NISTIR 6476

CONTAMW 1.0 User Manual

Multizone Airflow and Contaminant Transport Analysis Software

W. Stuart Dols 

George N. Walton 

Kevin R. Denton 
NISTIR 6476

CONTAMW 1.0 User Manual 

Multizone Airflow and Contaminant Transport Analysis Software

W. Stuart Dols 

George N. Walton 

Kevin R. Denton 

June 2000 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

U.S. Department of Commerce

William M. Daley, Secretary

Technology Administration

Dr. Cheryl L. Shavers, Undersecretary of Commerce for Technology

National Institute of Standards and Technology

Raymond G. Kammer, Director

iii

Abstract 

This manual describes the computer program CONTAMW developed by NIST. CONTAMW is 

a multizone indoor air quality and ventilation analysis program designed to help you determine: 

airflows ñ infiltration, exfiltration, and room-to-room airflows in building systems driven by 

mechanical means, wind pressures acting on the exterior of the building, and buoyancy effects 

induced by temperature differences between the building and the outside; contaminant 

concentrations ñ the dispersal of airborne contaminants transported by these airflows and 

transformed by a variety of processes including chemical and radio-chemical transformation, 

adsorption and desorption to building materials, filtration, and deposition to building surfaces; 

and/or personal exposure ñ the prediction of exposure of building occupants to airborne 

contaminants for eventual risk assessment. 

CONTAMW can be useful in a variety of applications. Its ability to calculate building airflows is 

useful for assessing the adequacy of ventilation rates in a building, to determine the variation in 

ventilation rates over time, to determine the distribution of ventilation air within a building, and 

to estimate the impact of envelope airñtightening efforts on infiltration rates. The prediction of 

contaminant concentrations can be used to determine the indoor air quality performance of 

buildings before they are constructed and occupied, to investigate the impacts of various design 

decisions related to ventilation system design and building material selection, to evaluate indoor 

air quality control technologies, and to assess the indoor air quality performance of existing 

buildings. Predicted contaminant concentrations can also be used to estimate personal exposure 

based on occupancy patterns. 

Key Words: airflow analysis; building technology; computer program; contaminant dispersal; 

indoor air quality; multizone analysis; smoke control; ventilation 
iv 

Disclaimer 

The Department of Commerce makes no warranty, expressed or implied, to users of the 

CONTAMW computer program, and accepts no responsibility for its use. Users of CONTAMW 

assume sole responsibility under Federal and State law for determining the appropriateness of its 

use in any particular application; for any conclusions drawn from the results of its use; and for 

any actions taken or not taken as a result of analyses performed using CONTAMW. 

Users are warned that CONTAMW is intended for use only by persons competent in the field of 

airflow and contaminant dispersal in buildings and is intended only to supplement the judgment 

of the qualified user. The computer program described in this report is a prototype methodology 

for computing the airflows and contaminant migration in a building. The calculations are based 

upon a simplified model of the complexity of real buildings. These simplifications must be 

understood and considered by the user. 

Certain trade names and company products are mentioned in the text or identified in an 

illustration in order to adequately specify the equipment used. In no case does such an 

identification imply recommendation or endorsement by the National Institute of Standards and 

Technology, nor does it imply that the products are necessarily the best available for the purpose. 
v

Table of Contents 

Abstract.........................................................................................................................................iii

Disclaimer ..................................................................................................................................... iv

1 Introduction ............................................................................................................................. 1

1.1 What is CONTAMW?...................................................................................................... 1 

1.2 What's New in This Version?........................................................................................... 1 

1.3 System Requirements....................................................................................................... 1

2 Getting Started ........................................................................................................................ 2

2.1 Installing CONTAMW..................................................................................................... 2 

2.2 Running CONTAMW...................................................................................................... 2 

2.3 User Tasks........................................................................................................................ 3 

2.4 The CONTAMW Graphical User Interface..................................................................... 5 

2.5 Components of a CONTAMW Project ............................................................................ 7 

3 Using CONTAMW................................................................................................................ 10

3.1 Working with the SketchPad.......................................................................................... 10 

3.2 Working with Project Files ............................................................................................ 15 

3.3 Configuring CONTAMW .............................................................................................. 17 

3.4 Working with Walls ....................................................................................................... 18

3.5 Working with Levels...................................................................................................... 20

3.6 Working with Zones....................................................................................................... 22

3.7 Working with Airflow Paths .......................................................................................... 25 

3.8 Working with Simple Airñhandling Systems ................................................................ 44 

3.9 Working with Ducts ....................................................................................................... 49

3.10 Working with Contaminants .......................................................................................... 61 

3.11 Working with Sources and Sinks ................................................................................... 67 

3.12 Working with Occupant Exposure ................................................................................. 74 

3.13 Working with Data and Libraries................................................................................... 77 

3.14 Working with Weather and Wind .................................................................................. 81 

3.15 Working with Schedules ................................................................................................ 87 

3.16 Working with Simulations ............................................................................................. 90 

3.17 Working with Simulation Results .................................................................................. 96 

3.18 Working with Project Annotations............................................................................... 105 

3.19 Getting Help ................................................................................................................. 105 

4 Special Applications of CONTAMW ................................................................................ 106

4.1 Building Pressurization Test ........................................................................................ 106 

4.2 Smoke Control Systems ............................................................................................... 107 

4.3 Shafts............................................................................................................................ 107 

5 Theoretical Background ..................................................................................................... 109

5.1 Model Assumptions...................................................................................................... 109 

5.2 Contaminant Analysis .................................................................................................. 111 

5.3 Airflow Analysis .......................................................................................................... 115 

6 References ............................................................................................................................ 132
vi 

 INTRODUCTION ñ WHAT IS CONTAMW? 

1

1 Introduction 

1.1 What is CONTAMW? 

CONTAMW is a multizone indoor air quality and ventilation analysis computer program 

designed to help you determine: 

 (a) airflows: infiltration, exfiltration, and room-to-room airflows in building systems driven 

by mechanical means, wind pressures acting on the exterior of the building, and 

buoyancy effects induced by the indoor and outdoor air temperature difference. 

(b) contaminant concentrations: the dispersal of airborne contaminants transported by these 

airflows; transformed by a variety of processes including chemical and radio-chemical 

transformation, adsorption and desorption to building materials, filtration, and deposition 

to building surfaces, etc.; and generated by a variety of source mechanisms, and/or 

(c) personal exposure: the predictions of exposure of occupants to airborne contaminants for 

eventual risk assessment. 

CONTAMW can be useful in a variety of applications. Its ability to calculate building airflows is 

useful to assess the adequacy of ventilation rates in a building, to determine the variation in 

ventilation rates over time and the distribution of ventilation air within a building, and to 

estimate the impact of envelope air tightening efforts on infiltration rates. The prediction of 

contaminant concentrations can be used to determine the indoor air quality performance of a 

building before it is constructed and occupied, to investigate the impacts of various design 

decisions related to ventilation system design and building material selection, and to assess the 

indoor air quality performance of an existing building. Predicted contaminant concentrations can 

also be used to estimate personal exposure based on occupancy patterns in the building being 

studied. Exposure estimates can be compared for different assumptions of ventilation rates and 

source strengths. 

1.2 What's New in This Version? 

CONTAMW runs under the Windows operating system and employs a Windows graphical 

user interface. CONTAMW maintains the same features as CONTAM96 [Walton 1997] and is 

backwards compatible with that version of the program. This means that you can use 

CONTAMW to work with projects created with CONTAM96. 

1.3 System Requirements 

CONTAMW must be run under Windows 95/98 or Windows NT. 
GETTING STARTED ñ INSTALLING CONTAMW 

2

2 Getting Started 

2.1 Installing CONTAMW 

Obtaining CONTAMW 

CONTAMW installs from a set of installation files that you can obtain from NIST. These files 

can either be downloaded from the NIST website (www.bfrl.nist.gov/863/contam) directly onto 

your computer's hard disk, or you can obtain a set of floppy disks that contains the setup files 

from the Indoor Air Quality and Ventilation Group (301) 975-6431. 

Installing CONTAMW 

If you downloaded CONTAMW from the NIST website then you first double click the selfextracting archive file "contamz.exe" to decompress the setup files. Extract the files to the 

subdirectory of your choice, or simply select the default location. Once you have extracted the 

setup files, you can run the setup program, "setup.exe." This will prompt you to perform an 

automatic installation of the program. Read the directions to complete the installation. 

To install from a set of floppy disks, insert the disk labeled "Disk 1" into the floppy drive and run 

the program, "setup.exe." This will prompt you to perform an automatic installation of the 

program. Follow the directions to complete the installation. 

Uninstalling CONTAMW 

The CONTAMW setup program will also provide you with an uninstall feature. You uninstall 

CONTAMW much as you would a typical Windows program. Access the Control Panel from 

the Settings selection of the Start menu. Select Add/Remove Programs from the Control Panel. 

Select CONTAMW from the list of installed programs and click the "Add/RemoveÖ" button to 

uninstall CONTAMW. 

2.2 Running CONTAMW 

After you install CONTAMW, you can run it by selecting CONTAMW from the NIST program 

group of the Start menu. 
GETTING STARTED ñ USER TASKS 

3

2.3 User Tasks 

The use of CONTAMW to analyze of airflow or contaminant migration in a building involves 

five distinct tasks: 

1. Building Idealization: Form an idealization or specific model of the building being 

considered, 

2. Schematic Representation: Develop a schematic representation of the idealized building 

using the CONTAMW SketchPad to draw the building components, 

3. Define Building Components: Collect and input data associated with each of the building 

components represented on the SketchPad, 

4. Simulation: Select the type of analysis you wish to conduct, set simulation parameters, 

and execute the simulation, 

5. Review & Record Results: Review the results of your simulation and record selected 

portions of the results. 

Task 1 ñ Building Idealization 

Building idealization refers to the simplification of a building into a set of zones that are 

relevant to the userís goal in performing an analysis. A building can be idealized in a number 

of ways depending on the building layout, the ventilation system configuration and the 

problem of interest. This idealization phase of analysis requires some engineering knowledge 

on the part of the user and is an acquired skill that you can develop through experience in 

airflow and indoor air quality analysis and by becoming familiar with the theoretical 

principles and details upon which indoor air quality analysis is based. 

It is important to note that CONTAMW provides a macroscopic model of a building. In this 

macroscopic view, each zone is considered to be well-mixed. Well-mixed means that a zone 

is characterized by a discrete set of state variables, i.e., temperature, pressure and 

contaminant concentrations. CONTAMW is well suited for analyzing the interaction between 

the zones of a building on a macroscopic level but is not well suited for the analysis of the 

microscopic airflow and contaminant characteristics within a given zone of a building. 

Computational Fluid Dynamics (CFD) analysis is better suited for analyzing the airflow and 

contaminant transport characteristics of a given zone of a building. However, to date the 

computational resources required to perform a CFD analysis for an entire building is 

prohibitive. 

Task 2 ñ SketchPad Representation 

Developing the SketchPad representation will be the focus of your interaction with 

CONTAMW. With CONTAMW's SketchPad you will be able to draw a diagram - a 

SketchPad diagram - of your building idealization using drawing tools and libraries of icons 

to represent components of the building system. CONTAMW translates your diagram into a 

system of equations that will than be used to model the behavior of the building when you 

perform a simulation. 
GETTING STARTED ñ USER TASKS

4

Task 3 ñ Define Building Components 

Data entry can be one of the more timeñconsuming parts of the process of using 

CONTAMW. It involves the determination and input of the numerical values of the 

parameters associated with each of the SketchPad icons. These icons represent the elements 

of the building model and include air leakage paths (windows, doors, cracks), ventilation 

system elements (fans, ducts, vents), contaminant sources, filters, and sinks. Each of these 

elements is associated with a number of parameters, and you must obtain the values of these 

parameters for entry into the model. Depending on the element and the application, these 

values can be obtained from buildingñspecific data, engineering handbooks, and product 

literature. In many cases, a degree of engineering judgment will be involved. CONTAMW 

allows you to create libraries of these elements that you can use in current and future 

modeling efforts. 

Task 4 ñ Simulation 

Simulation is the use of CONTAMW to solve the system of equations assembled from your 

SketchPad representation of a building to predict the airflow and contaminant concentrations 

of interest. This step involves determining the type of analysis that is needed; steady- state, 

transient or cyclical, and a number of other simulation parameters. These parameters depend 

on the type of analysis you wish to perform (steady state or transient), and include 

convergence criteria and in the case of a transient analysis, time steps and the duration of the 

analysis. 

Task 5 ñ Review & Record Results 

CONTAMW allows the user to view the simulation results on the screen and to output them 

to a file for input to a spreadsheet program or a data analysis program developed by the user. 

Airflows and pressure differences at each flow element can be viewed directly on the 

SketchPad. Contaminant concentrations for a zone can also be plotted as a function of time 

directly from the SketchPad. The user can then decide which data they wish to examine more 

closely and export these to a file for later analysis. 
 GETTING STARTED ñ THE CONTAMW GRAPHICAL USER INTERFACE 

5

2.4 The CONTAMW Graphical User Interface 

The CONTAMW graphical user interface (GUI) is what you use to create and view your airflow 

and contaminant dispersal analysis projects. It consists mainly of a drawing region referred to as 

the SketchPad, a set of drawing tools, a title bar, a set of menus, and a status bar. The following 

sections provide brief explanations of each of the features of the CONTAMW GUI. See the 

Using CONTAMW section for details on how to use these features. 

Title Bar 

Menu 

Toolbar 

SketchPad 

Status Bar 

2.4.1 SketchPad 

The SketchPad is the region of the CONTAMW screen where you draw the schematic 

representation of a building you wish to analyze. This representation is in the form of a set of 

simplified floor plans that represent the levels of a building. The SketchPad is used to establish 

the geometric relationships of the relevant building features and is not intended to produce a 

scale drawing of a building. It should be used to create a simplified model where the walls, 

zones, and airflow paths are topologically similar to the actual building (See Working with the 

SketchPad).

2.4.2 Title Bar 

The title bar is the typical rectangular region at the top of the main CONTAMW window. The 

CONTAMW project filename will be displayed within this region. 

2.4.3 Menu 

The menu is typical of a Windows program with differences that provide functionality specific 

to the CONTAMW application. It is through this menu that most CONTAMW operations can be 

performed including: saving and retrieving project files, selecting various modes of display, 

setting up and performing simulations, as well as accessing the on-line help system. Note that 

some of the menu items have shortcuts or hot-keys that enable quick access; for example, to save 

the current project file use the Ctrl+S key combination. 
GETTING STARTED ñ THE CONTAMW GRAPHICAL USER INTERFACE

6

2.4.4 Toolbar 

The toolbar, shown in the following figure, appears below the menu and provides convenient 

shortcuts to some of the menu items. Several of the toolbar buttons are similar to those found in 

other Windows applications. Other buttons provide a shortcut to functionality specific to 

CONTAMW. 

 

2.4.5 Status Bar 

The status bar, shown in the following figure, is the region displayed below the SketchPad at the 

bottom of the main window. This region is broken up into three separate panes that display 

various information depending on the current mode of the SketchPad. In the normal mode of 

operation, the leftmost pane displays summary information of the currently highlighted cell or 

icon. In the simulation results viewing mode, the leftmost pane displays the results for the 

currently highlighted icon. In the normal mode of operation, the center pane indicates the 

location of the currently highlighted icon or cell in SketchPad coordinates (numbered from the 

top-left corner). In the simulation results viewing mode the center pane displays the current 

simulation time step for which the results are being displayed. The rightmost pane displays the 

name and number of the current level and the total number of levels in the project. 

 

Status Bar during Normal Mode of operation 

 

Status Bar during Results Viewing Mode of operation 
 GETTING STARTED ñ COMPONENTS OF A CONTAMW PROJECT 

7

2.5 Components of a CONTAMW Project 

This section provides an overview of the components with which you will work when 

developing projects and performing analyses with CONTAMW. These components include the 

files generated by CONTAMW, building components you use to develop building descriptions, 

occupants used for performing exposure analysis, weather and simulations. 

2.5.1 Project Files 

All data related to the characteristics of the projects you work with are stored in a "project" file 

having a "PRJ" extension (See Working with Project Files). This is an ASCII file, which is 

intended to be "viewed" only by the CONTAMW program. You should keep careful records of 

your project files and establish a naming convention that is meaningful to you for the various 

versions of a project that you may wish to save. 

There are other files utilized by CONTAMW including: simulation results files, weather files, 

library files, and the log file. Simulation results are stored in files created automatically by 

CONTAMW with the same name as the PRJ file except that the "PRJ" extension is replaced by 

the "SIM", "SUM" and "EXP" extensions depending on the type of results generated by the 

simulation (see Working with Simulation Results). Weather files, typically given the "WTH" 

extension, may contain up to a years worth of weather and outdoor contaminant data and are 

used when performing transient simulations (see Working with Weather). Weather files are 

ASCII files, but the data is of a format unique to CONTAMW. Library files are the means by 

which you can share various types of data between CONTAMW projects. Each type of library 

data has a different extension: "LB1", "LB2", "LB3" or "LB4". You create libraries of data using 

CONTAMW (see Working with Data and Libraries). The log file, "CONTAMW.LOG," is 

created in the directory in which the executable program resides each time you run the program. 

This file keeps track of operations that you perform during your session with CONTAMW and is 

a useful tool in the event that you require technical support from the program developers when 

working with the program (see Getting Help). 

2.5.2 Building Components 

Building components are the items that characterize the physical makeup of a building that you 

define using the CONTAMW graphical user interface. This section briefly describes these 

components. 

Levels 

CONTAMW represents buildings in terms of multiple levels, accounting for the 

communication of air and contaminants between these levels. Levels typically correspond to 

floors of a building, but a suspended ceiling acting as a return air plenum or a raised floor 

acting as a supply plenum may also be treated as a level. 

Walls 

Walls are used to designate zones which are regions surrounded by walls, floor and ceiling. 

These walls include the building envelope and internal partitions with a significant resistance 

to airflow. 
GETTING STARTED ñ COMPONENTS OF A CONTAMW PROJECT

8

Floors and Ceilings 

Floors and ceilings are included implicitly by CONTAMW for building zones. When you 

draw a zone on the SketchPad, CONTAMW automatically includes the floor of the zone. To 

create a roof with penetrations into the floor below requires a blank level above the top floor. 

It is also possible to create a phantom zone with no floor or ceiling as might be required to 

create an atrium that spans multiple levels (see Working with Zones).

Zones 

A zone indicates a volume of air with uniform temperature and contaminant concentration. 

There are three types of zones in CONTAMW: normal, phantom and ambient. Normal zones 

are separated from the zone below by a floor. The ambient zone, which surrounds the 

building is implicitly defined and is identified by the symbol at the upper-left corner of the 

SketchPad. Any additional ambient zones must be connected to the default ambient zone. For 

example, you could use an ambient zone icon to define a courtyard. Phantom zones indicate 

that the area on the current level is actually part of the zone on the level immediately below. 

There is no floor between a phantom zone and the zone below. You could use the phantom 

zone to define building features such as an atrium.

Airflow Paths 

An airflow path indicates some building feature by which air can move from one zone to 

another. Such features include cracks in the building envelope, open doorways, and fans. 

Path symbols placed on the walls are used to represent openings between zones or to 

ambient; any other placement represents an opening in the floor to the zone on the level 

below. CONTAMW can implement several different models or airflow elements to define 

airflow paths. The basic categories of airflow elements or models are as follows: small and 

large crack/openings represented by power-law and quadratic pressure relationships, small 

and large doorways elements, and fan/forced airflow elements. (See Working with Airflow 

Paths) 

Simple Airñhandling Systems 

The simple airñhandling system (AHS) provides a simple means of introducing an airñ

handling system into a building without having to draw a duct system. It provides a 

reasonable model of an airñhandling system that delivers userñspecified flows where the 

system is properly balanced and the fan is not impacted by any other pressurizing effects in 

the building. The AHS consists of two implicit airflow nodes (return and supply), three 

implicit flow paths (recirculation, outdoor, and exhaust air), and multiple supply and return 

points that you place within the zones of the building. You can set the airflows of the AHS to 

vary according to a schedule. 

Ducts 

You can use ducts to implement a more detailed model of an airñhandling system that 

handles a broader range of conditions. For example, when an air handler is off, the ductwork 

may provide flow paths between zones which are significant in relation to the normal 

construction cracks or openings. Ductwork consists of duct segments (paths) and junctions or 

terminal points (nodes). CONTAMW can implement several different duct segment models 

or duct flow elements to define duct segments. The basic categories of duct flow elements are 
 GETTING STARTED ñ COMPONENTS OF A CONTAMW PROJECT 

9

as follows: resistance models, fan performance curves, and back-draft dampers. (See 

Working with Ducts) 

Contaminants, Sources and Sinks 

You can define up to ten contaminants within a single project with a practically limitless 

number of sources associated with the contaminants. CONTAMW can simulate contaminant 

transport via airflow between zones, removal by filtration mechanisms associated with flow 

paths, and removal and addition by chemical reaction. CONTAMW can also implement 

several source and sink models to generate contaminants within or remove contaminants 

from a zone. These models include: constant generation, pressure driven, decaying source, 

cutoff concentration, reversible boundary layer diffusion, and burst models. (See Working 

with Contaminants and Working with Sources and Sinks) 

Schedules 

Schedules are used to control or modify various properties of building components as a 

function of time. You can set schedules for airflow paths, duct flow paths; contaminant 

sources and sinks; and inlets, outlets and outdoor air delivery of simple airñhandling systems. 

The effect of setting a schedule on a building component varies depending on the properties 

of the component. For example, you can set a schedule to adjust the airflow delivered to a 

zone by an inlet of a simple airñhandling system. (See Working with Simple Air Handling 

Systems) 

2.5.3 Occupants 

Occupants can be used to determine the amount of contaminant exposure a person would be 

subjected to within a building. Occupants can also generate contaminants. You can set a schedule 

to establish each occupantís movement within a building. Occupant schedules can also be used 

to define periods of times when occupants are not in the building. (See Working with Occupant 

Exposure) 

2.5.4 Weather 

CONTAMW enables you to account for either steady-state or varying weather conditions. 

Weather conditions consist of ambient temperature, barometric pressure, wind speed and 

direction, as well as ambient contaminant concentrations. 

2.5.5 Wind Pressure Profiles 

Wind pressure profiles are used to describe the wind direction effects on the envelope of a 

building. Wind pressure profiles simplify the somewhat difficult process of accounting for the 

fact that the facades of a building envelope are affected differently depending on their orientation 

relative to the wind. 

2.5.6 Simulation 

In CONTAMW, simulation is the process of forming a set of simultaneous equations based upon 

the information stored in the project file, performing the numerical analysis to solve the set of 

nodal equations according to user-defined specifications, and creating a simulation results file 

that can be viewed using the CONTAMW interface. There are three basic types of simulations 

that you can perform for airflow and contaminant analysis using CONTAMW: steady state, 

transient and cyclical. (see Working with Simulations) 
USING CONTAMW ñ WORKING WITH THE SKETCHPAD

10

3 Using CONTAMW 

This section provides detailed information on how to use the features of the CONTAMW 

application as well as a detailed explanations of the terminology of the user interface. You 

should think of this section as your detailed conceptual and contextual guide to working with the 

CONTAMW program. 

3.1 Working with the SketchPad 

The SketchPad is the region of the CONTAMW screen where you draw the schematic 

representation of a building you wish to analyze. This representation is in the form of a set of 

simplified floor plans that represent the levels of a building. The SketchPad consists of an 

invisible array of cells into which you place various icons to form your schematics of a building. 

The SketchPad is used to establish the geometric relationships of the relevant building features 

and is not intended to produce a scale drawing of a building. It should be used to create a 

simplified model where the walls, zones, and airflow paths are topologically similar to the actual 

building. 

When working with CONTAMW you will notice a blinking square on the SketchPad. This is 

known as the system caret, and it is the size of a single SketchPad cell. This caret is the same 

thing as the blinking vertical bar that is common to many word processing applications. The 

caret indicates the currently selected cell of the SketchPad. Any icon-related information that 

appears in the status bar is associated with the location of the caret. To move the caret around the 

SketchPad you can use the keyboard arrow keys or you can move the system cursor with the 

mouse and click the left mouse button to set the caret position. 

The specific operations that you will perform using the SketchPad are as follows: 

 1. Drawing Walls and Ducts 

 2. Drawing building component icons 

 3. Defining building component icons 

 4. Viewing results 

 5. Viewing envelope pressure differentials due to wind effects 
 USING CONTAMW ñ WORKING WITH THE SKETCHPAD 

11

3.1.1 Drawing Walls and Ducts 

You use various tools to draw the physical features of the building such as walls and ducts. All 

drawing can be accomplished with either the mouse or the keyboard. When drawing, the 

following mouse and keyboard keys produce common behavior. The left mouse button (LMB) 

corresponds to the ↵, or Enter key; the right mouse button (RMB) to the Esc key. Vertical 

motion of the cursor corresponds to the ↑ and ↓ cursor keys, and horizontal motion corresponds 

to the ← and → cursor keys. 

The basic steps for drawing walls and ducts are as follows: 

1. Activate drawing tool, 

2. Set the initial location of the object, 

3. Draw the object, 

4. Undo current drawing, 

5. Finalize drawing the object, and 

6. Deactivate drawing tool. 

Activating a Drawing Tool 

There are three drawing tools available, two for drawing walls and one for drawing ducts. To 

activate a drawing tool either select it from the toolbar, select it from the "Tools" menu, or use 

the shortcut associated with the menu item. The toolbar button of a selected drawing tool will 

remain depressed as long as that tool is active. The toolbar buttons and associated menu shortcuts 

are shown here. 

 rectangle (or box) drawing tool (Ctrl+B) 

 free-form wall drawing tool (Ctrl+W) 

 duct drawing tool (Ctrl+D) 

Once you have selected the tool, the drawing cursor will be displayed. The drawing cursor is a 

pink square the size of a single SketchPad cell. Initially, the cursor appears with a transparent 

center. 

Setting the Initial Location of the Object 

To begin drawing the object, you set the initial location by first moving the drawing cursor either 

with the mouse or the keyboard arrow keys and then you either click the LMB or press ↵ on the 

keyboard. This will anchor the beginning of the object at the nearest valid SketchPad cell for the 

type of object you are drawing. When you select a valid beginning location, the drawing cursor 

will become solid and you can begin drawing your object. 

Drawing the Object 

After you anchor the beginning of the object, you simply use the mouse and/or keyboard arrow 

keys to draw the desired shape. While you are drawing, the cursor will be restricted to the 

SketchPad region and constrained to specific movements in order to maintain drawing within 

valid cells of the SketchPad. As you move the cursor, a dark line will appear on the SketchPad 

representing the shape of the object you are drawing. 
USING CONTAMW ñ WORKING WITH THE SKETCHPAD

12

Undoing the Current Drawing 

Prior to finalizing the drawing of the object, you can undo your drawing. To undo what you have 

drawn, either single-click the RMB or press the Esc key. This will erase the thick dark line, but 

you will still be in the drawing mode. To begin drawing again, set the initial location again and 

continue drawing another object. 

Finalizing the Drawing Object 

Once you are satisfied with your drawing, you finalize the object by either single-clicking the 

LMB or pressing the ↵ key. This will replace the cells that had the thick dark line with the icons 

appropriate for completing the type of object you are drawing. If you have attempted to draw an 

invalid object, you will be prompted with a dialog box containing a message indicating the type 

of error, and then you will be allowed to repair the drawn object. 

Deactivating Drawing Tools 

When you are finished using a drawing tool you click the RMB or press Esc until your system 

cursor reappears. Also, selecting a different drawing tool will automatically deactivate the 

current tool if you do not currently have an object anchored. 

3.1.2 Drawing Building Component Icons 

A set of icons is used to represent various building components such as airflow paths 

(representing doors, windows, cracks, etc.), contaminant sources and sinks, occupants and airñ

handling systems. You place icons on the SketchPad using the Right Mouse Button to display 

a pop-up menu and then selecting the desired building component from the menu. 

This icon placement menu is context-sensitive. The menu selections that you can choose from 

the icon placement menu will depend on the contents of the cell occupied by the caret and 

whether the SketchPad is currently displaying simulation results. When results are being 

displayed, you will not be allowed to place additional icons on the SketchPad. The icon 

placement menu will also prevent you from placing icons on invalid SketchPad locations. For 

example, you cannot place an inlet or outlet of a simple airñhandling system within the ambient 

zone. 

The following figure shows the pop-up icon placement menu. 

 
 USING CONTAMW ñ WORKING WITH THE SKETCHPAD 

13

The following table is a list of the icons that you will see on the CONTAMW SketchPad. This 

list shows the icons by categories of building components. Some of these icons are placed on the 

SketchPad using the drawing tools, and others are placed using the pop-up icon placement menu. 

3.1.3 Defining Building Component Icons 

When a new building component icon is drawn upon the SketchPad, it appears as a red icon. The 

color red indicates that the parameters of the component must still be defined. To define a 

building component, you double-click (LMB) on the icon or move the caret (represented by a 

black square) to the icon and press the Enter key. This will activate the associated dialog box or 

property sheet for the selected component, into which you enter the parameters that define the 

component. After you have entered the parameters of the component, click the OK button to 

accept the parameters or the Cancel button not to accept the parameters. The detailed properties 

of each component icon will be presented throughout the "Using CONTAMW" section of this 

manual. You can also access detailed descriptions of the component properties by pressing the 

F1 key (Help) while running the CONTAMW application. 

3.1.4 Deleting Building Component Icons 

To delete undefined building component icons, you highlight the icon then delete it. You 

highlight the icon by either clicking (LMB) on the icon or moving the caret (represented by a 

black square) to the icon using the arrow keys. You delete the highlighted icon by either pressing 

the Delete key or using the menu command: Edit → Delete.

Icon Category Component Icons 

Walls 

Zones 

Duct Segments 

Duct Junctions 

Duct Terminals 

Simple AHS 

Airflow Paths 

Source/Sinks 

Occupants 
USING CONTAMW ñ WORKING WITH THE SKETCHPAD

14

3.1.5 Viewing Results on the SketchPad 

CONTAMW provides some graphical displays of simulation results upon the SketchPad. You 

can display airflow rates and pressure differences across airflow paths on the SketchPad if a 

simulation has been performed and results of the simulation are available (see Viewing Results 

in the Working with Results section of the manual). 

3.1.6 Viewing Envelope Wind Pressure Differentials 

CONTAMW provides a feature that allows you to visualize the effects of wind upon a building 

envelope. A graphical display of wind pressures at each of the flow paths that are adjacent to the 

ambient zone can be viewed on the SketchPad (see Checking Wind Pressure Data in the 

Defining Steady State Weather and Wind section of the manual). This feature enables you to 

verify input of wind speed and direction data with respect to the orientation of the building 

envelope to the wind. 
 USING CONTAMW ñ WORKING WITH PROJECT FILES 

15

3.2 Working with Project Files 

All information related to the layout, building components, and occupant information of your 

CONTAMW project are stored in a "project" file. When you save the project file, it will be 

stored with the ".prj" extension. CONTAMW project file names must conform to the file naming 

conventions of the Windows operating system. This project name is displayed in the Title bar 

of the CONTAMW application window. 

All project file operations are contained under the File menu. These operations include: New 

Project, Open ProjectÖ, Save Project, and Save Project AsÖ Note that some of these file 

operations have keyboard short-cuts and/or tool bar buttons associated with them. 

Creating a New Project 

Menu Command: File → New Project

Keyboard Shortcut: None 

Toolbar Button: 

Use this command if you are currently working on a project and you wish to create a new one. 

This command will clear the SketchPad and all data related to the current project from 

CONTAMW's program memory. If your current project has been not been saved prior to 

executing this command, you will be asked whether or not you wish to save it prior to clearing it. 

Opening an Existing Project 

Menu Command: File → Open ProjectÖ

Keyboard Shortcut: Ctrl+O

Toolbar Button: 

Use the menu item to open and existing CONTAMW project file. This command will display the 

File Open dialog box typical of Windows applications. This dialog box is set to display only 

those files having the ".PRJ" extension in order to simplify your search for CONTAMW project 

files. Follow the typical procedure for opening a file using the Windows operating system. 

Saving a Project 

Menu Command: File → Save Project

Keyboard Shortcut: Ctrl+S

Toolbar Button: 

This option saves the building description to the project file under its current name. Whenever 

the project file is saved, the current version of the file is copied to CONTAM.BKP before a 

revised project file is written. You may be able to use this file to restore a project file in the event 

that it becomes corrupted. 
USING CONTAMW ñ WORKING WITH PROJECT FILES

16

Renaming a Project 

Menu Command: File → Save Project AsÖ

Keyboard Shortcut: None 

Toolbar Button: None 

Use this command to save a copy of the current project file under a new name. This will display 

the Windows "Save As" dialog box and allow you to specify both a storage location and a file 

name for the project file. CONTAMW will automatically append the ".prj" extension to the 

filename, so you do not have to give the file an extension. If you do give the file an extension, 

".prj" will be appended as well as the extension you provide. If you specify the name of an 

existing file, you will be warned that saving the file will overwrite the existing file. If you try to 

save an untitled or new project file prior to giving it a name, the "Save As" dialog box will be 

displayed. 

