinke and Brosseau
(1997); Drivas (1982)
Little, etal. (1994)
Nazaroff and Cass
(1989)
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Table 1.2 Candidate simulation programs for future inclusion in IAQX.
No.
6
7
8
9
10
Program
PEST.EXE
WBC.EXE
WATER.EXE
CHEM.EXE
LATEX.EXE
Purpose
Fugacity models for indoor
application of pesticides
Models for VOC emissions from
indoor use of water-based cleaners.
For VOC emissions from clean water
use indoors (e.g., washing machine
and dish washer)
A model shell for indoor air
chemistry
Models for VOC emissions from
latex paint.
Reference
Matoba, etal. (1998)
To be determined
Howard and Corsi
(1998)
Not applicable
To be determined
1.3 Basic Framework
Like most IAQ models, the IAQX programs assume that a building is divided into air
zones and that, within each zone, the air is well mixed. For a given air pollutant, its
concentration in a given air zone i is determined by:
dC< V n ^ -, V ^
-JT = S ^ + P Q* Co + I Sfa-
ai j-i t-i
15 a Q -1 ^ ^ /(Q)
ft-0
Z-l
L-l
P-l
"
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nz = number of air zones;
Qkl = air flow rate from zone k to zone i and k * i (m3/h);
Ck = pollutant concentration in zone k (mg/m3);
Qlk = air flow rate from zone i to zone k and k * i (mVh);
ns = number of interior surface types;
SL = surface area for interior surface L in zone i (m2);
kaL = adsorption rate constant for surface L, whose unit depends on f(Q);
f(Cj) = certain function of Q;
kdL = desorption rate constant for surface L, whose unit depends on f(ML);
ML = amount of pollutant adsorbed on surface L (mg/m2);
f(ML) = certain function of ML;
nf = number of air filters/cleaners associated with zone i;
Rp = pollutant removal efficiency for air filter/cleaner p (unitless);
Qp = air flow rate passing through air filter/cleaner p (m3/h);
nx = number of gas-phase chemical reactions which either consume or produce the
pollutant; and
Xq = rate of chemical reaction q (mg/m3/h in Eq. 1.1; mole/m3/h in simulation).
Eq. 1.1 represents a system of ordinary differential equations that, in most cases, require
numerical solutions. The number of differential equations in the system depends on the
complexity of the IAQ model and is limited to 100 or less in IAQX. The primary simulation
output is a time-concentration table, from which personal inhalation exposure can be calculated:
(1.2)
*x ^B A 2
where ^ = inhalation exposure (mg);
RB = breathing rate (m3/h);
n = number of data points in the time-concentration table;
C, = concentration at time t, (mg/m3); and
C1+1 = concentration at time t1+1 (mg/m3).
1.4 About This Guide
This User's Guide consists of eight chapters. Chapter 1 -Introduction - gives an
overview of the software package. The user is urged to go through this chapter at least once.
Chapter 2 — Getting Started - contains information about software installation/uninstallation,
descriptions of the user interface, and ways to contact the developer. Chapters 3 to 7 are detailed
descriptions of individual IAQX programs. Each chapter is divided into three sections, an
overview, a brief tour of the program, and discussions on more features. These five chapters are
pretty much independent of each other. Thus, if you are interested in a particular program, go to
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that chapter directly. However, you should go though Section 3.2 at least once because basic
skills for using IAQX are introduced there. Chapter 8 -Inside IAQX- contains in-deplh
information about the development of IAQX including several key simulation techniques. Those
who write IAQ simulation programs of their own may find this chapter useful.
IAQX implements published models only. A complete list of references is provided at
the end of this Guide. The user is encouraged to read the original papers for more information
about the models.
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CHAPTER TWO
GETTING STARTED
2.1 System Requirements
Intel Pentium 90 or higher;
Microsoft Windows 95, 98, or NT 4.0;
16 Mb of RAM;
5 Mb hard disk space;
CD-ROM drive (for installation);
VGA or higher resolution monitor; and
Mouse or other pointing device.
2.2 Install IAQX
Installing the IAQX programs to your computer is fairly easy. Simply insert the program
CD in your CD-ROM drive. In some PC systems, the setup program will launch automatically.
If not, you have two options: (1) go to the Windows' Control Panel, select Add/Remove
Programs, and then click on the Install button or (2) use the Windows Explorer to find the
SETUP.EXE file in the program CD and then double click on it.
2.3 Uninstall IAQX
To uninstall IAQX programs, go to the Windows' Control Panel, select Add/Remove
Programs, and then click on the Uninstall button. Select IAQX from the program list and click
OK.
2.4 User-Interface Design
All IAQX programs have similar user interfaces. The basic screen layout is based on
multipage tabbed windows. Figure 2.1 shows the main window of the GPS program with five
pages visible, identified by tabs. Be aware that most IAQX programs have one or more hidden
pages, which are less commonly used and only become visible at the user's request. For
example, program GPS has three hidden pages, designated to sink, air filter/cleaner, and gas-
phase chemical reactions, respectively. They can be accessed by clicking the Add pages speed
button (i.e., the one with a red # sign). For specific features of each program, see corresponding
chapter for details.
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Title bar
Menu bar
Speed buttons
Page tabs
Status bar
Fie Model Simulate graphics Tools hMf:
IF&\ a] ga| il y| .1.1 M!
Bulding Ventilaliori Sources | Ccnditonsj OjtputJ
PNote Pad ' Building Cortfiguratoin '
Vour note goes here. ' \
Ho. of Air Zone(s)
Zone ID Zon5 EJaHie Volume (m;)
Ni,. r,t Sink Miit«rial(s)
p f JJ — g
Current page: Buldinj . | |[jj|[j| ft | | J_ IJose |
Previous page button
page button
cloge
Figure 2.1 The user interface of the GPS program.
2.5 How to Start and Exit an IAQX Program
To start a program, select IAQX from the Windows' Programs list and then click on one
of the program icons. After the welcome window is displayed, click the OK button to enter the
main window.
There are three ways to exit a program: (1) select File/Exit from the main menu, (2) click
the Close button near the bottom-right corner, or (3) click the Close Window button at the top-
right corner (i.e., the one with a X sign).
Keep in mind that a simulation may go wrong from time to time. A relatively benign
failure can be identified by unintelligent output. For instance, the output values look too large,
too small, negative, or zigzagging. In most cases, it is caused by unrealistic model parameters.
Check your input carefully and make changes if necessary. Sometimes, a program may fail to
respond to your command, which is often an indication of more serious problems. To shut down
the program, press Control-Alternate-Delete keys simultaneously. After the Close Program
window appears, select the program you want to stop and then click the End Task button.
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2.6 The Four-Step Procedure for a Simulation
With IAQX it takes four steps to make an IAQ simulation: define the IAQ model,
compile the model, make the simulation, and examine the results. These steps are discussed in
detail in Section 3.2 by using the general-purpose simulation program as an example. The user
should go through Section 3.2 at least once because the basic skills apply to the rest of the
programs as well.
2.7 Storage of IAQ Models
The user-created IAQ models can be saved to a disk file, which can be retrieved later.
This feature allows the user to define a building environment only once. It is important to know
that each IAQX program has its own default file extension (Table 2.1). An error-checking
procedure prevents an IAQX program from opening a file created by other IAQX programs or
other applications.
Table 2.1 Default file extensions for IAQX programs.
Program
GPS.EXE
VBX.EXE
SPILL.EXE
SLAB. EXE
PM.EXE
File Extension
.IAQ
.VBX
.SPL
.SLB
.PM
User-specified file extensions are allowed, but not preferred. To open a model file with
your own file extension, follow these steps: click the Open file speed button (or File/Open from
the main menu); find the File Type box near the bottom; select "Any files"; select the model file
by clicking on it; and click the Open button.
2.8 On-line Help
On-line help is available in all IAQX programs. It can be accessed by clicking Help from
the main menu. Typical items in the Help submenu include "Model description," "How-to's,"
"About IAQX," and "About this program." In addition, many pages have one or more Help
buttons, which provide hints to specific items in that page.
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2.9 Contacting the Developer
The user is encouraged to report bugs and other problems associated with this package.
In return, the user will receive a copy of the programs and/or the User's Guide with errors
corrected. The user will also be informed of any future developments of IAQX.
Limited technical support is available on a first-come-first-served basis. Be aware,
however, that the developer does not guarantee, nor is he obligated, to answer all the user
inquiries in a timely fashion.
In either case, the developer can be reached by mail, e-mail, or facsimile:
Zhishi Guo
MD-54
Air Pollution Prevention and Control Division
U.S. EPA
Research Triangle Park, NC 27711
U.S.A.
E-mail: guo.zhishi@epa.gov
Fax: 919-541-2157
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CHAPTER THREE
THE GENERAL-PURPOSE SIMULATION PROGRAM (GPS.EXE)
3.1 Program Description
Program GPS is a multizone, multipollutant simulation program, with which the user can
develop and execute a wide range of IAQ models. Simple mass-transfer models are all
implemented here. Program specifications are provided in Table 3.1.
Table 3.1 Main features of the GPS program.
Feature
Number of air zones
Number of sink materials
Ventilation modes
Number of HVAC systems
Number of source models
Number of sink models
Number of air filter models
Maximum number of chemical reactions
Non-zero initial concentrations
Simulation period
Simulation output
Limit
Ito 10
0 to 3 in each air zone
constant, cyclic, time/flow, and
period/flow
1
26
5
2
5
allowed
user specified
concentration, inhalation exposure,
and adequate ventilation rate
3.2 A Brief Tour of the Program
This section gives you a first look at the program and introduces you to basic skills
needed to work with the GPS program. Discussions on more advanced features are provided in
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Section 3.3.
3.2.1 Start the Program
To start the GPS program, select the IAQX folder from the Windows' Programs menu
and then click the GPS icon. The first you see is a welcome window, in which the program title
is displayed. To enter the program's main window, click the OK button. As you have seen in
Figure 2.1, the main components of the window include (from top to bottom): the title bar, main
menu, speed buttons, desk top area, and status bar.
The speed buttons provide quick access to frequently used menu items. Place the mouse
cursor over a speed button and leave it there for a second, a small help window will appear to
remind you of what the button does.