Exiting CONTAMW 

Menu Command: File → Exit

Keyboard Shortcut: None 

Toolbar Button: None 

You can also exit the program using the standard window-closing button located in the upper 

right-hand corner of the program window. 
 USING CONTAMW ñ CONFIGURING CONTAMW 

17

3.3 Configuring CONTAMW 

The project configuration settings of CONTAMW are available from the OptionsÖ selection of 

the View menu. This set of configuration properties will allow you to select the overall size of 

the SketchPad (i.e. the number cells that make up the height and width), the size of a single 

SketchPad cell, the default system of units (SI or IP), the default units of mass flow and the 

default zone temperature. All of these settings are saved with the CONTAMW project with the 

exception of the cell size that resets back to the smaller size whenever you exit CONTAMW. 

The following sections provide detailed descriptions of the specific configuration properties. 

They are the context-sensitive help topics that you can access by pressing F1 when working with 

property pages of the "Project Configuration Properties" property sheet. 

3.3.1 SketchPad Size 

Sketchpad Size (cells): This is the height and width of the SketchPad. The units (cells) represent 

each space where an icon may be placed upon the SketchPad. The default (and minimum) values 

are 66 cells wide and 58 cells high. 

Shift Drawing (cells): If you need more space on one side of a drawing you can shift the entire 

project on the SketchPad. You may need to increase the size of the SketchPad to make room for 

the project before shifting it. Entering a positive number in the "Horizontally" edit box will shift 

the project to the right relative to the SketchPad, and entering a positive number in the 

"Vertically" edit box will move the project down relative to the SketchPad. A negative number 

will have the opposite effect. 

Cell/Icon Size: You have two options for displaying icons on the SketchPad. The default option 

is Normal (8x8 pixels) and the other option is Large (16x16 pixels). "Large" doubles the size of 

the SketchPad and icons on the screen for better visibility. This is a visual aid and has no effect 

on the project simulation. 

3.3.2 Default Units and Values 

The following parameters define the units and selected values that will be used by default 

throughout the project when you are providing input to the program. You do not have to use 

these units throughout the project; however, you should select the primary set of units for 

convenience when entering data throughout a project. You can change these defaults at any time 

while working with a project, and you can select different units for individual parameters as you 

enter them. 

Default System of Units: You can select the appropriate radio button to set the system of units 

that you would like the program to use. You can either select the International System of Units 

(SI) or the Inch-Pound (IP) system of units. 

Default Units of Flow: You can select the appropriate radio button for the most commonly used 

units of flow in the current project. These are the units in which airflow simulation results will be 

displayed within the status bar. CONTAMW converts all airflow rates to and performs all 

calculations in mass flow units of kg/s. Note that all volumetric airflow rate units are at standard 

temperature and pressure. 

Default Zone Temperature: This value will be the default temperature used whenever you 

create a new zone within the current project. 
USING CONTAMW ñ WORKING WITH WALLS

18

3.4 Working with Walls 

In CONTAMW, walls separate regions of uniform air temperature and contaminant 

concentration on a given level. Walls include the building envelope and internal partitions with a 

significant resistance to airflow. The enclosed regions you create within walls are known as 

zones. You will note when drawing on the SketchPad that you can only draw walls in odd 

numbered rows and columns. This is done to avoid conflicts with ducts that can only be drawn 

on the even rows and columns of the SketchPad. 

It is important to realize that CONTAMW is not meant to provide drawing capabilities similar to 

that of a Computer Aided Drawing (CAD) program. The SketchPad drawing functions were 

designed to provide a strict environment for creating the input to the underlying multizone model 

upon which the CONTAMW simulation engine is based. 

3.4.1 Drawing Walls 

You can draw walls using either of the two wall drawing tools previously described in the 

"Working with the SketchPad" section. Use the box drawing tool to quickly draw a rectangular 

region and the wall drawing tool to draw a free form wall. Use the wall drawing tool to draw 

almost any shape wall. Walls must always form complete enclosures. Therefore, a wall cannot 

have an open or dangling end. It also may not be drawn across building component icons. You 

will receive a warning message if you attempt to draw an invalid wall. 

3.4.2 Deleting Walls 

You can delete a wall by moving the caret to any portion of the wall and selecting Delete from 

the Edit menu or using the keyboard shortcut Del key. CONTAMW will highlight the section of 

wall to be deleted and request confirmation to delete the indicated section. If the caret is on the 

intersection of three or more walls, you will be given multiple options of wall segments to delete. 

If you select "No" when asked to confirm deletion, the next option for deletion will become 

highlighted until you either delete a section or all of the options are exhausted. 
 USING CONTAMW ñ WORKING WITH WALLS 

19

3.4.3 Modifying Walls 

You modify the positions or shapes of walls by adding and deleting wall sections. For example 

in the following figures, if you want to modify the zone in figure (a) to obtain the zone in figure 

(d), you would first add the dark line in figure (b) then delete the dark line in figure (c). 

 

When modifying walls you may need to move or delete other icons. For example in the 

following figures, to create drawing (c) from drawing (a), you would delete the lighter line and 

the lighter zone icon from figure (b). You must delete one of the two zone icons, or you will end 

up with two zone icons within the same enclosed wall area. This is not permitted, and you will 

receive a message indicating a zone definition error. 
USING CONTAMW ñ WORKING WITH LEVELS

20

3.5 Working with Levels 

CONTAMW projects are organized by levels. Each level of a CONTAMW project contains a 

plan view drawing. Typically, each level of a CONTAMW project corresponds to a floor of a 

building. Depending on the detail required for your modeling purposes, you could represent a 

building floor using multiple CONTAMW layers. For example, a level could be used to 

represent a ceiling or floor plenum. 

3.5.1 Creating Levels 

When you first start CONTAMW, a default level is created so that you can begin working on a 

drawing right away without having to create a new level. There are three commands in the Level

menu that you use to when creating new levels. These are the Copy Level, Paste Level, and 

Insert Blank Level commands. Whenever you create a new level, whether it is blank or a copy 

of another level, CONTAMW will give it a default name that will consist of a number enclosed 

within the "<" and ">" characters. You can modify this name later by editing the data associated 

with a level. 

You must be careful when copying levels within CONTAMW. For example, you might have an 

air handler defined within a duct system on a level and then copy it to another level. This would 

create another air handler on the new level. If the ductwork is connected between the two levels, 

the two air handlers may act against each other. You must be careful to make connections 

between building levels in a manner that makes sense for your purposes. 

Creating Blank Levels 

Menu Command: Level → Insert Blank Level (Above/Below Current Level) 

Keyboard Shortcut: None 

Toolbar Button: None 

Use these commands to create a blank level. When you create a blank level, you must select 

whether you want it created above or below the current level. 

Copying and Pasting levels 

Menu Command: Level → Copy Level along with 

 Level → Paste Level (Above/Below Current Level) 

Keyboard Shortcut: None 

Toolbar Button: None 

With CONTAMW you can copy an entire level and insert it as an entire level anywhere within 

the current project. Use the Copy Level command to copy the level currently displayed on the 

SketchPad; move to either the level above or below where you wish to insert the copied level and 

use one of the Paste Level commands to insert the copied level. 
 USING CONTAMW ñ WORKING WITH LEVELS 

21

3.5.2 Viewing Levels 

If a project has more than one level, you can specify the level that you want to view or modify on 

the SketchPad by using the level commands. All level-related commands are located under the 

Level menu. There are also some shortcut keys and toolbar buttons provided for your 

convenience. 

Changing the Currently Active Level 

Menu Command: Level → Go to (Level Above/Below) 

Keyboard Shortcut: Page Up, Page Down

Toolbar Button: 

Use this command to change which level you want the SketchPad to display. 

Displaying Multiple Levels 

Menu Command: Level → Reveal Level Below

Keyboard Shortcut: Ctrl+Shift+B

Toolbar Button: None 

Use this command to see both the current level and the level below the current level at the same 

time. CONTAMW will displays the walls and building component icons of the level below in 

gray. This feature is useful for aligning building features between adjacent levels. 

3.5.3 Deleting Levels 

Menu Command: Level → Delete Level

Keyboard Shortcut: None 

Toolbar Button: None 

Use this command to delete an entire level. Once you have deleted a level, you cannot undo the 

deletion. You may want to save a copy of the file prior to deleting a level; this is the only way to 

prevent losing your work. 

3.5.4 Modifying Levels 

To modify level data, you access the Level Data dialog box using the Edit Level DataÖ

command of the Level menu. You can also use the keyboard shortcut F8 to display the dialog 

box. The following section shows the information contained on the "Level Data" dialog box. 

3.5.5 Level Data 

This is the information associated with each level that you create. CONTAMW will provide 

default values for this data, but you can modify it as required for your particular building. 

Name: Name to identify the level. All level names must be unique. 

Elevation of this level: The elevation of the base of the level above ground. 

Distance to level above: This is the height of the level from floor to ceiling. CONTAMW will 

use this value to calculate zone volumes based on the floor area of each zone. 
USING CONTAMW ñ WORKING WITH ZONES

22

3.6 Working with Zones 

A zone is a volume of air with uniform temperature and contaminant concentration. There are 

three different types of zones: normal, phantom and ambient. A normal zone icon represents a 

zone that is separated by a floor from the zone below. A phantom zone is used to indicate that 

there is no floor below the enclosed region on a given level. That is, the region on this level is 

actually part of the zone below and has the same temperature and contaminant concentration. An 

ambient zone icon represents the outdoor air. The ambient zone, which surrounds the building, is 

already identified by default by the icon at the upperñleft corner of the SketchPad. 

You create zones on the SketchPad by first drawing walls that enclose a region, placing a single 

zone icon within the enclosed region, and then defining the zone icon. Eventually, every zone 

must be connected to the ambient zone either directly or indirectly via any set of paths that 

prevents the zone from being isolated from ambient. 

3.6.1 Creating Zones 

You create zones by drawing walls upon the SketchPad. The wall drawing operations are 

described in the Drawing Walls section of this manual. The shape and size of zones as drawn 

upon the SketchPad do not provide the underlying model with any scaling information. 

However, the manner in which the enclosed regions border each other is significant. Any zones 

between which you wish to provide a direct connection (via an airflow path) must share a 

common wall. Therefore, when drawing a building floor plan, you should try to maintain the 

general topology of the actual floor plan. While scale is not significant, CONTAMW does 

provide you with the SketchPad coordinates that may help you when laying out your project. 

The dimensions of your zones are determined when you define them. If you change the shape or 

size of a region on the SketchPad that contains a zone icon, the dimensions do not change 

according to the model unless you actually modify the properties of the associated zone icon. 

3.6.2 Deleting Zones 

You delete a zone by first deleting the zone icon. After you delete the zone icon, delete the wall 

or walls necessary to eliminate the enclosed region that is left behind. You must avoid the 

existence of an enclosed region without a zone icon; CONTAMW will not perform a simulation 

with an undefined zone icon in a project. 

3.6.3 Modifying Zones 

You modify the SketchPad representation of a zone by adding and removing walls. This 

procedure is described in the Modifying Walls section of this manual. To modify the parameters 

of a zone, you use the icon definition procedure (See Defining Building Component Icons) to 

display its properties and make the desired changes. 

Once you define a zone, you can move the zone icon anywhere within the zone using the Cut

and Paste functions of the Edit menu. These commands will only allow you to paste the icon 

into the zone in which it is currently located. 

3.6.4 Defining Zones 

After you draw the enclosed region of a zone, you must define the zone. To define a zone you 

must first draw a zone icon within the enclosed region (See Drawing Building Component Icons) 
 USING CONTAMW ñ WORKING WITH ZONES 

23

and then use the icon definition procedure (See Defining Building Component Icons) to display 

and edit the properties of the zone. 

The properties of each zone include a name, temperature, pressure, volume and information 

describing contaminant behavior within the zone. You must provide each zone with a name that 

is unique to each level of a project. For this reason, you cannot copy zone data within a level. 

However, you can copy entire levels of data, including zone data, from one level to another (See 

Creating Levels). Detailed descriptions of zone properties are given under Zone Properties 

below. 

Only normal zones require definition. Ambient and phantom zone icons appear as defined icons 

as soon as you place them onto the SketchPad. However, you must include the volume of 

phantom zones in the volume of the associated normal zone below it. 

3.6.5 Zone Properties 

This section provides detailed descriptions of the specific zone properties. The following 

sections are the context-sensitive help topics that you can access by pressing F1 when working 

with property pages of the "Zone Properties" property sheet. 

3.6.5.1 Zones ñ Zone Data Properties 

These are the basic properties that describe a zone. 

Zone Name: This is the symbolic name of the zone. Enter a name up to four characters in length. 

Zone names must be unique within each level of a building. 

Temperature: This is the constant temperature of the zone. CONTAMW will provide the 

default value that you can override by entering another value. You can set the default zone 

temperature via the OptionsÖ command of the View menu. 

Pressure: The zone air pressure relative to ambient can be specified as either variable or 

constant. Typically you would set the zone pressure to be variable and let CONTAMW 

determine it. However, you might set the pressure to be constant if you want to simulate a fan 

pressurization (blower door) test of a building (see Building Pressurization Test in the 

Applications section of the manual) or to perform analytic test cases of CONTAMW. 

Volume: Zone volume is used in the dynamic contaminant calculations. For phantom zones, the 

zone volume is set at the standard zone icon on the lowest level for the entire height of the zone 

and includes the volume of the phantom zones on the levels above. 

Floor Area: Instead of the volume, you may enter a floor area. Floor area is then multiplied by 

the height of the current building level to compute a volume. This area is not used for any other 

purpose by CONTAMW. 
USING CONTAMW ñ WORKING WITH ZONES

24

3.6.5.2 Zones ñ Contaminant Properties 

These are the contaminant-related properties of a zone. Contaminants must be defined prior to 

defining contaminant data for a zone. To define contaminants, select Data then ContaminantsÖ

from the main program menu. 

Zone Name: This is the symbolic name of the zone as entered on the Zone Data property page. 

Contaminant Concentrations: Select variable or constant. Typically you would set this to 

variable and allow CONTAMW to calculate the contaminant concentration within the zone. 

However, you may wish to set this to constant as a simple means of creating a simple 

contaminant source within a zone. If you set this to constant, the contaminant concentrations in 

this zone will begin and remain at the values you set for the initial concentrations. 

Initial Concentration: Select a contaminant from the list and enter the initial contaminant 

concentrations for dynamic (transient) simulations. You can reset these initial values through the 

Run Control parameters of the Simulation Parameters (see Simulation Parameters in the Using 

CONTAMW section of the manual). 

Kinetic Reactions: If there are previously defined kinetic reactions within the current project, 

you may select one from the list of names. Click the "New Reaction" button to define a new 

kinetic reaction. To view or modify existing kinetic reaction data click the "Edit Reaction" 

button. Setting this field to <none> indicates no reactions in the zone. You must have previously 

defined at least one contaminant prior to creating a kinetic reaction. 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

25

3.7 Working with Airflow Paths 

An airflow path is a CONTAMW building component through which air can move between two 

adjacent zones. These components can be cracks in the building envelope, open doorways, 

exhaust fans, etc. The air pressures in the adjacent zones and the flow characteristics of the flow 

path itself determine the flow through most of these paths. The location of the SketchPad icon 

that represents a flow path determines the two zones that are connected by a flow path. If the 

path icon is placed on a wall, it connects the zones on opposite sides of the wall. If it is placed in 

a blank cell of a zone (i.e. on the floor), it connects the zone containing the flow path icon to the 

zone located directly below the flow path icon. 

You can place airflow paths on the SketchPad, define their flow characteristics, move, copy, and 

delete them. You must provide each airflow path with specific information that describes its flow 

characteristics. Much of the information that describes the flow characteristics of airflow paths is 

contained in airflow elements that you must create when defining the airflow paths. The details 

of drawing, defining and modifying airflow paths are described in the following sections. 

3.7.1 Airflow Elements 

Each airflow path must refer to an airflow element. Airflow elements describe the mathematical 

relationship between the flow through an airflow path and the pressure drop across the path. 

CONTAMW provides you with several mathematical models or types to choose from. Each of 

these airflow element types is described in detail in the Airflow Path Properties section. While 

every airflow path must refer to a single airflow element, multiple paths can refer to the same 

airflow element. Airflow elements can also be stored within a CONTAMW library file and shared 

between different CONTAMW project files (See Working with Data and Libraries). 

3.7.2 Creating Airflow Paths 

You create airflow paths by placing an airflow path icon on the SketchPad (See Drawing 

Building Component Icons). Because flow paths connect only two adjacent zones, there are 

several restrictions on the placement of flow paths. You may not place airflow path icons on the 

corner of a zone or on the blank cell of a level that does not have a zone located directly below it. 

Note that you can place an airflow path icon on the "roof" of a building that connects a zone 

below to the ambient. In this case, the roof level would be a level that does not contain walls but 

contains airflow path icons located in the floor of the roof level (above zones on the level below). 

The context-sensitive feature of the pop-up icon placement menu enforces these restrictions. The 

"Flow Path" menu selection will be disabled (grayed out) if you pop-up on a location where 

CONTAMW does not allow the icon to be placed. 

This list shows the various flow path icons and provides a brief description of each. 

Icons Description 

 Small and large one-way flow paths 

 Small and large two-way flow paths 

 Directional fan flow paths 
USING CONTAMW ñ WORKING WITH AIRFLOW PATHS

26

3.7.3 Deleting Airflow Paths 

You delete airflow path icons using the icon deletion procedure (See Deleting Building 

Component Icons). Deleting airflow path icons from the SketchPad does not delete any airflow 

elements that you may have defined. These flow elements can only be deleted using the 

CONTAMW Library Manager, accessible through the Data menu for each type of data element. 

3.7.4 Modifying Airflow Paths 

To modify the parameters of an airflow path, you use the icon definition procedure (See Defining 

Building Component Icons) to display its properties and make the desired changes. You can also 

move and copy airflow paths. 

Moving Airflow Path Icons 

Once you define an airflow path, you can move the path icon using the Cut and Paste functions 

of the Edit menu. CONTAMW will constrain the movement of path icons according to the 

following rules. You can only move a flow path through a wall onto a wall, not onto the floor of 

a zone. You can only move a flow path through a floor to another location on the floor, not onto 

a wall. You can only move a path icon within the same level upon which it is located. 

Copying Airflow Path Icons 

Once you define an airflow path, you can copy the path icon using the Copy and Paste functions 

of the Edit menu. CONTAMW will constrain the copying of path icons according to the 

following rules. You can only copy a flow path through a wall onto a wall, not onto the floor of a 

zone. You can only copy a flow path through a floor to another location on the floor, not onto a 

wall. You may copy a path icon from one level to another. 

3.7.5 Defining Airflow Paths 

After you draw a Flow Path icon on the SketchPad you must define it using the icon definition 

procedure (See Defining Building Component Icons) to display and edit the properties of the 

airflow path. This will display the "Airflow Path Properties" property sheet. Detailed 

descriptions of all airflow path properties are given in the Airflow Path Properties section of this 

manual. Once you have defined the properties of an airflow path, the icon will be displayed in 

black. The icon representing the defined airflow path may be slightly different from the original 

undefined icon depending on the type of airflow element you associate with the path (See the list 

below). From now on, you use this icon to access the properties of the airflow path. 

Some of the properties associated with an airflow path are optional: contaminant filtration, 

schedule, wind pressure and pressure limit. You can associate contaminant filters with any flow 

path, and you can define a filter for each contaminant contained in your CONTAMW project. A 

filter could be used, for example, to simulate the penetration of particles through a wall cavity. 

You can use a schedule to vary the flow through a path as a function of time. For example, you 

could use a schedule to open and close a path that represents a window. CONTAMW allows you 

to account for the direct effects of wind pressure on the envelope of a building. The envelope is 

considered to be any wall that is adjacent to the ambient zone. If an airflow path is directly 

connected to the ambient zone, a "Wind Pressure" property page will be displayed to allow you 

to account for the effects of wind pressure on the path through the building envelope. Pressure 

limits are useful when you are using CONTAMW to design a smoke control system. For 

example, you could set pressure limits (maximum and minimum) for stairwell doors so that those 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

27

doorways for which the pressure limits are violated will be highlighted upon the SketchPad when 

you view simulation results. 

3.7.6 Airflow Path Properties 

This section provides detailed descriptions of the specific airflow path properties. Each of the 

following subsections are the context-sensitive help topics that you can access by pressing F1

when working with property pages of the "Airflow Path Properties" property sheet. 

3.7.6.1 Airflow Path ñ Airflow Element Properties 

Path Number: This is the number that appears in the status bar when you highlight a path icon. 

CONTAMW automatically assigns this number to each airflow path once they are defined. This 

number could change as you add and remove paths to or from a project. Each time you save a 

project, the path numbers are reassigned. Numbers are assigned beginning on the top level, 

starting from the upper-left corner of the SketchPad, moving left-to-right and top-to-bottom of 

the SketchPad. Paths include inlets and outlets of simple air handling systems. 

Airflow Element Name: You may select a previously defined airflow element from those 

contained in the Name list. Click the "New Element" button to define a new airflow element. To 

view or modify airflow element data click the "Edit Element button. Every airflow path must 

have an airflow element associated with it. This field may not be left blank. 

Model Summary: This summarizes the information associated with the airflow element whose 

name is currently displayed in the Name field. 

3.7.6.2 Airflow Path ñ Filter and Schedule Properties 

Filter: You may select a previously defined filter from those contained in the associated Name 

list. Click the "New Filter" button to define a new filter. Click the "Edit Filter" button to view or 

modify existing filter data. Setting this field to "<none>" indicates no filter for this airflow path. 

(See Contaminant Filters under Working with Contaminants) 

Schedule: If there are previously defined schedules within the current project, you may select 

one from the Name list. Click the "New Schedule" button to define a new schedule. To view or 

modify an existing schedule click the "Edit Schedule" button. Setting this field to "<none>" 

indicates no schedule. (See Working with Schedules) 
USING CONTAMW ñ WORKING WITH AIRFLOW PATHS

28

3.7.6.3 Airflow Path ñ Flow Path Properties 

Relative Elevation: The elevation of the path will determine how it responds to, and influences, 

the building stack effect. Enter the elevation of the mid-height of the flow path minus the 

elevation of the current building level, i.e., the level named in the lower left corner of the screen. 

For example, the relative elevation for a path in the floor is typically zero. 

Multiplier: The multiplier is a constant value allowing you, for example, to use a flow element 

description of one window and a multiplier of 5 to describe 5 windows in a particular wall. If 

you have specified a "leakage area" flow element, complete the description here by giving the 

reference area, length, or number of units. 

Positive Flow Direction: In the cases of fans, wind, and pressure/flow limits (see below) it is 

necessary to know which direction is defined as positive. The arrows indicate the positive 

direction for pressure drop and flow. For a positive wind pressure to tend to force inward flow, 

the positive direction must be from ambient into the building. 

Limits: In the design of smoke control systems there are often limits on the maximum and 

minimum pressure or flow on a path. For example, a stairwell door can require a minimum 

pressure drop from the stairwell to the zone to prevent smoke entering the evacuation route, but 

there is also a maximum pressure drop above which some people may not be able to open the 

door. You may specify either type of limits (default: no limits) and set the values. When you 

display the results of a simulation, those paths with pressures or flows outside the limits will be 

highlighted. 

3.7.6.4 Airflow Path ñ Wind Properties 

Wind Pressure Option: There are three wind pressure options for openings in the building 

envelope: 

1. No wind pressure 

2. Constant pressure 

3. Pressure dependent on wind speed and direction 

When you select one of the above options, the following data entry options that correspond to the 

wind pressure option that you selected will be made available for your input. 

Constant Pressure Data: Enter a constant wind pressure (wind speed and direction 

independent). 

Variable Pressure Data: Variable wind pressures are computed from the product of the 

following three parameters: 

1. The dynamic pressure of the wind at some reference height. CONTAMW will determine 

this pressure based on either the steady state wind data (See Wind Properties) or the 

transient wind data from a weather file (See Defining Transient Weather and Wind). 

2. A coefficient accounting for local terrain effects (Wind Pressure Modifier). 

3. A pressure coefficient accounting for relative wind direction (Wind Pressure Profile). 

Wind Pressure Modifier: CONTAMW uses this value to account for differences between 

wind velocity profiles at the building site and that at a measurement location, e.g. an airport 

weather station (See Working with Weather and Wind). CONTAMW only requires this value 

if you are implementing Variable Wind Pressure for an airflow path. CONTAMW will 

provide a default value for this based on the data entered via the Weather and Wind 

Parameters Property Page or you can override the default value for a particular airflow path. 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

29

Wall Azimuth Angle: Enter the direction the wall faces (clockwise from north). 

Profile: The wind pressure profile accounts for the wind direction effects. You may select a 

previously defined wind pressure profile from those contained in the Name list. Click the 

"New Profile" button to define a new wind pressure profile. To view or modify wind pressure 

profile data, click the "Edit Profile" button. After you press the "New Profile" or "Edit 

Profile" button, the "Wind Pressure Profile" page will be displayed with a graphical 

representation of the profile. 

Wind Pressure Profile 

Wind Pressure Profiles are used to account for the wind direction effects in flow elements. 

CONTAMW refers to the function relating the average wind pressure coefficient for the face of a 

building to the angle of incidence of the wind on the face of the building as the wind pressure 

profile or f(θ). A more detailed explanation of this function is given in the Working with 

Weather and Wind section. The profile is displayed graphically at the bottom of the screen for a 

visual review of the data. 

Name: This is the name you give to the wind pressure profile. Wind profile names must be 

unique within a project. 

Description: Use this field to enter a more detailed description of the specific wind pressure 

profile. 

Data Points: You may enter up to 16 angle/pressure coefficient pairs. Pressure coefficients are 

in the range -1 to 1. The first value must be at a wind direction of zero degrees. The angle zero 

indicates a wind blowing directly toward the surface in which the opening lies. An identical 

value at angle 360 degrees is automatically assumed. 90 degrees indicates a wind blowing 

parallel to the wall from the right, and 270 degrees is from the left. By making these angles 

relative to the wall, the same profile might be used on different walls around the building without 

modification depending on building geometry. 

To update entered data points on the graph press the "Redraw" button in the curve fit frame. 

Pressing this button will re-plot the data on the graph and will sort the data points by angle. 

Select Curve Fit: 

Curve Fit 1: This curve fit simply connects the data points and linearly interpolates the point 

between. 

Curve Fit 2: This curve fit will connect all the user data points and will use a nonlinear curve 

fit between the points. 

Curve Fit 3: This curve fit will attempt to fit a trend line to all the data points, and may not 

actually go through all the user provided data. 
USING CONTAMW ñ WORKING WITH AIRFLOW PATHS

30

3.7.7 Airflow Element Types 

These are the different types of airflow elements that CONTAMW provides. When creating and 

defining an airflow path, you select the type of airflow element that you want CONTAMW to 

utilize to model airflow through the path. Theoretical explanations of the various types of airflow 

models that CONTAMW implements are provided in the Airflow Analysis subsection of the 

Theoretical Background section of the manual. 

One-way Flow using Powerlaw Models 

These one way flow models permit flow in the direction of the pressure drop. CONTAMW 

provides you with the following powerlaw flow models. 

1. Q = C(∆P)n: This is the general form of the powerlaw model in volumetric flow form that 

allows you to directly input the coefficient, C, and exponent, n. 

2. F = C(∆P)n

: This is the general form of the powerlaw model in mass flow form that 

allows you to directly input the coefficient, C, and exponent, n. 

3. Leakage Area Data: This model refers to effective leakage areas as described in Chapter 

25 of the 1997 ASHRAE Handbook of Fundamentals. 

4. Connection (ASCOS) Data: Refers to the airflow description used in the ASCOS 

program [Klote 1981]. 

5. Orifice Area Data: Relates the opening description to the orifice area data. 

6. Crack Description: A narrow opening described by its length and width. 

7. Test Data (1-point): Uses a single flow rate and pressure drop along with an estimate for 

the pressure exponent, n. 

8. Test Data (2-points): Uses two flow rates with their corresponding pressure drops to 

define the flow using the powerlaw model. 

9. Stairwell: Data corresponding to a stairwell is fit to the powerlaw model. 

10. Shaft: Describes the flow in a large shaft. 

One-way Flow using Quadratic Models 

These models permit flow in only one direction through the path based on the pressure drop. 

1. ∆P = aQ + bQ2

 and ∆P = aF + bF2: These models allow you to directly input the 

coefficients a and b for the quadratic models.

2. Crack Description: This model describes a narrow opening in greater detail than the 

powerlaw version of the crack model. 

3. Test Data (2- point): This model uses two flow rates and their corresponding pressure 

drops to define the flow using the quadratic model. 

Two-way Flow Models 

These models are used to represent tall openings where temperature differences across the 

opening may cause two-way flow across the opening, e.g., doorways. 

1. Single Opening Model with 2-way Flow: This models the flow through a path as a single 

large opening. 

2. Two-opening Model: This model divides an opening vertically and models the flow using 

two powerlaw models, one for each opening. Results are obtained in the form of the net 

flow rate in each direction. 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

31

Backdraft Damper Flow Models 

The models allow you to model a feature that has different resistances depending on the direction 

of the pressure drop, e.g., a smoke control damper. CONTAMW implements both a volume flow 

and a mass flow version of the backdraft damper model, both of which are based on the 

powerlaw model. 

1. Backdraft Damper Model: F = C(∆P)n: This is the volumetric flow form of the Backdraft 

Damper model. You input separate values of C and n depending on the sign of the 

pressure drop across the damper. 

2. Backdraft Damper Model: Q = C(∆P)n: This is the mass flow form of the Backdraft 

Damper model. You input separate values of C and n depending on the sign of the 

pressure drop across the damper. 

Fan and Forced Flow Models 

These models allow you to create airflow paths that represent fans or other paths for which you 

want to designate a flow rate. 

1. Constant Mass Flow Fan: This model provides for a constant mass flow rate. 

2. Constant Volume Flow Fan: This model provides for a constant volumetric flow rate, but 

the mass flow will vary based on the actual density. 

3. Cubic Polynomial Fan Model: This model implements a user-defined fan performance 

curve to relate pressure to airflow rate. 

User-defined Flow Models 

Not implemented in this version of CONTAMW 
USING CONTAMW ñ WORKING WITH AIRFLOW PATHS

32

3.7.7.1 One-way Flow Using Powerlaw Models 

CONTAMW performs airflow calculations using the mass flow powerlaw formula, F = C(∆P)n, 

for the following types of airflow elements, where F is the mass flow rate, ∆P is the pressure 

difference across a flow path, C is the flow coefficient and n is the flow exponent. However, for 

some of the powerlaw models, CONTAMW enables you to input parameters that describe an 

opening in terms other than the coefficient C and exponent n. These parameters are then 

converted internally by CONTAMW to determine the C and n for the mass flow version of the 

powerlaw model. 

Powerlaw Model: Q = C(∆P) n

This model allows you to directly enter the coefficient C and exponent n for the volume flow 

version of the powerlaw model. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Flow Coefficient (C): The coefficients may only be expressed in SI units due to the conversion 

method used. Use the following conversion to convert from IP units to SI units. 

n n n Pa

m s

in H O

cfm

249

2119 multiplyby / To convertfromunits of to the SI units of

3

2 

Flow Exponent (n): Flow exponents vary from 0.5 for large openings where the flow is 

dominated by dynamic effects, and 1.0 for narrow openings dominated by viscous effects. 

Measurements usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is provided for organizational purposes. There are two 

icon options for this Powerlaw model, one for a large opening and one for a small opening. 

Powerlaw Model: F = C(∆P) n

This model allows you to directly enter the coefficient C and exponent n for the mass flow 

version of the powerlaw model. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Flow Coefficient (C): The coefficients may only be expressed in SI units due to the conversion 

method used. Use the following conversion to convert from IP units to SI units. 

n n n Pa

kg s

in H O

lbm s

249

0.4536 multiplyby /

to the SI units of / To convertfromunits of

2 

Flow Exponent (n): Flow exponents vary from 0.5 for large openings where the flow is 

dominated by dynamic effects, and 1.0 for narrow openings dominated by viscous effects. 

Measurements usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

33

Powerlaw Model: Leakage Area 

Leakage area refers to a description of airflow features given in Chapter 25 of the 1997 

ASHRAE Handbook of Fundamentals. This reference provides a large table of typical leakage 

areas for residential buildings. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Leakage Area: There are three possible ways to enter the leakage area: per item, per unit length, 

and per area. Select the radio button for the type of leakage area to be described, then enter the 

appropriate value for the type of leakage selected. 

Per Item: Enter a total leakage value for an item, this is usually used for a doorway or 

window - something that can be classified as an item. 

Per Unit Length: This is usually used to describe an interface such as a wall/ceiling 

junction. 

Per Unit Area: Used to describe an area such as a wall or floor. 

Reference Conditions: Be sure to check the reference condition for the reported leakage areas. 

Two sets of reference conditions are common: 

 Discharge coefficient of 1.00 at a reference pressure of 4.0 Pa and 

 Discharge coefficient of 0.61 at a reference pressure of 10 Pa. 

Discharge Coefficient: Enter the discharge coefficient for the leakage area at the 

reference pressure. 

Flow Exponent: Enter the flow coefficient for the leakage area at the reference pressure. 

The flow exponent is not reported and therefore must be estimated. For openings 

associated with infiltration, measurements usually indicate an exponent between 0.6 and 

0.7. 

Pressure Drop: Enter the reference pressure drop. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is provided for organizational purposes. There are two 

icon options for this Powerlaw model, one for a large opening and one for a small opening. 
USING CONTAMW ñ WORKING WITH AIRFLOW PATHS

34

Powerlaw Model: Connection (ASCOS) 

Data describing a connection is reduced to the powerlaw model; an exponent of 0.5 is assumed. 