For clarity and easy access to all parts of the program, IAQX adopts a user-interface
design called multipage tabbed windows. In GPS you can see five pages, identified by the tabs.
They are: Building, Ventilation, Sources, Conditions, and Output. To turn to a page, simply click
on the tab. You can also use the two arrow keys on the bottom to turn one page atime.
As mentioned in Chapter 2, it takes four steps to complete an IAQ simulation with the
IAQX programs: define the IAQ model, compile the model, make the simulation, and examine
the results. These steps and several more features are explained in Sections 3.2.2 to 3.2.8.
3.2.2 Define the IAQ Model
When defining an IAQ model, you should always start from the first page, where the
basic structure of your model is laid out (Figure 3.1). The first thingyou need to do is to specify
the number of air zones in your model. You can have up to 10 air zones, although most IAQ
models contain only one, two, or three zones. Click the up/down arrows to adjust the value.
Note that, when you change the zone number, the size of the Building Configuration table
changes accordingly. After the zone number is selected, move to the Building Configuration
table, where the name and volume (m3) of each zone are defined. If you consider the heating,
ventilation, and air-conditioning (HVAC) system as an air zone, define it as the last zone and
name it either "HVAC" or "HAC." See Section 3.3.7 for more information about representation
of the HVAC system.
An IAQ model is often considered inadequate nowadays without consideration of the sink
effect. GPS allows each zone to have up to three sink materials. The default value is zero.
When you change the number of sink materials, the Building Configuration table expands
horizontally and the sink areas must be entered. In this brief tour, let's keep it simple by leaving
alone the default value (zero) for the sink materials.
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STKi 1.0 / Progiam GPS NoN ame. IAQ
File Model l,'mu'a'e iI.raP^'cs X°°'£ He'P
_BJ _B] JSJ
Building I Ventilation | Sources] Conditions] Output)
Note Pad
Building Configuration
Tour note goes here.
Define zone number here
_J
Zone ID Zone Name Volume fms)
[I] MBH^^^Iiao
Define building
features here
Define sinks here
No. of Air Zane(s)
No. of Sink Material(s)
Current page: Building
Jl
Figure 3.1 The main window of the GPS program.
The note pad on the left is a text editor where you can make notes. It is always a good
practice to describe your IAQ by words, and perhaps to record the date and time as well. Delete
the default text and add a few words of your own if you wish. You are now finished with the
first page.
Click the Ventilation tab or click the Next Page button (the one with a right-arrow logo)
to move to the next page. When you define the ventilation rate flow rates, remember that the
outdoor air is always designated zone 0. IAQX allows four types of air exchange data: constant,
cyclic, time-varying in time/flow format, and time-varying in period/flow format. See section
3.3.1 for more details about how to use these flow modes. The default setting is the constant
flow mode, meaning that the ventilation rate does not change over time. Again, we'll use the
default values for this demonstration.
Most IAQ models contain one or more emission sources. In GPS they are defined in the
Sources page. As shown in Figure 3.2, there are four buttons on the right panel: Add, Delete,
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Modify, and Help. To add a source, click the Add button. A dialog box will appear to show the
categories of source models. Select a category then click the Select button. Or you can simply
double-click on the selected item. If you want to add a first-order decay model to your IAQ
model, select category 2 - "first-order & higher order models." A new dialog box will appear to
show all the models in this category. Select the first model (No. 21) by clicking on it and then
click the Continue button to bring up the model entry window. As you can see in Figure 3.3, this
dialog box contains all the information you need to define the source model.
STKi 10 / Program GPS NoName IAQ
File Model .Simulate jGraphics Jools Help
ll vl
Building Ventilation Sources Conditions Output
Source Models
Description
Pollutant Zone Param 1 Pararn 2 P
LUJ
Current page: Sources
JL Close
Figure 3.2 The layout of the Sources page of the GPS program. The source model table is empty.
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J*JAdd a source model
Model Description
Source Model 21
First-order decay (E0/k)
Model Parameters
S
EO
10
R(t) = S E0 e
-k.t
J500
BIT
where
R(t) = emission rate at time t(rng/h);
S = source area (m2);
Eg = initial emission factor (mg/m2/h);
k = decay constant (h ); and
t = time (h).
Notes:
Application-phase simulation is available.
-Application-Phase Simulation-
No r Yes
Pollutant Name
Location (zone)
VOC1
Start Time
Remove Time
0.0
1E10
% Apply
X Cancel
Figure 3.3 Layout of the model entry dialog box of the GPS program.
On the left is a text box containing the description of the model. Below it, the pollutant
name and the source location are defined. Let's change the pollutant name from VOC1 to
TVOC. Note that pollutant names are not case-sensitive. For instance, TVOC, Tvoc, and tvoc
are considered identical by the program.
The next step is to enter the model parameters on the right panel. Be aware that the
default values serve only as a starting point and that they do not represent the real source you are
dealing with. It is your responsibility to enter the correct values.
After entering the parameters (S, E0, and k in this case), click the Apply button. The
source model will be added to the Sources page (Figure 3.4). You can add a virtually unlimited
number of sources to your IAQ model. Available source models in GPS are listed in Section
3.3.2.
To delete a source model from the table, click a cell in the row that you want to delete,
and then click the Delete button. To modify or review a model in the table, select the item, then
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click the Modify button (or simply double-click on the item) to bring back the model entry dialog
box.
/' STKi 1.0 / Piogiam GPS NoName IAQ
File Model Simulate graphics Jools JHelp
Building Ventilation Sources Conditions Output
Source Models
Item Type Description
Pollutant Zone
Param 1 Param 2
21
First-order decay (EO/k)
TVOC
10
500
LLJJ
Current page: Sources
Figure 3.4 The GPS' Sources page after adding a source model.
Let's move to the Conditions page, where the user specifies the simulation period and
number of data points in the output. If your model has non-zero initial concentrations, they
should be entered here, too (see Section 3.3.9). For this demonstration, keep the default values.
3.2.3 Compile the Model
Now you have finished a simple but workable IAQ model. The next step is to let the
program "compile" your model — a process for the program to detect obvious errors in the user
input and, if there are no errors, to read in all the parameters. Click the Compile speed button
(i.e., the one with a red check sign). If you receive an error message, go to the corresponding
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page and make corrections and compile again until the model is error free.
3.2.4 Make the Simulation
A successfully compiled model is ready to run. To start the simulation, click the Simulate
speed button (i.e., the one with a calculator logo). Depending on the complexity of your model,
the length of simulation period, and the speed of your computer, the time needed to complete a
simulation may vary greatly, from a few seconds to a few minutes. During a simulation, the
program keeps you informed of the simulation status by displaying a small message box. After
the simulation is finished, click the OK button to go back to the main window. The resulting
time-concentration data are displayed in the Output page (i.e., the last page).
3.2.5 Examine the Results
There are several ways to examine the results. The first thing you may want to do is to
view a time-concentration plot. Click the Quick Plot speed button (the rightmost one with a bar-
chart logo) to see an instant display of the x-y diagram. To print the diagram, click the Print
button.
Often people want to export the data for further analysis. IAQX allows you to export the
results to a spreadsheet, save them to an ASCII file, or print them to a hard copy. The five
buttons in the Output page (Copy, Copy All, Help, Save, and Print) are self-explanatory. Both
Copy and Copy All buttons can copy the data to the Windows clipboard but they work
differently. If you would like to copy only part of the output data to the clipboard, you need to
highlight the data section first and then click the Copy button. If you would like to copy all the
data in the output table, you can click the Copy All button without having to highlight the data.
Click the Help button in case you are confused. To paste the data to a spreadsheet, go to the
spreadsheet application, move the cursor to a cell, and then click the Paste speed button.
3.2.6 Calculate Inhalation Exposure
Once the time-concentration data is generated, calculation of personal inhalation exposure
is easy. Select Tool/Inhalation exposure from the main menu, enter the breathing rate and then
click the OK button. The results will be displayed in a separate table next to the concentration
table and there will be two tabs ("Concentration" and "Exposure") near the bottom-left corner
when you turn to the Output page. Like the concentration data, the inhalation exposure data can
be viewed in a diagram or exported to a spreadsheet. For a quick plot, click the Quick plot
speed button and then select Inhalation exposure. For more options, select Graphics/Select items
from the main menu.
3.2.7 Calculate the Adequate Ventilation Rate
Conventional IAQ simulations take a set of parameters as the input and calculate the
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indoor concentrations as the output. From time to time, the question may be raised in the
opposite way: what is the adequate ventilation rate to keep the indoor pollution level below
certain criteria? The IAQX programs can answer such a question by providing a special
simulation mode. To utilize this feature, click Simulate/Adequate Vent from the main menu. In
the Adequate Ventilation Rate dialog box (Figure 3.5), select peak concentration as the IAQ
criterion. The simulation you have just finished gives a peak concentration of about 300 mg/m3
if you did not change the default values. Assume the goal is to have the peak concentration
below 100 mg/m3. Then enter 100 as the acceptable value. Leave other parameters unchanged,
and then click the OK button. The simulation results show that the indoor concentration can be
reduced to 103 mg/m3 if the ventilation rate is increased to 3.95 air changes per hour.
Note that IAQX version 1 can estimate the adequate ventilation rate for single-zone
models only and that you should always run a conventional simulation and examine the output
before trying to estimate the adequate ventilation rate.
J*-'Adequate Ventilation Rate
S elect C rit e ri o n
<•" Peak concentration
C Average concentration
f Inhalation exposure
^Acceptable Value (mg/m3)
100
Tolerance 5%^1
Select Pollutant
VOC1
rSeleetZone^
Zonel
Scan Range for Ventilation Rate (1/h)
Minimum p.2
Maximum 20
X Cancel I
Figure 3.5 GPS dialog box for estimating the adequate ventilation rate.
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3.2.8 Save Your IAO Model
You can save your IAQ model to a disk file and retrieve it later. This feature is not only
important for record-keeping, it also saves you time because, for a given scenario, the building
configuration and ventilation rates do not change and you need to enter these parameters only
once. To save an IAQ model, click the Save speed button (i.e., the one with a floppy disk logo)
or select File/Save model from the main menu. Remember that each IAQX program has its own
default file extension (see Table 2.1). The default file extension for this program is ".IAQ."
3.3 More About the GPS Program
3.3.1. Define the Ventilation Rate
Four Ventilation Modes
This program allows the user to choose from four ventilation modes:
— constant;
— cyclic;
— time-varying in time/flow format; and
— time-varying in period/flow format.
Constant Mode
The constant ventilation mode is the simplest, and the flow rates are entered in the form
of a matrix (Figure 3.6). Note that the ambient air is always designated zone 0, and that the value
in the From [i] row and To [j] column is the flow rate from zone i to zone j. The Flow Balance
button checks and reports the balance of flow rates for each zone, a feature especially useful for a
multizone flow matrix.
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/ STKi 1.0 / Program GPS NoName IAQ
File Model Simulate Graphics Tools Help
Building Ventilation Sources Conditions Output
-Ventilation Mode-
s'' Constant
T Cyclic
r Time-varying
Air Exchange Flow Rates (rnVh)
-Data Forrnat-
(f Time / Flow
Constant Flow
Current page: Ventilation
Figure 3.6 Constant ventilation mode in the GPS program. The matrix shown is for a single-
zone model.
Cyclic Mode
When the cyclic mode is selected, the user is asked to provide two air flow matrices and
the cyclic periods for them. During the simulation, the two ventilation patterns will be used
alternatively. For the data in Figure 3.7, the simulation will start by using flow matrix 1 for 2
hours, then shift to flow matrix 2 for 1 hour. This cycle will be repeated until the simulation is
finished (Figure 3.8).
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/ STKi 1.D / Program GPS NoName IAQ
File Model Simulate Graphics Jools Help
m\ vi il m\
Building Ventilation Sources Conditions Output
-Ventilation Mode-
f* Constant
f* [Cyclic!
r Time-varying
-Data Format-
-Cycling Periods (h)-
Period 1 (h)
Period 2 (h)
Air Exchange Flow Rates (ms/h)
Cyclic Flow (1) Cyclic Flow (2)
Current page: Ventilation
Close
Figure 3.7 Cyclic ventilation mode in the GPS program. Note the two tabs near the bottom. The
user is also prompted to enter the cycling periods (h) for the two ventilation patterns.
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c
o
"15
4—1
c
0)
o
c
o
O
246
Elapsed Time (h)
10
Figure 3.8 Concentration profile generated by a constant source under the cyclic ventilation
mode.
Two Time-varying Modes
The two time-varying modes - time/flow and period/flow - provide the user with more
flexibility. When using these modes, be aware of the differences between them. In the time/flow
format, the ventilation rates are given as a series of time/flow points. That is, the ventilation
rates change from one point to another. The ventilation rates between two adjacent points are
obtained by means of linear interpolation. This ventilation mode is useful when:
- The air flow rates are generated by a predictive infiltration/ventilation model; or
The building has a variable air volume (VAV) air handling system.
In the period/time format, a series of constant ventilation rates are specified for different
time periods. The important point is that, within each period, the ventilation rate remains
constant. This ventilation mode is used when there are a limited number of ventilation patterns
during a simulation.
The differences between these two modes are illustrated in Figure 3.9 by using data in
Tables 3.2 and 3.3.
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Table 3.2 Time-varying ventilation mode in the time/flow format (one zone).
Time (h)
0
1
2
3
4
5
6
7
8
9
10
Flow Rate (m3/h)
15
22
24
28
22
25
33
45
49
42
46
Table 3.3 Time-varying ventilation mode in the duration/flow format (one zone).
Duration (h) Flow Rate (m3/h)
3 20
5 50
2 35
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60
40 +
0)
£ 20
o
. -B '
246
Elapsed Time (h)
10
-a- Time/Flow Format
Duration/Flow Format
Figure 3.9 Comparison between the two time-varying flow modes. The plot was generated by
using data in Tables 3.2 and 3.3.
Simplified Data Format for One-zone Models with the Time-varying Ventilation Mode
If there are n air zones, the number of all possible air flows is n(n+l). Thus, for a one-
zone model, there are two flow rates, which are always equal. In this program, simplification is
made for single-zone models with either time-varying ventilation mode: the user needs to enter
only one flow rate in the time-varying flow table, like Tables 3.2 and 3.3. To minimize any
potential confusion, the data table adjusts its size automatically.
3.3.2 Add Pages
In addition to the five pages that are permanently displayed, four more pages are available
when you need them. They are labeled Sinks, Air cleaner/Filters, Reactions, and Input Data,
respectively.
To add a page to your model, click on the Add Page speed button (i.e., the one with a red
pound sign), select the page (or pages) you need, and then click the OK button. Adding models
for sinks, air cleaning devices, or chemical reactions is similar to adding source models: go to the
corresponding page, and then click on the Add button near the top-right corner.
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The Input Data page is for accepting data for two time-varying sources: time-varying
indoor sources and the ambient air as a time-varying source. For more information see Section
3.3.8.
Occasionally, you may add a page and then decide to remove it. To hide an added page,
click the Add Page speed button again and uncheck the page you want to hide.
3.3.3 Source Models
Twenty-six source models are available in the GPS program. Some of them are mass
transfer models. Table 3.4 lists all available models and references. Descriptions of each model
can be found in the program by clicking the Add button in the Sources page. After you select a
model, the model entry dialog box will appear with the model description on the upper-left
corner. The user should consult with the original publications for more information about a
specific model.
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Table 3.4 Source models available in the GPS program.
Model
Group
Constant &
Instant
First-order &
Higher-order
Solvent
Evaporation
Dry
Sources
Emissions
from Water
Time-varying
Combined5 &
Miscellaneous
ID No.
11
12
13
15
16
21
22
23
24
25
26
31
32
33
41
42
43
44
51
52
61
62
71
72
73
74
Model
Description
constant (as mass/time)
constant (as flow rate and concentration) :
constant (as mass/area/time)
ambient air as a constant source
instant pollutant release
first-order (as E0 and k)
first-order (as M0 and k)
double first-order (+/+)
double first-order (+/-)
second-order
nth-order
Evaporation from a solvent pool 2
VB model for TVOCs
VBX model for individual VOCs
HCHO emission from particleboard
VOC from PVC flooring (1)
VOC from PVC flooring (2)
biocide emissions from treated wood
VOC from water w/ known kL J
VOC from water w/ known kg 4
time-varying indoor source
ambient air as a time-varying source
VOC from latex paint and plaster during
and after application
power law model for building materials
ambient air as a sine function
ambient air as a cosine function
Reference
Dunn, 1987
Dunn, 1987
ASTM, 1990
Shair& Heitner, 1974
Chang &Guo, 1992a
Dunn, 1987
Clausen, 1993
Chang &Guo, 1992b
Chang &Guo, 1998
Clausen, et al., 1993
Tichenor, et al., 1991
Chang &Krebs, 1992
Tichenor, etal., 1993
Guo, etal., 1998
Hoetjer&Koerts, 1986
Christiansson, et al., 1993
Christiansson, et al., 1993
Jayjock, etal., 1995
Lyman, etal., 1990
Lyman, etal., 1990
Koontz & Nagda, 1991
Shair& Heitner, 1974
Zeh, etal., 1994
Zhu, etal., 1998
Shair & Heitner, 1974
Shair & Heitner, 1974
1 This is a variant of source model 11.
2 A similar model was first used for the outdoor environment (Mackay and Matsugu, 1973).
3 kL = overall liquid-phase mass transfer coefficient;
4 kg = overall gas-phase mass transfer coefficient;
5 Combined models are those with two or more distinctive terms.
3.3.4 Sink Models
Five sink models are available in the GPS program (Table 3.5). As for source models,
model descriptions can be found in the program. Note that, when you select a non-zero value for
the sink materials in the Building page, the Sinks page becomes visible automatically. Always
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remember to enter the sink areas in the Building Configuration table. To add a sink model, click
the Sinks page tab, then click the "Add" button on the right. After you select a model, the model
entry window will appear with the description on the upper-left corner.
Table 3.5 Sink models available in the GPS program.
ID
Number
1
2
3
4
5
Model Description
first-order deposition (irreversible)
first-order reversible
higher-order reversible
reversible w/ pollutant degradation
two-node model
Reference
Nazaroff & Cass, 1986
Tichenor, etal., 1991
Sparks, 1991
Jayjock, etal., 1995
J0rgensen, et al., 2000
3.3.5 Models for Air Cleaners
Models for air filters and air cleaners are still rare. Two models are available in the GPS
program, one for constant removal rate and the other for declining removal rate. Depending on
whether the filter/cleaner is stand-alone or in the HVAC system, each model has two different
forms (Table 3.6). The on-line description of these models can be found the same way as for the
source and sink models. By default, the Filters & Cleaners page is hidden. Use the Add Page
speed button to bring it up.
Table 3.6 Air cleaner/filter models available in the GPS program.
ID Number
11
12
21
22
Cleaner/Filter Type
stand-alone
stand-alone
in HVAC system
in HVAC system
Model Description
constant removal rate
declining removal rate
constant removal rate
declining removal rate
Reference
Sparks, 1996
None
Sparks, 1996
None
3.3.6 Chemical Reactions
The user needs to remember two things when dealing with gas-phase chemical reactions.
First, this program is not designed to run indoor photochemical models, which will be taken care
of by a special-purpose simulation program in IAQX. Second, the concentration units used in
chemical reactions are incompatible with those commonly used in conventional IAQ simulations.
Chemical reactions take place on a molecule-to-molecule basis. The most commonly used
concentration units in atmospheric chemistry are molecules/cm3 and parts per million (ppm).
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This program has several features that help the user ease the unit conflict problem. However, it
is ultimately the user's responsibility to keep different parts of the model in harmony.
The GPS program requires that concentrations be given in mole/m3 whenever chemical
reactions are involved in an IAQ model. Consequently, the emission rate will be mole/h, instead
of mg/h. Conversion between mg/m3 and mole/m3 is easy:
= (mole I m*) (3.1)
1000 mw
where mw = molecular weight (g/mole).
More conversion factors are provided in the program. Just select Tool/Conversion factor from
the main menu.
Add Chemical Reactions
To add chemical reactions, make the Chem Rex (for chemical reaction) page visible:
click the page tab, click the Add button near the top-right corner, and then follow instructions.