The term "connection" refers to the element used in the ASCOS program [Klote and Milke 

1992]. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Flow Coefficient: The flow coefficient C is related to the dynamic effects and is typically close 

to 0.6 for an orifice and slightly higher for other openings in buildings. 

Flow Area: Refers to the observable area of the opening. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 

Powerlaw Model: Orifice Area 

This airflow element allows you to input the description of an orifice. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Cross-sectional Area: This refers to the observable area of the opening. 

Flow Exponent (n): Flow exponents vary from 0.5 for large openings where the flow is 

dominated by dynamic effects, and 1.0 for narrow openings dominated by viscous effects. 

Measurements usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Discharge Coefficient: The discharge coefficient, C, is related to the dynamic effects and is 

typically close to 0.6 for an orifice and slightly higher for other openings in buildings. 

Hydraulic Diameter: The hydraulic diameter is equal to (4 ⋅ Area / Perimeter). For square 

openings this equals the square root of the area, and for long thin openings it is two times the 

width. 

Reynolds Number: The transition from laminar flow to turbulent flow occurs over a very broad 

range of Reynolds numbers with the flow being fully laminar approximately below 100. 

Note: The hydraulic diameter and Reynolds number have little impact on the calculations. Generally you should use 

the default values except for special circumstances where they need to be modified. The three values above describe 

the flow characteristics of an orifice in typical operation. At extremely low pressure drops the use of the powerlaw 

model leads to a division by zero during the network solution process. CONTAMW avoids this problem by changing 

to a linear model in this region. The model is based conceptually on the flow changing from turbulent to laminar at 

very low pressures. The Hydraulic diameter and Reynolds number are used to determine a point where the model 

changes from the powerlaw to linear. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

35

Powerlaw Model: Crack Description 

This airflow element is allows you to enter the description of a crack and is based upon the 

relationships developed between flow through cracks and the powerlaw model [Clark 1985]. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Crack Length/Width: Enter the length and width of the crack. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Note: CONTAMW automatically uses the icon for a small opening for the powerlaw model crack description. 

Powerlaw Model: Test Data (1 point) 

This airflow element allows you to provide a single test data point that CONTAMW reduces to 

the powerlaw model based on the value input for the pressure exponent, n. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Pressure Drop: Enter the pressure drop of the data point. Be sure to select the proper units from 

the drop down box for the pressure drop before entering a value. 

Flow Rate: Enter the flow rate of the data point. Be sure to select the proper units from the drop 

down box for the flow rate before entering a value. 

Pressure Exponent (n): The flow exponent is a guess used to fit the single point to the 

powerlaw model. A value of 0.6 to 0.7 is typical for an infiltration element. A value of 0.5 is 

more appropriate for large openings. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 

Powerlaw Model: Test Data (2 points) 

This airflow element allows you to provide two test data points that CONTAMW reduces to the 

powerlaw model. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Pressure Drop: Enter the pressure drop for each of the two data points. Be sure to select the 

proper units from the drop down box for each pressure drop before entering a value. 

Flow Rate: Enter the flow rate for each data point. Be sure to select the proper units from the 

drop down box for each flow rate before entering a value. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 
USING CONTAMW ñ WORKING WITH AIRFLOW PATHS

36

Powerlaw Model: Stairwell 

This airflow element allows you to enter a description of a stairway, and CONTAMW converts 

the information to a powerlaw relationship assuming a pressure exponent of 0.5. A stairwell will 

normally be modeled as a vertical series of zones connected by low resistance openings (this 

stairwell flow element) through the floors. The resistance is based on a fit to experimental data 

[Achakji & Tamura 1998]. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Distance Between Levels: This is the distance between openings for the stairwell. Be sure to 

select the correct units from the drop down box provided before entering a value. 

Cross-sectional area: This is the horizontal, cross-sectional, area of the shaft. Be sure to select 

the correct units from the drop down box provided before entering a value. 

Density of People: A large number of people in the stairwell influence the flow resistance of the 

stairwell. The experiment used densities of 1, 2, and 3 people per square meter. These are the 

only units available in CONTAMW. The following conversion is provided for your convenience. 

2 2 1m =10.76 ft

Stair Treads: There are two options for this field: open tread and closed tread. This option refers 

to the front of the tread; whether or not the tread is open affects flow. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 

Powerlaw Model: Shaft 

This airflow element allows you to enter a description of a shaft, and CONTAMW converts the 

information to a powerlaw relationship assuming a pressure exponent of 0.5. A shaft will 

normally be modeled as a vertical series of zones connected by low resistance openings (this 

shaft airflow element) through the floors. The resistance is based on a conduit friction model 

using the Darcy-Weisbach relation and Colebrookís equation for the friction factor [ASHRAE 

1997, p2.8]. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Distance Between Levels: This is the distance between openings for the stairwell. 

Cross-sectional area: This is the horizontal, cross-sectional area of the shaft. 

Perimeter: The perimeter of the horizontal cross-section of the shaft. This number is used in 

conjunction with the area to create the hydraulic diameter. 

Roughness: This refers to the average size of the protrusions from the shaft wall into the airflow. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

37

3.7.7.2 One-way Flow Using Quadratic Flow Models 

CONTAMW performs airflow calculations using the mass flow quadratic relationship (∆P = aF 

+ bF2) between mass flow rate and pressure difference across a flow path for the following types 

of airflow elements, where F is the mass flow rate, ∆P is the pressure difference across a flow 

path, and a and b are flow coefficients. 

Quadratic Model: ∆P = aQ + bQ2 

This model allows you to directly enter the coefficients, a and b, into the volume flow version of 

the quadratic flow model. ∆P is the pressure drop and Q is the volumetric flow rate. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Coefficients: The coefficients must be expressed in SI units because of the way CONTAMW 

handles unit conversions. The units of the coefficients at standard conditions are as follows: 

a [Pa ⋅ s/m3

] 

b [Pa ⋅ (s/m3)

 2] 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 

Quadratic Model: ∆P = aF + bF2 

This model allows you to directly enter the coefficients, a and b, into the mass flow version of 

the quadratic flow model. ∆P is the pressure drop and F is the mass flow rate. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Coefficients: The coefficients must be expressed in SI units because of the way CONTAMW 

handles unit conversions. The units of the coefficients are as follows: 

a [Pa ⋅ s/kg] 

b [Pa ⋅ (s/kg) 2] 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 
USING CONTAMW ñ WORKING WITH AIRFLOW PATHS

38

Quadratic Model: Crack Description 

This model employs a quadratic relationship of the form ∆P = aQ + bQ2 where Q is the volume 

flow rate [Baker, Sharples, and Ward 1987]. CONTAMW uses the mass flow version of that 

formula: ∆P = aF + bF2 where ∆P is the pressure drop and F is the mass flow rate. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Crack Dimensions: 

Length: Length of the crack 

Width: Width of the crack 

Depth: Distance along the direction of airflow 

Number of Bends: The number of bends in the flow path. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Quadratic Model: Test Data (2 points) 

Measured data (2 points) is reduced to the mass flow version of the quadratic model. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Data: Data consists of two sets of pressure drops and corresponding flow rates. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

39

3.7.7.3 Two-way Flow Models 

These models enable you to model large openings through which two-way airflow might occur. 

When viewing results of these models, the bi-directional flow will be indicated on the SketchPad 

if it occurs. You can also use CONTAMWís airflow plotting feature to plot both airflows or to 

simply plot the net airflow. There must be a temperature difference across the associated airflow 

path in order for bi-directional flow to occur. 

Two-way Flow Model: Single Opening 

This is a model for flow through large openings such as doorways through which air can flow in 

two directions simultaneously throughout the opening. See Doorways (Large Openings) in the 

Theory section for a more detailed explanation. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Height: The overall height of the opening, not to be confused with the openingís position. 

Before entering the dimension be sure to select the proper units from the drop down menu. 

Width: The width of the opening. Again, before entering the dimension make sure to select the 

proper units from the drop down menu. 

Flow Coefficient: An experimentally determined value. Experiments by Weber and Kearney 

have shown the default value of 0.78 to work well for most applications. 

Minimum Temperature Difference for Two-Way Flow: A two-way flow is driven by the 

temperature (actually air density) difference between the two zones. When this temperature 

difference approaches zero the algorithm used for solving the flow tends towards a division by 

zero problem. To avoid this undefined situation the two-way model reverts to a one-way power 

law model at this "minimum temperature difference" using the opening size to define the orifice 

at ∆T set in this field. CONTAMW uses a default value of 0.01 °C. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 
USING CONTAMW ñ WORKING WITH AIRFLOW PATHS

40

Two-way Flow Model: Two-opening 

This model accounts for two-way flow due to the stack effect acting over the height of a tall 

opening. It uses two power law flow models at different heights to approximate a single tall 

opening. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Height: The overall height of the opening, not to be confused with the openingís position. 

Width: The width of the opening. 

Flow Coefficient: This is an experimentally determined value. Experiments by Weber and 

Kearney have shown the default value of 0.78 to work well for most applications. 

Minimum Temperature Difference for Two-Way Flow: A two-way flow is driven by the 

temperature (actually air density) difference between the two zones. When this temperature 

difference approaches zero the algorithm used for solving the flow tends towards a division by 

zero problem. To avoid this undefined situation the two-way model reverts to a one-way power 

law model at this "minimum temperature difference" using the opening size to define the orifice 

at ∆T set in this field. CONTAMW uses a default value of 0.01 °C. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Icon: Choose the style icon appropriate for the specific airflow element. Note that the icon has 

no effect on the simulations; the choice is based on user preference. There are two icon options 

for this Powerlaw model, one for a large opening and one for a small opening. 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

41

3.7.7.4 Backdraft Damper Flow Models 

The Backdraft Damper models make it possible to model a feature that has different flow 

resistances depending on the direction of the pressure drop, with greatly reduced (or zero) flow 

in one direction. Note that there are similar models available for duct flow elements. 

Backdraft Damper Model: Q = C(∆P) n

This is the volumetric flow form of the backdraft damper airflow model. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Pressure Difference ∆P>0 or ∆P<0: This indicates the direction of predominant flow for the 

model. 

Flow Coefficients: The coefficients may only be expressed in SI units due to the conversion 

method used. Use the following conversion to convert from IP units to SI units. 

n n n Pa

m s

in H O

cfm

249

2119 multiplyby / To convertfromunits of to the SI units of

3

2 

Flow Exponents: Flow exponents vary from 0.5 for large openings where the flow is dominated 

by dynamic effects, and 1.0 for narrow openings dominated by viscous effects. Measurements 

usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Backdraft Damper Model: F = C(∆P) n

This is the mass flow form of the backdraft damper airflow model. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Pressure Difference ∆P>0 or ∆P<0: This indicates the direction of predominant flow for the 

model. 

Flow Coefficients: The coefficients may only be expressed in SI units due to the conversion 

method used. Use the following conversion to convert from the IP units to SI units. 

n n n Pa

kg s

in H O

lbm s

249

0.4536 multiplyby /

to the SI units of / To convertfromunits of

2 

Flow Exponents: Flow exponents vary from 0.5 for large openings where the flow is dominated 

by dynamic effects, and 1.0 for narrow openings dominated by viscous effects. Measurements 

usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Description: Use this field to enter a more detailed description of the specific airflow element. 
USING CONTAMW ñ WORKING WITH AIRFLOW PATHS

42

3.7.7.5 Fan and Forced-Flow Models 

These airflow element models enable you to easily create forced airflow elements as airflow 

paths between two zones, as opposed to implementing a duct model or simple air handling 

system. You can either specify a constant mass flow rate, constant volumetric flow rate, or to 

create a fan based on fan performance data. 

Fan Model: Constant Mass Flow 

This model describes an airflow element having a constant mass flow rate. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Design (maximum) Flow: Enter the maximum mass flow rate. This value can be modified by 

the path schedule. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Fan Model: Constant Volume Flow 

This model describes an airflow element having a constant volume flow rate that can vary with 

density. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Design (maximum) Flow: Enter the maximum volume flow rate. This value can be modified by 

the path schedule. 

Description: Field for entering a more detailed description of the specific airflow element. 

Fan Model: Fan Performance Curve 

This airflow element allows you to create a fan based on a fan performance curve. You provide 

CONTAMW with a set of pressure rise and airflow rate data points, and CONTAMW performs a 

polynomial curve fit to the data point. 

Name: Enter the name you want to use to identify the airflow element. The airflow element will 

be saved within the current project and can be associated with multiple airflow paths. 

Fan off conditions: These values specifies how the fan is modeled when the speed of the fan is 

insufficient to provide a flow. 

Control Value: The actual speed of the fan divided by the rated speed of the fan. When 

this ratio is below the specified limit the fan is modeled as a simple orifice. 

Equivalent Orifice: The size of the orifice used to model the fan opening when the 

control value drops below the specified limit. 

Description: Use this field to enter a more detailed description of the specific airflow element. 

Fan Performance Data: Click the "Edit Fan Curve Data" to input/modify the fan curve for this 

airflow element. A detailed explanation of this data is given in the next section, Fan Performance 

Data. 
 USING CONTAMW ñ WORKING WITH AIRFLOW PATHS 

43

Fan Performance Data 

Between four and ten data points are required to fit a line for CONTAMW to fit a cubic 

polynomial to create a performance curve for the fan. The graphís range may not contain a point 

of contraflecture; if it does an error message will be displayed. If this error message is displayed 

the pressure rise data must then be modified to eliminate the point of contraflecture. 

Entering Fan Curve Data Points 

You only need to fill in the "Flow rate" and "Pressure rise" data entry when entering fan curve 

data. When adding a new data point, the flow rate must be entered in the "Flow rate" edit box 

and the pressure rise must be entered in the "Pressure rise" edit box. Use the "Revised dP" box 

when making changes to a pressure rise that has already been entered. This will preserve the 

original data point but use the revised value when performing the curve fit. After entering the 

flow rate and the pressure rise into the appropriate edit boxes, the next step is to press the "<< 

Insert <<" button. Once you have entered four data points a cubic fit line will automatically be 

generated. 

Revising Fan Curve Data Points 

To edit existing data points, highlight the line of data to revise in the list of Fan Curve Data to 

the left of the Insert, Replace and Delete buttons. The values from that data set will then appear 

in the edit boxes to the right of the buttons. 

If you need to modify the flow rate, enter the new flow rate in the "Flow rate" edit box and then 

press the "<< Replace <<" button. The new data will now replace the old data. 

If the Pressure Rise needs to be modified there are two available options: 

1. Replace the data point completely. To overwrite an existing pressure rise and refit the fan 

curve, select the data set to be modified by highlighting it in the data list and then type 

the new pressure rise in the "Pressure rise" edit box then press the "<< Replace <<" 

button. 

2. Change the point used to fit the cubic polynomial but leave the marker for the original 

data point intact. With this option you may "tweak" the curve in the event there is some 

issue with the originally entered fan curve, such as a point of contraflecture. 
USING CONTAMW ñ WORKING WITH SIMPLE AIRñHANDLING SYSTEMS

44

3.8 Working with Simple Airñhandling Systems 

The simple airñhandling system (AHS) provides a convenient means of incorporating an airñ

handling system into a building without having to draw and define an entire duct system. Each 

simple airñhandling system consists of two implicit airflow nodes (supply and return), three 

implicit flow paths (recirculation, outdoor, and exhaust), and multiple inlets to zones (supply) 

and outlets from zones (return) that you can place within zones throughout the building. You 

specify the airflow rates of each supply and return point. Simple airñhandling systems do not 

require you to associate both supplies and returns with them. You may use the simple airñ

handling system to only supply outdoor air to a building or to only exhaust air from the building. 

The following figure shows a schematic representation of a simple airñhandling system. 

 

Determination of System Airflows 

CONTAMW determines the airflows rates associated with each air-handling system according to 

the following algorithm. More detailed explanations for the values that you must input for this 

algorithm are explained in the Defining Air-Handling Systems section that follows. 

First, the summation of all inlet (supply to the zone) airflow rates and the summation of all outlet 

(return from the zone) airflow rates are determined in terms of mass flow. 

ΣWs ≡ the sum of all supplies 

ΣWret ≡ the sum of all returns 

The amount of outdoor air that the system requires is then determined by 

W'o = max( fo·ΣWs, min( ΣWs, Wo_min ) ), 

where, fo ≡ the fraction outdoor air parameter that you input, and 

Wo_min ≡ the "minimum outdoor airflow" parameter that you input. 
 USING CONTAMW ñ WORKING WITH SIMPLE AIRñHANDLING SYSTEMS 

45

The rate at which air is recirculated via the implicit recirculation flow path, Wrec, is determined 

by 

Wrec = min( ΣWret, ΣWs - W'o ). 

The rate at which outdoor air is brought in by the system via the implicit outdoor airflow path, 

Wo, is determined by 

Wo = ΣWs - Wrec. 

And the rate at which exhaust airflows to the ambient via the implicit exhaust flow path, Wex, is 

determined by 

Wex = ΣWret - Wrec. 

This algorithm basically means the amount of outdoor air the system will provide, Wo, will be 

between Wo_min and fo⋅ΣWs as long as the demand for supply air, ΣWs, is sufficient to provide 

this value. Otherwise the system will provide ΣWs. When the sum of the supply flows, ΣWs, 

exceeds the sum of the return flows, ΣWret, the balance is made up from outdoor air. Any excess 

return air is exhausted via the implicit exhaust flow path. 

3.8.1 Creating Simple Airñhandling Systems 

You create simple airñhandling systems by placing an Airñhandling System (AHS) icon on the 

SketchPad along with some combination of inlet and/or outlet icons (See Drawing Building 

Component Icons). You may place an AHS icon on any blank cell of the SketchPad on any level. 

You do not have to place it within a zone. However, you must place Inlet icons and Outlet icons

within a zone. The pop-up menu selections will be disabled (grayed out) if you pop-up on a 

location where CONTAMW does not allow these icons to be placed. 

3.8.2 Deleting Simple Airñhandling Systems 

You delete icons related to simple airñhandling systems using the icon deletion procedure (See 

Deleting Building Component Icons). If you delete an AHS icon, , all of the inlets and outlets 

associated with that system will be deleted. You will be warned of this when you attempt to 

delete the icon. However, you can delete individual inlets and outlets without affecting any other 

icons. Deleting any AHS-related icons from the SketchPad does not delete any filter, schedule, 

or kinetic reaction elements that you may have defined for the AHS. These flow elements can 

only be deleted using the CONTAMW Library Manager, accessible through the Data menu for 

each type of data element. 

3.8.3 Modifying Simple Airñhandling Systems 

To modify the parameters of a simple airñhandling system, you use the icon definition procedure 

(See Defining Building Component Icons) to display its properties and make the desired 

changes. You can move airñhandling system icons and move and copy inlet and outlet icons; 

however, you cannot copy airñhandling system icons. 

Moving Airñhandling System Icons 

You can move AHS icons using the Cut and Paste functions of the Edit menu. CONTAMW 

will only allow you to move an AHS icon within the same level upon which it is located. 
USING CONTAMW ñ WORKING WITH SIMPLE AIRñHANDLING SYSTEMS

46

Moving Inlet and Outlet Icons 

Once you define an inlet or outlet icon, you can move them using the Cut and Paste functions of 

the Edit menu. CONTAMW will only allow you to move an inlet or outlet icon within the same 

zone in which it is currently located. 

Copying Inlet and Outlet Icons 

Once you define an inlet or outlet icon using the Copy and Paste functions of the Edit menu. 

You can copy inlet and outlet icons into any zone on any level. 

3.8.4 Defining Simple Airñhandling Systems 

After you place an AHS-related icon (AHS, Inlet and Outlet) onto the SketchPad you must define 

them using the icon definition procedure (See Defining Building Component Icons) to display 

and edit the properties of the icon. This will display the property sheet associated with the icon. 

Detailed descriptions of all AHS properties are given in the Airñhandling System Properties 

section of this manual. 

The following table shows the various AHS-related icons and provides a brief description of 

each. 

Icon Description 

 Airñhandling system 

 Room air inlet (supply) of an airñhandling system 

 Room air outlet (return) of an airñhandling system 

Airñhandling System Icon 

The properties associated with each AHS include outdoor air intake data, supply and return 

contaminant information, and system filters. Outdoor air intake data consists of a minimum 

outdoor air intake rate, Woa_min and a schedule for varying the outdoor air intake rate as a 

percentage of the supply airflow rate. The schedule will set the value of fo in the algorithm 

above. The default value of fo is 1.0 if you don't use a schedule. Supply and return system data 

refers to the implicit zones that are created for each AHS. Just as for any zone you create, you 

can provide a zone volume, initial zone concentration and a kinetic reaction for each contaminant 

defined for the project. You can also associate contaminant filters with the implicit outdoor and 

recirculation flow paths. 

Inlet and Outlet Icons 

The properties associated with each AHS include airflow rate and contaminant filtration 

information. You must enter a design airflow rate for each inlet and outlet icon that you create. 

Enter the design maximum value that you anticipate requiring. You can also provide a schedule 

to the design airflow rate to adjust down the design flow rate. As with other airlfow paths, you 

can provide a contaminant filter to these items. 
 USING CONTAMW ñ WORKING WITH SIMPLE AIRñHANDLING SYSTEMS 

47

3.8.5 Simple Airñhandling System Properties 

This section provides detailed descriptions of the specific properties of simple airñhandling 

systems. Each of the following subsections are the context-sensitive help topics that you can 

access by pressing F1 when working with property pages of the "Simple Airñhandling System 

Properties," "Supply Point Properties," and "Return Point Properties" property sheets. 

3.8.5.1 Airñhandling System ñ AHS Properties 

System Name: The name used to identify the Air Handling System. Air handling system names 

must be unique from one another. 

Minimum OA Flow: This is the minimum outside air introduced into the AHS supply flow. If 

the sum of the return flows plus the minimum outside airflow exceeds the supply flow then the 

excess return air is vented outside. Similarly if the return flow plus the minimum outside airflow 

do not sum to the supply flow then outside air is added to make up the difference. 

Outside Air Schedule: A new Outside Air schedule is defined by pressing the "New Schedule" 

button and following the directions for editing a Week Schedule. 

Description: Field that shows a more detailed description of the specific schedule if entered 

by the user. This description can be modified by pressing the edit schedule button next to the 

description field and then changing the description field for the schedule. 

Name: This drop down box contains the names of all previously created schedules. The 

schedule selected from this box will then define the particular schedule for the exposure 

being viewed. 

3.8.5.2 Airñhandling System ñ Supply and Return System Properties 

System Volume: System Volume is used in the dynamic contaminant concentration calculations. 

Enter a value for the entire supply/return system. 

Contaminant Data: All of the defined contaminants in the project will be displayed in this list 

box. 

Initial Concentration: This box provides the user with the ability to set the initial concentration 

of the selected contaminant. 

Kinetic Reaction: You define a new kinetic reaction by pressing the "New Reaction" button and 

then completing the kinetic reaction matrix. You can edit an existing matrix by selecting the 

proper matrix from the drop down box and pressing the "Edit Reaction" button. You must have 

previously defined contaminants in order to implement a kinetic reaction. 

Description: Field that shows a more detailed description of the specific reaction if entered 

by the user. This description can be modified by pressing the "Edit Reaction" button next to 

the description field and then changing the description field for the reaction. 

Name: This contains a list of names of all previously created reactions. The reaction selected 

from this box will define the behavior of the specific supply system being modified. 
USING CONTAMW ñ WORKING WITH SIMPLE AIRñHANDLING SYSTEMS

48

3.8.5.3 Airñhandling System ñ Filter Properties 

As the names suggest, outdoor air filters affect the air brought in by the simple air handling 

system from outside the building, while recirculation air filters affect the return air being 

circulated back through the air handler. You may either select a previously defined filter from the 

drop down box provided, or you can create a new filter by pressing the "New Filter" button. 

Creating a new filter or modifying an existing one will display the Contaminant Filter Properties 

dialog box. Use this dialog box to define the filter properties. For an explanation of contaminant 

filters see Contaminant Filters in the Using CONTAMW section of the manual. 

3.8.6 Inlet/Outlet (Supply/Return) Point Properties 

These are the properties of inlet and outlet icons (supply and return points) of simple airñ

handling systems. 

Design Flow Rate: This value is design flow rate for the supply/return element (i.e. the 

maximum flow rate specified for a particular vent). 

AHS: You must associate each supply and return point with an existing air handling system. 

Name: This drop down box contains the names of all previously created Air Handling 

Systems. The AHS selected from this box will define the behavior of the specific 

supply/return system being modified. Once an existing AHS is selected it may be edited by 

pressing the "Edit AHS" button. 

Description: Field that shows a more detailed description of the specific schedule if entered 

by the user. This description can be modified by pressing the "Edit AHS" button next to the 

description field and then changing the description field for the AHS. 

Schedule: You can associate a schedule with the supply/return point to control the fraction of the 

design airflow rate that flows to/from the zone in which the supply/return point is located 

according to the time of day and day of the week. 

Description: Field that shows a more detailed description of the specific schedule if entered 

by the user. You can modify this description by pressing the "Edit Schedule" button next to 

the description field and then changing the description field for the schedule. 

Name: This drop down box contains the names of all previously created schedules. The 

schedule selected from this box will define the behavior of the specific supply/return system 

being modified. 

Filter: You can associate a filter with the supply/return point that will act upon the associated 

contaminant(s) as airflows to/from the zone in which the supply/return point is located. 

Description: Field that shows a more detailed description of the specific filter if entered by 

the user. This description can be modified by pressing the "Edit Filter" button next to the 

description field and then changing the description field for the schedule. 

Name: This drop down box contains the names of all previously created filters. The filter 

selected from this box will define the behavior of the specific supply/return system being 

modified. 
 USING CONTAMW ñ WORKING WITH DUCTS 

49

3.9 Working with Ducts 

As an alternative to the simple airñhandling system, CONTAMW allows you to model HVAC 

systems using detailed duct systems. Duct systems are made up of duct segments, junctions, 

terminal points, and forced air components. A duct segment is a section of a duct between any 

two junctions, terminal points or combination of the two. A terminal point is an endpoint of a 

duct segment, and a junction is the connection between two duct segments. Only horizontal 

segments can be displayed on the CONTAMW SketchPad, but vertical segments can be 

implemented as well. Vertical segments are connected with special junctions and terminal points 

that reveal the location of the vertical segments on the SketchPad. 

You draw the layout of the duct system, and CONTAMW will insert junctions and terminal 

points where appropriate. Once you have drawn a duct system, you must define the drawing by 

providing detailed segment, junction and terminal point information. You must provide each duct 

segment with specific information that describes the flow characteristics and physical 

dimensions of that segment. Much of this information is in the form of duct flow elements that 

you must create when defining the duct segments. The details of drawing and defining a duct 

system are described in the following sections. 

3.9.1 Duct Flow Elements 

Each duct segment must refer to a duct flow element. Duct flow elements describe the 

mathematical relationship between flow through and pressure drop along the duct, the flow 

resistance or forced flow characteristics, cross-sectional geometry, and optional leakage per unit 

length of a duct. CONTAMW provides you with several different mathematical models or 

element types to choose from. Each of these duct flow element types is described in detail in the 

Duct Segment Properties section. While every duct segment must refer to a single duct flow 

element, multiple duct segments can refer to the same duct flow element. Duct flow elements can 

also be stored within a CONTAMW library file and shared between different CONTAMW 

project files. 

3.9.2 Drawing Ducts 

You draw ducts using the duct drawing tool previously described in the Working with the 

SketchPad section. After you complete the "finalize drawing object" stage of duct drawing, the 

completed duct will appear as an undefined set of red duct icons. The color red indicates that the 

duct is not yet defined. Once you have defined the duct components, they will be displayed in 

blue. A directional duct segment icon will be displayed within each duct segment, and each 

junction and terminal point will be replaced with an icon indicating the type of junction or 

terminal point you have defined. 

Drawing Duct Segments 

CONTAMW provides certain constraints when drawing ducts to insure that a valid duct system 

will be drawn that conforms to the underlying model of nodal equations upon which 

CONTAMW is based. When drawing a duct, you cannot cross over a line that you are currently 

drawing. Ducts can cross over walls, but you cannot draw ducts over any other building 

component icons. After each duct segment is drawn, the ends of the segment will be 

automatically replaced by either an undefined terminal point or junction icon. You can only 

begin or end a duct segment drawing in an unoccupied SketchPad cell or on an undefined duct 

icon. For this reason, you are advised to draw the entire duct system, on a given level, before you 

define the individual duct segments. If you cross over a previously drawn duct segment, either 
USING CONTAMW ñ WORKING WITH DUCTS

50

defined or undefined, while drawing a new duct segment, no junction will be placed where the 

two segments cross. 

Vertical duct segments do not appear directly on the SketchPad, because the SketchPad displays 

only plan-view drawings. Vertical duct segments are associated with vertically connected 

junctions or terminal points. These vertical junction and terminal icons provide access to the 

properties of the vertical segments that are located below the level upon which the vertical 

junction or terminal appears. 

Drawing Duct Junctions 

Undefined horizontal duct junction icons are drawn automatically at the intersections of the ducts 

after you finalize drawing a duct. Each time you begin or end drawing a duct segment upon an 

undefined duct segment, junction or terminal point, CONTAMW will automatically provide an 

undefined junction icon if there is not yet one at the junction location. 

All vertical junctions are connected to vertical duct segments that are located below the level 

upon which the vertical junction appears. You can create a vertical junction that is isolated from 

other ducts on a level that is connected either up, down or both up and down to ductwork on 

adjacent levels. To do this, finalize the drawing object immediately after setting the initial 

location of the duct object. To do this, you simple press LMB (double click) or ↵ twice at the 

desired location on the SketchPad when you have the duct drawing tool selected. This will place 

a single undefined terminal point icon within the SketchPad cell. You can later define this 

undefined terminal point icon as the specific type of junction that you need and associate it with 

a vertical duct segment. 

Drawing Duct Terminal Points 

Undefined horizontal terminal point icons are automatically drawn by CONTAMW at the end of 

each duct segment that does not end on another previously drawn duct icon. 

You can also create terminal points that are isolated from other ducts on a level but connected 

either up or down to ductwork on an adjacent level by finalizing the drawing object immediately 

after setting the initial location of the duct object. To do this, you simply press LMB (double 

click) or ↵ twice at the desired location on the SketchPad when you have the duct drawing tool 

selected. This will place a single undefined terminal point icon within the SketchPad cell. You 

can later define this terminal point as the specific type that you need and associate it with a 

vertical duct segment. 

3.9.3 Deleting Ducts 

Deleting currently defined ducts is a two-step process. That is, if you want to delete a duct 

segment, junction or terminal, you must first undefine the item. To undefine a duct segment you 

must highlight the special duct segment icon (that indicates the positive flow direction) and press 

the Delete key or select Delete from the Edit menu. This will highlight the entire duct segment 

from its two end-points and prompt you to confirm the undefine operation by displaying a 

message box. Once you undefine a duct segment, it will again be displayed in red and the special 

duct segment icon will be converted back to a straight segment icon. To delete the duct segment

you highlight any portion of the undefined segment or associated undefined terminal and 

perform the deletion. The entire segment to be deleted will be highlighted, and you will be asked 

to confirm the deletion. 
 USING CONTAMW ñ WORKING WITH DUCTS 

51

There are several items you should consider when deleting ducts. You cannot delete an 

undefined junction that is still connected to a defined duct segment. If you delete a junction that 

is between two undefined segments, the junction will be removed to form a single segment. You 

cannot delete a terminal without deleting its associated segment. 

Deleting the ducts defined on the SketchPad does not delete any duct flow elements that you may 

have defined. These flow elements can only be deleted using the CONTAMW Library Manager, 

accessible through the Data menu for each type of data element. 

3.9.4 Modifying Ducts 

In order to modify the layout of a duct system, you must undefine any portions to which you 

want to connect a new duct (i.e. form a junction). To modify the parameters of a duct segment, 

junction or terminal, you use the icon definition method to display its properties and make the 

desired changes. You do not have to undefine the item to change its properties, only to change 

the physical layout. 

To remove a junction from between two segments, you should first undefine the two duct 

segments, remove the junction and then redefine the newly formed longer segment. To split a 

segment into two segments, simply double-click the LMB with the duct drawing tool on the 

segment where you wish to place the junction. 

3.9.5 Defining Ducts 

After you draw a duct, you must define each duct segment, junction, and terminal point. Each of 

these duct components is defined using the icon definition procedure (See Defining Building 

Component Icons) to display and edit the properties of the component. 

Defining Duct Segments 

You define each duct segment by using the icon definition procedure on any portion of an 

undefined duct segment. This will display the "Duct Segment Properties" property sheet. 

Detailed descriptions of all duct segment properties are given in the Duct Segment Properties 

section of this manual. Once you have defined the properties of a duct segment, a special icon 

will be displayed indicating the positive flow direction of the duct segment (see Directional Duct 

Segment Icons). From now on, you use this icon to access the properties of the duct segment. 

When defining a duct segment, you must associate the segment with a duct flow element. 

CONTAMW combines duct flow element data with segment specific data such as length and 

dynamic losses to determine the frictional resistance, volume, and leakiness of a particular duct 

segment. 

You can also define contaminant filtering properties of duct segments. You can define a filter for 

each contaminant contained in your CONTAMW project. A duct filter could be used, for 

example, to simulate the deposition of particles on the inside surface of a duct. 

As previously mentioned, duct flow elements contain duct leakage information. The 

CONTAMW model implements all leakage at the junctions and terminals of a duct segment. 

This means that half of the leakage associated with a duct segment occurs at each end of the 

segment. The leakage between a junction and the zone in which the junction is located (as 

determined on the SketchPad) is a function of the duct element leakage characteristics and the 

pressure difference between the junction and the zone. You should consider this leakage model 

when accounting for leakage of a duct that passes through multiple zones. You should put a least 

one junction (or terminal) in each zone within which you want to account for duct leakage. 
USING CONTAMW ñ WORKING WITH DUCTS

52

Directional Duct Segment Icons 

These are the icons that indicate a defined duct segment. The direction that the small arrow 

points indicates the positive flow direction of the duct segment. 

Defining Duct Junctions and Terminals 

You define each duct junction and terminal by using the icon definition procedure on a duct 

junction or terminal icon. This will display the "Duct Junction Properties" property sheet. If a 

terminal icon is located in the ambient zone, a Wind Pressure property page will be displayed to 

allow you to account for the effects of wind pressure on the exterior terminal. All junctions and 

interior terminal icon will not produce the Wind Pressure property page. Detailed descriptions of 

duct junction properties are given in the Duct Junction and Terminal Properties section of this 

manual. Once you have defined the properties of a duct junction, a special icon will be displayed 

indicating the specific type of junction you have selected (see the following list). From now on, 

you use this icon to access the properties of the duct junction. 

Junction and Terminal Icons 

Icon Description 

 Junction connected to ducts on the same level 

Junction connected to the vertical duct of a junction on the level above 

Junction and downward vertical duct connected to a junction on the level below 

Junction and downward vertical duct connected to a junction on the level below 

and connected to the vertical duct of a junction on the level above 

 Terminal connected to a duct on the same level 

 Terminal connected to the vertical duct of a junction on the level above 

 Terminal and downward vertical duct connected to a junction on the level 

below 
 USING CONTAMW ñ WORKING WITH DUCTS 

53

3.9.6 Duct Segment Properties 

This section provides detailed descriptions of the specific duct segment properties. Each of the 

following subsections are the context-sensitive help topics that you can access by pressing F1

when working with property pages of the "Duct Segment Properties" property sheet. 

3.9.6.1 Duct Segments ñ Flow Element Properties 

Duct Segment Number: This is the number that appears in the status bar when you highlight a 

duct segment icon. CONTAMW automatically assigns this number to each duct segment once 

they are defined. This number could change as you add and remove duct segments to or from a 

project. Each time you save a project, the duct segment numbers are reassigned. Numbers are 

assigned beginning on the top level, starting from the upper-left corner of the SketchPad, moving 

left-to-right and top-to-bottom of the SketchPad. 

Duct Flow Element Name: You may select a previously defined airflow element from those 

contained in the Name list. Click the "New Element" button to define a new airflow element. To 

view or modify airflow element data click the "Edit Element" button. Every duct segment must 

have an airflow element associated with it. This field may not be left blank. 

Model Summary: This summarizes the information associated with the duct flow element 

currently displayed in the Name field. 

3.9.6.2 Duct Segments ñ Segment Properties 

Segment Data: 

Duct Segment length: Enter the length of the duct segment. This will be used along with 

the cross-sectional area to determine the volume of the duct segment. 

Sum of loss coefficients: This is the sum of all dynamic loss coefficients due to junction 

losses and all fittings in the segment. 

Positive Flow Direction: In the case of fans it is necessary to know which direction is 

defined as positive. The arrows represent the positive direction for pressure drop and 

airflow. 

Segment Summary Information: This field displays information about the selected ductflow 

element. 

3.9.6.3 Duct Segments ñ Filter & Schedule Properties 

Filter: You may select a previously defined filter from those contained in the associated Name 

list. Click the "New Filter" button to define a new filter. Click the "Edit Filter" button to view or 

modify existing filter data. Setting this field to <none> indicates no filter for this airflow path. 

(See Contaminant Filters under Working with Contaminants) 

Schedule: If there are previously defined schedules within the current project, you may select 

one from the Name list. Click the "New Schedule" button to define a new schedule. To view or 

modify an existing schedule click the "Edit Schedule" button. Setting this field to "<none>" 

indicates no schedule. (See Working with Schedules) 
USING CONTAMW ñ WORKING WITH DUCTS

54

3.9.6.4 Duct Flow Element ñ Shape, Size and Leakage 

These are the properties of duct flow elements that define the shape, size and duct leakage 

characteristics of the element. 

Duct Shape: You can implement several different shapes of ducts including: round, rectangular, 

oval or other. Select the shape you want and the appropriate dimensions will be made available 

for you to enter under the Duct Dimension parameters. 

Duct Dimensions: The data entered here is dependent on the duct shape. For circular ducts, the 

diameter is the only parameter needed. Rectangular ducts require you to enter the width and 

height, and oval ducts require you to input the major and minor dimensions. The other option 

allows you to enter a perimeter and a flow area to define the dimensions for a duct of any other 

shape. 

Leakage: Leakage of air between the duct and the surrounding zone may be described in terms 

of a leakage rate at a given pressure or by use of the leakage classification. If you enter a leakage 

rate and a pressure difference, the value for the leakage class is automatically calculated by 

CONTAMW and placed in the "Leakage Class" field. Similarly, if you input a leakage class, a 

default value of 250 Pa is used for the pressure difference, and a leakage rate will be calculated 

based on the pressure difference and the leakage class you entered. See [ASHRAE 1997, Chapter 

32] 

3.9.7 Duct Flow Element Types 

These are the different types of duct flow elements that CONTAMW provides. When creating 

and defining a duct segment, you select the type of duct flow element that you want 

CONTAMW to utilize to model airflow through the duct segment. 

The most common model is the Darcy-Weisbach relation and Colebrookís natural roughness 

function. 

Darcy-Colebrook Model 

Three versions of the powerlaw model are included: 

Orifice resistance model 

Resistance: F = C(∆P)n

Resistance: Q = C(∆P)n

Three types of forced flow models are included: 

Fan - performance curve 

Constant mass flow 

Constant volume flow 

The backdraft damper elements allow you to model a flow that has different flow resistances 

depending on the direction of the pressure drop. 

Backdraft Damper: Q = C(∆P)n

Backdraft Damper: F = C(∆P)n
 USING CONTAMW ñ WORKING WITH DUCTS 

55

3.9.7.1 Darcy-Colebrook Model 

This model uses the Darcy-Weisbach relation and Colebrookís natural roughness function 

[ASHRAE 1997 pp 2.8 and 32.7]. 

Name: Enter a unique name you want to use to identify the duct flow element. The element will 

be saved within the current project and can be associated with multiple duct segments. 

Description: Use this field to enter a more detailed description of the specific duct flow element. 

Roughness: The flow resistance due to friction is calculated from Colebrookís function and the 

roughness factor [ASHRAE 1997 p 32.7]. Some typical values are given here. 

Shape Size and Leakage: You must enter data to physically describe each duct airflow element. 

You input these values on the Shape Size and Leakage property page associated with each duct 

airflow element. 

3.9.7.2 Powerlaw Model: Orifice Area 

This airflow element allows you to describe the airflow through an orifice, and CONTAMW 

converts it to a powerlaw relationship. 

Name: Enter a unique name you want to use to identify the duct flow element. The element will 

be saved within the current project and can be associated with multiple duct segments. 

Description: Use this field to enter a more detailed description of the specific duct flow element. 

Flow Exponent (n): Flow exponents vary from 0.5 for large openings where the flow is 

dominated by dynamic effects, to1.0 for narrow openings dominated by viscous effects. 

Measurements usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Discharge Coefficient (C): The discharge coefficient is related to the dynamic effects and is 

typically close to 0.6 for an orifice and slightly higher for other openings in buildings. 

Hydraulic Diameter: The hydraulic diameter is equal to (4 ⋅ Area / Perimeter). For square 

openings this equals the square root of the area, and for long thin openings it is two times the 

width. 

Reynolds Number: The transition from laminar flow to turbulent flow occurs over a very broad 

range of Reynolds numbers with the flow being fully laminar below approximately 100. 

Note: The hydraulic diameter and Reynolds number have little impact on the calculations. Generally you should use 

the default values except for special circumstances where they need to be modified. The three values above describe 

the flow characteristics of an orifice in typical operation. At extremely low pressure drops the use of the powerlaw 

model leads to a division by zero during the network solution process. CONTAMW avoids this problem by changing 

to a linear model in this region. The model is based conceptually on the flow changing from turbulent to laminar at 

very low pressures. The Hydraulic diameter and Reynolds number are used to determine a point where the model 

changes from the powerlaw to linear. 

Shape Size and Leakage: You must enter data to physically describe each duct airflow element. 

You input these values on the Shape Size and Leakage property page associated with each duct 

airflow element. 

Smooth 0.03 mm 0.0001 ft 

Medium Smooth 0.09 mm 0.0003 ft 

Average 0.15 mm 0.0005 ft 

Medium Rough 0.9 mm 0.003 ft 

Rough 3.0 mm 0.01 ft 
USING CONTAMW ñ WORKING WITH DUCTS

56

3.9.7.3 Powerlaw Model: Q=C(∆P)n

This airflow element allows you to directly enter the coefficients C and n for the volumetric flow 

version of the powerlaw model. 

Name: This is the name you give to this airflow element. This name must be unique within a 

project. 

Description: Use this field to enter a more detailed description of the specific duct flow element. 

Flow Coefficient (C): The coefficients may only be expressed in SI units due to the conversion 

method used. Use the following conversion to convert from IP units to SI units. 

n n n Pa

m s

in H O

cfm

249

2119 multiplyby / To convertfromunits of to the SI units of

3

2 

Flow Exponent (n): Flow exponents vary from 0.5 for large openings where the flow is 

dominated by dynamic effects, to 1.0 for narrow openings dominated by viscous effects. 

Measurements usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Shape Size and Leakage: You must enter data to physically describe each duct airflow element. 

You input these values on the Shape Size and Leakage property page associated with each duct 

airflow element. 

3.9.7.4 Powerlaw Model: F=C(∆P)n

This airflow element allows you to directly enter the coefficients C and n for the mass flow 

version of the powerlaw model. 

Name: Enter a unique name you want to use to identify the duct flow element. The element will 

be saved within the current project and can be associated with multiple duct segments. 

Description: Use this field to enter a more detailed description of the specific duct flow element. 

Flow Coefficient (C): The coefficients may only be expressed in SI units due to the conversion 

method used. Use the following conversion to convert from IP units to SI units. 

n n n Pa

kg s

in H O

lbm s

249

0.4536 multiplyby /

to the SI units of / To convertfromunits of

2 

Flow Exponent (n): Flow exponents vary from 0.5 for large openings where the flow is 

dominated by dynamic effects, to 1.0 for narrow openings dominated by viscous effects. 

Measurements usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Shape Size and Leakage: You must enter data to physically describe each duct airflow element. 

You input these values on the Shape Size and Leakage property page associated with each duct 

airflow element. 
 USING CONTAMW ñ WORKING WITH DUCTS 

57

3.9.7.5 Fan Model: Constant Mass Flow 

This airflow element allows you to describe the airflow through a duct as a constant mass airflow 

rate. 

Name: Enter a unique name you want to use to identify the duct flow element. The element will 

be saved within the current project and can be associated with multiple duct segments. 

Description: Use this field to enter a more detailed description of the specific duct flow element. 

Design (max) Flow: Enter the maximum mass flow rate. You can use the duct segment schedule 

to modify this value. 

Shape Size and Leakage: You must enter data to physically describe each duct airflow element. 

You input these values on the Shape Size and Leakage property page associated with each duct 

airflow element. 

3.9.7.6 Fan Model: Constant Volume Flow 

This airflow element allows you to describe the airflow through a duct as a constant volumetric 

airflow rate. 

Name: Enter a unique name you want to use to identify the duct flow element. The element will 

be saved within the current project and can be associated with multiple duct segments. 

Description: Use this field to enter a more detailed description of the specific duct flow element. 

Design (max) Flow: Enter the maximum volume flow rate. You can use the duct segment 

schedule to modify this value. 

Shape Size and Leakage: You must enter data to physically describe each duct airflow element. 

You input these values on the Shape Size and Leakage property page associated with each duct 

airflow element. 

3.9.7.7 Fan Model: Performance Curve 

This airflow element allows you to create a fan based on a fan performance curve. You provide 

CONTAMW with a set of pressure rise and airflow rate data points, and CONTAMW performs a 

polynomial curve fit to the data point. 

Name: Enter a unique name you want to use to identify the duct flow element. The element will 

be saved within the current project and can be associated with multiple duct segments. 

Fan-off Data: These values specify how the fan is modeled when the speed of the fan is 

insufficient to provide a flow. 

Control Value: The actual speed of the fan divided by the rated speed of the fan. When this ratio 

is below the specified limit the fan is modeled as a simple orifice. 

Equivalent Orifice: The size of the orifice used to model the fan opening when the control value 

drops below the specified limit. 

Description: Use this field to enter a more detailed description of the specific duct flow element. 

Fan Performance Data: Click the "Edit Fan Curve Data" button to input/modify the fan curve 

for this duct flow element. A detailed explanation of this data is given in the Fan Performance 

Data section under Working with Airflow Paths. 

Shape Size and Leakage: You must enter data to physically describe each duct airflow element. 

You input these values on the Shape Size and Leakage property page associated with each duct 

airflow element. 
USING CONTAMW ñ WORKING WITH DUCTS

58

3.9.7.8 Backdraft Damper Model: Q=C(∆P)n

This is the volumetric flow version of the Backdraft Damper duct flow element. The Backdraft 

Damper models make it possible to model a feature (e.g. a smoke control damper) that has 

different flow resistances depending on the direction of the pressure drop, with greatly reduced 

(or zero) flow in one direction. 

Name: Enter a unique name you want to use to identify the duct flow element. The element will 

be saved within the current project and can be associated with multiple duct segments. 

Description: Use this field to enter a more detailed description of the specific duct flow element. 

Pressure Difference ∆P>0 or ∆P<0: This indicates the direction of flow for the model. 

Flow Coefficients: The coefficients may only be expressed in SI units due to the conversion 

method used. Use the following conversion to convert from IP units to SI units. 

n n n Pa

m s

in H O

cfm

249

2119 multiplyby / To convertfromunits of to the SI units of

3

2 

Flow Exponents: Flow exponents vary from 0.5 for large openings where the flow is dominated 

by dynamic effects, to 1.0 for narrow openings dominated by viscous effects. Measurements 

usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Shape Size and Leakage: You must enter data to physically describe each duct airflow element. 

You input these values on the Shape Size and Leakage property page associated with each duct 

airflow element. 

3.9.7.9 Backdraft Damper Model: F=C(∆P)n

This is the mass flow version of the Backdraft Damper duct flow element. The Backdraft 

Damper models make it possible to model a feature (e.g. a smoke control damper) that has 

different flow resistances depending on the direction of the pressure drop, with greatly reduced 

(or zero) flow in one direction. 

Name: Enter a unique name you want to use to identify the duct flow element. The element will 

be saved within the current project and can be associated with multiple duct segments. 

Description: Use this field to enter a more detailed description of the specific duct flow element. 

Pressure Difference ∆P>0 or ∆P<0: This indicates the direction of flow for the model. 

Flow Coefficients: The coefficients may only be expressed in SI units due to the conversion 

method used. Use the following conversion to convert from the IP units to SI units. 

n n n Pa

kg s

in H O

lbm s

249

0.4536 multiplyby /

to the SI units of / To convertfromunits of

2 

Flow Exponents: Flow exponents vary from 0.5 for large openings where the flow is dominated 

by dynamic effects, to 1.0 for narrow openings dominated by viscous effects. Measurements 

usually indicate a flow exponent of 0.6 to 0.7 for typical infiltration openings. 

Shape Size and Leakage: You must enter data to physically describe each duct airflow element. 

You input these values on the Shape Size and Leakage property page associated with each duct 

airflow element. 
 USING CONTAMW ñ WORKING WITH DUCTS 

59

3.9.8 Duct Junction and Terminal Properties 

This section provides detailed descriptions of the specific duct junction and terminal properties. 

The following sections are the context-sensitive help topics that you can access by pressing F1

when working with property pages of the "Duct Junction Properties" property sheet. 

3.9.8.1 Duct Junction and Terminal ñ Junction Properties 

Junction Number: This is the number that appears in the status bar when you highlight a duct 

junction or terminal icon. CONTAMW automatically assigns this number to each duct junction 

or terminal once they are defined. This number could change as you add and remove duct 

junctions and terminals to or from a project. Each time you save a project, the junction numbers 

are reassigned. Numbers are assigned beginning on the top level, starting from the upper-left 

corner of the SketchPad, moving left-to-right and top-to-bottom of the SketchPad. 

Elevation & Temperature: The elevation and temperature of the junction are used to determine 

how the duct flow responds to and influences the building stack effect. Enter the height of the 

midpoint of the junction/terminal point relative to the current building level. 

Define Downward Duct: If the you define a downward duct the downward flows must be 

defined by pressing the Define Downward Duct button. 

3.9.8.2 Duct Junction and Terminal ñ Wind Pressure Properties 

Wind Pressure Option: There are three wind pressure options for duct terminals located in an 

ambient zone: 

1. No wind pressure 

2. Constant pressure 

3. Pressure dependent on wind speed and direction 

When you select one of the above options, the following data entry options that correspond to the 

wind pressure option that you selected will be made available for your input. 

Constant Pressure Data: Enter a constant wind pressure (wind speed and direction 

independent). 

Variable Pressure Data: Variable wind pressures are computed from the product of the 

following three parameters: 

1. The dynamic pressure of the wind at some reference height. CONTAMW will determine 

this pressure based on either the steady state wind data (See Wind Properties) or the 

transient wind data from a weather file (See Defining Transient Weather and Wind). 

2. A coefficient accounting for local terrain effects (Wind Pressure Modifier). 

3. A pressure coefficient accounting for relative wind direction (Wind Pressure Profile). 

Wind Pressure Modifier: CONTAMW uses this value to account for differences between 

wind velocity profiles at the building site and that at a measurement location, e.g. an airport 

weather station (See Working with Weather and Wind). CONTAMW only requires this value 

if you are implementing Variable Wind Pressure for an airflow path. CONTAMW will 

provide a default value for this based on the data entered via the Weather and Wind 

Parameters Property Page or you can override the default value for a particular airflow path. 

Wall Azimuth Angle: Enter the direction the wall faces (clockwise from north). 
USING CONTAMW ñ WORKING WITH DUCTS

60

Profile: The wind pressure profile accounts for the wind direction effects. You may select a 

previously defined wind pressure profile from those contained in the Name list. Click the 

"New Profile" button to define a new wind pressure profile. To view or modify wind pressure 

profile data, click the "Edit Profile" button. After you press the "New Profile" or "Edit 

Profile" button, the Wind Pressure Profile page will be displayed with a graphical 

representation of the profile. 
 USING CONTAMW ñ WORKING WITH CONTAMINANTS 

61

3.10 Working with Contaminants 

Airborne contaminants are dispersed throughout buildings due to several different transport 

mechanisms. These include air movements into, out of, and within a building system; heating, 

ventilating, and air-conditioning (HVAC) systems; removal by filtration, settling, and sorption; 

generation; chemical reaction; and radio-chemical decay. CONTAMW provides you with the 

ability to simulate these methods of dispersal of airborne contaminants within built structures. 

This version of CONTAMW allows you to include up to ten contaminants in each project you 

create. 

It is important to note that CONTAMW handles only trace contaminants, those that exist at 

concentrations that do not cause a "significant" change in the density of air. Another important 

underlying assumption of the model implemented by CONTAMW is that each zone is 

characterized by a single concentration value at any given time. This assumption is sometimes 

referred to as the "well-mixed" zone assumption. With respect to contaminant analysis, this 

means that there are no concentration gradients within a given zone. 

You can use CONTAMW to perform steady state, transient, and cyclical contaminant analysis. 

Steady state analysis refers to the determination of contaminant concentrations under steady flow 

conditions. Transient analysis refers to the determination of the time history of contaminant 

concentrations within each zone for a set of discrete time-steps. With a transient analysis you can 

implement the effects of ambient contaminants using a weather file (See Defining Transient 

Weather and Wind). A cyclic analysis determines the time history of contaminant concentrations 

for a 24-hour period such that the concentrations at the beginning and end of the 24-hour period 

are the same for each zone. 

You must define contaminants in order to utilize the features that CONTAMW provides to 

simulate the generation of contaminants by sources, the removal by sinks (including filters and 

kinetic reactions), and to determine occupant exposures. Contaminants must be created/defined 

prior to implementing any of these contaminant-dependant features of CONTAMW. Prior to 

implementing contaminants within a project, you can first define the building layout on the 

SketchPad, define all airflow paths (including ducts) and test your building model by performing 

a steady state airflow simulation. 

3.10.1 Creating Contaminants 

You create contaminants by activating the Project Contaminants dialog box via the 

ContaminantsÖ selection of the Data menu. This dialog box will enable you to create and 

modify up to ten contaminants for a project. A detailed description of each of the contaminant 

properties is given in the Contaminant Properties section of this manual. Contaminants are 

associated with the CONTAMW project in which you define them and are not sharable between 

projects using the CONTAMW Library Manager. 

Each contaminant has a default concentration associated with it that you define (or leave zero). 

You can use this default concentration to set the initial concentrations within a building without 

having to utilize a source element. 
USING CONTAMW ñ WORKING WITH CONTAMINANTS

62

3.10.2 Deleting Contaminants 

You delete contaminants by activating the Project Contaminants dialog box via the 

ContaminantsÖ selection of the Data menu. To delete contaminants, you must delete all 

contaminants from a project. When you attempt to perform the contaminant deletion operation, 

CONTAMW will warn you that all contaminants and related information will be deleted and that 

this is an irreversible operation. The warning will be given to you in the form of a dialog box that 

will allow you to cancel the deletion operation. If you want to maintain a copy of a project that 

contains the currently defined contaminants, you should save it under a different name prior to 

deleting all contaminant related information. Deleting contaminants will also remove all related 

sources and sinks that you have created in the project. You should realize that you don't have to 

delete contaminants in order for CONTAMW to ignore them when performing a simulation. You 

can set CONTAMW simulation parameters to prevent the simulation of contaminants (See 

Working with Simulations ). 

3.10.3 Modifying Contaminants 

Once you have created contaminants for a project, you can modify any of the related parameters. 

You do this by activating the "Project Contaminants" dialog box via the ContaminantsÖ

selection of the Data menu. CONTAMW will even allow you to change the name of an existing 

contaminant. This will not affect any of the currently associated sources, sinks, filters or kinetic 

reactions as they reference contaminants by an internal index created by CONTAMW. 

3.10.4 Project Contaminants 

Contaminants must be defined before any contaminant related features (e.g. source/sinks and 

filters) can be defined. From the Project Contaminants page, any previously defined 

contaminants may be viewed, new contaminants may be defined, and existing contaminants can 

be deleted. 

Contaminants: All of the defined contaminants in the project will be displayed in this list box. 

Properties: The properties for the selected contaminant will be displayed here. 

Click the "New" button to create a new contaminant. To modify the properties of an existing 

contaminant, highlight the contaminant in the contaminant list and click the "Edit" button. Click 

the "Delete" button to delete all contaminants. 

3.10.5 Contaminant Properties 

This section provides detailed descriptions of the specific contaminant properties. This 

information is also the context-sensitive help topic that you can access by pressing F1 when 

working with "Contaminant Properties" dialog box. 

Name: <Required> You will use this contaminant name to refer to the contaminant throughout 

the program. You must give each contaminant a name that is unique to the current project. The 

name can be up to twelve characters long. 

Molecular Weight: <Required> The molecular weight in g/mol or kg/kmol. CONTAMW uses 

this value to convert volumetric concentrations to mass fractions, which are then used in all 

internal calculations. You must enter a value of at least 1.0. 
 USING CONTAMW ñ WORKING WITH CONTAMINANTS 

63

Default Concentration: CONTAMW will apply this value as the default initial concentration 

for each zone that you create as well as for the ambient zone for a steady state simulation. You 

can revise this value for individual zones as needed. 

Decay Rate: CONTAMW will use this value to perform unit conversions for radioactive 

contaminants. Radioactive contaminants are only distinguished from other contaminants by the 

units associated with them, not by modeling the radioactive decay process. To model a 

radioactive decay process, use a kinetic reaction. 

Specific Heat: Currently not implemented. 

Guideline Value: Currently not implemented. 

Guideline Description: Currently not implemented. 

3.10.6 Contaminant Filters 

CONTAMW provides some building components with the ability to act as contaminant removal 

devices or filters. To use contaminant filters, you must have already defined at least one 

contaminant for the project. You define contaminant filters that you can associate with one or 

more building components within a project. You can access the Filter Properties dialog box via 

any of the building component property sheets that provide a Filter definition page. You can also 

access the Filter Properties dialog box using the CONTAMW Library Manager to create and edit 

local project data. However, you cannot share filters between CONTAMW projects, because 

they are dependent on previously defined project contaminants that may not exist between 

projects. 

The following building components provide for contaminant filtering: 

1. Airflow paths 

2. Duct segments 

3. Simple airñhandling systems 

4. Supply and return points of simple airñhandling systems 

When you are defining each of these types of building components, you will be able to select a 

currently defined filter to associate with it, define new filters, or modify existing filters. All 

filters are defined and modified using the "Filter Properties" dialog box as described in the 

following section. 

3.10.7 Contaminant Filter Properties 

Name: Enter a unique name you want to use to identify the filter. The filter will be saved within 

the current project and can be associated with multiple building components. 

Description: Use this field to provide a more detailed description of the filter. 

Contaminants: This is a list of all the contaminants defined in the current project. Select the 

contaminant for which you want to set a filter efficiency. 

Filter Efficiency: This shows the filter efficiency for the associated contaminants. Filter 

efficiencies must be between 0.0 and 1.0. 

Edit Efficiency: Use this edit field to modify the efficiency of the currently highlighted 

contaminant. Once you have entered the efficiency, click the "<< Replace <<" button to make 

the change. 
USING CONTAMW ñ WORKING WITH CONTAMINANTS

64

3.10.8 Kinetic Reactions 

CONTAMW provides the ability to model chemical reactions of contaminants within zones of a 

building. Kinetic reactions in CONTAMW are modeled as first-order rate expressions and are 

described by kinetic reaction matrices that contain the first-order reaction rate coefficients 

between the reactant and product contaminants. See Axley [1988] and Axley [1995] for a 

detailed presentation of the kinetic reaction simulation method employed by CONTAMW. The 

production or destruction of a contaminant α is given by 

= ( ) ⋅ βRα Kα ,β Cβ

where 

Ra is the rate of production or destruction of contaminant α,

Kα,β are the reaction rate coefficients between contaminants α and β, in units of s-1, and 

Cβ is the concentration of a reactant. 

CONTAMW uses the convention that positive reaction coefficients produce an increase in 

contaminant concentration and negative coefficient decrease contaminant concentrations. The 

units of concentration are kg contaminant / kg air. 

Kinetic reactions can occur within zones of a building including the implicit supply and return 

nodes of a simple airñhandling system. To use kinetic reactions, you must have already defined 

at least one contaminant for the project. You can associate kinetic reactions matrices with one or 

more zones within a project. You can access the Kinetic Reaction Matrix dialog box via the 

property sheets of the zones that provide a kinetic reaction definition section (i.e. zones and 

simple airñhandling systems). You can also access the Kinetic Reaction Matrix dialog box using 

the CONTAMW Library Manager to create and edit local project data. However, you cannot 

share kinetic reactions between CONTAMW projects, because they are dependent on previously 

defined project contaminants that are not shared between projects. 

When you are defining building zones, you will be able to select a currently defined kinetic 

reaction to associate with it, define new kinetic reactions, or modify existing kinetic reactions. 

All kinetic reactions are defined and modified using the Kinetic Reaction Matrix dialog box as 

described in the following section. 

3.10.9 Kinetic Reaction Matrix 

These are the properties that describe a kinetic reaction. 

Name: Enter a unique name you want to use to identify the reaction matrix. The reaction matrix 

will be saved within the current project and can be associated with multiple zones within the 

project. 

Description: Use this to provide a more detailed description of the kinetic reaction. 

Matrix: The first-order reaction rate coefficients are displayed in matrix form. Reactant 

contaminants are shown in the column on the left, and product contaminants are shown in the 

row across the top. Enter the desired coefficients, in units of s-1, for each combination of 

contaminants whose reaction is being simulated. 

Examples: The following are examples of kinetic reactions as implemented with CONTAMW. 
 USING CONTAMW ñ WORKING WITH CONTAMINANTS 

65

Kinetic Reaction Example 1 

To simulate the first-order decay of a contaminant, you would set the value on the diagonal to the 

negative of the reaction rate in units of s-1. 

This figure shows kinetic reaction coefficients for two contaminant reactions that will yield 

exponential decays of each contaminant according to the equation C(t) = Coe

Kt

. 

Where, 

C(t) = concentration at time t 

Co = initial concentration at time 0 

K = reaction rate coefficient (time constant) 

In the above example, the reaction rate coefficients are as follows: 

KC1,C1 = -0.0001388 s-1 

KC1,C2 = 0.0 

KC2,C2 = - 0.0000347 s-1 

KC2,C1 = 0.0 

If the reaction is the only means of contaminant removal, i.e., there is no dilution due to airflow, 

then contaminant C1 would decay at 0.5 h-1, (0.0001388 · 3600) and C2 would decay at 

0.125 h-1, (3.4722 x 10-5 · 3600). 
USING CONTAMW ñ WORKING WITH CONTAMINANTS

66

Kinetic Reaction Example 2 

This example illustrates the first-order decay of contaminant C1 (reactant) and the first order 

build-up of another contaminant C2 (product). 

This figure above shows kinetic reaction coefficients for two contaminant reactions that will 

yield an exponential decay of contaminant C1 according to the equation C(t) = Coe

Kt

, and the 

build-up of C2 according to C(t) = Co(1- eKt). 

In the above example, the reaction rate coefficients are as follows: 

KC1,C1 = -0.0001388 s-1 

KC1,C2 = 0.0 

KC2,C2 = 0.0 

KC2,C1 = 0.0001388 s-1

Note that both the decay and build-up are dependant on the concentration of C1. 

Kinetic Reaction Example 3 

You can also use the kinetic reaction to simulate a consecutive first-order reaction series. The 

radioactive decay chain of Radon gas is an example of such a reaction. 

A two-step consecutive reaction series involving a single reactant at each step is indicated as 

α → β 

β → products 

You would model this reaction chain by inputting coefficients into the reaction matrix based on 

the half-life of the radioactive reactants. Convert half-life τ1/2 to a first-order reaction coefficient, 

K, using the following equation: 

1/ 2 K = −0.693/τ

In CONTAMW, you would require two contaminants C1 and C2 (corresponding to α and β

above) and three reaction coefficients. 

KC1,C1 and KC2,C2 would have negative non-zero values. 

KC2,C1 would have a non-zero positive value. 

KC1,C2 would be set to zero. 
 USING CONTAMW ñ WORKING WITH SOURCES AND SINKS 

67

3.11 Working with Sources and Sinks 

Sources and sinks are used to generate contaminants within and remove contaminants from 

zones. Sources can be used to simulate building materials such as carpet, pieces of furniture, and 

episodic events such as the use of cleaning products. You can define an almost unlimited number 

of sources within a project. 

To implement a source/sink, you must first define the contaminant with which you want the 

source/sink to be associated. You then place a source/sink icon within a zone on the SketchPad. 

Once you place source/sinks on the SketchPad, you can define their characteristics, move, copy, 

and delete them. You must associate each source/sink with a predefined contaminant and provide 

specific information that describes its contaminant emission and/or removal characteristics. 

Much of the information that describes the characteristics of a source/sink is contained in 

source/sink elements that you must create when defining source/sinks. The details of drawing, 

defining and modifying sources and sinks are described in the following sections. 

3.11.1 Source/Sink Elements 

CONTAMW uses mathematical relationships referred to as source/sink elements or models to 

implement sources and sinks when performing contaminant simulations. CONTAMW can 

implement several source/sink models to generate contaminants within or remove contaminants 

from a zone. Depending on the source/sink model, it could be used to emulate either a source, a 

sink or both. Each of these source/sink element types is described in detail in the Source/Sink 

Element Types section. Every source/sink must refer to a single source/sink element; however, 

multiple source/sinks can refer to the same source/sink element. Unlike airflow elements 

CONTAMW does not support the storage of source/sink elements within CONTAMW library 

files for sharing between different CONTAMW project files. 

3.11.2 Creating Sources and Sinks 

You create source/sinks by placing a source/sink icon on the SketchPad (See Drawing Building 

Component Icons). Each source/sink must be placed within a building zone. You cannot place 

them in the ambient zone. Ambient sources are handled using either the initial concentration 

property of a contaminant (for steady state simulations) or the concentration contained within a 

weather file (for transient simulations). The "Source/sink" menu selection will be disabled 

(grayed out) if you pop-up on a location where CONTAMW does not allow the icon to be 

placed. 

3.11.3 Deleting Sources and Sinks 

You delete source/sink icons using the icon deletion procedure (See Deleting Building 

Component Icons). Deleting source/sink icons from the SketchPad does not delete any 

source/sink elements that you may have defined. These flow elements can only be deleted using 

the CONTAMW Library Manager, accessible through the Data menu for each type of data 

element. 
USING CONTAMW ñ WORKING WITH SOURCES AND SINKS

68

3.11.4 Modifying Sources and Sinks 

To modify the parameters of a source/sink, you use the icon definition procedure (See Defining 

Building Component Icons) to display its properties and make the desired changes. You can also 

move and copy source/sinks. 

Moving Source/Sink Icons 

Once you define a source/sink, you can move the icon using the Cut and Paste functions of the 

Edit menu. You can move the source/sink icon anywhere within the zone in which it is currently 

located. 