Reaction Orders
Most chemical reactions that may occur in the indoor air are either of first or second
order. The following reactions are of first order:
A = B (3.2)
A = B + C (3.3)
The following reactions are of second order:
A + B = C + D (3.4)
2A = B + C (3.5)
Add Reactions with Unknown Products
When the products of a chemical reaction are unknown, you can leave the right-hand side
of the reaction equation empty. The following equations are all valid:
A= (3.6)
2A= (3.7)
A + B= (3.8)
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3.3.7 Defining the HVAC System
In IAQX, the heating, ventilation, and air-conditioning (HVAC) system is treated as a
special air zone with all the properties (such as volume and sink areas) and functions (such as air
exchanges with outdoor air and other zones) that a regular zone has, plus several special
functions. For instance, the mixing pattern is different from that of a regular zone, and the air
filters can be placed in three possible locations: recirculation, makeup, or supply air streams
(Figure 3.10).
This program recognizes the existence of an HVAC system if the last zone is named
either HVAC or HAC. The volume of the HVAC system is often difficult to estimate. However,
since the flow-to-volume ratio is much greater for the HVAC than for regular air zones, it is not
necessary to accurately determine the total volume of the HVAC system. A rough estimation
will not affect the accuracy of the simulation. Use the Filters & Cleaner page to add models for
HVAC filters.
Exhaust
fl
Return
Makeup —
£2
T
Recirculation
Mixing Zone
Supply
f3
Figure 3.10 Diagrammatic description of the air handling system. Three possible positions for
the air filter are marked fl, f2, and f3.
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3.3.8 Time-Varying Sources
This program accepts two types of time-varying sources: time-varying indoor source
(source No. 61) and ambient air as a time-varying source (source No. 62). Like other source
models, they are defined in the Sources page. However, the user is required to provide the time-
varying emission rate or outdoor concentration in the form of a data table. Two data tables are
available in the Input Data page (Figure 3.11). The data formats are slightly different for these
two models. Make sure you enter the data in the right place. There is a Data Format button in
each page. Click on it to display the data format before you enter the data.
5TKi 1.0 / Program GPS NoName IAQ
File Model Run Graphics Tools Help
JIJ
Building Ventilation Sources Conditions Input Data Output
Emission Data for Time-Varying Indoor Source (Type 61)
UJJ
? Data Format
IQS, Paste
B Load
Clear
Indoor Source Ambient Air
Current page: Input Data
JL £'
Figure 3.11 The layout of the Input Data page of the GPS program. Note the two tabs near the
bottom-left corner and the Data Format button near the top-right corner.
3.3.9 Non-Zero Initial Concentrations
Non-zero initial concentrations are entered in the Conditions page. You should do this
after you finish with all other pages.
There are two radio buttons in the selection box near the bottom-left corner labeled "Are
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there non-zero initial air concentrations?" Select Yes to make the table on the right visible
(Figure 3.12). When you click the Scan button, the program will search different parts of your
model to find all the pollutant names and put them in the table. The only thing you need to do is
to enter the concentration values. If a pollutant name does not exist in the other parts of your
model, you can always add it to the table manually.
/ STKi 1 0 / Program GPS NoName IAQ
File Model Simulate Graphics Tools Help
Building Ventilation Sources Filters & Cleaners Chem Rex Conditions input Data Output
-Simulation Period (h)-
10
Simulation Conditions
nitial Concentration Table (
Pollutant
Zonel
-Output Data Points-
100
Are there non-zero initial air concentrations?
r NO
Current page: Conditions
JLClose
Figure 3.12 Layout of the Conditions page of the GPS program. The Initial Concentration Table
is visible.
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CHAPTER FOUR
MODELS FOR VOC EMISSIONS FROM SOLVENT-BASED
INDOOR COATING PRODUCTS (VBX.EXE)
4.1 Model Description
4.1.1 Overview
The VBX program utilizes three source models to predict the emissions of total volatile
organic compounds (TVOCs) and/or individual volatile organic compounds (VOCs) from
solvent-based indoor coating materials based on product formulation (Guo et al., 1999).
Depending on the user's knowledge of the VOC contents in the product, this program offers two
options for data entry: "Bulk analysis" and "MSDS."
The "Bulk analysis" option utilizes two mass transfer models (see Sections 4.1.2 and
4.1.3) and requires the user to provide the contents of major VOCs in the liquid product. A
dozen or so major VOCs are usually sufficient, and the minimum number allowed is five.
The "MSDS" option is useful when information about the contents of major VOCs is not
available. In this option, the first-order decay model is used (Section 4.1.4) and its parameters
are estimated based on the information that can be found in the Material Safety Data Sheet
(MSDS).
The required user input for the source is listed in Table 4.1. Note that similar source
models are available in the general-purpose simulation program (GPS.EXE). However, GPS
does not have the capability to estimate the model parameters based on the product formulation.
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Table 4.1 User input required by the VBX program.
Pollutant
Model Implemented
Source area
Wet film thickness
Product density
Contents of major VOCs
Content of VOC of interest
Most abundant VOC
Room temperature
VOC Data Option
Bulk Analysis
TVOC
VB
X
X
X
X
X
Individual
VOC
VBX
X
X
X
X
X
X
MSDS
Individual
VOC
1 st-order
decay
X
X
X
X
X
X
4.1.2 The VB Model for TVOCs
The rate of TVOC emissions is estimated by using the VB model:
m MT
-^T-C)
(4.1)
where E(t) = emission factor (mg/m2/h);
k^ = gas-phase mass transfer coefficient (m/h);
P0 = total vapor pressure for TVOCs (mmHg);
m = average molecular weight for TVOCs (g/mole);
vm = mole volume (m3); vm = 0.0243 m3 at latm and 23 °C;
MT = amount of TVOCs remaining in the source (mg/m2);
MTO = amount of TVOCs applied (mg/m2); and
C = indoor TVOC concentration (mg/m3).
The coefficient 1.32 in Eq. 4.1 is for converting the total vapor pressure to the saturated
concentration. Methods for estimating the total vapor pressure, average molecular weight, and
gas-phase mass transfer coefficient are described in Sections 4.1.4 and 4.1.5.
4.1.3 The VBX Model for Individual VOCs
The emission rate of an individual VOC is estimated by the VBX model:
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m Mi
&<0=M1.32P,-- — -Q) (4.2)
where E^t) = emission factor for compound i (mg/m2/h);
P, = vapor pressure for pure compound i (mm Hg);
M, = amount of compound i remaining in the source (mg/m2); and
C, = concentration of compound i in indoor air (mg/m3).
4.1.4 The First-Order Decay Model for Individual VOCs
If you do not know the contents of major VOCs in the product, but you know the TVOC
content and the contents of individual VOCs in which you are interested, the emission factor can
be estimated from:
E(t)= Ev&kt (4.3)
m y,
£o = 1.32 km Pt — — (4.4)
(4.5)
where E0 = initial emission factor (mg/m2/h);
k = first-order decay rate constant (h"1);
t = time (h);
m = average molecular weight for TVOCs (g/mole), represented by the molecular weight
for the most abundant VOC in the product;
m, = molecular weight for component i (g/mole);
y; = content of an individual VOC in the product (mg/g);
y0 = content of TVOCs in the product (mg/g);
z = wet film thickness (|im); and
d = product density (g/mL).
This model requires less information from the user, and the application-phase simulation
can be easily implemented. However, it is less accurate than the VBX model and works only for
individual VOCs.
4. 1.5 Estimation of the Total Vapor Pressure and Average Molecular Weight for TVOCs Based
on the VOC Contents in the Product
The two parameters P0 and TO in the VB model (Eq. 4.1) can be estimated from the
contents of major VOCs in the product
-33-
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(4.6)
m = — (4.7)
ra V
where P, = vapor pressure for compound i (mm Hg);
y; = content of compound i in the liquid product (mg/g); and
m, = molecular weight for compound i (g/mole).
4.1.6 Model for Estimating Gas-Phase Mass Transfer Coefficient
A model developed by Sparks, et al. (1996) is used to estimate the gas-phase mass
transfer coefficient
*•„ -0.33£>£7(— )* (4.8)
where D = diffusivity of the VOC in air (m2/h);
Lc = characteristic length of the source, equal to the square root of the source area (m);
v = air velocity over the source, (m/h);
d = density of the air (g/m3); and
|l = viscosity of the air (g/h/m).
4.2 A Brief Tour of the Program
Click on the VBX icon to launch the program. You will find that the main window
(Figure 4.1) is very similar to that for the GPS program. In fact, all IAQX programs have similar
user interfaces.
Six tabbed pages are permanently displayed: Building, Ventilation, VOC Contents,
Source, Conditions, and Output. The Building page is almost identical to that in the GPS
program. However, the zone number is limited to 3 instead of 10 and the number of sink
materials is limited to 2.
-34-
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The Ventilation page is simpler than its counterpart in the GPS program. Currently,
special-purpose models allow only constant flow rates. For single-zone models, only the left
panel is visible (Figure 4.2a), and the user can enter either the air exchange rate or the flow rate.
For multizone models, the right panel is visible, and the flow table is identical to those in the
GPS program (Figure 4.2b). The display changes automatically (no user intervention is needed).
4! STKi 1.0 / Program VBX NoName.VBX
File Model Run Graph Tool Help
I p| BI j|| I HI -/"I
Building 1 Ventilation 1 VOC Contents 1 Source 1 Conditions I Output
Note Pad
Vour note goes here.
Building Configuration
Number of Air Zones?
Number of Sinks
r I
\° I
JX Close
Figure 4.1 The main window of the VBX program (showing the Building page).
-35-
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File Model Run Graph Tool Help
I] ii
Building Ventiiation | VOC Contents ) Source | Conditions j Output |
Single-Zone Ventilation Rate
Select Data Type
r? Air Exchange Rale C Air Flow Rate
- Air Exchange Rate
per hour
JlCIo
^STKM.O/ Program VBX NoName.VBX BEIDI
File Model Run Graph Tool {Help
Building Ventilation VOC Contents Source | Condit
•I I
ons Output |
Multi-Zone Air Flow Table
Toflfl To[l] To[Z]
From[0] '/y.«< 130 30
From[l] 30 XxX>C< 30
From [2] 30 30 >0000<
< I » I ii Close]
Figure 4.2 Layout of the Ventilation page of the VBX program: single zone (top); multi-zone
(bottom)
-36-
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Now turn to the VOC Contents page (Figure 4.3). The first thing you need to do with this
page is to determine what kind of VOC content data you want to use. In the upper-left corner,
there two radio buttons in a selection box labeled "VOC Data Options." As mentioned in
Section 4.1.1, you can choose either "Bulk analysis" or "MSDS" depending on whether or not
you know the content of major VOCs in the product. Table 4.2 compares these two options with
more details. For this demonstration, select "Bulk analysis."
JiSTKi 1.0 / Program VEX NoName.VBX
File Model Simulate Graph Tools Help
HI j£J Ml Ji]
Building j Ventilation VOC Contents | Source Conditions | Output
VOC Data Options
(• Bulk analysis
r MSDS
? Help
••
TVOC Content (mg/g)-
VOC Contents in Product - Excluding TVOC
Compound
Formula
MW
Vp (mmHg)
D (rrflh)
Content (mg/g)
5 Database ^1 vj Delete
Current page = VOC Contents
Jlclose
Figure 4.3 Layout of the VOC Contents page of the VBX program.
-37-
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Table 4.2 Differences between the two VOC data options.
VOC Data Option
Data required from user
Typical data source
Minimum number of
VOCs required
Model used
Bulk Analysis
Contents of T VOCs
and major VOCs
GC analysis for VOC
content in product
5
VB/VBX
MSDS
Contents of T VOCs
and VOCs of interest
MSDS
1
First-order decay
Now, move to the bottom-left corner of the window, where you give the TVOC content in
(mg/g product). For this demonstration, enter 500.
Move to the VOC content table on the right. The required information for each
compound is:
compound name;
molecular weight;
vapor pressure;
diffusivity in air; and
content in product.
Entering these parameters for a dozen or so compounds is tedious. This program simplifies the
data entry by providing the user with a mini-database.
Click the Database button below the table. A dialog window will display the available
VOC names in the database (Figure 4.4).
-38-
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9 Select VOCs from Database
Available
ipctane
nonane
decane
undecane
dodecane
toluene
ethyl benzene
o-xylene
m-xylene
p-xylene
0-ethyl toluene
m-ethyl toluene
p-ethyl toluene
1,2,3-tri methyl benzene
1,2,4-trirnethyl benzene
1,3,5-trimethyl benzene
n-propyl benzene
isopropyl benzene
trans-decalin
Selected
Hold down Ctrl key for multiple selection.
OK
X Cancel
Figure 4.4 Dialog window for the built-in database of the VBX program.
Select VOCs from the left panel, then click the right arrow to copy selected compounds to
the right panel. For multiple selection, hold down the Control key while you select. As an
example, let's select the first five compounds. After you finish, click OK. As you can see, all
the parameters are entered to the VOC table except VOC contents (Figure 4.5). Let's enter 20,
50, 100, 50, and 20 (mg/g) for the five compounds, respectively. Note that, for real coating
products, the sum of the contents for individual VOCs is always less than the TVOC content
because routine GC analysis cannot identify and quantify all the compounds in petroleum-based
solvents. See the demonstration model file "BULK. VBX' for an example.
-39-
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,« STKi 1 0 / Program VBX for Solvent-Based Coalings NoName.VBX
File Model Run Graph Tools Help
Building | Ventilation VOC Contents | Source | Conditions Output
VOC Data Options
<• Bulk analysis
C MSDS
? Help
WOC Content (mg/g)
350
VOC Contents in Product - Excluding TVOC
Compound Formula MW
octane C8H18 114
nonane C9 H20 128
decane C10H22 142
undecane C11 H24 156
dodecane C12H26 170
Vp(rnmHg) D (rrvVh) I Content (mg/g) I _±|
12.324 0.0234 ^^^I^^H —
4144 0.0219 0
1.575 0.0207 0
0.616 0.0199 0
0.253 0.0188 0
Current page = VOC Contents
Close
Figure 4.5 Layout of the VOC Contents page of the VBX program. Five VOCs have been
entered by using the built-in mini-database.
Next, turn to the Source page, in which you specify four parameters for the source and
select the VOCs for output (Figure 4.6). The source parameters are: product density (g/mL), wet
film thickness (|im), coated area (m2), and source location (zone ID). The recommended wet
film thickness can be found in the product label. For alkyd paint, the typical value is in the 75-
100 |lm range. For this demonstration, enter 75 |lm for the wet film thickness.
With the "Bulk analysis" option, often you do not need to simulate all the VOCs you
enter. This program allows you to select the species in which you are interested. There are two
list boxes on the right. To choose TVOCs and decane for output, select them from the Available
Species box and then click the Select button to make them appear in the Selected Species box.
Note that if a compound name does not appear in the Selected Species box, its simulation results
will be ignored in the output data table.
-40-
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/> STKi 1.0 / Solvent-Based Coatings New-1 .VBX
File Model Run Graph Tools jHelp
Building | Ventilation VOC Contents Source Conditions | Output |
-P roduct Properties & AppIicatio n
Product density (g/ml) 1.35
Wet film thickness (urn) |20
Coated area (m2)
10
Source location Zonel
Select Species for Output
Available Species J r Selected Species
TVOC
octane
nonane
decane
undecane
dodecane
WOC
decane
±••1 Delete a^ Clear
Current page = Source
Jl Clo
Figure 4.6 Layout of the Source page of the VBX program.
To finish this IAQ model, turn to the Conditions page to enter several more parameters -
all are self-explanatory. Now compile and run the program the same way you did with the GPS
program.
4.3 More About the VBX Program
4.3.1 What If a VOC Does Not Exist in the VOC Database?
If a VOC does not exist in the database, go to the last row of the table in the VOC
Contents page and enter the parameters manually. In addition, this program has tools to help the
user compute the molecular weight, diffusivity, etc. Simply select Tools from the main menu
and find the tool you need.
4.3.2 About the MSDS Option
With the MSDS option, the user can enter only one compound in the VOC content table.
-41-
-------
The user is also required to specify the most abundant VOC in the solvent (Figure 4.7). This
information will be used to estimate the average molecular weight for TVOCs. In most cases it
is decane. In rare cases, it can be undecane (in some alkyd paint) or xylene (in some conversion
varnish). Also note that the MSDS option allows for the application-phase simulation (Section
8.3) and that the related parameters are entered in the Conditions page (Figure 4.8).
JTKi 1.0 / Solvent-Based Coatings Msds.vbx
File Model Bun Graph Tools Help
D| IB |
a I
-------
«STKi1.0/Program VBX Msds.vbx
File Model Simulate firaph Joels Help
Building | Ventilation | VOC Contents | Source Conditions j Output |
Environmental Conditions Simulation Conditions
Room temperature (°C)
Air velocity/speed (cm/s) 10.0
Simulation Period (h)
10
Output Data Points 100
Application-Phase Simulation?
No
-------
*STK.i 1.0 /Program VBX Bulk.VBX
File Model Simulate Graph look He\p
Jj jd JJ ^
Building | Ventilation | VOC Contents | Source Sink | Conditions | Output j
Select Model for Sink (1)
list-order reversible
ka = adsorption rate constant (rn/h)
kd = desorption rate constant (1/h)
toluene
Compound
Model Parameters
ka (m/h) kd (1/h)
0
0
Sink Material 1 |
Current page = Sink
< I > I
JL Close T I
Figure 4.9 Layout of the Sink page of the VBX program.
-44-
-------
CHAPTER FIVE
MODELS FOR SMALL-SCALE SOLVENT SPILLS (SPILL.EXE)
5.1 Model Description
Program SPILL contains three mass transfer models for estimating the indoor VOC
concentrations following unstrained, small-scale solvent spills on hard flooring.
5.1.1 Model for Single-Component Solvent
Reinke and Brosseau (1997) evaluated several methods for predicting the indoor VOC
concentrations following spills of pure solvent and concluded that the Penetration Theory or the
Mackay and Matsugu Method under the isothermal assumption performed better than the rest of
the methods. This program uses the latter method, which estimates the emission factor from:
NA = 2.778 x ID' m oaa (5.1)
where NA = molar flux of compound A (kg-mol A / m2 / s);
k^ = gas-phase mass transfer coefficient (m/s);
yA* = mole fraction of A at saturation (kg-mol A / kg-mol gas);
YAroom = m°le fraction of A in well-mixed air (kg-mol A / kg-mol gas); and
Vsplll = gas molar volume at solvent pool temperature (m3 / kg-mol);
The authors recommend that the mass transfer coefficient (kjj be calculated from a method
proposed by Mackay and Mastugu (1973):
Jtw= Q0292«0'78 X'011 Sc~0-67 (5.2)
where u = velocity of air flowing across the solvent pool (m/s);
X = pool diameter (m), approximated by the square root of the spill area; and
Sc = Schmidt number (unitless).
More discussion on calculating the mass transfer coefficient is provided in Section 5.3.2.
5. 1 .2 Model for Solvent Mixture Whose Exact Composition Is Known
For a solvent mixture with n components, a model developed by Drivas (1982) is used to
-45-
-------
predict the emission of an individual component i:
W-
-------
5.1.4 Estimation of the Spill Area
The emission rate is the product of the emission factor and source area:
j?(0= XO^CO (5.6)
where R(t) = emission rate (mg/h);
A(t) = spill area (m2); and
E(t) = emission factor (mg/m2/h).
A special problem associated with solvent spills is that the spill area decreases with time.
According to Drivas (1982) and Reinke and Brosseau (1997), the spill area at anytime (A) can
be ap proxim ate d by :
W(t)
where A0 = initial spill area (m2);
W(t) = amount of solvent remaining on the floor (mol); and
W0 = initial amount of solvent spilled (mol).
Eq. 5.7 assumes that an unrestrained small spill maintains a constant depth and decreases only in
area and not in depth, as it evaporates.
5.2 A Brief Tour of the Program
The user interface for this program is very similar to that for the VBX program. The first
two pages (Building and Ventilation) are identical to those in the VBX program. The next four
pages relate to: Solvent, Source, Conditions, and Output, respectively. In this demonstration, we
will use the default values in the first two pages. Now, move to the Solvent page (Figure 5. 1) by
clicking its tab.