Copying Source/Sink Icons 

Once you define a source/sink, you can copy the icon using the Copy and Paste functions of the 

Edit menu. You can copy a source/sink to any blank cell within a zone on any level of a project. 

3.11.5 Defining Sources and Sinks 

After you draw a Source/Sink icon on the SketchPad you must define it using the icon definition 

procedure (See Defining Building Component Icons) to display and edit the properties. This will 

display the "Source/Sink Properties" property sheet. Detailed descriptions of all source/sink 

properties are given in the Source and Sink Properties section of this manual. Once you have 

defined the properties, the icon will be displayed in black. From now on, you use this icon to 

access the properties of the source/sink. 

Among the properties associated with a source/sink are optional multiplier and schedule

information. You would use the multiplier to proportionally increase the generation or removal 

of a contaminant for a particular source/sink. For example, if you have created a source/sink 

element with a certain emission rate per square meter of surface area (such as a floor covering), 

you could use this multiplier to account for the surface area of the source/sink for each zone in 

which you place a source/sink implementing this source/sink element. You could use a schedule

to vary the emission/removal characteristics of a source/sink with time. For example, you could 

provide a schedule for an episodic source (burst source) that would periodically cause the release 

of a contaminant when performing a transient simulation. 
 USING CONTAMW ñ WORKING WITH SOURCES AND SINKS 

69

3.11.6 Source/Sink Properties 

This section provides detailed descriptions of the specific source/sink properties. Each of the 

following subsections are the context-sensitive help topics that you can access by pressing F1

when working with property pages of the "Source/Sink Properties" property sheet. 

3.11.6.1 Source/Sink ñ Source/Sink Element Properties 

Source/Sink Number: This is the number that appears in the status bar when you highlight a 

source/sink icon. CONTAMW automatically assigns this number to each source/sink once they 

are defined. This number could change as you add and remove source/sinks to or from a project. 

Each time you save a project, the source/sink numbers are reassigned. Numbers are assigned 

beginning on the top level, starting from the upper-left corner of the SketchPad, moving left-toright and top-to-bottom of the SketchPad.

Source/Sink Element: 

Description: Field that shows a more detailed description of the specific sink/source element 

if entered by the user. This description can be modified by pressing the "Edit Element" 

button next to the description field. 

Name: This drop down box contains the names of all previously created source/sink 

elements. The element selected from this box will then be associated with particular 

source/sink being modified. 

Note: External libraries are not implemented for source/sinks. 

Constituent Contaminants: Currently not implemented.

3.11.6.2 Source/Sink ñ Multiplier and Schedule Properties 

Contaminant: This is the contaminant associated with the source/sink. 

Multiplier: A constant value by which the source is multiplied. This allows for a contaminant 

source to be defined per unit area and then multiplied by the area of the zone. 

Schedule: You can use a schedule to modify the source/sink rate as a function of time, and two 

source types, burst and decaying, require the use of a schedule. If there are previously defined 

schedules within the current project, you may select one from the Name list. Click the "New 

Schedule" button to define a new schedule. To view or modify an existing schedule click the 

"Edit Schedule" button. Setting this field to "<none>" indicates no schedule. (See Working with 

Schedules) 
USING CONTAMW ñ WORKING WITH SOURCES AND SINKS

70

3.11.7 Source/Sink Element Types 

These are the source/sink element types or models that you can implement with CONTAMW. 

Refer to the related information for each specific model to obtain detailed descriptions of them. 

CONTAMW Elements:

Constant Coefficient Model: The general source/sink model allows constant 

contaminant generation and deposition rates. 

Pressure Driven Model: This model is for contaminant sources that are governed by the 

pressure differences between zones. 

Cutoff Concentration Model: This model will reduce emissions as the concentration 

within the zone in which it is implemented approaches a specified cutoff concentration. 

This model may be appropriate for some sources of volatile organic compounds (VOC). 

Decaying Source Model: This model provides a source that will exponentially decay 

with time according to a user-defined time constant. This model may also be appropriate 

for some VOC sources. 

Boundary Layer Diffusion Model: Used to model reversible diffusion of a contaminant 

through the air-phase boundary layer of a material surface. 

Burst Source Model: Used to model an instantaneous release of a mass of contaminant 

within a zone. 

NRCC Elements: 

Currently not implemented. 
 USING CONTAMW ñ WORKING WITH SOURCES AND SINKS 

71

3.11.7.1 Source/Sink Element: Constant Coefficient Model 

S(t) = G − D ⋅C(t)

where 

S(t) = contaminant source strength

G = generation rate 

D = effective deposition (removal) rate 

C(t) = concentration at time t

Name: Enter a unique name you want to use to identify the source/sink element. The element 

will be saved within the current project and can be associated with multiple source/sinks. 

Generation Rate: The rate at which the contaminant is introduced into the zone. 

Removal Rate: The rate at which the contaminant is removed from the zone. 

Contaminant: Select a previously defined contaminant from the drop down box. 

Description: Use this field to enter a more detailed description of the specific sink/source 

element. 

3.11.7.2 Source/Sink Element: Pressure Driven Model 

The pressure source/sink model is intended to model contaminant sources that are controlled by 

the pressure differences between interior and exterior zones, e.g., radon or soil gas entry. The 

governing equation is as follows: 

n S = G ⋅ ∆P

where 

S = contaminant source strength 

G = generation rate coefficient 

∆P = pressure difference 

n = pressure exponent 

Name: Enter a unique name you want to use to identify the source/sink element. The element 

will be saved within the current project and can be associated with multiple source/sinks. 

Generation Rate: This coefficient describes the rate at which the contaminant is introduced into 

the zone as a function of pressure difference. 

Pressure Exponent: Used to describe the dependence on pressure of the contaminant entry. 

Contaminant: Select a previously defined contaminant from the drop down box. 

Description: Use this field to enter a more detailed description of the specific sink/source 

element. 
USING CONTAMW ñ WORKING WITH SOURCES AND SINKS

72

3.11.7.3 Source/Sink Element: Cutoff Concentration Model 

For volatile organic compounds the source model is sometimes expressed as: 















 = − Ccut

C t S t G ( ) ( ) 1

where 

S(t) = contaminant source strength 

G = generation rate coefficient 

C(t) = concentration at time t

Ccut = cutoff concentration at which emission ceases 

Name: Enter a unique name you want to use to identify the source/sink element. The element 

will be saved within the current project and can be associated with multiple source/sinks. 

Generation Rate: This coefficient describes the rate at which the contaminant is introduced into 

the zone as a function of concentration. 

Cutoff Concentration: The concentration level where the source ceases its emission. 

Contaminant: Select a previously defined contaminant from the drop down box. 

Description: Use this field to enter a more detailed description of the specific sink/source 

element. 

3.11.7.4 Source/Sink Element: Decaying Source Model 

c t t Go S t / ( ) e− = ⋅

where 

S(t) = contaminant source strength 

Go = initial generation rate 

t = time since the start of emission 

tc = time constant 

Name: Enter a unique name you want to use to identify the source/sink element. The element 

will be saved within the current project and can be associated with multiple source/sinks. 

Initial Generation Rate: Contaminant generation is controlled by a schedule. Contaminant 

generation begins when the schedule changes from a zero to a non-zero value (between zero and 

one). The initial emission rate of the source will be equal to the schedule value times the initial 

generation rate as defined by this value. A single schedule may be used to initiate several 

emissions at different times. 

Time Constant: The time at which the generation rate reaches 0.37 of the original rate. 

Contaminant: Select a previously defined contaminant from the drop down box. 

Description: Use this field to enter a more detailed description of the specific sink/source 

element. 

Note: You must associate a schedule with this type of source. 
 USING CONTAMW ñ WORKING WITH SOURCES AND SINKS 

73

3.11.7.5 Source/Sink Element: Boundary Layer Diffusion Model 

The boundary layer diffusion controlled reversible sink/source model follows the descriptions 

presented in Axley [1991]. The boundary layer refers to the region above the surface of a 

material through which a concentration gradient exists between the near-surface concentration 

and the air-phase concentration. The rate at which a contaminant is transferred onto a surface 

(sink) is defined as: 





 



 = ⋅ ⋅ − k

C S t h d A C t S

i ( ) ( )

where 

S(t) = contaminant source strength 

h = film mass transfer coefficient over the sink 

d = film density of air 

A = surface area of the adsorbent 

Ci = concentration in air at time t

CS = concentration in the adsorbent 

k = Henry adsorption constant or the partition coefficient 

Name: Enter a unique name you want to use to identify the source/sink element. The element 

will be saved within the current project and can be associated with multiple source/sinks. 

Film Transfer Coefficient: The average mass transfer coefficient of the contaminant within the 

boundary layer (or film) above the surface of the adsorbent. 

Film Density of Air: This is the average of the bulk air density and the near-surface density. 

Surface Mass: Enter the sorbent mass per unit surface area and use the source/sink multiplier, 

on the Multiplier and Schedule property page, to enter the total area of the adsorbent. 

Partition Coefficient: Coefficient that relates the concentration of the contaminant in the bulkair to that at the surface of the adsorption material. 

Contaminant: Select a previously defined contaminant from the drop down box. 

Description: Use this field to enter a more detailed description of the specific sink/source 

element. 

3.11.7.6 Source/Sink Element: Burst Source Model 

The burst model simulates an instantaneous addition of contaminant mass to a zone. 

Name: Enter a unique name you want to use to identify the source/sink element. The element 

will be saved within the current project and can be associated with multiple source/sinks. 

Mass added to zone: Enter a value for the instantaneous mass release into the zone. The 

addition of mass is controlled by a schedule; when the schedule changes from zero to non-zero 

value, mass is added to the zone in one simulation time step. The amount of mass added is equal 

to the mass added to zone value times the schedule value. A single schedule can initiate several 

events at different times. 

Contaminant: Select a previously defined contaminant from the drop down box. 

Description: Use this field to enter a more detailed description of the specific sink/source 

element. 

Note: You must associate a schedule with this type of source. 
USING CONTAMW ñ WORKING WITH OCCUPANT EXPOSURE

74

3.12 Working with Occupant Exposure 

CONTAMW provides you with the ability to simulate the existence of occupants within a 

building. You can simulate the movement of occupants throughout the building, allow the 

occupant to leave the building, determine the amount of exposure to contaminants to which the 

occupant will be susceptible, and determine potential dose, and dose based on occupant 

characteristics such as inhalation rate. Occupants can also generate contaminants within a 

building, so you can represent a contaminant source that moves through the building with an 

occupant. 

To implement an occupant, you must first define at least one contaminant. You then place an 

exposure icon (shown below) on the SketchPad. Once you place the exposure icon on the 

SketchPad, you can define its characteristics, move, copy, and delete it. You must then define an 

occupant schedule for the exposure icon. The details of drawing, defining and modifying 

occupants are described in the following sections. 

Occupant exposure icon 

3.12.1 Creating Occupants 

You create an occupant by placing an exposure icon on the SketchPad (See Drawing Building 

Component Icons). You can place occupants in any blank cell of the SketchPad. The "Exposure" 

menu selection will be disabled (grayed out) if you pop-up on a location where CONTAMW 

does not allow the icon to be placed. 

3.12.2 Deleting Occupants 

You delete exposure icons using the icon deletion procedure (See Deleting Building Component 

Icons). Deleting occupant exposure icons from the SketchPad deletes the occupant data 

associated with the icon, but it does not delete any occupant-related schedules that you might 

have created. These schedules can only be deleted using the CONTAMW Library Manager, 

accessible through the Data menu for each type of data element. 

3.12.3 Modifying Occupants 

To modify the parameters of an occupant, you use the icon definition procedure (See Defining 

Building Component Icons) to display its properties and make the desired changes. You can also 

move and copy occupants. 

Moving Occupant Exposure Icons 

Once you define an occupant, you can move the icon using the Cut and Paste functions of the 

Edit menu. You can move the occupant exposure icon anywhere within the level upon which it 

is currently located. 

Copying Occupant Exposure Icons 

Once you define an occupant, you can copy the icon using the Copy and Paste functions of the 

Edit menu. You can copy an occupant to any blank cell on any level of a project. 
 USING CONTAMW ñ WORKING WITH OCCUPANT EXPOSURE 

75

3.12.4 Defining Occupants 

After you draw an exposure icon on the SketchPad you must define it using the icon definition 

procedure (See Defining Building Component Icons) to display and edit the properties. This will 

display the "Occupant Exposure Properties" property sheet. Detailed descriptions of all occupant 

exposure properties are given in the Occupant Properties section of this manual. Once you have 

defined the properties, the icon will be displayed in black. From now on, you use this icon to 

access the properties of the occupant. 

Among the optional properties associated with an occupant are multiplier, inhalation, and 

contaminant generation information. You would use the multiplier to proportionally increase the 

contaminant generation rate associated with an individual exposure icon to represent the 

contaminant generation of multiple occupants. You would input inhalation information if you 

want CONTAMW to calculate the dose of a given occupant to the contaminants within a 

building. You would input contaminant generation information if you want to account for the 

contaminants generated by an occupant while they are in the building. 

3.12.5 Occupant Properties 

This section provides detailed descriptions of the specific occupant properties. Each of the 

following subsections are the context-sensitive help topics that you can access by pressing F1

when working with property pages of the "Occupant Exposure Properties" property sheet. 

3.12.5.1 Occupant ñ Occupant Data Properties 

Occupant Number: This is the number that appears in the status bar when you highlight an 

icon. CONTAMW automatically assigns this number to each exposure icon once it is defined. 

This number could change as you add and remove occupants to or from a project. Each time you 

save a project, the occupant numbers are reassigned. Numbers are assigned beginning on the top 

level, starting from the upper-left corner of the SketchPad, moving left-to-right and top-tobottom of the SketchPad. 

Body weight/Peak Inhalation Rate: These parameters are used to compute a contaminant dose. 

Inhalation is defined in terms of a peak rate and a schedule. Body weights for typical persons and 

inhalation values for different activity levels are available in EPA [1989].

Description: Use this field to enter a more detailed description of the specific occupant. 

Inhalation Schedule: Use this when you want to modify the peak inhalation rate according to a 

schedule. If there are previously defined schedules within the current project, you may select one 

from the Name list. Click the "New Schedule" button to define a new schedule. To view or 

modify an existing schedule click the "Edit Schedule" button. Setting this field to "<none>" 

indicates no schedule. (See Working with Schedules) 

Edit Occupancy Schedule: Press the "Edit Occupancy Schedule" button to display the 

Occupancy Week Schedule dialog box and define the movement of this occupant within the 

building.
USING CONTAMW ñ WORKING WITH OCCUPANT EXPOSURE

76

3.12.5.2 Occupant ñ Contaminant Generation Properties 

Multiplier: Use the multiplier to modify the generation rate of an occupant. You could define 

the contaminant generation rate(s) for a single occupant and use the multiplier to represent a 

generation rate of multiple occupants. 

Generate Contaminants: This checkbox is used to turn on and off the contaminant generation 

of the occupant. If the box is checked, contaminants will be generated. This is useful for 

contaminant generation such as that of carbon dioxide due to human metabolism. 

Generation Data: A list of available contaminants is displayed in the textbox provided. The user 

can highlight these contaminants and select the generation rate for each in the box below the 

contaminant list. 

Generation Schedule: A new inhalation schedule is defined by pressing the "New Schedule" 

button and following the directions for editing a Week Schedule. 

Description: This field shows a more detailed description of the specific schedule if 

previously entered by the user. This description can be modified by pressing the Edit 

Schedule button next to the description field and then changing the description field for the 

schedule. 

Name: This drop down box contains the names of all previously created schedules. The 

schedule selected from this box will then define the generation schedule for the exposure 

element being viewed. 
 USING CONTAMW ñ WORKING WITH DATA AND LIBRARIES 

77

3.13 Working with Data and Libraries 

CONTAMW enables you to share certain types of data between building components contained 

within a project as well as between projects. The sharing of data within a project (locally) is 

accomplished by allowing you to associate multiple building components with data elements

defined within a project. Sharing data between projects is accomplished by allowing you to 

export data elements from one project into CONTAMW library files and then retrieving the data 

elements into another project from the library files. The following table lists the different types 

of data elements implemented by CONTAMW. All of the data elements can be shared within a 

project, but only those listed as Library Data Elements can be shared between projects. You'll 

note that you can only share contaminant-related elements locally. 

Library/Local Data Elements Local-Only Data Elements 

Week Schedules (LB1) Contaminants 

Wind Pressure Profiles (LB2) Contaminant Filters 

Airflow Elements (LB3) Source/Sink Elements 

Ductflow Elements (LB4) Kinetic Reactions 

 Occupancy Schedules 

Data Elements 

You create and modify data elements according to the procedures given throughout the "Using 

CONTAMW" section of this manual for the specific data elements. Once you have created a data 

element, you can associate it with the relevant building components as you create them. You do 

this by selecting the desired element from the local list that CONTAMW presents to you when 

you are editing the properties of a particular building component. To share data elements 

between project files, you must utilize the CONTAMW Library Manager. You must also use the 

CONTAMW Library Manager to delete data elements from either the local project or the library. 

To delete local data elements, they must not be referenced by any building components. 

Library Files 

CONTAMW Libraries are files that contain the descriptions of sharable data elements. Each type 

of sharable data element is stored in a different library file. You can create as many of each type 

of library file that you want, and store them anywhere within the file structure of your computer. 

Each type of library file is associated with a different three-character extension as shown in the 

table above. 
USING CONTAMW ñ WORKING WITH DATA AND LIBRARIES

78

CONTAMW Library Manager 

The CONTAMW Library Manager, shown in the following figure, is a dialog box that is 

displayed when you access data elements from the Data menu or by clicking on a "LibraryÖ" 

button when editing the properties of one of the building components that utilizes library data 

elements. This dialog box is divided into three sections: Library File, Library Elements and 

Local Project Elements sections. The Library File section displays the name of the currently 

displayed library file and allows you to save, rename and open new and existing library files. The 

Library Elements section displays the data elements contained in the library file that is currently 

listed in the Library File section. The Local Project Elements section displays the data elements 

that are contained in the current project file. Each of these sections is automatically activated or 

deactivated depending on the type of data element with which you are currently working. 
 USING CONTAMW ñ WORKING WITH DATA AND LIBRARIES 

79

3.13.1 Opening Libraries 

If a library file is currently opened, the name of the file will be displayed in the "Name" field of 

the "Library File" section of the Library Manager. You can open a CONTAMW library file using 

the "BrowseÖ" button of the Library Manager. This will activate the File Open dialog box 

typical of Windows applications. This dialog box is set to display only those files having the 

three-character file extension associated with the type of data elements with which you are 

currently working. Follow the typical procedure for opening a file using the Windows operating 

system. 

3.13.2 Creating Libraries 

Using the CONTAMW Library Manager, you create new libraries one of two ways. You can 

either save an existing library under a new name using the "Save AsÖ" button, or use the "New" 

button of the Library File section of the CONTAMW Library Manager dialog box. The "Save 

AsÖ" method makes a copy of the currently displayed library file under a new name, but 

maintains the original file. The "New" method clears the data currently displayed and allows you 

to start with an empty library file. 

3.13.3 Deleting Libraries 

You must use the file deletion commands of your operating system to delete CONTAMW library 

files. 

3.13.4 Modifying Libraries 

You modify CONTAMW library files using the CONTAMW Library Manager. The 

CONTAMW Library Manager allows you to create new data elements within the library, copy 

data elements from the local project into the library, modify library data elements, and delete 

data elements from the library. 

Creating Library Data Elements 

You use the "New" button contained within the "Library Elements" section of the CONTAMW 

Library Manager to create a new data element. You can only create the type of data element that 

is currently being displayed by the Library Manager (e.g. airflow elements, ductflow elements, 

schedules, etc. ). The "New" button will activate the CONTAMW dialog box associated with 

creating the type of data element that you are currently working with. 

Copying Library Data Elements 

You can either copy data elements from a library to the local project or from the local project to 

the library. All copying is done between the local project and the library file that is currently 

indicated in the "Name" box of the Library File section of the CONTAMW Library Manager. If 

the name box is blank, then you are using a new/unnamed library file. To copy data elements, 

you use the "Copy ->" and "<- Copy" buttons. These copy buttons indicate the direction of the 

copy operation. If an element exists in both the library file and the local project, then the copy 

buttons will be disabled to prevent you from overwriting elements with the same name. You may 

rename local data elements without affecting their associations with building components that 

refer to them in the local project. 
USING CONTAMW ñ WORKING WITH DATA AND LIBRARIES

80

Modifying Library Data Elements 

To modify a library data element, you must first highlight the Element Name within the list of 

elements in the Library Elements section of the CONTAMW Library Manager. You then click 

on the "Edit" button next to the list. This will activate the CONTAMW dialog box associated 

with displaying the properties of the type of data element with which you are currently working. 

You then make the desired changes and click the "OK" button. 

Deleting Library Data Elements 

To delete a library data element, you highlight the Element Name in the Library Elements 

section of the CONTAMW Library Manager then click on the "Delete" button next to the list. 

You will be prompted to confirm the deletion, and the data element will no longer be displayed 

in the list of Library Elements. However, the deletion will not be affected until you save the 

library file. You can retrieve the previously deleted data elements by reopening the library file as 

long as you don't save the file after deleting the elements. 

3.13.5 Modifying Local Data 

You modify local lists of data elements using the CONTAMW Library Manager. The Library 

Manager allows you to create new local data elements, copy data elements from the library into 

the local project, modify local data elements, and delete local data elements. 

Creating Local Data Elements 

You use the "New" button contained within the "Project Elements" section of the Library 

Manager to create a new data element. You can only create the type of data element that is 

currently being displayed by the Library Manager (e.g. airflow elements, ductflow elements, 

schedules, etc. ). The "New" button will activate the CONTAMW dialog box associated with 

creating the type of data element that you are currently working with. 

Copying Local Data Elements 

See Copying Library Data Elements. 

Modifying Local Data Elements 

The Library Manager provides you with another means of accessing local project elements. This 

is in addition to the method of accessing building component properties presented throughout the 

Using CONTAMW section of this manual. You must first highlight the Element Name within 

the list of elements in the Project Elements section of the Library Manager. You then click on the 

"Edit" button next to the list. This will activate the CONTAMW dialog box associated with 

displaying the properties of the type of data element with which you are currently working. You 

then make the desired changes and click the "OK" button to make the changes take affect. 

Deleting Local Data Elements 

You can only delete local data elements if they are not referenced by any building components 

within the project. To delete a project data element, you highlight the Element Name in the 

Project Elements section of the CONTAMW Library Manager then click on the "Delete" button 

next to the list. The "Delete" button will only be enabled if the currently highlighted element is 

not referenced within the project. You will prompted to confirm the deletion, and the data 

element will no longer be displayed in the list of Project Elements. However, the deletion will 

not be affected until you save the project file. You can retrieve the previously deleted data 

elements by reopening the project file as long as you don't save the file after deleting the 

elements. 
 USING CONTAMW ñ WORKING WITH WEATHER AND WIND 

81

3.14 Working with Weather and Wind 

CONTAMW enables you to incorporate the effects of weather on a building. Weather 

parameters include ambient temperature, barometric pressure, wind speed, wind direction and 

outdoor contaminant concentrations. The type of weather data you require for a simulation 

depends on the type of simulation you are performing, whether you want to account for the 

effects of wind, and whether or not you are simulating contaminants. If you are performing a 

steady-state airflow simulation, you will only need steady state weather and wind data. However, 

if you are performing a transient airflow simulation, you will need to use a transient weather file. 

Steady State Weather 

When you use steady state weather data, CONTAMW keeps the ambient temperature, wind 

speed and direction, and ambient contaminant concentrations constant during a simulation. 

Detailed descriptions of these parameters are given in the following sections. 

Transient Weather 

You can use transient weather data to simulate the changing outdoor weather and wind 

conditions when performing a transient simulation. Transient weather data is stored in a weather 

file that you must create according to a special format as specified under the Weather File 

Format section that follows. Weather files contain ambient temperature, pressure, wind speed, 

wind direction and contaminant concentrations for discrete intervals of each day for at least one 

day and up to one year. If the intervals between data in the weather file don't match the 

simulation time step, CONTAMW will interpolate the weather data to obtain a value. 

Wind 

Wind pressure can be a significant driving force for air infiltration through a building envelope. 

It is a function of wind speed, wind direction, building configuration, and local terrain effects. 

CONTAMW enables you to account for the effects of wind pressure on flow paths through the 

building envelope (external airflow paths). You define how you want to account for wind effect 

for each external flow path on a case-by-case basis. In CONTAMW, you can either choose to 

ignore the effects of wind on an envelope penetration, define wind pressure to be constant for 

each envelope penetration, or implement variable wind pressures for envelope penetrations. 

CONTAMW provides a general approach to handling the variable effects of wind on the 

building envelope. This approach requires you to provide CONTAMW with information related 

to the determination of a local wind pressure coefficient for the building surface. 

For a general introduction to the effects of wind pressure on buildings, see Chapter 15, Airflow 

Around Buildings, in the 1997 ASHRAE Fundamentals Handbook [ASHRAE 1997]. The 

following is an overview of how CONTAMW handles these effects. 

The equation for wind pressure on the building surface (Pw) is 

p

H

w C V P

2

2 ρ =

where 

ρ = ambient air density 

VH = approach wind speed at the upwind wall height (usually the height of the building) 

Cp = wind pressure coefficient 
USING CONTAMW ñ WORKING WITH WEATHER AND WIND

82

The wind pressure coefficient can be further generalized in terms of a local terrain effects 

coefficient and the direction of the wind relative to the wall under consideration. The following 

equation is that used by CONTAMW when calculating wind pressures on the building. 

( ) 2

2

θ ρ C f V P h

met

w =

where 

ρ = ambient air density 

Vmet = wind speed measured at meteorological station 

Ch = wind speed modifier coefficient accounting for terrain and elevation effects 

f(θ ) = a coefficient that is a function of the relative wind direction. CONTAMW refers to 

this function as the wind pressure profile. 

The relative wind direction is given by 

θ ≡ θ w −θ s 

where 

θw = wind azimuth angle (N = 0°, E = 90°, etc.), and 

θs = surface azimuth angle. 

ρV2

met/2 in the above equation is computed by CONTAMW from the steady state or weather file 

temperature, pressure and wind speed data. 

Cp, the pressure coefficient used by ASHRAE, is equivalent to f(θ ) in the CONTAMW 

formulation. In CONTAMW, you must define the function f(θ ) in the form of wind pressure 

profiles as explained later. See page 25.8 of the 1997 ASHRAE Fundamentals Handbook 

[ASHRAE 1997] for details relating to pressure coefficient data. 

The wind pressure modifier, Ch, accounts for the difference between Vmet and VH. The value for 

Ch will typically be constant for all openings on a given building. However, CONTAMW allows 

you to define a default value that CONTAMW will use for each flow path connected to the 

ambient (See Wind Properties) or to set this value individually for each of these paths. 

CONTAMW uses the following formula to compute the value of Ch: 

a

ref

h o H

H C A

2

2















 =

 

where H is the wall height and Ao and a depend on the terrain around the building [ASHRAE 

1989, p 14.3]: 

Terrain Type Coefficient 

(Ao) 

Exponent 

(a) 

 Urban 0.35 0.40 

 Suburban 0.60 0.28 

 Airport 1.00 0.15 
 USING CONTAMW ñ WORKING WITH WEATHER AND WIND 

83

The wind speed, Vmet, is usually measured at an airport (open terrain) at an elevation, Hmet = 10m, 

above the ground. The wind speed, Vo, at that same elevation at the building site is given by 

Vo = Ao V

The wind speed, VH, at the top of the wall, elevation H, is then given by 

a

m

V Vo 















Η

Η

Η =

 

3.14.1 Defining Weather and Wind 

You define weather that you want CONTAMW to use based on the type of simulation you want 

to perform. You will either define steady state weather or transient weather. It is best to perform 

a set of steady state simulations prior to performing transient simulation. This may enable you to 

better identify any problems that may arise from working with transient weather. CONTAMW 

also provides a means to verify that you have your wind related data input correctly (See 

Checking Wind). 

3.14.1.1 Defining Steady State Weather and Wind 

To define the steady state weather and wind data you use the Edit Weather DataÖ selection of 

the Weather menu or the F7 keyboard shortcut. This will display the "Weather and Wind 

Parameters" property sheet. The property sheet contains four pages of parameters including: 

Weather, Wind, Location and Wind Pressure Display. Detailed descriptions of all wind and 

weather properties are given in the Weather and Wind Properties section of this manual. 

You use the Weather page to define steady state weather and wind data. The Location page 

allows you to input the altitude of the building site which CONTAMW will use to determine a 

default barometric pressure if you do not know what it should be for a given building site. 

Default values of these two pages will provide conditions of no wind, 20°C and a barometric 

pressure of 1 atmosphere (approximately 101 kPa). 

The Wind page parameters allow you to enter the prevailing wind direction and other values 

used by CONTAMW to determine a wind speed modifier. The wind speed modifier is 

determined from the local terrain constant and the velocity profile exponent. Default values are 

provided for suburban terrain. 

Checking Wind Pressure Data 

You use the Wind Pressure Display page to input values that will be used to display wind 

pressures on the building envelope when you display the Wind Pressure Results. These values 

are not used by CONTAMW when performing a simulation. To display the wind pressure results 

use the Wind Pressure selection of the View menu. This feature is provided so that you can 

verify the wind speed and direction information visually on the SketchPad. The wind pressures 

that are displayed here are not necessarily the same as will be displayed when viewing 

simulation results on the SketchPad. 

When you choose to display wind pressure results, red lines will appear on the SketchPad 

indicating the wind pressure at certain airflow paths. Wind pressure will only be displayed for 

those airflow paths connected to the ambient zone, having the Wind Pressure Option set to 

Variable and having a wind induced pressure drop across the opening that is not equal to zero. 

The wind pressure display will reveal the relative magnitude of the pressure drop and the 
USING CONTAMW ñ WORKING WITH WEATHER AND WIND

84

direction of airflow across the openings in the building envelope. You can move the caret to each 

of the airflow paths for which a wind pressure is being displayed to show the wind pressure, 

azimuth angle and elevation of the airflow path in the CONTAMW status bar. When reviewing 

this display, you should look to see if the direction of flow makes sense based on the information 

that you entered within the Wind Pressure Display property page. 

3.14.1.2 Defining Transient Weather and Wind 

In order to implement transient weather and wind, you must create a CONTAMW-compatible 

weather file. You must create the weather file external to CONTAMW. NIST provides a utility 

program, WEATHER.EXE, to create a CONTAMW-compatible weather file, and 

W94TOW96.EXE is provided to convert a CONTAM93/94 weather file to the new 

CONTAMW/CONTAM96 format. 

Weather File Format 

The CONTAMW weather file is an ASCII text file. It is described below because it may be 

necessary for you to create a weather file from sources not already provided. In the listing below, 

I1 indicates a character string, I2 indicates a short integer, I4 indicates a long integer, and R4

indicates a four-byte real number. The variable names refer to names used in the CONTAMW 

code. Individual lines of data are separated by dashes. 

HEADER DATA:

I1 descr[]; /* weather file description (up to 78 characters long) */

-----

I2 nc; /* number of contaminants */

-----

for each contaminant:

I1 name[]; /* contaminant name (each on a separate line; in order) */

-----

I2 start date; /* day of year */

I2 end date;

-----

DAILY WEATHER DATA:

for each day:

I2 dayofy; /* day of year (1-365) */

I2 month; /* month (1-12) */

I2 dayofm; /* day of month (1-31) */

I2 dayofw; /* day of week (1-7) */

I2 daytyp; /* type of day (1-12) for schedules */

I2 DSTind; /* daylight savings time indicator */

R4 suncos[3]; /* solar direction cosines */

-----

for each time: /* from 00:00 through 24:00; step may be variable */

I4 time; /* time- of- day [s] */

R4 tmpambt; /* ambient temperature [K] */

R4 barpres; /* barom. pressure(Pa) NOT corrected to sea level */

R4 windspd; /* wind speed (m/s) */

R4 winddir; /* wind direction: 0 = N, 90 = E, 180 = S, ... */

R4 solhtot; /* total solar flux on horizontal surface [W/m^2] */

R4 solhdif; /* diffuse solar flux on horizontal surface [W/m^2] */

R4 tskyeff; /* effective sky temperature [K] */

for each contaminant; in order:

R4 CC; /* mass fraction [kg/kg] */

-----

The solar and sky values are not used in CONTAMW. They are reserved for thermal analysis, if 

it is added to the program. 
 USING CONTAMW ñ WORKING WITH WEATHER AND WIND 

85

3.14.2 Weather and Wind Properties 

This section provides detailed descriptions of the specific steady state weather properties. Each 

of the following subsections are the context-sensitive help topics that you can access by pressing 

F1 when working with property pages of the "Weather and Wind Properties" property sheet. 

3.14.2.1 Weather and Wind ñ Weather Properties 

The following constant values are used by CONTAMW when you specify the use of steady state 

weather conditions when performing either steady state or transient airflow simulations (See 

Working with Simulations). 

Temperature: CONTAMW uses the ambient temperature when calculating outside air density 

and building stack effects. 

Pressure: Absolute barometric pressure (not corrected to sea level). If you don't know this value, 

you can enter the altitude of the building site on the Location Properties page to have 

CONTAMW calculate the barometric pressure for you. 

Wind Speed: Magnitude of the wind velocity.

Wind Direction: Direction from which the wind blows as measured in degrees clockwise from 

true north. 