-47-
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.* STKi 1.0 / Program foi Indoor Solvent Spill NoName SPL
File
Simulate Gjaph Xools Hd
Compound
Formula
Building I Ventilation Solvent J soures | Conditions | Output]
-Solvent Type
<* Single component
f" Mixture (exact)
f Mixture (major VOCs)
- Help
Vp (mmHg)
[H Database M 9 Dilete
far Clear
Help
Current page = Solvent
JTL
Figure 5.1 Layout of the Solvent page of the SPILL program.
The first thing you need to determine is the solvent type. There are three choices:
— Single component: for single-component solvent;
— Mixture (exact): for multicomponent solvent whose exact composition is known;
or
— Mixture (major VOCs): for petroleum-based solvent, whose major components
are known.
These choices are discussed in Sections 5.1.1 - 5.1.3. There is also a Help button in the Solvent
page. Click on it to find more information about how to select the solvent type. For this
demonstration, select type I — single component.
The next step is to enter the properties of the solvent components. The required
parameters for each component include: component name, molecular formula, molecular weight,
-48-
-------
molecular diffusivity in air, and vapor pressure. Although you can enter these parameters
manually, it will save you time to use the built-in VOC database. Click the Database button,
select a compound from the list in the left panel (toluene, for example), then click the right arrow
(>) to copy it to the right panel. Click OK to close the database. Now look at the Solvent page.
All required physical properties for toluene (formula, molecular weight, vapor pressure, and
diffusivity in air) are copied to the table. Note that, if you are dealing with a multiple component
solvent, the content of each component (in mg/g) is also required.
Now move to the Source page by clicking its tab. In addition to the VOC content data
entered in the previous page, four more parameters are needed to define the source: solvent
density, amount of solvent spilled, spill area, and the cleanup time. The first three parameters are
fairly straightforward. If you have no idea about how to estimate the spill area, click the button
with a question mark for help.
STKi 1.0 / Program for Indoor Solvent Spill NoName.SPL
File Model Simulate Graph lools Help
vi
Building I Ventilation | Solvent Source | Conditions | Output)
r Solvent Properties & Spill Conditions
Solvent density (g/rnl) O.B5
Volume spilled (ml)
Spill area (m1)
100
0.2
|rClean-Up After Spill?
T No
(*• jYes!
Clean-up Time (h)
Es
I Available Species--
Select Species for Output
1 rSelected Species-
toluene
B> Select
toluene
*"i Delete %fr Clear
Current page = Source
JL close
Figure 5.2 Layout of the Source page of the SPILL program.
-49-
-------
In real life, a solvent spill is often followed by some cleanup actions. This program
allows the user to specify a time to shut off the source. The cleanup time is the elapsed time
when the source is removed as a result of any cleanup actions. To use this feature, click Yes near
the bottom-left corner and then enter the cleanup time.
On the right side of the Sources page, there are two list boxes. The one on the left shows
all available VOCs in the solvent, and the one on the right is for selected compounds for the
simulation output. This feature is useful when the solvent contains many compounds and you do
not want simulations for every one of them. For a single-component solvent, the selection is
done automatically. Otherwise, the user can select compounds from the left box and then click
the Select button.
Turn to the Conditions page, where the user specifies the environmental and simulation
conditions. Inmost part, this page is self-explanatory except for the selection box at the bottom-
right corner, labeled "How to estimate gas-phase mass transfer coefficient?" By default, the
Mackay & Matsugu method (Mackay & Matsugu, 1973) is used for solvent types I and II; and
the Sparks method (Sparks, et al., 1996) for solvent type III. The user does have the option to
choose either of them, however. See Section 5.3.2 for more discussions on this matter.
Now compile and run the model as you do in other IAQX programs. There are two
demonstration files in the "demo" folder: "solvent-2.spl" and "solvent-3.spl." They are example
cases using the other two models. They can be loaded into the program by clicking File/Open
from the main menu, or clicking the Open File speed button.
5.3 More About the SPILL Program
5.3.1 Adding Sink Models
Adding a sink model in this program is the same as in the VBX program. See Section
4.3.5 for details.
5.3.2 Comparison of the Two Methods for Estimating the Gas-Phase Mass Transfer Coefficient
This program provides two methods for calculating the gas-phase mass transfer
coefficient: the Mackay and Matsugu method (Eq. 5.2) and the Sparks method (Eq. 4.8). The
default selections are the Mackay and Matsugu method for the first two models (i.e., Eqs. 5.1 and
5.3) and the Sparks method for the third model (Eqs. 5.4 and 5.5). Both selections are
recommended by the authors of the emission models.
The user should be aware that the two methods differ significantly in the air velocity
range commonly found in indoor environments (Figure 5.3). Currently, there are no reported
data to determine which of the two methods is more accurate for solvent spills. Thus, if you are
unfamiliar with gas-phase mass transfer theories, using the default method is probably the better
choice. This program does, however, give advanced users the option to choose either method for
-50-
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any of the three models.
10
JZ
1
8
-*-
Eq.
5
.2---
Eq.
4
.8
0)
O -
0 6H
10 20 30
Air Velocity (cm/s)
40
Figure 5.3 Comparison of the gas-phase mass transfer coefficient for decane estimated by the
two methods.
5.3.3 Dealing with the Temperature Drop
Solvent evaporation is an endothermic process. Consequently, the temperature of spilled
solvent is often lower than its surroundings. Reinke and Brosseau (1997) evaluated models that
take this factor into consideration and found that adding the heat transfer term does not seem to
improve the model performance.
Very limited data suggest that the temperature drop can be 2 to 4 °C depending on the
volatility of the solvent and the properties of the flooring. Practically, this factor can be taken
into consideration by using the vapor pressure at a lower temperature. This is an area that needs
more experimental data.
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5.3.4 About the Short Circuiting Factor
The original model proposed by Reinke and Brosseau (1997) has a short circuiting factor
to adjust for the short circuiting of the air exchange flow in a room. This program does not
include this feature. In otherwords, each air zone is considered well-mixed. If short circuitingis
an important factor, the user can divide the room into multiple air zones.
-52-
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CHAPTER SIX
A MODEL FOR VOC EMISSIONS FROM DIFFUSION-
CONTROLLED HOMOGENEOUS SLABS (SLAB.EXE)
6.1 Model Description
Program SLAB implements an emission model developed by J. C. Little, A. T. Hodgson,
and A. J. Gadgil (Little, et al., 1994) for predicting the VOC emissions from diffusion-controlled
homogeneous slabs. This model was initially developed based on the experimental data for new
carpet backing. It can be used for other similar sources, however. The mathematical expressions
for this model are fairly long. The user is encouraged to go through the original paper for more
details. A brief description is provided below.
This model was derived based on the standard diffusion equation:
= D
dt
where C(x,t) = pollutant concentration in the slab (mg/m3);
D = diffusion coefficient in the slab (m2/h);
x = linear distance from the bottom of the slab (m); and
t = time (h).
The actual model is an approximate solution to the above diffusion model applied to a one-zone
environment with a constant air exchange rate. Calculation of indoor air concentration involves
five steps:
Step 1 : calculate coefficient h from
h = - - - (6.2)
ADK
V
where Q = air exchange flow rate (m3/h);
A = area of the slab (m2);
Ky = partition coefficient (unitless).
Step 2: calculate coefficient k from
-53-
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k = (6.3)
AKv
where V = volume of the room or test chamber (m3).
Step 3: calculate coefficient q, by finding n smallest positive roots (n = 1,2, ... up to 200) of the
following non-linear equation:
L^-qn (6.4)
where L = thickness of the slab (m).
Step 4: calculate the pollutant concentration at the top surface of the slab, C(L,t), from:
where x = linear distance from the bottom of the slab, x = L at the slab surface (m);
C0 = initial concentration in the slab (mg/m3); and
n = 1 to °° is the number of terms for the summation and, practically, n < 200.
Step 5: calculate the air concentration from:
(6.6)
where y = pollutant concentration in the air (mg/m3); and
C|X=L = pollutant concentration at the top surface of the slab (mg/m3).
In this model, the source is described with four parameters: source area S, initial pollutant
concentration in the slab (C0), molecular diffusivity of the pollutant in the slab (D), and the
thickness of the slab (L). Discussions on estimation these parameters are provided in Section
6.3.
There are two reasons why IAQX implements this model with a stand-alone program.
First, it requires special numerical treatment to compute the indoor concentration. Second, since
the authors give the indoor concentration directly without an expression for the emission factor,
-54-
-------
this model, in its current form, can be applied only to a one-zone environment; it cannot coexist
with models for indoor sinks and air cleaners, which are available in other IAQX programs.
6.2 A Brief Tour of the Program
Click the SLAB.EXE logo to start the program. As shown in Figure 6.1, there are only
two tabbed pages in this program: Model and Output. All the parameters are entered in the
Model page. The source is described by five parameters: the area (m2), the VOC content in the
slab (g/m3); the molecular diffusivity of the VOC in the slab (m2/s or m2/h), the air/solid partition
coefficient (unitless), and the thickness of the slab (m). There are already default values in each
input box. The user needs to replace them by proper values for a given VOC in a given product.
After entering all the parameters, click the Compile speed button (the one with a red
check sign). After successful compilation, click the Simulation speed button. Like in other
IAQX programs, the output results can be viewed graphically or exported to a spreadsheet.
STKi 1.0 / Program CRT NoName.CPT
File Model Bun Graph Tools IHelp
J1J Jl
a
Model I Output |
f Source Parameters
| Carpet area (rn2)
120
VOC cone, in slab (mg/m3) Il5000
Diffusivily in slab
Partition coefficient
I.5E-12 | m2 / s -r I
3500
Thickness of slab (m) Id.001
Environment Parameters
Room volume (m3)
Airexch.flow(m3/h)
300
150
Simulation Control Parameters
Simulation period (hours) |100
Number of data points 1100
Current page = Model
Figure 6.1 The main window of the SLAB program.
-55-
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6.3 More About the SLAB Program
6.3.1 Model Parameters for New Carpet Backing
Among the five parameters that describe the source, the area and thickness of the slab are
easy to determine. The other three parameters are usually obtained from experiments.