Day Type: This is the type of day you want to use when performing a simulation with steady 

airflows and no weather file. The Day Type corresponds to one of the twelve day schedules that 

you can create. 

3.14.2.2 Weather and Wind ñ Wind Properties 

The wall height, terrain and exponent are used to calculate the wind speed modifier. 

Relative North: The direction to relative north will be used relating wall angles on the 

SketchPad to true north for determining wind direction effects. Enter the clockwise angle from 

vertical on the CONTAMW SketchPad to true north. 

Roof or Wall Height: Enter the height of the building. This is the value of H in the equations 

presented in the section Working with Weather and Wind. Entering a value of zero will reduce 

the wind speed modifier to zero. This will cause computed wind pressures to be zero no matter 

what the wind speed, unless you override the wind pressure coefficients of exterior airflow paths. 

Figure 5 in Chapter 14 of the 1993 ASHRAE Fundamentals Handbook [ASHRAE 1993] shows 

relative wind pressures on the face of a building based on the local wind pressure at the top of 

the wall. 

Terrain & Exponent: Enter the values that describe the wind speed profile for the type of 

region in which your building is located. Figure 4 in Chapter 14 of the 1993 ASHRAE 

Fundamentals Handbook [ASHRAE 1993] shows terrain constants and velocity profile 

exponents for representative areas. 

Modifier: This is the wind speed modifier, Ch, calculated by CONTAMW based on the Wall 

Height, Terrain and Exponent values above. This value will be the default provided for each 

envelope airflow path that you create on the SketchPad and for which you select the variable 

wind pressure option. See section Working with Weather and Wind for a more detailed 

explanation of this term. 
USING CONTAMW ñ WORKING WITH WEATHER AND WIND

86

3.14.2.3 Weather and Wind ñ Location Properties 

Longitude, latitude, and time zone are currently not used by CONTAMW. They have been 

included for potential use in the future if heat transfer analysis is implemented within the 

program. 

Altitude: CONTAMW uses the site altitude to determine a default absolute barometric pressure 

for the steady state weather data. 

3.14.2.4 Weather and Wind ñ Wind Pressure Display Properties 

The wind pressure display values are used to calculate the wind pressures displayed on the 

screen in the wind pressure display mode. You activate the wind pressure display mode by 

selecting Wind Pressure from the View menu. 

NOTE: These values are not used by CONTAMW when performing a simulation. To display the 

wind pressure results use the Wind Pressure selection of the View menu. This feature is 

provided so that you can verify the wind speed and direction information visually on the 

SketchPad. (See Checking Wind Pressure Data in the Defining Steady State Weather and Wind 

section) 

Ambient Temperature: The ambient temperature is used to calculate outside air density and 

building stack effects. 

Absolute Pressure: Be sure to enter the absolute barometric pressure instead of pressure 

corrected to sea level. 

Wind Speed/Direction: Enter the wind speed for the site. The wind direction is calculated in 

degrees clockwise from true north. 

Day Type: This is the day type as defined in the Week Schedule . 
 USING CONTAMW ñ WORKING WITH SCHEDULES 

87

3.15 Working with Schedules 

Schedules provide you with the ability to modify various parameters based the time of day and 

day of the week. Schedules only apply when performing transient simulations. You use 

schedules to provide a fractional multiplier to parameters at times which you define. You can 

schedule items such as the flow through airflow paths, the outdoor air intake of simple air 

handling systems, contaminant sources and sinks, and the location of an occupant within a 

building. 

CONTAMW provides occupant schedules and non-occupant schedules which are split up into 

week schedules which are in turn made up of one or more day schedules. Non-occupant week 

schedules can be associated with as many schedulable items as you need, whereas occupant 

week schedules can only be applied to a single occupant. Only non-occupant schedules can be 

shared between CONTAMW project files using the CONTAMW Library Manager. Occupant 

schedules can't be shared between projects, because they are dependant on the level and zone 

names which may be different between projects. The following sections provide detailed 

information related to the creation, modification and deletion of schedules in CONTAMW. 

3.15.1 Creating Schedules 

You can create schedules using either the CONTAMW Library Manager (see Working with Data 

and Libraries) or wherever a "New Schedule" button is provided when working with various 

building component property sheets (e.g. airflow paths, ducts, source/sinks, and occupant icons). 

Non-occupancy Schedules 

You create non-occupant schedules by first selecting to create a new week schedule as outlined 

above which will display the Week Schedule dialog box. You must then define one or more day 

schedules that you then associate with each day of the week schedule. Each week schedule 

consists of 12 days - one for each day of the week and five more days that you can use for 

special situations such as holidays. New day schedules are created from the Week Schedule 

dialog box by clicking on the "New Schedule" button. This will display the Day Schedule dialog 

box whose features are explained below. 

Occupancy Schedules 

You create occupant schedules by first creating an occupant exposure icon (see Creating 

Occupants). You then click on the "Edit Occupancy Schedule" button that is provided on the 

Occupant Data property page of the "Occupant Exposure Properties" property sheet. 

3.15.2 Modifying Schedules 

You modify existing non-occupancy week and day schedules through the Week Schedule and 

Day Schedule dialog boxes respectively. Edit occupancy schedules by editing the properties of 

existing occupant exposure icons. The details of editing schedules are presented in the following 

sections. 

3.15.3 Deleting Schedules 

You can only delete occupancy week schedules by deleting the associated occupant exposure 

icon. Deleting all other schedules can only be accomplished using the CONTAMW Library 

Manager (see Working with Data and Libraries) which will only allow you to delete those 

schedules that are no longer associated with any occupants or building components. 
USING CONTAMW ñ WORKING WITH SCHEDULES

88

3.15.4 Week Schedule Properties 

These are the properties and methods you use to define non-occupancy week schedules. You 

must associate a day schedule with each day of a week schedule (7 days of the week plus 5 extra 

days). The extra days are provided for any day that may have an atypical schedule, such as a 

holiday. This information is displayed when you press the F1 key while working with the Day 

Schedule dialog box of CONTAMW. Once defined, the you may display the schedule 

graphically by pressing the "Display Graphically" button. 

Name: This is the name you give to this week schedule. This name must be unique among the 

week schedules within this project. 

Description: Use this field to enter a more detailed description of the specific schedule. 

Day Schedules: Every "Week Schedule" consists of 12 days that must be defined. The days are 

defined by "Day Schedules." These day schedules may or may not be unique for each of the 12 

days. If the project has no available day schedules a new day schedule must be defined. Do this 

by pressing the "New Day Schedule" button, then editing the day schedule as explained in the 

section entitled "Day Schedule." You can edit existing day schedules by selecting them in the 

"Available Schedules" list box and then pressing the "Edit Day Schedule" button, then following 

the procedure explained in the Day Schedule section. If a day has already been associated with a 

day schedule you can change it by first highlighting the day to be changed in the Day Schedules 

list box, highlighting the day schedule to replace the existing schedule, and then pressing the "<< 

Replace <<" button. 

3.15.5 Day Schedule Properties 

These are the properties and methods you use to define day schedules. This information is 

displayed when you press the F1 key while working with the Day Schedule dialog box of 

CONTAMW. You may display the schedule graphically by pressing the "Display Graphically" 

button. 

Name: This is the name you give to this day schedule. This name must be unique among the day 

schedules within this project. 

Description: Use this field to enter a more detailed description of the specific schedule. 

Shape: Use this check box to set how CONTAMW interprets values between the data points you 

define. A rectangular graph will create a step function for the data points. A trapezoidal graph 

will generate a sloped line between the data points provided by interpolating a straight line 

between the data points. 

Schedule Data: These are the time/multiplier pairs that you set to define a day schedule. The 

times are entered in the hh:mm:ss format, and you must provide leading and trailing zeroís; for 

example 9:30 am would be entered as 09:30:00 not as 9:30:00. The value is a multiplier between 

0.0 and 1.0 used to adjust the entered value for the simulation feature at the associated time 

defined in the schedule. 

To insert a new data point: Highlight the data point after which you want to insert a new 

schedule point, enter the new time/multiplier pair in the "Time" and "Value" edit box next to the 

insert button, press the "<< Insert <<" button to add the value to the list. 
 USING CONTAMW ñ WORKING WITH SCHEDULES 

89

To modify an existing data point: Select the data point that you wish to modify from the list, 

enter the revised data, and press the "<< Replace <<" button to overwrite the previously entered 

data point. 

To delete an existing data point: Select the data point you want to delete from the list and click 

the "Delete" button. You can not delete 00:00:00 or 24:00:00. 

3.15.6 Occupant Week Schedule Properties 

These are the properties and methods you use to define occupant week schedules. This 

information is displayed when you press the F1 key while working with the Occupant Week 

Schedule dialog box of CONTAMW. 

Description: Use this field to enter a more detailed description of the specific schedule. 

Day Schedules: Every Occupancy Week Schedule consists of 12 days that must be defined. The 

days are defined by Occupant Day Schedules. These schedules may or may not be unique for 

each of the 12 days. If the project has no available day schedules a new day schedule must be 

defined. This is done by pressing the "New Day Schedule" button then editing the day schedule 

as explained in the Occupant Day Schedule section. You may edit existing day schedules by 

selecting them in the "Available Schedules" list box, pressing the "Edit Schedule" button, and 

then following the procedure explained in the Occupant Day Schedule section. If a day has 

already been associated with a day schedule, you may changed it by first highlighting the day to 

be changed in the "Day Schedules" list box, then highlighting the day schedule to replace the 

existing schedule, and finally pressing the "<< Replace <<" button. 

3.15.7 Occupant Day Schedule Properties 

These are the properties and methods you use to define occupant day schedules. This information 

is displayed when you press the F1 key while working with the Occupant Day Schedule dialog 

box of CONTAMW. 

Name: This is the name you give to this occupant day schedule. This name must be unique 

among the occupant day schedules within this project. 

Description: Use this field to enter a more detailed description of the specific schedule. 

Schedule Data: These are the time/location data points that you set to define an occupant day 

schedule. The times are entered in the hh:mm:ss format, and you must provide leading and 

trailing zeroís; for example 9:30 am would be entered as 09:30:00 not as 9:30:00. The location 

consists of a level and zone in which the occupant resides for the indicated time period. Select a 

value of "null" from the zone list to indicate the occupant is not in the building for a given time 

period. 

To insert a new data point: Highlight the data point after which you want to insert a new 

schedule point, enter the new time/location pair in the "Modify Data" block to the right of the 

insert button, press the "<< Insert <<" button to add the data to the list. 

To modify an existing data point: Select the data point that you wish to modify from the list, 

enter the revised data, and press the "<< Replace <<" button to overwrite the previously entered 

data point. 

To delete an existing data point: Select the data point you want to delete from the list and click 

the "Delete" button. You can not delete 00:00:00 or 24:00:00. 
USING CONTAMW ñ WORKING WITH SIMULATIONS

90

3.16 Working with Simulations 

CONTAMW allows you to perform several types of simulations. The type of simulation you 

wish to perform depends on the goal of your analysis. You can perform simulations to determine 

just interzonal airflows and pressure differences, or you can also have CONTAMW solve for 

contaminant concentrations within each zone of a building. CONTAMW provides the ability to 

perform several combinations of steady state, transient and cyclical simulations of both airflow 

and contaminant dispersal. 

The following table shows the different combination of simulation methods you can apply using 

CONTAMW. 

Airflow 

Simulation 

Contaminant 

Simulation 

Purpose 

Steady State None Used to obtain airflows and pressure differentials under 

constant building system and/or weather conditions. 

Steady State Steady State Used to obtain equilibrium contaminant concentrations under 

conditions of steady airflow. 

Steady State Transient Used to obtain a time history of contaminant concentrations 

under conditions of steady airflow. This is similar to the 

previous table entry but will allow you to observe the 

contaminant concentrations for each time step leading up to 

the final time step. 

Steady State Cyclic Used when it's important for initial contaminant 

concentrations to match the final concentrations under steady 

airflow conditions. This provides a method of simulating a 

typical pattern of operation by simulating only a 

representative time period (e.g. one day). 

Transient None Used to obtain a time history of airflows and pressure 

differentials under changing building system and/or weather 

conditions. 

Transient Steady State Not allowed 

Transient Transient Used to obtain time histories of airflows, pressure 

differentials and contaminant concentrations under changing 

building system and/or weather conditions. 

Transient Cyclic Used when it's important for initial contaminant 

concentrations to match the final concentrations under 

transient airflow conditions. This provides a method of 

simulating a typical pattern of operation by simulating only a 

representative time period (e.g. one day). 
 USING CONTAMW ñ WORKING WITH SIMULATIONS 

91

To perform a simulation, you must set the simulation parameters, run the simulation, and view 

simulation results. Simulation parameters are categorized by Run Control, Numeric, and Output 

properties. Run Control properties include the simulation methods, simulation dates and times, 

type of weather data to use (steady or transient), and simulation time step. Numeric properties 

include convergence criteria, maximum iterations and relaxation coefficients. Output properties 

are used to set the type and amount of data you wish to have sent to the simulation results files. 

CONTAMW provides default settings for these parameters. You will probably work quite a bit 

with the Run Control and Output parameters, but you are not likely to need to change the 

numeric parameters. 

3.16.1 Setting Simulation Parameters 

To set simulation parameters you use the Set Simulation ParametersÖ selection of the 

Simulation menu or the F4 keyboard shortcut. This will display the "Simulation Parameters" 

property sheet. The property sheet contains three different pages of parameters including: Run 

Control, Numeric, and Output. Detailed descriptions of all simulation properties are given in the 

Simulation Parameters section of this manual. 

3.16.2 Running Simulations 

Once you have set the simulation parameters, you can run the simulation. To run a simulation, 

select Run Simulation from the Simulation menu. This will display the "CONTAMW 

Simulation" dialog box. This dialog box allows you to start a simulation, view the status of a 

simulation in progress and stop a simulation in progress. If running a simulation would result in 

replacing some results files, you will be given a warning with the option to not proceed with the 

simulation. This allows you the opportunity to save the current project file under a different 

name before proceeding with the simulation. 

While there are many factors that can affect the ability of CONTAMW to quickly and 

successfully obtain a solution (converge), there are situations that can cause the simulation to not 

converge or to converge very slowly. The relative magnitudes of the flow coefficients have some 

effect on the convergence of the nonlinear equation solver of CONTAMW [Wray and Yuill 

1993]. Airflow networks containing paths whose resistances differ by many orders of magnitude 

will typically require more iterations than networks with paths of similar resistances. Reducing 

the relaxation coefficient from its default value of 0.75 to a value nearer one-half can often help 

convergence of these more difficult cases. The maximum number of iterations can also be 

increased. However, the most effective way to improve convergence is to remove those very low 

resistance paths that are not likely to effect the computed airflow rates. For example, when 

simulating a shaft (See Shafts), represent a shaft using phantom zones as opposed to using 

airflow elements with large cross-sectional areas between zones on adjacent levels. 

3.16.3 Viewing Simulation Results 

Once you have successfully run a simulation, you can use CONTAMW to view simulation 

results or to create files that can be imported into a spreadsheet. These capabilities are explained 

in the Working with Simulation Results section. 
USING CONTAMW ñ WORKING WITH SIMULATIONS

92

3.16.4 Simulation Parameters 

Simulation parameters are those used to control the type of simulation that you wish 

CONTAMW to perform and the type of results output you wish CONTAMW to provide. This 

section provides detailed descriptions of the specific simulation parameters. Each of the 

following subsections are the context-sensitive help topics that you can access by pressing F1

when working with property pages of the "Simulation Parameters" property sheet. 

3.16.4.1 Simulation ñ Run Control Properties 

The "simulation time step" is the constant time step for the transient or cyclic simulation. Shorter 

time steps are more accurate but require more computation time. During the simulation, 

simulation progress is updated at every "display time step". 

Simulation Method: Set the type of simulation you wish to perform for both Airflows and 

Contaminants by checking the appropriate radio buttons. Refer to the Working with Simulations 

section for a table of allowable combinations of simulation method settings. 

Airflows: You can choose to have CONTAMW perform either a steady state simulation or a 

transient simulation of airflows. A steady state simulation will utilize the ambient weather set 

by pressing the Edit Weather Button on the Run Control property page. A transient 

simulation requires a weather file that defines the weather for the time period of the 

simulation. You can either create this file using a text editor or spreadsheet program and 

following the format described previously or by using the weather file creation program also 

available from NIST. See Defining Transient Weather and Wind in the Working with 

Weather and Wind section for more details. 

Contaminants: You can choose one of the following contaminant simulation options: None, 

Steady, Transient or Cyclic. The "None" selection uses no contaminants (e.g. you only want 

to model building airflows). The steady contaminant model can only be used in conjunction 

with steady airflows and will run until the system reaches equilibrium. Contaminant sources 

are modeled as continuous sources with a constant generation rate and all schedules are 

ignored. A cyclic simulation repeats a 24-hour cycle until steady-periodic conditions are 

achieved. Transient models may run for all the days of the weather file with transient 

airflows or for a single day with steady-state airflows. 

Reset initial contaminant concentrations: Use this feature to reset the initial contaminant 

concentrations of all zones, including the implicit supply and return zones of simple air 

handling systems, prior to running a simulation. You can reset initial concentrations to Zero, 

Ambient or Current Results Concentrations. If you do not check one of these boxes, 

CONTAMW uses the Initial Concentrations indicated on the Contaminant Property page for 

each zone (See Contaminant Data). Checking one of these boxes causes the Initial 

Concentration values for each zone to be overwritten. 

Zero: This option sets the initial contaminant concentrations to zero. 

Ambient Concentrations: This option sets the initial contaminant concentrations to the 

default contaminant concentrations as set when defining Project Contaminants (See 

Contaminant Properties). 

Current Results Concentrations: This option sets the initial contaminant concentrations to 

be the same as the concentrations in each zone at the time step for which CONTAMW is 

currently displaying results on the SketchPad. You must be in the results viewing mode 
 USING CONTAMW ñ WORKING WITH SIMULATIONS 

93

to utilize this feature. The current time step is displayed in the middle pane of the 

CONTAMW Status Bar (See the Status Bar section). This option is especially useful for 

cyclic simulation, where you may continue a simulation that has been interrupted before 

convergence, continue simulation with tighter convergence criteria, or create a project 

file for archive which can be rerun as a one-day transient simulation to quickly compute 

cyclic results. 

Simulation Dates and Times: These dates and times are used to set the date and time labels put 

on steady state simulation results and to control the duration of transient simulations by allowing 

you to set the start and stop dates and times. Depending on the simulation method chosen, 

different simulation "Dates" and "Times" fields will be enabled or disabled. 

Enter dates and times according to the following formats. 

Date Format - MMMDD Example - enter January 18 as Jan18 

Time Format - HH:MM:SS Example - enter 1:00 AM as 01:00:00 

 enter 1:00 PM as 13:00:00 

Cyclic & Steady Simulations: This date field is only used to label the simulation results, 

however, the time field is used to determine any control values of scheduled items for the 

associated day type for which the simulation is set to utilize. You must set the day type of the 

steady state Weather and Wind Parameters property sheet (See the Weather Properties in the 

Working with Weather and Wind section). CONTAMW will then utilize the day type and 

time to select control values of any of the elements that have schedules associated with them. 

Transient Simulation, Start and Stop: These date and time fields are used to set the 

starting and stopping date and time of transient simulations. You should be sure to use only 

those dates available in the weather file. The available dates will be displayed in the 

Transient Weather Data section of the Run Control property page in the fields labeled 

"Weather data from ___ to ___." 

Use restart file: Each transient and cyclic simulation produces a restart file that contains the 

status of the simulation at midnight for each simulation day. You can have CONTAMW use 

a restart file from a previous simulation to run an abbreviated (one to two days) transient 

simulation. You can use this shorter simulation to output much more data than is practical for 

a longer simulation. 

To use this feature, you must first run a transient or cyclic simulation. If a restart file is 

available, the dates for which restart data is available will be listed as "Restart data from ___ 

to ___" below the "Use restart file" check box. Enter the date and time in the edit boxes 

labeled "Restart data beginning: ___ / _____." 

Steady State Weather Data: This is a summary of the steady state weather data settings. You 

can change this data by pressing the "Edit Weather DataÖ" button which will display the 

weather and wind related property sheet (see Defining Steady State Weather and Wind). You can 

have CONTAMW use steady state weather data for both steady state and transient simulations. 

Transient Weather Data: Select the weather file to be used by pressing the "BrowseÖ" button 

and then selecting an appropriate weather file for the simulation. You can either create this file 

using a text editor or spreadsheet program and following the format described previously or by 

using the weather file creation program also available from NIST. See Defining Transient 

Weather and Wind in the Working with Weather and Wind section for more details. 
USING CONTAMW ñ WORKING WITH SIMULATIONS

94

Time Steps: These are the time increments that CONTAMW uses for performing and displaying 

progress of transient and cyclic simulations. 

Enter time steps according to the following format. 

HH:MM:SS Example - enter 1 minute as 00:01:00 

Simulation Time Step: The simulation time step is that used by CONTAMW when 

performing transient airflow and contaminant calculations for the transient and cyclic 

simulations. Shorter time steps provide for greater accuracy of results but require more 

computation time. There must be an integral number of simulation time steps in an hour. See 

Output Properties to set the listing time step CONTAMW uses to write data to the results file. 

Display Time Step: CONTAMW uses the display time step to determine how often the 

simulation progress is updated on the CONTAMW Simulation Control dialog box. The 

display time step must be a multiple of the simulation time step. 

3.16.4.2 Simulation ñ Numerical Properties 

AIRFLOW CALCULATIONS 

Linear Equation Solver: This is currently the only method implemented for solving the linear 

equations generated by the Newton-Raphson (N-R) method. CONTAMW uses the skyline 

algorithm, which is a direct solution of the equations. It appears that large problems may benefit 

from an iterative conjugate gradient solver. This may be implemented in the future. 

Non-Linear Equation Solver: Convergence of the N-R solution of the non-linear simultaneous 

flow equations is controlled by four parameters: 

Maximum Iterations: Use this value to prevent endless calculations if the flow iterations are 

not converging. This should not be a problem with an appropriate relaxation coefficient. 

Relaxation Coefficient: This coefficient modifies the adjustment of the pure N-R method. 

Tests have found values near 0.75 to work well. Values near 1.0 may lead to non-convergent 

solutions. Values closer to 0.5 may be more reliable but take longer to solve. 

Relative Convergence Factor (e1) and Absolute Convergence Factor (e2): The flow 

iterations are determined to have converged when the sum of all flows in and out of the zone 

are less than the relative flow convergence, e1, times the sum of the absolute values of those 

flows. If the sum of the absolute values of the flows is less than the absolute flow 

convergence, e2, the zone is assumed to be converged. This is done to prevent division by 

zero. 

Adjust temperatures in flow elements: This modifies the element flow coefficients to account 

for the actual properties of the air flowing through the elements. This may change the computed 

flows by a few percent. 
 USING CONTAMW ñ WORKING WITH SIMULATIONS 

95

CONTAMINANT CALCULATIONS 

Linear Equation Solver: The simultaneous linear equations for the implicit calculation of 

contaminant concentrations may be solved by any of three methods: 

Skyline: The direct skyline algorithm 

BCG: The iterative biconjugate gradient algorithm 

SOR: the iterative successive over-relaxation algorithm 

The skyline algorithm is the most reliable solution, but slow for large problems. SOR requires 

much less memory and is faster unless there are convergence problems. In that case try the BCG 

solution. 

The "maximum flow iterations" applies to the BCG and SOR algorithms, and is used to prevent 

endless calculations if the flow iterations are not converging. 

An optimum over-relaxation coefficient, ω, (1.0 ñ 2.0) speeds the convergence of the SOR 

algorithm. Determination of an optimum will require some experimentation with different 

values. 

The BGC and SOR iterations are determined to have converged when the relative difference 

between the values on successive iterations are less than the relative flow convergence, e1. With 

the SOR algorithm, the absolute flow convergence, e2, is used to prevent a division by zero. 

Convergence for Cyclic Simulations: Convergence is assumed when the relative difference in 

the peak concentrations (for all contaminants in all zones) is less than the relative convergence, 

e1. The absolute convergence, e2, is used to prevent a division by zero. 

3.16.4.3 Simulation ñ Output Properties 

When you run a simulation with CONTAMW, simulation outputs are saved to binary files as the 

simulation proceeds. Detailed results for airflows and/or zone contaminant concentrations are 

saved to the .SIM file. These data will be used to display airflow results on the SketchPad or as 

graphs of transient values. Output is created at every "listing time step" which must be an even 

multiple of the simulation time step shown in parentheses. Shorter steps allow you to see the 

results in more detail, but they create a larger simulation results file. 

For long transient simulations it may be better to request the "summary data" for flows, 

contaminants, and exposures. These results will be presented graphically as "box-whisker data" 

which shows the average value, maximum and minimum values, and standard deviation of the 

values for all simulation time steps. For multi-day runs, daily displays are available in addition to 

the final summary. 

Detailed Results: All of the simulation results are saved in the simulation results file (See 

Working with Results). You can reduce the size of this file by saving only part of the available 

data. The flow data is necessary to display any results involving airflows. The contaminant data 

is necessary to display any results involving contaminant concentrations. Output is created at 

every listing time step which must be an even multiple of the simulation time step which is 

displayed as the "Current simulation time step." Shorter time steps allow you to see the results in 

more detail, but also create a larger simulation results file. 

Enter the listing time step according to the following format. 

HH:MM:SS Example - enter 1 minute as 00:01:00 
USING CONTAMW ñ WORKING WITH SIMULATION RESULTS

96

3.17 Working with Simulation Results 

CONTAMW can provide you with several types of simulation results. The results available after 

a simulation depend on the simulation method and output parameter settings. Once the results are 

available, you can view results using CONTAMW or you can export results to a commaseparated format file that you can then import to a spreadsheet program for further analysis. 

When CONTAMW performs a simulation, it creates a set of results files within the same 

directory that the project file is stored. These results files have the same file name as the project 

file with different extensions appended to it indicating the type of results file. The files that are 

created and the contents of files depend on the run control and output simulation parameters that 

were set prior to running the simulation. The following table lists the different file extensions and 

gives a brief description of the files. 

Extension Description 

.SIM Detailed simulation result: airflow, ∆P and contaminant 

concentrations for each time step. 

.SUM Summary results 

.EXP Occupant exposure results 

.RST Simulation restart file 

3.17.1 Viewing Results 

This section describes how to activate the results display mode of CONTAMW and to display 

the results at different time-steps upon the SketchPad of transient simulations. 

Results Display Mode 

To view results using CONTAMW you activate the results-display mode by checking either the 

SketchPad Results or the Results Display Window selection of the View menu. This will occur 

automatically after the successful completion of a simulation or after opening a project file that 

has simulation result files associated with it. Once the results-display mode is activated, the 

status bar will display result-related information (See Status Bar) and you will be able to utilize 

all of the Results Display Methods outlined below. 
 USING CONTAMW ñ WORKING WITH SIMULATION RESULTS 

97

Simulation Time Step 

If you have performed a transient simulation, results will be available for each time step. 

However, the SketchPad results (as described in the following section) can only be displayed for 

a single time step at a time. You can change the time step for which results are currently 

displayed upon the SketchPad using the following menu and keyboard shortcut commands. 

Show Next Time Step

Menu Command: View → Next Time Step

Keyboard Shortcut: End

Show Previous Time Step 

Menu Command: View → Previous Time Step

Keyboard Shortcut: Home

Show Last Time Step (of the day)

Menu Command: View → Last Time Step

Keyboard Shortcut: Ctrl+End

Show First Time Step (of the day)

Menu Command: View → First Time Step

Keyboard Shortcut: Ctrl+Home

3.17.2 Results Display Methods 

This section describes the various methods that CONTAMW uses to present simulation results. 

These methods include SketchPad for airflow paths, a Results Display Window for more detailed 

information on the icon currently highlighted on the SketchPad, plotting transient results on 

graphs, shaft reports, and exporting results to various types of external files. You can also print 

copies of the graphs you view with CONTAMW or copy them to the Windows clipboard to be 

pasted into other applications (e.g. word processor applications for written reports). 

3.17.2.1 SketchPad Results 

CONTAMW will display color-coded bars indicating the relative airflow rates and pressure 

drops associated with each airflow path, duct terminal, or the inlet and outlets of simple airñ

handling systems for the current time step on the current level of the SketchPad. Airflow rates 

are shown in blue and pressure differences in red. These result-bars will only appear if you have 

selected the Airflows option on the Output page of the Simulation Parameters property sheet. If 

you have set flow or pressure limits for a given airflow path (see Airflow Path Properties), and 

they have been exceeded, the icon will be highlighted in red as a warning indicator. 

3.17.2.2 Results Display Window 

When you activate the results display mode, it activates the CONTAMW Results Display 

window. This window will display different types of information depending on the type of 

simulation that was performed (steady state or transient) the type of output that you selected and 

the currently (or most recently) highlighted icon on the SketchPad. The results display window 

will display information associated with zone icons and exposure icons. Once in the results 

display mode, you can control the visibility of the Results Display window using the Results 

Display Window selection of the View menu. However, you can only display the Results 

Display window while the SketchPad results are displayed. 
USING CONTAMW ñ WORKING WITH SIMULATION RESULTS

98

Contaminant Concentration Results 

If the currently highlighted icon is a zone icon, then contaminant results will be displayed in the 

Results Display Window. The contaminant concentration results displayed in the Results Display 

Window depend on whether you performed a steady state or transient simulation. For transient 

simulations, results will be displayed for the current time step. For steady state contaminant 

simulations the steady state contaminant concentration will be displayed. If you are viewing 

transient simulation results, select the simulation time step for which you want results to be 

displayed using the Simulation Time Step commands outlined in the previous section on 

Viewing Results. 

Age-of-Air Results 

The "age-of-air" refers to the mean time since the air molecules in the zone entered the building. 

Short values indicate high ventilation rates. In CONTAMW age-of-air is computed assuming 

steady state conditions [Roulet and Vandaele 1991]. If you had CONTAMW generate detailed 

results for airflows, then you can have CONTAMW determine the age-of-air using the flow 

values for the current time-step. This value will be displayed in the status bar when you move the 

cursor to the zone icon while in the results viewing mode. (Note: Calculating the age-of-air 

involves inverting a matrix. This can be time-consuming for buildings with many zones and duct 

junctions.) 

Exposure Results 

If the currently highlighted icon is an exposure icon, then both exposure and dose results will be 

displayed in the Results Display Window for that icon. 

3.17.3 Plotting Results 

CONTAMW provides you with some powerful charting features for plotting transient simulation 

results. You can plot airflow, contaminant and exposure results using these features. Charting is 

only available for transient simulation results of the currently loaded CONTAMW project. You 

can plot results for airflows and pressure differences, contaminant concentrations, and occupant 

exposure and potential dosage. You access these charting features from the Simulation menu 

when the results-display mode is active. 

Plotting Airflow Results 

Menu Command: Simulation → Plot Airflow ResultsÖ 

This command will display the Chart Control dialog box that you use to select and modify the 

chart settings for plotting airflow and pressure difference results for airflow paths. With this 

charting tool you can select multiple flow paths; plot one or more days of simulations; select the 

units of display; and plot either airflow, pressure difference or both on the same plot. You can 

also plot two-way flow rates for those flow paths that implement two-way airflow elements. If 

you select not to show two-way flows, CONTAMW will plot the net flow rate for airflow paths 

that implement two-way airflow elements. 

NOTE: If you select this menu item when the CONTAMW caret is highlighting an icon having 

airflow results associated with it (airflow path icon, duct flow icon, duct junction icon, or 

inlet/outlet icon of a simple airñhandling system), it will appear in the list of paths to plot when 

the Chart Control dialog box is displayed. This feature allows you to plot results for a particular 

flow path by highlighting it on the SketchPad as opposed to finding it in the list of flow paths on 

the Chart Control dialog box. 
 USING CONTAMW ñ WORKING WITH SIMULATION RESULTS 

99

Plotting Contaminant Results 

Menu Command: Simulation → Plot Contaminant ResultsÖ 

This command will display the Chart Control dialog box that you use to select and modify the 

chart settings for plotting the time-history of contaminant concentrations of zones. With this 

charting tool you can select which contaminant to plot, plot multiple zones on the same graph, 

plot one or more days of results, and select the units of display. 

NOTE: If you select this menu item when the CONTAMW caret is highlighting a zone icon, it 

will appear in the list of paths to plot when the Chart Control dialog box is displayed. This 

feature allows you to plot results for a particular zone by highlighting it on the SketchPad as 

opposed to finding it in the list of zones on the Chart Control dialog box. 

Plotting Exposure Results 

Menu Command: Simulation → Plot Exposure ResultsÖ 

This command will display the Chart Control dialog box that you use to select and modify the 

chart settings for plotting the time-history of occupant exposure to and potential dosage of 

contaminants. With this charting tool you can select which contaminant to plot; plot multiple 

occupants on the same graph; plot one or more days of results; select the units of display; and 

plot either exposure, potential dosage or both on the same plot. 

NOTE: If you select this menu item when the CONTAMW caret is highlighting an exposure 

icon, it will appear in the list of occupants to plot when the Chart Control dialog box is 

displayed. This feature allows you to plot results for a particular occupant by highlighting it on 

the SketchPad as opposed to finding it in the list of occupants on the Chart Control dialog box. 

3.17.3.1 Chart Control: Transient Airflow Results 

This section provides detailed descriptions of the specific properties associated with plotting 

transient airflow results. This is the context-sensitive help that you can access by pressing F1

when working with Chart Control for plotting Transient Airflow Results. 

Paths to Plot/Paths Available: The plotted data for each airflow element will appear as a 

separate trace. The "Paths to Plot" lists the airflow elements that will be graphed. To add an item 

to this list select the appropriate airflow element type (paths, ducts, or junctions), scroll through 

the list of available elements or enter the element number directly if known, then press the "

Add" button. To remove an item from the Paths to Plot field select the zone to be deleted and 

then press the "Remove" button. 

Date(s) to Plot: This field allows the you to select the dates of data you wish to plot on the 

graph. The available dates for the given simulation file are shown for your reference. You must 

set the dates to fall within this range of dates. Enter dates in the following format: 

MMMDD - the first 3 letters of the month and then the day of the month with or without spaces 

Data to Plot: You can plot airflow rates, pressure differences, or both. If you plot both airflow 

and pressure difference, then CONTAMW will produce a graph with two vertical axis - one for 

airflow and one for pressure difference. You can select the units of these axis using the "Airflow 

Units" and "Pressure Units" drop-down combo boxes on this dialog box. 

You can also show two-way flows for flow elements that utilize two-way flow models. If you 

leave "Show two-way flows" unchecked, then CONTAMW will plot the net flow rate for all 

flow paths. If you check "Show two-way flows," then a zero component will be plotted for all 

flow paths that do not implement two-way models. 
USING CONTAMW ñ WORKING WITH SIMULATION RESULTS

100

3.17.3.2 Chart Control: Transient Contaminant Results 

This section provides detailed descriptions of the specific properties associated with plotting 

transient contaminant results. This is the context-sensitive help that you can access by pressing 

F1 when working with Chart Control for plotting Transient Contaminant Results. 

Contaminant to Plot: This lists all the currently defined project contaminants. Select the 

contaminant for which you want results plotted. 

Zones to Plot/Zones Available: The plotted contaminant data for each zone will appear as a 

separate trace. The "Zones to Plot" lists the zones that will be graphed. To add an item to this list 

select the appropriate level and zone name from the drop down boxes in the Zones Available 

field and then press the "<- Add" button. To remove an item from the Zones to Plot field first 

select the zone to be deleted and then press the "Remove" button. 

Date(s) to Plot: This field allows the you to select the dates of data you wish to plot on the 

graph. The available dates for the given simulation file are shown for your reference. You must 

set the dates to fall within this range of dates. Enter dates in the following format: 

MMMDD - the first 3 letters of the month and then the day of the month with or without spaces 

3.17.4 Exporting Results 

CONTAMW also provides you with the ability to export results to external files. These files are 

comma-delimited, so you can easily import them into a spreadsheet. This feature provides you 

with greater charting flexibility as well as the ability to perform more sophisticated data analysis 

of your simulation results. You access this feature of CONTAMW by selecting Export 

ResultsÖ from the Simulation menu or using the F5 shortcut key when the results-display 

mode is active. This will display the "Export Data" dialog box as described in the following 

section. 

3.17.4.1 Export Data 

This section provides detailed descriptions of the specific properties associated with exporting 

results to external files. This is the context-sensitive help that you can access by pressing F1

when working with Export Data dialog box. 

Transient Results: The date ranges of the available data are displayed in the first half of this 

section. You can input a date/time range for the data to be exported to file. The format of the date 

is the first 3 letters of the month followed by the day of the month (mmmdd) with or without 

spaces in the leftmost edit box, then the time entered in the right edit box in the form hh:mm:ss. 

Airflow Data: There are three options for exporting airflow data. 

1. You can export all the airflow data for a specific airflow element. The total number of 

airflow elements is given in a text box to the right of entry text box. The airflow element 

number must be between zero and this number. 

2. You can enter a date and time and export the data for all the airflow elements at that time. 

3. You can choose to export an average airflow for each airflow element throughout the 

selected export date range. 

Contaminant Concentration Data: There are two options for exporting contaminant data. 

1. You can export all the contaminant data from the simulation for the entire project file. 

2. You can export the contaminant data for a specific zone. The zone name and building 

level must both be selected from the provided drop down boxes. 
 USING CONTAMW ñ WORKING WITH SIMULATION RESULTS 

101

3.17.4.2 Shaft Report 

CONTAMW is well suited for the analysis of smoke control systems. Because of the importance 

of shafts for some smoke control systems [Klote and Milke 1992], CONTAMW provides a 

special reporting feature for shafts. 

Defining Shafts 

You define shafts during the drawing phase of project development by placing zone icons 

directly below one another (in the same column and row) on adjacent levels of a building. If 

there is a zone icon in the same position on the level above or below the current level, those 

zones are part of the shaft when CONTAMW generates a shaft report. The shaft consists of 

zones that exist on contiguous levels having a zone icon in the same location on the SketchPad. 

You create the shaft report by selecting Generate Shaft Report from the Simulation menu. 

This will display a dialog box prompting you to execute the following three steps to define the 

shaft zone icon and primary and secondary flow paths associated with the shaft across which you 

want CONTAMW to report the airflows and pressure drops. The zone icon would typically 

represent a stairwell, and the primary flow path would typically represent a stairwell door. 

Steps to select a shaft for a shaft report are: 

1) Left-click on the zone icon that defines the shaft 

2) Left-click on the primary airflow path icon 

3) Left-click on the secondary airflow path icon 

NOTE: Click the right mouse button to cancel the shaft report generation process. 

Once you have completed the above steps, the shaft report will be displayed in a dialog box. The 

report will display pressure drop, airflow rates and direction of airflow on every level of the shaft 

where there are airflow path icons in the same location on the SketchPad as that of the primary 

and secondary airflow paths. You can use the Shaft Report dialog box to select the units in which 

the airflow rate and pressure drops are reported, and you can save a copy of the report to a text 

file. 
USING CONTAMW ñ WORKING WITH SIMULATION RESULTS

102

3.17.4.3 TRNSYS Input Files 

You can use CONTAMW to generate input data for the TRNSYS airflow module TYPE96. Use 

the Create TRNSYS Input File selection of the Simulation menu. The data will be written to a 

file having the same name as the current project but the .PRJ extension will be replaced and .AIR 

extension. The following CONTAMW airflow elements are currently supported when creating 

TRNSYS input files. If any other elements exist within the current project, you will receive a 

warning message from CONTAMW that unsupported airflow elements exists within the project. 

Powerlaw Models: 

Q = C(∆P)n

 F = C(∆P)n Leakage Area Data 

Connection (ASCOS) Data Orifice Area Data Crack Description 

Test Data (1-point) Test Data (2-points) Stairwell 

Shaft 

Two-way flow: Two-opening Model 

In addition, the supply and return paths associated with the simple air handling system model are 

also included. The AHS implicit paths ─ recirculation, exhaust, and outside air ─ are not 

included. All the CONTAMW building zones, AHS supply and return nodes, and the ambient 

zone are included. A complete list of the inputs to and the outputs from the TYPE96 subroutine 

are listed at the end of the .AIR file. 

The inputs from TRNSYS to TYPE96 are: 

Temperatures for all zones including ambient [oC] 

Absolute barometric pressure [Pa] 

Wind speed at the building reference elevation [m/s] 

Wind direction [degrees clockwise from north] 

All AHS supply and return flows [kg/s] 

Any other specified mass flow rates [kg/s] 

The relative areas of any variable openings 

All flow and relative area inputs must be greater than zero. 

The outputs from the TYPE96 subroutine to TRNSYS are the interzone airflows including flows 

to and from ambient. There are a maximum of two flows reported between any two zones ─ the 

sum of all flows from zone 1 to zone 2 and the sum of all flows from 2 to 1. There may be 

multiple paths between any two zones. 
 USING CONTAMW ñ WORKING WITH SIMULATION RESULTS 

103

TRNSYS Input File Format: 

The following listing shows the format of a TRNSYS input file created by CONTAMW having 

the .AIR file extension. An I indicates an integer value and R indicates a four-byte real number. 

HEADER DATA:

Line 1: debug control

I LIST - non-zero value initiates data dumps.

Line 2: counts

I NWPP - number of wind pressure profiles.

I NZONE - number of zones/simultaneous equations.

I NPATH - number of airflow paths.

I NELMT - number of airflow elements.

Line 3: run control

I ITMAX - maximum number of iterations.

R RELAX - under-relaxation coefficient.

R ACNVG1 - relative airflow convergence factor.

R ACNVG2 - absolute airflow convergence factor.

I TADJ - non-zero to do temperature adjustment.

Line 4: weather data

R PBAR - absolute barometric pressure [Pa].

R WSPD - wind speed [m/s].

R WDIR - wind direction [deg clockwise from north].

Line 5: end of section indicator

I J - should equal –999

WIND PRESSURE PROFILES:

One line for each wind pressure profile consisting of

I NR - profile number, starting at 1.

I TYPE - profile type.

I NPTS - number of data points.

followed by one line with 5 real values for each data point.

Last line: end of section indicator

I J - should equal –999

AIR FLOW ELEMENTS:

One line with 3 real values for each flow element.

R LAM - laminar flow coefficient

R TURB - turbulant flow coefficient

R EXP - powerlaw exponent

Last line: end of section indicator

I J - should equal –999

ZONE DATA:

One line for each zone consisting of

I NR - zone number, starting at 1.

I CP - 1 indicates constant pressure zone.

R TZ - initial zone temperature [K].

R PZ - initial zone pressure [Pa].

R VOL - zone volume [m^3].

R HT - zone elevation [m].

Last line: end of section indicator

I J - should equal –999

PATH DATA:

One line for each airflow path consisting of

I NR - path number, starting at 1.

I NZ - number of zone air flows from (to be positive).

I MZ - number of zone air flow to.

R HT - path elevation [m].

I TYPE - path type: 0=flow, 1 = PLR, 2=QCN, 3=FCN.

I NE - number of the air flow element.

R MULT - path multiplier.

I XIN - index (>0) of XIN input value (type 0).

I PWP - index (>0) of the wind pressure profile.

R WIND - wind pressure modifier.

R AZM - surface azimuth angle.

R CTRL - flow or control value depending on type.

Last line: end of section indicator

I J - should equal –999

INPUT & OUTPUT DATA:

First line:

I NIN - number of input variables.

I NOUT - number of output variables.

One line for each output variable consisting of

I NR - output number (index to XOUT).

I NZ - number of zone the air flows from.

I MZ - number of zone the air flows to.

Last line: end of section indicator

I J - should equal –999
USING CONTAMW ñ WORKING WITH SIMULATION RESULTS

104

3.17.4.4 CONTAMX Input Files 

You can use CONTAMW to generate input data for the CONTAMX stand-alone simulation 

engine. This is the same simulation engine that is coupled with CONTAMW. However, with the 

CONTAMX program, you can perform batch mode operations to process multiple project files. 

Use the Create CONTAMX Input File selection of the Simulation menu. The data will be 

written to a file having the same name as the current project but the .PRJ extension will be 

replaced and .NDF extension. If you require the use of CONTAMX, you can contact NIST to 

obtain a copy of the program CONTAMX.EXE. 
 USING CONTAMW ñ WORKING WITH PROJECT ANNOTATIONS 

105

3.18 Working with Project Annotations 

Project annotations provide you with a simple project documentation feature. You simply place 

an annotation icon onto the SketchPad (see Drawing Building Component Icons) and then use 

the icon definition procedure (see Defining Building Component Icons) to edit the text for the 

annotation. Once you have defined the text associated with the annotation icon, the text will 

appear in the status bar whenever you highlight the icon with the caret. You can edit, delete, and 

move the icon as you would any other building component icon. 

3.19 Getting Help 

This on-line help manual that is also available in printed form accompanies CONTAMW. There 

are several ways to access the on-line help system. You can either use the Help ContentsÖ

selection of the Help menu to display the contents of the help manual or use the context-sensitive 

feature to access help. 

Help Contents 

You can browse the contents or index of the help system to view the topic of your choice and use 

the search feature to display a list of help topics that contain the keyword in which you are 

interested. 

Context-Sensitive Help 

The context-sensitive help feature is designed to provide you with specific information related to 

the currently active CONTAMW window or dialog box. To activate the context-sensitive help 

system, press the F1 key. 

Obtaining Technical Support 

If you need to contact the CONTAMW developers for guidance on using the program or to 

report a technical problem with the program, you can do so via email or phone to the addresses 

and numbers below. If you encounter an error while working with CONTAMW, and you require 

assistance solving the problem, you should immediately (before running CONTAMW again) 

make copies of the CONTAMW.LOG, PROJECT.BKP and WEATHER.BKP files located in the 

CONTAMW program directory. You can email these files to NIST so that we may be better 

equipped to address your particular problem. 

NIST Contact Information 

1. George Walton gwalton@nist.gov 301-975-6421 

2. W. Stuart Dols wsdols@nist.gov 301-975-5860 

3. IAQ and Ventilation Group 301-975-6431 

4. www.bfrl.nist.gov/863/iaq.html 
SPECIAL APPLICATIONS OF CONTAMW ñ BUILDING PRESSURIZATION TEST

106

4 Special Applications of CONTAMW 

This section includes instructions, or considerations, for using CONTAMW to simulate several 

different building features (e.g. atria, stairwells and chimneys) and perform special building 

analysis such as fan pressurization. 

4.1 Building Pressurization Test 

The building pressurization test (sometimes referred to as a "blower door test") is a common way 

of determining the airtightness of a building's envelope. Fan pressurization is relatively quick 

and inexpensive and it characterizes building envelope airtightness independent of weather 

conditions. In this procedure, a large fan or blower is mounted in a door or window and induces a 

large and roughly uniform pressure difference across the building shell. [ASHRAE 1997, p 

25.15; ASTM 1999] A common airtightness rating is the airflow rate at 50 Pa divided by the 

building volume to give units of air changes per hour. 

You may wish to do a simulated pressurization test to determine the airtightness rating of your 

building model. This is done by setting one of the zones on the zero elevation level to a constant 

pressure of 50 Pa, running the simulation, and then observing the total airflow out of that zone. 

(Don't forget flows to other building levels.) Use standard m3

/h flow units and divide by the 

building volume in m3

 to get the air change rate at 50 Pa. Alternatively, the flow rate at a 

selected reference pressure (e.g. 50 Pa) can be converted to an effective leakage area (ELA) 

using equations in Chapter 25 of the 1997 ASHRAE Fundamentals Handbook [ASHRAE 1997]. 

Use the CONTAMW results display to check that the building has been properly pressurized by 

moving the cursor to each path on the envelope to get the pressure drop reported in the status bar. 

You can use the report of all flows to get a listing of all flow and pressure drops. The pressure 

drop on every path to the ambient zone should be close to -50 Pa. The value is negative because 

of the default direction assigned for positive flow. 

The reported pressure drop across various flow paths will not be exactly 50 Pa because of density 

effects. Minimize these differences by running all zones and ambient at the same (standard) 

temperature and no wind. Differences in pressure due to elevation make it critical that the 

constant pressure zone be on the level with zero elevation. 

In a multizone building the effects of partitioning (internal walls and floors) usually are 

significant. There are two solutions depending on the goal of the simulation. If the goal is only to 

achieve a uniform pressure difference across the entire building shell, add some very large 

openings across each partition. If the goal is to reproduce a field test, simulate the internal doors 

as being open to get a relatively uniform pressure inside the building. 

Prior to performing these tests, you should make a copy of the project file so you do not have to 

reverse the changes to restore the original project file. 
 SPECIAL APPLICATIONS OF CONTAMW ñ SMOKE CONTROL SYSTEMS 

107

4.2 Smoke Control Systems 

For a stairwell pressurization system, you may want to record the pressurization flows by 

creating a simple AHS model with supply points in the shaft. Make these supply points the 

secondary path. You may use supply point icons aligned on every level with some or most of the 

flows set to zero, or you may use icons only on those levels with a pressurization flow. 

Alternatively, for shafts on an exterior wall of the building, you may wish to use constant flow 

rate path elements through exterior walls to provide the pressurization air. This type of flow path 

will also report the pressure difference between the shaft and ambient. You may want to align 

these constant flow paths above the open doorway on the first level. For details on viewing shaft 

reports, see Working with Simulation Results in the Using CONTAMW section of the manual. 

4.3 Shafts 

Buildings contain several architectural features which offer very low resistance to airflow 

between building levels. These features include atria, elevator shafts, and stairwells. 

CONTAMW provides two ways of modeling such a low resistance path: the phantom zone and 

the low-resistance (or large) opening. Select the most appropriate model based on how this path 

interacts with the rest of the model. 

This interaction can be understood by using three flow resistances in series to model a shaft 

between two levels. There is a resistance to flow through the shaft and resistances representing 

the paths (doors) connecting the shaft to the two different levels. Using the powerlaw 

relationship, Q = C(∆P)1/2, and assuming C = 3.10 for the shaft, 1.55 for an open door, and 0.01 

for a closed door, the following equivalent flow coefficients, Ce = ( Σ Ci

-2 )-1/2, are computed for 

four different assumptions: 

1. both doors closed, ignore shaft resistance: Ce = 0.007070 

2. both doors closed, include shaft resistance: Ce = 0.007066 

3. both doors open, ignore shaft resistance: Ce = 1.096 

4. both doors open, include shaft resistance: Ce = 0.984 

Cases (1) and (2) show that when flow resistance is dominated by the closed doors, it is not 

necessary to include the shaft flow resistance. Cases (3) and (4) show that when the resistances at 

the (open) doors are of the same order as the shaft resistance, it is important to include the shaft 

resistance in the model. For a quick estimate of relative flow coefficients, remember that the 

flow coefficient is usually roughly proportional to the opening area. 

4.3.1 Atria 

If an atrium were modeled as individual zones on each level, the inter-level flow resistances 

would be very low. A cursory comparison of the inter-level opening areas to the sum of all 

openings from the atrium to other zones will usually indicate that an atrium should be modeled 

using phantom zones. This is done by placing a standard zone icon at the atrium's lowest level. 

You use this zone icon to define the atrium temperature and total volume. You should ignore the 

floor area of the normal zone icon that is used to define the atrium zone. Place a phantom zone 

icon at all higher levels which contain parts of the atrium. A phantom zone icon indicates that the 

region within the walls on this level are actually part of the zone on the level below the icon. If it 

is necessary to have different temperature or contaminant concentrations at the different levels in 

an atrium, then those levels must be modeled as normal zones connected by flow paths with very 

large openings. 
SPECIAL APPLICATIONS OF CONTAMW ñ SHAFTS

108

4.3.2 Stairwells 

Data to describe the airflow characteristics of a stairwell in terms of an equivalent orifice is 

provided in [Achakji and Tamura 1988]. This representation is very well suited to being 

implemented by CONTAMW, which allows you to create a powerlaw flow element from the 

physical characteristics of the stairwell. Stairwell characteristics include the cross-sectional 

(horizontal) area of the stairwell shaft, whether the fronts of the stair treads are open or closed, 

and the number of people on the stairs. This last item might be important in an evacuation 

scenario. Since the equivalent orifice area of the shaft is on the same order as it's cross-sectional 

area, and this area is likely to be smaller than the sum of the areas of the doors entering the 

stairwell, it is generally best to model a stairwell as individual zones on each level connected by 

openings which have been defined using the CONTAMW stairwell airflow element that 

implements the Achakji/Tamura model. 

4.3.3 Elevator Shafts 

Elevator shafts (hoistways) will generally lie in some modeling regime that falls between 

stairwells and atria. Measured data for the flow resistance of an elevator shaft have not yet been 

identified. CONTAMW provides a powerlaw flow element based on flow resistance from the 

Darcy/ Colebrook model of a conduit or duct. A significant difference between an elevator shaft 

and a stairwell is that the door between the shaft and the building is never fully open because, 

when it is open, air must flow through openings in the elevator car to pass between the building 

and the shaft. In several computational examples the equivalent orifice area for closed elevator 

doors is about 0.15 m2

 [Klote and Milke 1992]. This is fairly small compared to the crosssectional area of the shaft, especially for hoistways with multiple cars, so it is likely that the 

airflow in most elevator shafts can be modeled with sufficient accuracy by phantom zones. 

However, it may be necessary to split the shaft into several sections to achieve sufficient 

accuracy in modeling contaminant transport. 

4.3.4 Chimneys 

You can use a duct to create a simple chimney model. At its simplest this will involve only a 

single duct connecting the inside of the building to the outside with the Darcy-Colebrook duct 

element used to model the flow resistance of the chimney. The height of the duct terminal points 

must reflect the height of the chimney and a special high temperature zone must be created 

around the inside terminal point so that the proper stack effect will result. Be sure to allow an 

appropriate low resistance path from this special zone to the rest of the building. 
 THEORETICAL BACKGROUND ñ MODEL ASSUMPTIONS 

109

5 Theoretical Background 

This section provides theoretical background of the CONTAMW program. There are basically 

three subsections: the first provides a summary of underlying assumptions of the model and the 

others address the contaminant and airflow analysis respectively. 

5.1 Model Assumptions 

CONTAMW is a powerful tool that models airflow and contaminant dispersal in buildings. It is 

important to realize that this tool implements mathematical relationships to model airflow and 

contaminant related phenomenon and therefore incorporates assumptions that simplify the model 

from that of the modeled phenomenon. The following is a brief description of these modeling 

assumptions. 

Well-mixed zones ñ This assumption refers to the treatment of each zone as a single node, 

wherein the air has uniform (well-mixed) conditions throughout. These conditions include 

temperature, pressure and contaminant concentrations. Therefore, localized effects within a 

given zone cannot be accounted for using CONTAMW. For example, if you utilize a 

contaminant source that introduces a mass of contaminant into a zone at a certain time (burst 

source), the contaminant will be diluted to the entire volume of the zone within a single time 

step. 

Trace contaminants ñ Trace contaminants are those that are found at low enough concentrations 

levels that they do not affect the density of air within a zone. You must be careful not to rely on 

the model to handle contaminant concentrations that would cause a change in the density of air. 

The program will allow for contaminants to reach levels that would, in actuality, affect the 

density, but the program will still treat them as if they were trace contaminants. That is, the 

concentration of a contaminant within a zone would be determined as the ratio of the mass of 

contaminant to the volume of the zone. However, the mass of air within the zone will not change, 

because the model maintains each zone at a constant temperature and volume and assumes 

differences due to changes of pressure within a zone to be negligible. 

Thermal effects ñ The model does not handle heat transfer phenomenon. The temperatures in all 

zones are constant as set by the user. You can set different zones to different temperatures, but 

they remain constant throughout a simulation. However, you can vary the outdoor temperature 

for transient simulations. The model does determine airflows induced by temperature differences 

between zones including ambient as caused by the stack effect. 

Airflow paths ñ The airflow paths are represented by nonlinear mathematical models relating the 

flow through the path to the pressure drop across the path. The airflow path models are drawn 

from the literature and it is up to the user to select the appropriate model for each flow path. See 

Airflow Elements for detailed explanations of these models. 

Quasi-steady airflows ñ CONTAMW uses the flow/pressure drop of the flow paths and a mass 

balance in each zone to create a set of simultaneous nonlinear algebraic equations that is solved 

to determine the zone pressures and interzone mass flow rates. Even a "transient simulation" 

involves the calculation of airflows at each time step assuming steady conditions followed by a 

fully implicit numerical integration of the transient differential equations representing the 

contaminant concentration. A true transient solution would be required to allow the mass of air in 

the zone to vary over time. This was not implemented in CONTAMW because zone 
THEORETICAL BACKGROUND ñ MODEL ASSUMPTIONS

110

temperatures are constant and the variation of mass due to transient pressure changes is generally 

small. 

Source/sink models ñ CONTAMW provides several different source/sink elements or 

representations of contaminant generation/removal processes. These elements are based upon 

models found throughout the literature. You should be sure to utilize models that are appropriate 

for the contaminant source/sink that you want to represent. See Contaminant Source/Sink 

Elements for detailed explanations of these models. 

The previous assumptions relate to the mathematical representations utilized by CONTAMW in 

performing analysis. These assumptions should be distinguished from assumptions made by you, 

the user, when creating a model of a building referred to as a building idealization (See User 

Tasks in the Getting Started section). Engineering judgment is required on your part to insure 

that your building representation is adequate for the purposes of your analysis. 
 THEORETICAL BACKGROUND ñ CONTAMINANT ANALYSIS 

111

5.2 Contaminant Analysis 

The CONTAMW contaminant dispersal model is an implementation of Axley's methods [Axley 

1987 and 1988]. He states: "The central concern of indoor air quality analysis is the prediction of 

airborne contaminant dispersal in buildings. Airborne contaminants disperse throughout 

buildings in a complex manner that depends on the nature of air movements in-to, out-of, and 

within the building system; the influence of the heating, ventilating, and air-conditioning 

(HVAC) systems; the possibility of removal, by filtration, or contribution, by generation, of 

contaminants; and the possibility of chemical reaction, radio-chemical decay, settling, or sorption 

of contaminants. In indoor air quality analysis we seek to comprehensively model all of these 

phenomena." 

The mass of contaminant α in zone i is 

mα ,i mi Cα ,i = ⋅ (1) 

where mi is the mass of air in zone i and Cα,i is the concentration mass fraction of α. A zone is a 

region of uniform contaminant concentration which may correspond to a single room, a portion 

of a room, or several well-coupled rooms. Selection of the zones is a matter of engineering 

judgment. In CONTAMW the contaminant concentration must be low enough so as not to 

significantly change the density of the air-contaminant mixture. 

5.2.1 Solution of Contaminant Equations 

Contaminant is removed from the zone i by: 

1. outward airflows from the zone at a rate of Σj Fi,j⋅Cα,j 

where Fi,j is the rate of airflow from zone i to zone j, 

2. removal at the rate Cα,i⋅Rα,i where Rα,i is a removal coefficient, and 

3. first-order chemical reactions with other contaminants Cβ,i at the rate mi⋅Σβ κα,β⋅Cβ,i

where κα,β is the kinetic reaction coefficient in zone i between species α and β. (Sign 

convention: positive κ for generation and negative κ for removal) 

Contaminant is added to the zone by: 

1. inward airflows at the rate Σj (1-ηα,j,i) Fj,i⋅Cα,j where ηα,j,i is the filter efficiency for 

contaminant α in the path from zone j to zone i, 

2. generation at the rate Gα,i , and 

3. reactions of other contaminants. 

Conservation of contaminant mass for each species (and assuming trace dispersal, i.e., mα,i << 

mi) produces the following basic equation for contaminant dispersal in a building: 

= − − + ( ) − +  +

β

α α α α α α β β α

α η i κ i i

j

j i j i j

j

i i i j i

i R C F C F C m C G

dt

dm , , , , , , , , , , ,

, 1 (2) 

This differential equation is approximated by a difference equation: 





 



 ≈ + ∆  − +  + − +

j

j i j i i i i i j i

j

m i m ,i t Fj,i , , C , m , C , G , R , F , C ,

*

, (1 ) ( ) α α α

β

α α ηα α κ α β β (3) 

where the * indicates a value at time t+∆t. 
THEORETICAL BACKGROUND ñ CONTAMINANT ANALYSIS

112

Instead of the generalized trapezoidal method used by Axley, CONTAMW uses a fully implicit 

numerical approximation to solve equation (3): 

m t R F C t F C m t C m C G t j i j i i i i i

j

i j i

j

i i i j  − ∆ − − ∆ ≈ + ∆



 





+ ∆ +   , ,

*

, ,

*

, , , ,

*

, , , ( ) (1 ) α α

β

α α ηα α κ α β β (4)

mi is considered to be constant. Some special cases are handled by variants of the above 

equation. If zone i is specified as having no mass (e.g., in the ductwork), equation (4) becomes: 

+ − − ≈ j jR i Fi j C i j i Fj iC j G ,i

*

, , , ,

*

, , , ( ) (1 ) α α ηα α α (5) 

Note that the kinetic reactions cannot be considered in this case. If a steady state solution is 

desired, equation (4) becomes: 

j i j i i i

j

R ,i fromjFi, j C ,i , j,i F , C , m , C , G , ( ) (1 ) α

β

α + α − −ηα α − κ α β β ≈ (6) 

If the mass flows and Rα,i should happen to be zero in equations (5) or (6), they cannot be solved. 

This case is handled by the simple expedient of letting Cα,i remain at its default value. These 

equations must be solved simultaneously for all zones and contaminants. 

There are two major limitations in the equations presented above. First is constant zone air mass. 

This is consistent with the zone temperatures being constant and contaminant mass fractions 

being low. Second is the use of linear analysis which limits the kinds of kinetic reactions which 

can be modeled. 

CONTAMW maintains the same equation ordering for the contaminant equations as is used for 

airflows except that for each zone there is an equation for each contaminant species. These 

simultaneous linear equations for the implicit calculation of contaminant concentrations may be 

solved by any of three methods: a direct skyline algorithm, an the iterative biconjugate gradient 

(BCG) algorithm, or an iterative successive over-relaxation (SOR) algorithm [Press 1992]. The 

skyline algorithm is the most reliable solution, and it is very fast for small problems but can be 

slow for large problems. The SOR algorithm requires much less memory and is faster unless 

there are convergence problems. In that case try the BCG solution. Before doing a long 

simulation, it may be useful to test the different methods to determine which will give optimum 

performance. 
 THEORETICAL BACKGROUND ñ CONTAMINANT ANALYSIS 

113

5.2.2 Contaminant Source/Sink Elements 

CONTAMW allows you to define the generation, Gα, and removal, Rα, coefficients for some 

simple cases. 

The general source/sink model uses the following equation: 

Sα Gα Rα Cα = − ⋅ (7) 

where 

Sα = source strength of contaminant α [kgα / s] 

Gα = generation rate [kgα / s] 

Rα = effective removal (deposition) rate [kgair / s] 

Cα = current concentration [kgα / kgair] 

Units are given in terms the internal units of CONTAMW, i.e., the units CONTAMW uses to 

save parameters and perform calculations. You may express these values in a large number of 

units with automatic conversion to the internal values. 

For a room air filtering device, Gα = 0.0 and Rα = fe where f is the flow rate of the room air 

passing through the filter and e is the single pass removal efficiency of the device. 

The pressure source/sink model is intended to model contaminant sources which are governed by 

the inside-outside pressure difference, such as radon or soil gas entry into a basement. In this 

case the source equation is: 

n G Pambt Pi S = ⋅( − ) α α (8) 

For volatile organic compounds the source equation is sometimes expressed in the form 















 = −

cutoff c

c S G α

α α 1 (9) 

where Ccutoff is the cutoff concentration at which emission ceases. 

Another source equation for volatile organic compounds is the exponentially decaying source 

which is expressed in the form 

t tc S G e− / = (10) 

where 

S = the contaminant source strength, 

G = the initial emission rate, 

t = the time since the start of emission, and 

tc = the decay time constant. 
THEORETICAL BACKGROUND ñ CONTAMINANT ANALYSIS

114

The boundary layer diffusion controlled reversible source/sink model follows the descriptions 

presented by Axley in [Axley 1991]. The rate at which a contaminant is transferred into the sink 

is 





 



 ⋅ ⋅ − k

C h A C s ρ i (11) 

where 

h = average film mass transfer coefficient over the sink, 

ρ = film density of air, average of bulk & surface densities, 

A = surface area of the adsorbent, 

Ci = concentration in the air, 

Cs = concentration in the adsorbent, and 

k = Henry adsorption constant or partition coefficient. 
 THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS 

115

5.3 Airflow Analysis 

Over the years many methods have been developed to compute the building airflows which are 

necessary for the contaminant analysis. Feustel and Dieris report 50 different computer programs 

for multizone airflow analysis [Feustel and Dieris 1992]. Note that "zones" go by many other 

names in these programs, e.g., nodes, cells, and rooms are common alternatives. The airflow 

calculations in CONTAMW are based on the algorithms developed in AIRNET [Walton 1989a 

and 1989b]. 

5.3.1 Basic Equations 

The airflow rate from zone j to zone i, Fj,i [kg/s], is some function of the pressure drop along the 

flow path, Pj - Pi: 

( ) j i Pj Pi F , = f − (1) 

The mass of air, mi [kg], in zone i is given by the ideal gas law 

i

i i

i i i RT

PV

m = ρ V = (2) 

where 

ρi = air density in zone [kg/m3], 

Vi = zone volume [m3], 

Pi = zone pressure [Pa], 

Ti = zone temperature [K], and 

R = 287.055 [J/kg⋅K] (gas constant for air). 

For a transient solution the principle of conservation of mass states that 

=  +

j

j i i

i F F

dt

dm , (3) 

where 

mi = mass of air in zone i, 

Fj,i = airflow rate [kg/s] between zones j and zone i: positive values indicate flows from j to 

i and negative values indicate flows from i to j, and 

Fi = non-flow processes that could add or remove significant quantities of air from the 

zone. 

Such non-flow processes are not considered in CONTAMW and flows are evaluated by 

assuming quasi-steady conditions, dmi/dt = 0, leads to: 

0  , = jFj i (4) 
THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS

116

5.3.2 Solving the Equations 

The steady-state airflow analysis for multiple zones requires the simultaneous solution of 

equation (4) for all zones. Since the function in equation (1) may be, and usually is, nonlinear, a 

method is needed for the solution of simultaneous nonlinear algebraic equations. The NewtonRaphson (N-R) method [Conte and de Boor 1972 p 86] solves the nonlinear problem by an 

iteration of the solutions of linear equations. In the N-R method a new estimate of the vector of 

all zone pressures, {P}*

, is computed from the current estimate of pressures, {P}, by 

{} {} {} P = P − C ∗ (5) 

where the correction vector, {C}, is computed by the matrix relationship 

[ ] J {} {} C = B (6) 

where {B} is a column vector with each element given by 

= 

j

Bi Fj,i (7) 

and [J] is the square (i.e. N by N for a network of N zones) Jacobian matrix whose elements are 

given by 

 ∂

∂ = i j

j i

i j P

F ,

, J (8) 

In equations (7) and (8) Fj,i and Fj,i/Pj are evaluated using the current estimate of pressure {P}. 