According to the authors, these parameters vary significantly from compound to compound and
from carpet to carpet. The following ranges are reported by the authors:
VOC content in slab: from 340 to 255000 mg/m3;
Partition coefficient: from 1 to 450000;
Diffusivity in slab: from 6xlQ-14to IxlO'11 m2/s (2.2xlQ-14to 3.6xlQ-8 m2/h);
Thickness of slab: from 1 to 2 mm.
Several recent articles (Bodalal, et al., 2000, for instance) have reported the experimentally
determined molecular diffusivities for common indoor VOCs in various substrates. Certain
empirical correlations have also been developed .
6.3.2 Dealing with Zero Ventilation Rate
For some reason, this model does not allow a zero ventilation flow rate. Sometimes, one
may want to calculate the upper limit of the indoor concentrations by setting the ventilation flow
rate to zero. In such cases, the SLAB program will display an error message and prompt the user
to enter a small positive value (e.g., 1E-4).
6.3.3 Source Reduction Simulation Mode
In addition to the two simulation modes that other IAQX program have (i.e., the
conventional simulation and the adequate ventilation rate), program SLAB has a third simulation
mode called Source Reduction. This simulation mode allows the user to estimate the degree of
pollutant reduction in the source needed to satisfy certain IAQ criteria. As shown in Figure 6.2,
the dialog box is very similar to that for the adequate ventilation mode. To choose this mode,
select Simulate/Source reduction from the main menu.
-56-
-------
^gf. Input for Source Reduction
Select Criterion
^ Peak concentration
r" Average concentration
<~ Inhalation exposure
-Acceptable Value (mg/m3)^
Tolerance I 5%il
HHEI
Select Pollutant
VOC1
rSelectZone-
Zone 1
Range for Pollutant Content in Product (mg/m3)-
Minimum 1150
Maximum 15000
&} Go
X Cancel
Figure 6.2 The SLAB dialog box for the Source Reduction simulation mode.
-57-
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CHAPTER SEVEN
A MODEL FOR INDOOR PARTICIPATE MATTER (PM.EXE)
7.1 Model Description
Program PM.EXE implements a generic model for indoor particulate matter (PM)
developed by W. W. Nazaroff and G. R. Cass (Nazaroff and Cass, 1989). The model takes into
consideration: infiltration of ambient PM, interzone air movement, indoor sources, deposition,
filtration, and coagulation. Coagulation is not implemented in this program, however.
The authors describe their model with several equations. See the reference for more
details. Briefly, for a given size group (or section, or bin), its mass concentration in zone i is
calculated from:
V, -£- = p Qn Q +E (i- /js) Qj> Cj - Z £ S + Z ** - *a PS C) - q E GO - fi) (7.1)
"* j-0 j-0 ft-l M
where V; = volume of zone i (m3);
Q = concentration in zone i (|lg/m3);
t = time (h);
p = penetration factor (unitless);
Q01 = air flow from outside to zone i (m3/h);
C0 = concentration in the ambient air (|lg/m3);
fji = filter's removal efficiency for air flow from zone j to zone i and j ^i (unitless);
Qji = air flow rate from zone j to zone i and j ^i (m3/h);
Cj = concentration in zone j (|lg/m3);
Qij = air flow rate from zone i to zone j and j^i (m3/h);
Rk = emission rate for indoor source k (|ig/h);
kD = first-order deposition rate constant (h"1);
Q! = air flow rate passing through the free-standing air filter 1 (m3/h);
f = removal efficiency for the free-standing air filter 1 (unitless);
n = number of air zones;
m = number of indoor sources in zone i; and
q = number of free-standing air filter/cleaners in zone i.
The HVAC system is handled as a special air zone (see Section 7.3.4). For PM deposition, this
program accepts either the first-order deposition rate constant (shown in Eq. 7.1) or the
deposition velocity (not shown in Eq. 7.1). See Section 7.3.1 for more details.
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7.2 A Brief Tour of the Program
NOTE: In this program, the PM concentration is expressed in (|lg/m3), while all other
IAQX programs use (mg/m3) for pollutant concentrations.
As shown in Figure 7.1, seven pages are permanently displayed in this program: Building,
Ventilation, PM Properties, Outdoor Sources, Indoor Sources, Conditions, and Output. Three
more pages are hidden and available on demand (see Section 7.3.1).
1 STKi 1.0 / Indoor Particulale Matter NoName PM
File Model Simulate Graph Jools Help
Building Ventilation PM Properties Outdoor Sources Indoor Sources Conditions Output
^Note Pad
Your note goes here.
^Building Configuration
r Consider Deposition?
N'esi r HO
Units of Deposition Constant:
(Deposition rate const. (1/h) •H
^Number of Air Zone(s)^
Current page = Building
Close
Figure 7.1 Layout of the Building page of the PM program. Note that the user has selected
"Deposition rate const. (1/h)" for calculating deposition rate.
The first page of this program is slightly different from those in other special-purpose
programs. First, unlike other special-purpose programs, this program allows the user to define an
HVAC system in the Building Configuration table. This feature is necessary because air filters
are most likely to be found in the HVAC system. Second, this program allows the user to define
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three types of sink surfaces instead of two. Unlike gas-phase air pollutants, the PM deposition
rate has to do with the orientation of the surfaces. For example, the surface types can be: floor,
ceiling, and walls. The characteristic constant for PM deposition in the indoor environment is
reported in the literature as either deposition velocity or deposition rate constant. This program
accepts either description. See Section 7.3.3 for more details. There are three Help buttons in
this page, two of which are shown in Figure 7.1 The third will appear when you select deposition
velocity rather than deposition rate constant. Click on those buttons for more information about
how to define the HVAC system, deposition rate, and sink types.
The Ventilation page is identical to those in VBX.EXEand SPILLEXE. You should
have no problem entering ventilation parameters. The PM Properties page (Figure 7.2) is used to
define the particle size groups and their deposition velocities or rate constants, depending on your
selection in the Building page. Use the spin editor above the Help button to specify the number
of PM size groups. The minimum value is 1 and the maximum 10. Give each size group a name
that you understand (such as "PM10," "PM2.5," "2-5 |lm," and "<1") and then enter the
deposition velocity or rate constant for each size group.
JSTKi 1.0 / Indoor Particulate Mattel NoName.PM
File Model Simulate Graph Tools Help
@
Building Ventilation PM Properties | Outdoor Sources | Indoor Sources | Conditions | Output]
Number of Size Groups—
P 1
Size Group and Deposition Rate Constant (Dk in 1/h)
Current page = PM properties
Close
Figure 7.2 Layout of the PM Properties page of the PM program.
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Penetration of the outdoor PM is defined in the Outdoor Sources page (Figure 7.3), where
the user is asked to provide the following information:
— type of outdoor PM concentration data;
— infiltration factor; and
— outdoor PM concentrations.
The outdoor PM concentrations can be either constant or time-varying. A demonstration
file called "ambient.pm" shows how to define the time-varying outdoor sources.
;TKi 10 / Indoor Participate Matter NoName.PM
File Model Simulate Graph Jools Help
Building 1 Ventilation I PM Properties Outdoor Sources indoor Sources I Conditions I Output I
Concentration Type^
<•* Constant
r Time-varying
(~ Not aplicable
Outdoor PM Sources
Infiltration Factor (I.F.; Unitless)
Ambient Particle Concentrations (|ig/ms
Cone.
Sizel
Size 2
100
hoo
Current page = Outdoor Sources
Close
Figure 7.3 Layout of the Outdoor Sources page of the PM program.
In the Indoor Sources page (Figure 7.4), the user can define up to five indoor PM sources:
the number is controlled by the spin editor near the top-left corner. If there is more than one
source, you can navigate from one to another by clicking the tabs near the bottom (labeled
"Source (1)," "Source (2),"...).
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Parameters for each source are: (1) source location, (2) emission type, and (3) emission
rate. Currently, you can choose from three emission types: constant, on/off, and time-varying.
See Section 7.3.2 for more information about these emission types.
JSTKi 1.0 /Indoor Participate Mallet NoName.PM HBE3
File Model Simulate Graph Tools Help
DJ B| EB| i| vi ij ml
----- J " * J * J * ""'
Building | Ventilation | PM Prope
rNumber of Indoor Sources
t 3
F7V
rties
| Outdoor Sources Indoor Sources Conditions | Output |
Indoor PM Sources
Location ot source (1) emission type
Zonel J Constant (continous) J
H Emission Rate (E.R.) for Source (1) in ( ug/h ) III
^' Clear |
ft Paste
Source(1) [sourceg) |
Current page = Indoor Sources ^ ^ Jl — ose
Figure 7.4 Layout of the Indoor Sources page of the PM program.
In the Conditions page (Figure 7.5), the user enters the simulation period, output data
points, and non-zero initial concentrations. To define non-zero initial concentrations, click
"Yes" in the selection box labeled "Are There Any Non-Zero Initial Concentrations?" and then
enter the initial concentrations in the table below. The table for initial concentrations will
become invisible if the user clicks "No" in the selection box. The default setting is "No."
After you finish entering all the parameters, compile and then run the model.
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1 STKi 1.0 / Indoor Pacticulate Mallei NoName.PM
File Model Simulate (3raph Joels Help
a
Building J Ventilation | PM Properties | Outdoor Sources ] Indoor Sources Conditions j Output |
Simulation Conditions Are There Any Non-Zero Initial Concentrations?
Simulation Period (h)
Output Data Points
r NO
lYesi
Initial Concentration Table (ug/nr*)
Current page = Conditions
Figure 7.5 Layout of the Conditions page of the PM program.
7.3 More About the PM Program
7.3.1 Calculation of PM Deposition Rate
The PM deposition rate is size dependent. The first-order deposition rate can be
expressed in two ways:
R=
(7.2)
= DkVC
(7.3)
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where R = deposition rate (|J.g/h);
C = indoor concentration of PM in certain size (|J,g/m3);
DV1 = deposition velocity for surface i (m/h);
S; = area for surface i (m2);
n = number of surface materials;
Dk = first-order deposition rate constant (h"1); and
V = room volume (m3).
Since both DV1 and Dk can be found in the literature, this program allows the user to select either
equation to compute the deposition rate. When you choose Eq. 7.2, you can specify more than
one surface type in each zone. On the other hand, Dk in Eq. 7.3 is more of a lumped constant and
the user does not need to know the surface areas. Conversion between the two constants is fairly
straightforward:
D, = ^ (7.4)
V
There are a number of theoretical models in the literature for estimating the PM
deposition velocity in the indoor environment. An article by Lai and Nazaroff (2000) represents
the most recent development in this research area at the time this Guide was prepared. This
article contains a brief review of the previously published deposition models.
7.3.2PM Source Types
In this program, the PM emission rate from an indoor source can be represented by three
emission types: constant, on/off, and time-varying. For the constant type, the emission rate
remains constant during the entire simulation period, and the emission rate for each size group is
represented by a single value. The on/off type allows the user to define a source that is active
only in a user-specified time period. Examples of such sources are cigarette smoking and carpet
vacuuming. This source type requires the user to provide the source start time, end time, and the
emission rates at the start and end times (Table 7.1). Note that the two emission rates do not
have to be the same (see PM10 in Table 7.1). When the two values are different, the emission
rate at any time during the active period is calculated by linear interpolation.
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Table 7.1 An example data input for the on/off source type.
(The user enters values in the unshaded area.)
Time (h)
PM2.5
PM10
2.0
2.5
25000
25000
80000
120000
When the time-varying source type is selected, the user needs to provide a data table such
as the one shown in Table 7.2. Up to 1000 rows of data are allowed. If the emissions data are
stored in a spreadsheet, you can use the Windows clipboard to copy and paste the data from the
spreadsheet by clicking the Paste button.
Table 7.2 An example data input for the time-varying source type.
(The user enters values in the unshaded area.)
Time (h)
PM2.5
PM10
0
1
2.5
5
10
55000
25000
20000
20000
1200
150000
80000
65000
65000
6700
7.3.3 Adding Pages
There are three hidden pages in this program. You need them to define PM filters. To
add pages, click on the Add Page speed button (i.e., the one with a red pound sign) or select
Model/Add page from the main menu.
7.3.4 HVAC Filters. Interzone Filters, and Free-Standing Filters
For convenience, this program lists all filters in three groups: HVAC filters, interzone
filters, and free-standing filters (Figure 7.6 ). The HVAC filters are in-line and are considered
part of the HVAC system. The interzone filters treat the air flow between two zones, one of
which can be the HVAC system. Examples of this type of filter are those located in air registers.
Interzone filters can also be used to represent the PM removal process between two zones due to
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restricted air passage (such as a door seam or windows). Free-standing filters are self-
explanatory and require the user to specify the passing air flow rate.
HVAC System
Figure 7.6 Possible filter positions in three-zone (zone 1, zone 2, and HVAC) configuration.
A = HVAC filter, B = interzone filter, and C = free-standing filter.
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CHAPTER EIGHT
INSIDE IAQX
8.1 Programming Language
All the programs in IAQX version 1.0 are written in Delphi 5 (Professional Edition), a
Microsoft Windows-based Object Pascal compiler developed by Inprise Corporation, 100
Enterprise Way, Scotts Valley, CA 95066-3249, U.S.A.
8.2 Method for Numeric Integration
Except for SLAB. EXE which does not require an integration algorithm, all other IAQX
programs use a fourth-order/fifth-order Runge-Kutta-Fehlburg method (Cheney and Kincaid,
1980) to integrate the system of differential equations that represents the IAQ model. The
method makes six function evaluations at each step and computes simultaneously a fourth- and a
fifth-order approximation, from which an error estimation is made and the step size adjusted.
Computer implementation of this method was originally developed in Fortran by Watts and
Shampine (Forsythe, et al., 1977). This algorithm is fairly effective and does a reasonable job
for non-stiff and moderately stiff systems, but can not handle very stiff situations. The developer
made several minor changes to the code to improve its stability. The local error control was set
to 5x 10"6 (relative error).
8.3 Algorithm for Application-Phase Simulation
Indoor sources with large areas and decaying emission rates, such as newly painted walls,
require special treatment to estimate the emission rate during the application period because the
source area is changing. This is sometimes called application-phase simulation. The algorithm
used in IAQX is based on a method reported by Zeh, et al. (1994). Since the authors did not
provide any proof of the validity of the method, brief derivations are given below.
The most commonly used model for decaying sources is the first-order decay model. Eq.
8.1 (Clausen, 1993) is one of its forms:
ke~hf (8.1)
where R = emission rate (mg/m3);
S = source area (m2);
M0 = amount of pollutant applied to a unit area of surface (mg/m2);
k = first-order decay rate constant (h"1); and
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t = elapsed time (h).
Eq. 8.1 can be rewritten as:
(8.2)
where M = M0 e"kt is the amount of pollutant remaining in a unit area at time t (mg/m2); and
W = S M is the total amount of pollutant remaining in the source (mg).
If we divide a large source into n small increments, then the total emission rate at anytime can be
expressed as:
2, Wi = fc WT (8.3)
2-1
where RT = the total emission rate for the source (mg/h);
m = number of incremental areas; mtA) (8.4)
(8.5)
dt tA
dt
where W0 = total amount of the pollutant in the coating material to be applied (mg); and
tA = duration of the application phase (h).
IAQX adds Eqs. 8.4 and 8.5 to the system of differential equations when the user chooses to
include the application-phase simulation.
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8.4 Algorithm for Estimating Adequate Ventilation Rate (AVR)
Mathematically, this task is similar to the root-trapping process for a non-linear equation,
which involves solving the equation iteratively with different values of the independent variable
until a certain tolerance is met. However, this method requires many iterations and is too time-
consuming for a system of differential equations. IAQX minimizes the number of simulations by
using the third-order Lagrange interpolation.
The user input includes: (1) selection of an air quality criterion, which can be peak
concentration, time-averaged concentration, or cumulative inhalation exposure; (2) a search
range for the ventilation rate, defined by the minimum value Nmm and the maximum value Nmax
(the default values are 0.1 to 20 air exchanges per hour); and (3) a tolerance level (the default
value is 5%). IAQX then performs two simulations at Nmm and Nmax, respectively, followed by
two more simulations at air exchange rates between Nmm and Nmax. Using the four data points, a
third-degree polynomial can be established between the ventilation rate and the indoor pollution
level:
]nN= a + h CR + c CR2 + d Cp3 (8.6)
where N = trial ventilation rate (h"1); and
CR = an indicator of indoor air pollution level (e.g., the peak concentration).
The barycentric form of Lagrange interpolation (Pizer and Wallace, 1983) was used to estimate
coefficients a, b, c, and d in Eq. 8.6. Substituting the desired level of CR into Eq. 8.6 provides an
estimate of AVR (i.e., N in Eq. 8.6). A fifth simulation is then performed at the estimated AVR
to check if the tolerance level is met. If not, the new data point (Q, N) is inserted into the data
array, and the coefficients in Eq. 8.6 are recalculated. This checking process is repeated until the
tolerance is met. With this method, six simulations are usually required to find the AVR at the
tolerance level of 5%.
8.5 Handling of Time-varying Parameters
Time-varying parameters are those given as a data table. Examples are the time-varying
ventilation rate, ambient air as a time-varying pollutant source, and time-varying indoor sources.
If the data points are (tl3 x:), (t^ x2), ... (tn, xn), IAQX calculates the value for x and anytime t
during the simulation by means of linear interpolation. Eqs. 8.7 to 8.9 represent the actual
algorithm used.
x = 0 if ttn (8-7)
x = xf if t= ti (8.8)
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X =
(8.9)
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ACKNOWLEDGMENTS
The author would like to thank the following researchers for testing and/or commenting
on the beta versions of the IAQX (previously dubbed STKi) programs: Michael Jayjock (Rohm
& Haas Company), Stelios Kepalopoulos (European Commission Joint Research Center), Alvin
Lai (University of California at Berkeley), John Little (Virginia Polytechnic Institute and State
University), William Shade (Rohm & Haas Company), Leslie Sparks (U.S. EPANRMRL-RTP),
and Jianshun Zhang (formerly National Research Council Canada; currently University of
Syracuse). Special thanks go to Shirley Wasson of U.S. EPA NRMRL-RTP for a thorough
quality assurance review.
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1. REPORT NO. 2.
EPA-600/R-00-094
4. TITLE AND SUBTITLE
Simulation Tool Kit for Indoor Air Quality and
Inhalation Exposure (IAQX) Version 1.0 User's
Guide
7. AUTHORS
Zhishi Guo
9. PERFORMING ORGANIZATION NAME AND ADDRESS
See Block 12
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
3. RECIPIENT'S ACCESSION NO.
5. RE PORT DATE
October 2000
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1 1 . CONTRACT/GRANT NO.
NA (Inhouse)
1 3. TYPE OF REPORT AND PERIOD COVERED
User's Guide; 1-9/00
1 4. SPONSORING AGENCY CODE
EPA/600/13
TECHNICAL REPORT DATA
(Please read instructions on the reverse before completing)
15. SUPPLEMENTARY NOTES Author Guo can be reached at Mail Drop 54; 919/541-0185.
^.ABSTRACT
User's Guide describes a Microsoft Windows-based indoor air quality
(IAQ) simulation software package designed Simulation Tool Kit for Indoor Air
Quality and Inhalation Exposure, or IAQX for short. This software complements
and supplements existing IAQ simulation programs and is designed mainly for advan-
ced users. The package consists of a general-purpose simulation program and four
stand-alone, special-purpose simulation programs. The general-purpose program
performs multizone, multipollutant simulations and allows gas-phase chemical reac-
tions. The special-purpose programs implement fundamentally based models, which
are often excluded in existing IAQ simulation programs. In addition to performing
conventional IAQ simulations, which compute the time-concentration profile and in-
halation exposure, IAQX can estimate the adequate ventilation rate when certain air
quality criteria are provided by the user, a unique feature useful for product stew-
ardship and risk management. IAQX will be developed in a cumulative manner, and
more special-purpose simulation programs will be added to the package in the future.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Pollution
Mathematical
Models
Simulation
Respiration
Ventilation
18. DISTRIBUTION STATEMENT
Release to Public
b. IDENTIFIERS/OPEN ENDED TERMS
Pollution Control
Stationary Sources
Indoor Air Quality
User's Guide
19. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This Page)
Unclassified
c. COSATI Field/Group
13B
12A
14G
06P
13A
21. NO. OF PAGES
84
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION IS OBSOLETE
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