The CONTAMW program contains subroutines for each airflow element which return the mass 

flow rates and the partial derivative values for a given pressure difference input. 

Equation (6) represents a set of linear equations which must be set up and solved for each 

iteration until a convergent solution of the set of zone pressures is achieved. In its full form [J] 

requires computer memory for N2

 values, and a standard Gauss elimination solution has 

execution time proportional to N3

. Sparse matrix methods can be used to reduce both the storage 

and execution time requirements. A skyline solution process following the method presented in 

[Dhatt 1984] was chosen. This method can be used to solve equations with symmetric or 

nonsymmetrical matrices. It stores no zero values above the highest nonzero element in the 

columns above the diagonal and no zero values to the left of the first nonzero value in each row 

below the diagonal. In this case the Jacobian matrix is symmetric. 

Analysis of the element models will show that 

+

= j iJi,i Ji, j (9) 

This condition allows a solution without pivoting, although scaling may be useful. Note that the 

degree of sparsity of the Jacobian matrix after factoring is dependent on the ordering of the 

zones. Ordering can be improved by various algorithms or rules-of-thumb. In AIRNET it was 

easy to define an airflow network which had no unique solution. The CONTAMW user interface 

insures the correct interconnection the airflow elements in the network. 
 THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS 

117

CONTAMW allows zones with either known or unknown pressures. The constant pressure zones 

are included in the system of equations and equation (6) is processed so as to not change those 

zone pressures. This gives flexibility in defining the airflow network while maintaining the 

symmetric set of equations. A sufficient condition for the Jacobian to be nonsingular [Axley 

1987] is that all of the unknown pressure zones be linked, either directly or indirectly, by 

pressure dependent flow paths to a constant pressure zone. In CONTAMW the ambient (or 

outdoor) air is treated as a constant pressure zone. The ambient zone pressure is assumed to be 

zero for the flow calculation causing the computed zone pressures to be values relative to the true 

ambient pressure and helping to maintain numerical significance in calculating ∆P. 

Conservation of mass at each zone provides the convergence criterion for the N-R iterations. 

That is, when equation (4) is satisfied for all zones for the current system pressure estimate, the 

solution has converged. Sufficient accuracy is attained by testing for relative convergence at each 

zone: 

< ε





j j i

j j i

F

F

,

,

(10) 

with a test (Fj,i< ε1) to prevent division by zero. The magnitude of ε can be established by 

considering the use of the calculated airflows, such as in an energy balance. In any case, roundoff errors may prevent perfect convergence (ε = 0). 

Numerical tests of the N-R method solution indicated occasional instances of very slow 

convergence as the iterations almost oscillate between two different sets of values. In AIRNET, 

this was handled by a Steffensen acceleration process. More recent tests by the author and by 

Wray [Wray 1993] indicate that the use of a simpler constant under-relaxation coefficient 

produces a faster, reliable convergence acceleration process. Equation (5) for the iteration 

process becomes 

{} {} {} P = P −ω C * (11) 

where ω is the relaxation coefficient. A relaxation coefficient of 0.75 has been found to be usable 

for a broad range of airflow networks. This value is not a true optimum but appears to work quite 

well without the computational cost of finding the theoretically optimum value. 

When convergence is progressing rapidly, under-relaxation (ω < 1) slows convergence compared 

to no relaxation. To prevent this a global convergence value is computed: 



  =

i j j i

i j j i

F

F

,

,

γ (12) 

When γ

*

 < α γ, ω is set to 1. Currently CONTAMW uses α = 30%. This often reduces the 

number of iterations. 

Newton's method requires an initial set of values for the zone pressures. These may be obtained 

by including in each airflow element model a linear approximation relating the flow to the 

pressure drop: 
THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS

118

( ) j i j i j i Pj Pi F , = c , + b , − (13) 

Conservation of mass at each zone leads to a set of linear equations of the form 

[ ] A {} {} P = B (14) 

Matrix [A] in equation (14) has the same sparsity pattern as [J] in equation (6) allowing use of 

the same sparse matrix solution process for both equations. This initialization handles stack 

effects very well and tends to establish the proper directions for the flows. The linear approximation is conveniently provided by the laminar regime of the element models used by 

CONTAMW. When solving a set of similar problems, as when approximating a transient 

solution by successive steady-state solutions, it tends to be preferable to use the previous solution 

for the zone pressures as the initial values for the new problem. 

5.3.3 Airflow Elements 

Infiltration is the result of air flowing through openings, large and small, intentional and 

accidental, in the building envelope. Simulation programs require a mathematical model of the 

flow characteristics of the openings. For a general introduction see Chapter 25 of [ASHRAE 

1997] and section 2.2 of [Feustel 1990]. 

Flow within each airflow element is assumed to be governed by Bernoulli's equation: 

( ) 1 2

2

2

2

2

1

1 2 2 g z z

V P V P P + − 













 − + 













 ∆ = + ρ ρ ρ (15) 

where 

∆P = total pressure drop between points 1 and 2 

P1, P2 = entry and exit static pressures 

V1, V2 = entry and exit velocities 

ρ = air density 

g = acceleration of gravity (9.81 m/s2) 

z1, z2 = entry and exit elevations. 

The following parameters apply to the zones: pressure, temperature (to compute density and 

viscosity), and elevation. The zone elevation values are used to determine stack effect pressures. 

When the zone represents a room, the airflow elements may connect with the room at other than 

its reference elevation. The hydrostatic equation is used to relate the pressure difference across a 

flow element to the elevations of the element ends and the zone elevations, assuming the air in 

the room is at constant temperature. Pressure terms can be rearranged and a possible wind 

pressure for building envelope openings added to give 

∆P = Pj − Pi + PS + PW (16) 

where 

Pi, Pj = total pressures at zones i and j 

PS = pressure difference due to density and elevation differences, and 

PW = pressure difference due to wind. 
 THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS 

119

Equation (16) establishes a sign convention for direction of flow: positive is from zone j to zone 

i. Since the airflow elements will be described by a relationship of the form w = f(∆P), the partial 

derivatives needed for [J] in equation (8) are related by w/Pj = -w/Pi which establishes the 

relation in equation (9). Many forms of airflow elements are available in CONTAMW. 

5.3.3.1 Powerlaw Flow Elements 

Most infiltration models are based on the following empirical (powerlaw) relationship between 

the flow and the pressure difference across a crack or opening in the building envelope: 

( )n Q = C ∆P (17) 

The volumetric flow rate, Q [m3/s], is a simple function of the pressure drop, ∆P [Pa], across the 

opening. A common variation of the powerlaw equation is: 

( )n F = C ∆P (18) 

where the mass flow rate, F [kg/s], is a simple function of the pressure drop. A third variation is 

related to the orifice equation: 

ρ

P Q Cd A ∆ = 2

(19) 

where 

Cd = discharge coefficient, and 

A = orifice opening area. 

Theoretically, the value of the flow exponent should lie between 0.5 and 1.0. Large openings are 

characterized by values very close to 0.5, while values near 0.65 have been found for small 

crack-like openings. 

The primary advantage of equations (17-19) for describing airflow components is the simple 

calculation of the partial derivatives for the Newton's method solution of the simultaneous 

equations: 

P

nF

P

F j i

j

j i

∆ = ∂

∂ , , and

P

nF

P

F j i

i

j i

∆

− = ∂

∂ , , (20) 

The sign in equation (20) will agree with the sign of F. However, there is also a problem with 

equations (20): the derivatives become unbounded as the pressure drop (and the flow) go to zero. 

A simple way to avoid this problem is suggested by what physically happens at low flow rates: 

the physical character of the flow (and the form of the equation) changes. The flow goes from 

turbulent to laminar. Equations (17-19) can be replaced by 

μ

C ρ P

F k ∆ = (21) 

where 

Ck = laminar flow coefficient, and 

μ = viscosity. 
THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS

120

The partial derivatives are simple constants: 

μ

C P

P

F k

j

j i = ∂

∂ , and

μ

k ρ

i

j i C

P

F − = ∂

∂ , (22) 

The origin of this laminar relationship is shown by the duct equations in the next section. This 

technique has been independently discovered and used by several researchers [Axley 1987] and 

[Isaacs 1980]. Although there is physical reason for using equation (21) at low pressure drops, its 

purpose here is to assure convergence of the equations when ∆P approaches zero for one of the 

many flow paths in a complex network, instead of accurately representing airflows which are too 

small to be of interest. Because the linear flow expression is not used as a true flow model but as 

a mathematical artifice, it is not necessary to adjust its flow coefficient. Given the uncertainty in 

estimating the temperature of the air as it flows through an opening, especially a crack, this 

additional detail is of debatable usefulness. 

The CONTAMW functions for powerlaw elements calculate flows using both the laminar and 

the turbulent models and select the method giving the smaller magnitude flow. There is a 

discontinuity in the derivative of the F(∆P) curve where the two equations intersect. This 

discontinuity is a violation of one of the sufficient conditions for convergence of Newton's 

method [Conte and de Boor 1972, p 86]. However, numerical tests conducted by the author for 

flows at that point using a small airflow network have shown no convergence problem. 

Temperature Dependence 

It is useful to think of the coefficient C as a simple constant, Cα, evaluated at a particular set of 

conditions (μ0, ρ0 and ν0=μ0/ρ0) multiplied by a correction factor to account for actual air 

properties. Equations (17-19) are converted to a common form and summarized below with their 

appropriate temperature correction factors. 

∆P > 0 ∆P < 0 Correction Factor 

( )n Fj,i = KaCa ρ j ∆P ( )n Fj,i = −KaCa ρ i − ∆P ( )( )2 1 / / − = n

o

n

a o K ρ ρ v v

( )n Fj,i = KbCb ρ j ∆P ( )n Fj,i = −KbCb ρ i − ∆P ( )( ) 1/ 2 2 1

0 / / − − = no

n

b K ρ ρ v v (23)

( )n Fj,i = KcCc ∆P ( )n Fj,i = −KcCc − ∆P ( )( ) 1 2 1 / / − − = n

o

n

c o K ρ ρ v v

CONTAMW uses the following formulae for computing ρ and ν: 

ρ = P / (287.055 T) 

μ = 3.714310-6 + 4.928610-8 T

ν = μ / ρ

Using reference conditions of standard atmospheric pressure and 20 °C gives ρo = 1.2041 kg/m3

and νo = 1.508310-5 m2

/s. 
 THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS 

121

Fitting Powerlaw Coefficients 

Experimental data can be used to determine the coefficients in the orifice form of the powerlaw 

equation: 

= ± 0 () ( ) ± ∆ b =1 n F Cb ρ P K (24) 

If n is known or can be assumed, Cb can be computed from the inverse of equation (24) 

( ) b n P

F C

∆ = ρ 0

(25) 

When two points (F1, ∆P1) and (F2, ∆P2), are known, n can be computed from: 

() ()

()() 1 2

1 2

ln ln

ln ln

P P

F F

n

∆ − ∆

− = (26) 

with Cb then computed from equation (25). 

Leakage Areas 

The powerlaw model can be used with the component leakage area formulation which has been 

used to characterize openings for infiltration calculations [ASHRAE 1997, pp 25.18]. The 

leakage area is based on a series of pressurization tests where the airflow rate is measured at a 

series of pressure differences ranging from about 10 Pa to 75 Pa. The effective leakage area is 

based on a rearrangement of equation (19) 

d

r r

C

Q P

L

∆ = ρ / 2

(27) 

where 

L = equivalent or effective leakage area [m2], 

∆Pr = reference pressure difference [Pa], 

Qr = predicted airflow rate at ∆Pr (from curve fit to pressurization test data) [m3/s], and 

Cd = discharge coefficient. 

There are two common sets of reference conditions: 

Cd = 1.0 and ∆Pr = 4 Pa 

 or 

Cd = 0.6 and ∆Pr = 10 Pa. 

A leakage area can be converted to the flow coefficient in the orifice equation (19) by 

( ) n Cb LCd Pr

− = ∆ 1 / 2 2 (28) 

This equation requires a value for n. If it is not reported with the test results, a value between 0.6 

and 0.7 is reasonable. 
THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS

122

Stairwells 

A stairwell will normally be modeled as a vertical series of zones connected by low resistance 

openings through the floors. The CONTAMW model for airflow in stairwells is based on a fit to 

experimental data [Achakji and Tamura 1988]. They expressed the airflow resistance per floor as 

an effective area Ae in the orifice equation (19) with a 0.6 discharge coefficient. The effective 

area is expressed in terms of the area of the shaft AS, the distance between floors h, the density of 

people on the stairs d, and whether the treads are open or closed. A large number of people on 

the stairs, as in an evacuation scenario, influences the flow resistance. The experiment used 

densities of 0, 1, and 2 persons/m5. For open treads the effective area is approximately 

A A ( ) h ( d ) e ≈ s 0.089 1.0 − 0.14 (29) 

and for closed treads 

A A ( ) h ( d ) e ≈ s 0.083 1.0 − 0.24 (30) 

The coefficients for the powerlaw equation are 

n Co Ae = 0.5 and = 0.6 ⋅ 2 ⋅ (31) 

Cracks 

A relationship for flow through cracks that can be converted directly into a powerlaw airflow 

element is presented in [Clarke 1985, p 204] as: 

Q = ka( ) ∆P (32) 

where 

n = 0.5 + 0.5exp( ) −W / 2 , (33) 

and 

( )n k = 0.0097 ⋅ 0.0092 (34) 

with 

W = crack width (mm), and 

a = crack length (m). 

Therefore, n is in equation (20c) given by (33) and 

( )∗ Cb = ρ 0 a 0.0097 0.0092 (35) 
 THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS 

123

5.3.3.2 Quadratic Flow Elements 

Baker, Sharples, and Ward [Baker 1987] indicate that infiltration openings can be more 

accurately modeled by a quadratic relationship of the form 

Q, ∆P > 0 Q, ∆P < 0

2 ∆P = AQ + BQ 2 ∆P = AQ − BQ (36)

This form can be used as an airflow element by solving the quadratic equation for F (= ρQ). 

Letting a = A/ρ and b = B/ρ

2

 allows equations (36) to be rewritten as 

2 2 ∆P = aF + bF and ∆P = aF − bF (37) 

These quadratic equations solve as 

b

a a b P and F

b

a b P a F

2

4

2

4 2 2 − − ∆ = + ∆ − = (38) 

with the partial derivatives given by 

j i i

j i

j i i

j i

P a b F

F

and

P a b F

F

,

,

,

,

2

1

2

1

+

− = ∂

∂

+ = ∂

∂

 (39) 

Equations (38) require that b be nonzero to prevent a division by zero and equations (39) requires 

that a be nonzero to prevent a division by zero as F goes to zero. There are contrary opinions that 

the powerlaw relationship is better. 

Temperature Dependence 

It is useful to think of the coefficients a and b as simple constants evaluated at a particular set of 

conditions (μ0, ρ0 and ν0=μ0/ρ0) multiplied by correction factors to account for actual air 

properties as was done for the powerlaw equations. That is 

0

0

0

0

A A and a a













 = 













 = ν

ν

ν

ν

 (40) 

and 

0

0 0 B B and b b













 = 













 = ρ

ρ

ρ

ρ (41) 

Note that ρ0/ρ = T/T0 for a perfect gas of constant composition. 
THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS

124

Fitting Quadratic Coefficients 

The quadratic coefficients can also be computed from measured flow and pressure data. Given 

two points (F1, ∆P1) and (F2, ∆P2), the values of a0 and b0 are: 

1 2

2

2

1

1

0 F F

F

P

F

P

b −















 ∆ − ∆

= (42) 

and 

0 1

1

1

0 b F

F

P

a − ∆ = (43) 

The main advantage of the quadratic model over the powerlaw model is computation speed 

achieved by avoiding the slow power function. (Tests have shown pow(x) four to eight times 

slower than sqrt(x). This performance is hardware and software dependent.) It must still be 

determined which model is the most accurate representation for a particular airflow element. For 

example, it has been found that the powerlaw model is a better approximation for smooth ducts 

while the quadratic model is a better approximation for rough ducts. However, for very large 

openings the derivatives (39) can become quite large leading to slow convergence of the 

simultaneous mass balance equations. 

Crack Description 

Theoretical relationships have been developed between the coefficients A and B of the quadratic 

airflow element model and the physical characteristics of the openings [Baker 1987]. These are 

2 2

0 0

3

0 0 A =12μ z / Ld and B = ρ C / 2d L (44) 

where 

μ = viscosity, 

ρ = density, 

z = distance along the direction of flow, 

d = crack width, 

L = crack length, and 

C = 1.5 + number of bends in the flow path. 

For the mass flow form of the equations (37) the coefficients are 

2 2

0 0

3

0 0 0 a =12μ z / ρ Ld and b = C / 2ρ d L (45) 
 THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS 

125

5.3.3.3 Ducts 

The theory of flows in ducts (and pipes) is well established and summarized in chapter 32 of the 

1997 ASHRAE Handbook of Fundamentals and treated more extensively in [Blevins 1984] in a 

chapter on pipe and duct flow. See the Duct Fitting Database [ASHRAE 1994] for extensive 

data on dynamic losses in duct fittings. Analysis is based on Bernoulli's equation and its 

assumptions. The friction losses in a section of duct or pipe are given by 

2

2 V

D

L P f f

ρ ∆ = (46) 

where 

f = friction factor, 

L = duct length, and 

D = hydraulic diameter. 

The dynamic losses due to fittings and so forth are given by 

2

2 V Pd Cd

ρ ∆ = (47) 

where Cd = dynamic loss coefficient. Total pressure losses are given by 

∆P = ∆Pf +∆Pd (48) 

Since F = ρVA, where A is the cross section (or flow) area, 

+

∆ = D Cd fLA P F

/

2 2 ρ (49) 

The friction factor can be computed using the nonlinear Colebrook equation [ASHRAE 1997, p 

2.9, eqn. 29b]: 

( ) 















⋅ ⋅ = + ⋅ − ⋅ +D f

D

f Re /

9.3 1.44 2 log / 2 log 1 1

ε

ε (50) 

where 

ε = roughness dimension, and 

Re = Reynolds number = ρVD/μ = FD/μA. 

This nonlinear equation may be readily solved using the following iterative expression derived 

from equation (50) by Newton's method: 

( )

γβ ( ) β

α γ β

g

g g g g

+ +

− + + = − ∗

1 / 1

ln 1

 (51) 
THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS

126

where 

g = f

 -1/2, 

α = 1.14 - γ ln(ε/D), 

fl = 9.3/(Reε/D), and 

γ = 2log(e) = 0.868589. 

The convergent solution is achieved in 2 or 3 iterations of equation (51) using g = α as a starting 

value. If the value of g has been saved from the previous time it was computed for a particular 

duct element, and the flow rate has not changed greatly, only one iteration of equation (51) will 

be needed to compute the friction factor. 

The exact derivatives of equation (49) are difficult to compute, so CONTAMW uses a secant 

approximation. The derivatives suffer the standard problem of powerlaw equations, i.e., they go 

undefined as ∆P approaches zero. This is solved in CONTAMW by the linear approximation 

(21) with the coefficient computed to give the same flow as equation (49) at the user specified 

transition Reynolds number (default = 2000). A more detailed description of the flow in the 

laminar region could be developed, but that would probably exceed the level of detail with which 

the rest of the problem is described in CONTAMW. 

5.3.3.4 Fans 

This section describes the theory of how forced flow elements are modeled with CONTAMW. 

Forced flow elements include constant flow fans and variable flow fans. Constant flow fans 

include both constant volume and constant mass flow. Variable flow fans are modeled based on 

the input of a fan performance curve that relates pressure drop to airflow through the fan flow 

element. 

Constant Flow Fans 

One particularly simple but useful airflow element sets a constant flow between two nodes. Since 

the flow is constant, the partial derivatives of flow with respect to the node pressures must be 

zero. The constant flow element does not contribute to the Jacobian, [A], but it does add to the 

right side vector, {B}. 

Constant flow elements do not mathematically link the pressures of the adjacent nodes. It is 

necessary that all node in the network be linked to constant pressure nodes in order to have a 

unique solution. Violation of this restriction will produce a division by zero somewhere in the 

solution of the equations. Consider the following simple network: 

 !════C1════!════F1════!════C2════!════F2════!════C3════!

 P1 P2 P3 P4 P5 P6

where P1 and P6 are known pressures, and F1 and F2 are known flows. Since the flow through C2

is determined by P3 - P4, and no other flow is related to those pressures, there are not enough 

equations to determine P3 and P4 uniquely. This is a mathematical expression of the fact that it is 

possible for F1 and F2 to be assigned different flows, which produces a physically impossible 

condition. 

CONTAMW provides two constant flow elements: one for constant mass flow and one for 

constant volumetric flow. 
 THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS 

127

Variable Flow Fans 

The theory of flows induced by fans is summarized in Chapter 18 of the 1996 ASHRAE HVAC 

Systems and Equipment Handbook [ASHRAE 1996]. More extensive treatment is given in 

[Osborne 1977]. Fan performance is normally characterized by a performance curve which 

relates the total pressure rise to the flow rate for a given fan speed and air density. Conversion to 

another fan speed or density is done with the fan laws. 

0 0 Q / Q = N / N (52) 

or 

0 0 0 F / F = Nρ / N ρ (53) 

and 

0

2

0

2 P / P = N ρ / N ρ (54) 

where 

Q = volume flow rate, 

F = mass flow rate, 

P = total pressure rise, 

ρ = density, 

N = rotational speed, and 

subscript 0 indicates values at the rating conditions for the fan. 

These laws are valid if all flow conditions at the two speeds are similar. In particular, they will 

not apply at very low flows where fully turbulent conditions have not been developed. 

In CONTAMW the fan performance curve is represented by a cubic polynomial: 

3

3

2 P = a0 + a1F + a2F + a F (55) 

with 

2

1 2 3 a 2a F 3a F

dF

dP P′ = = + + (56) 

The polynomial coefficients are developed with air density and fan speed at the rating 

conditions. Therefore, when N and ρ are not at the rating conditions, convert the actual pressure 

rise P to P0. 

ρ ρ2

0

2

0 0 P = PN / N (57) 

Solve (55) for F0 and (56) for P0. Convert these values to current conditions. 

0 0 0 F = F Nρ / N ρ (58) 

and 

0 0 P′ = P N / N (59) 
THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS

128

The derivative for flow with respect to pressure drop is given by 

dP P

dF

′ = − 1

(60) 

There are two important factors to note on the shape of the fan performance curve. First, it is 

described by a relationship of the form P(F) instead of F(P) which would be more appropriate 

for the calculation of flow and partial derivatives for the Jacobian. The basic shape of the 

performance curve cannot be well represented by a simple polynomial with P as the independent 

variable. CONTAMW uses an analytic solution of the cubic polynomial (55) to determine F as a 

function of P. 

Second, it is common for the performance curve to contain points of contraflecture (where P = 

0) creating up to three different flow rates at certain values of fan pressure rise. This causes 

difficulty in solving for the flow rate and has points where dF/dP goes to infinity. However, it is 

usually not recommended that the fan operate in the region of the contraflecture points. 

Therefore, the fan can be modeled with a performance curve that does include the contraflecture 

so long as you make sure that the air distribution system has not operated in that region. 

You can identify the points of contraflecture from the coefficients of the polynomial. Solving 

equation (55) for F gives: 

3

1 3

2

2 2

6

2 4 12

a

a a a a

F − ± − = (61) 

4 12 1 3 2 a2 > a a There are two real points of contraflecture 

4 12 1 3 2 a2 = a a There is a point of inflection which still has the derivative 

problem 

4 12 1 3 2 a2 < a a The fan performance curve is monotonic and well-behaved for 

computing the derivatives for the Jacobian. 
 THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS 

129

5.3.3.5 Doorways (Large Openings) 

The powerlaw and quadratic models allow flow in only one direction at a time. Flows through 

large openings (e.g. doorways) tend to be more complex with the possibility of flows in opposite 

directions in different parts of the opening. The temperature and resulting density differences 

between two rooms may mean that the stack effect causes a positive pressure difference at the 

top of the doorway and a negative pressure difference at the bottom (or vice versa) allowing a 

two-way flow in the opening. A summary of research on heat transfer through doorways is 

presented in [Barakat 1987]. Most research has attempted to develop dimensionless correlations 

(using Nusselt, Prandlt, and Grashoff numbers) of the form 

b Nd C GrD / Pr = ⋅ (62)

where b is approximately 0.5 and C lies between 0.22 and 0.33 depending on the temperature 

difference used for the correlation. It has been shown that such a heat transfer is equivalent to an 

airflow which can be modeled by powerlaw elements by dividing the total opening into several 

smaller openings having the same total area but configured to properly account for the magnitude 

and direction of airflows at different heights in the opening. 

An alternative approach is to create a single airflow element which accounts for the flow over the 

entire opening. A simple theory which estimates the stack induced airflow through a large 

opening in a vertical partition is given in [Brown and Solvason 1962]. This model of a doorway 

tends to be faster that the multiple opening approach. However, it also complicates the assembly 

process for the Jacobian matrix because one or two flows may exist. More importantly, 

development of the doorway element model requires knowledge of the vertical temperature 

profile used in the node model (here assumed to be constant) in order to compute the pressure 

difference as a function of height across the opening. This requirement compromises the 

independence of the modularity of airflow network program. 

Multiple Opening Model 

By assuming that the air density in each room is constant, the hydrostatic equation is used to 

relate pressures at various heights in each room: 

( ) 0 0 P P g h h j = j + ρ j j − and ( ) P0i = Pi + ρ i g hi − h0 (63) 

P ( ) y P gy j = 0 j − ρ j and P ( ) y P gy i = 0i − ρ i (64) 

where 

P0j, P0i = pressure in zones j and i at y = 0, the reference elevation of the opening, 

ρj, ρi = air densities of zones j and i, 

Pj, Pi = reference pressures of zones j and i, 

hj, hi = reference elevations of zones j and i, and 

h0 = elevation of the center of the opening. 
THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS

130

Following [Brown and Solvason 1962] it is assumed that the velocity of the airflow as a function 

of height is given by the orifice equation: 

( ) ( ) () () 1/ 2

2















 − = ρ

P y P y V y C j i

d (65) 

where 

Cd = discharge coefficient, and 

ρ = density of the air going through the opening. 

The opening, H high by W wide, may be divided into multiple openings each representing a thin 

horizontal strip ∆y high and W wide. The mass flow through each strip would be 

F C P W y y = d 2ρ∆ ∆ (66) 

The coefficient for the powerlaw model (19) for each sub-opening is thus given by 

C C W y 0 = 2 d ∆ (67) 

Two Opening Model 

An approximate model can be constructed by considering an opening between two zones which 

have no flow paths to any other zones. Then the flow in each direction must be equal and P0j = 

P0i. Integration of equation (65) from y=0 to y=H/2 using (64) to compute ∆P gives the flow 

through the top half of the opening. 



=

=

= = ∆

/ 2

0

3

3

y H

y

d W g H

C

w ρVWdy ρ ρ (68) 

This is equivalent to a simple powerlaw model with 





 



 = 2 0 2 W H C Cd (69) 

(a simple orifice with one half the total opening area) placed at an elevation of y = 2H/9. The two 

opening model is completed with an identical opening at y = -2H/9 elevation allowing an equal 

flow in the opposite direction. Since the orifice is being modeled with simple orifice openings, 

any additional pressure drop between the zones due to other forces is included in the two opening 

model. The model becomes less accurate as the neutral plane shifts from the center of the 

opening. 
 THEORETICAL BACKGROUND ñ AIRFLOW ANALYSIS 

131

Single Opening Model 

A third approach is to create a single airflow element which accounts for the flow over the entire 

opening. Begin by defining the neutral height, Y, where the velocity of the air is zero. From 

equation (65) this must occur when Pj(y) = Pi(y). From equations (64) this must be 

( ) ( )















−

−

−

− =

i j

i oj

j i

j oi

g

P P

g

P P

Y

ρ ρ ρ ρ

0 0 (70) 

If |Y| < H/2, there is two-way airflow through the opening. If ρj = ρi, the neutral height cannot be 

computed, but, since there is no possibility of two-way flow, the opening can be considered a 

simple orifice opening. 

Define ∆ρ ≡ ρj - ρi and a transformed height coordinate z ≡ y - Y. Then the pressure difference 

across the opening is given by 

Pj() () z − Pi z = −gz∆ρ (71) 

The mass flow through the opening above the neutral height is given by 

F W V dz m j or i

H z

z

a = m = 

= −Υ

=

2

0

ρ (72) 

and the mass flow below the neutral height by 

F W V dz m j or i

x

H x

b = m = 

=

= −Υ

0

2

ρ (73) 

Whether the subscript m should be j or i depends on the direction of flow. Integration of 

equations (72) and (73) gives several different solutions for the airflow depending on the value 

of Y and the sign of ∆ρ. Defining: 

( )

3 / 2

3 / 2

1/ 2

2

, 2

2 , 3

2

Y H f

Y H f

G W C g P

b

a

d

≡ +

≡ −

≡ ∆

(74) 

gives the following equations for flows. 

Case ∆ρ > 0 ∆ρ < 0

Y ≤ −H / 2 i z b F = −G ρ f − f j z b F = G ρ f − f (75)

Y ≥ H / 2 j z b F = G ρ f − f i z b F = −G ρ f − f (76)

a j a F = −G ρ f a j a F = G ρ f (77)

− H / 2 < Y < H / 2

b j b F = G ρ f b j b F = −G ρ f (78)
REFERENCES

132

6 References 

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ASHRAE 1989. ASHRAE Handbook - 1989 Fundamentals, Atlanta GA. 

ASHRAE 1993. ASHRAE Handbook - 1993 Fundamentals, Atlanta GA. 

ASHRAE 1994. Duct Fitting Database, Atlanta GA. 

ASHRAE 1996. ASHRAE Handbook - HVAC Systems and Equipment, Atlanta GA. 

ASHRAE 1997. ASHRAE Handbook - 1997 Fundamentals, Atlanta GA. 

ASTM 1999. Standard Test Method for Determining Air Leakage Rate by Fan Pressurization. 

Standard E779-99. American Society for Testing and Materials, West Conshohocken, PA. 

Axley, J.W. 1987. "Indoor Air Quality Modeling Phase II Report", NBSIR 87-3661, National 

Bureau of Standards (U.S.). 

Axley, J.W. 1988. "Progress Toward a General Analytical Method for Predicting Indoor Air 

Pollution in Buildings, Indoor Air Quality Modeling Phase III Report", NBSIR 88-3814, 

National Bureau of Standards (U.S.). 

Axley, J.W. 1991. "Adsorption Modeling for Building Contaminant Dispersal Analysis", Indoor 

Air, 1:147-171. 

Axley, J.W. 1995. "New Mass Transport Elements and Components for the NIST IAQ Model", 

NIST GCR 95-676, National Institute of Standards and Technology(U.S.). 

Baker, P.H., S. Sharples, & I.C. Ward. 1987. "Air Flow through Cracks," Building and 

Environment, Pergamon, 22(4): 293-304. 

Barakat, S.A. 1987. "Inter-zone Convective Heat Transfer in Buildings: a Review," ASME 

Journal of Solar Engineering, Vol. 109, May. 

Blevins, R.D. 1984. Applied Fluid Dynamics Handbook, New York: Van Nostrand Reinhold. 

Brown, W.G., & K.R. Solvason. 1962. "Natural Convection through Rectangular Openings in 

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859-867. 

Clarke, J.A. 1985. Energy Simulation in Building Design, Adam Hilger Ltd., Briston and Boston, 

p 204. 

Conte, S.D. and C. de Boor. 1972. Elementary Numerical Analysis, McGraw- Hill, New York 

NY. 

Dhatt, G., G. Touzot, & G. Catin. 1984. The Finite Element Method Displayed, John Wiley & 

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EPA 1989. Exposure Factors Handbook. Publication number EPA/600/8- 89/043. 

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and Buildings, Vol 18, pp 79-100. 
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133

Isaacs, L.T. & K.G. Mills. 1980. "Linear Theory Methods for Pipe Network Analysis", Journal 

of the Hydraulics Division, Proceedings ASCE, Vol. 106, pp 1191-1201. (See also author's 

closure, 1982, Vol. 108, p 153) 

Klote, J.H. 1981. "A Computer Program for Analysis of Smoke Control Systems", NBSIR 80-

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Klote, J.H. & J.A. Milke. 1992. Design of Smoke Management Systems, ASHRAE, Atlanta GA. 

Osborne, W.C., 1977. Fans, 2nd edition, Pergamon Press. 

Press, W.H., S.A. Teukolsky, W.T. Vetterling & B.P. Flannery. 1992. Numerical Recipes in C: 

the Art of Scientific Computing, Second Edition, Cambridge University Press. 

Roulet, C-A, & L. Vandaele, Airflow Patterns Within Buildings Measurement Techniques, The 

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Modeling", NISTIR 89-4072, National Institute of Standards and Technology. 

Walton, G.N., 1989b. "Airflow Network Models for Element-Based Building Airflow 

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Walton, G.N. 1997. "CONTAM96 User Manual", NISTIR 6056, National Institute of Standards 

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Wray, C.P. & G.K. Yuill. 1993. "An Evaluation of Algorithms for Analyzing Smoke Control 

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