Overview Building Sources and Sinks Human Activities Exposure and Dosimetry Model Options Results References Execute Model
In the Building screen, you define the relevant characteristics of the building. This includes defining the number of zones in the building, their volumes, and the flowrates between building zones. The Building screen provides three different methods for describing the building to be modeled: (1) Simplified Selection, (2) Define Volumes and Flows, or (3) Select Building From Database. These options offer different levels of control over the building environment, with more control requiring more complex input.
1. Simplified Selection: The Simplified Selection approach offers a simple method for defining the building environment. The building parameters are assigned based on an analysis of U.S. housing characteristics. Select the Residence Size from the choices of Large, Medium, or Small, based on respective house volumes of 2500 square feet for a Large residence, 1500 square feet for a Medium residence; and 900 square feet for a Small residence. Unless designated explicitly, the house is modeled as one zone in the simplified selection; however, under the heading Zones to be Represented Explicitly, TEM provides the option to represent a variety of zones where water uses occur (i.e., those not combined with non-water using zones). Since most of the exposure to water-borne contaminants occurs at the point of use, these zones have a significant impact on the predicted exposure. In most cases, any zones with significant water uses should be represented explicitly.
Based on the selection of residence size, the volumes of bathrooms (including the shower zone) are assigned as room areas of 80, 60, and 40 square feet for large, medium, and small houses, respectively. The volumes of the kitchen and laundry rooms are assigned room areas of 100, 80, and 60 square feet for large, medium, and small houses, respectively. Interzonal airflows are assigned based on a correlation analysis conducted by Koontz and Rector, 1995 as Q = (0.078 +0.31*ACH) * (Zone Volume).
As shown in the figure, these selections are straightforward. In this example, the medium residence size with average air infiltration characteristics is selected, that is, a 1500 square foot home with a 0.6 ACH is used.
If this simplified method does not adequately serve to represent the building environment (e.g., more than two bathrooms), the Define Volumes and Flows method described above should be considered.
2. Define Volumes and Flows: The Define Volumes and Flows approach provides a method for completely defining the building environment. Select the number of zones, the volume of each zone, and the interzonal airflows between each pair of zones. As labeled in the following figure, the steps for defining the building are:
2.1 Click on the up and down arrow to set the number of desired zones. (This does not include the outdoor zone, which is always defined as zone 0.) Note that as you modify the number of zones, the Zone Properties and Interzonal Airflows tables will expand or contract to reflect the selected number of zones.
2.2 Fill in the Zone Properties table assigning a label to each zone and the desired volume in cubic meters. Note that the labels entered in this table will be used to refer to the zones elsewhere in the model setup and results. Also note that the sum of the indoor zones is given at the top of the table.
2.3 Fill in the Interzonal Airflow Table to reflect the desired interzonal airflows and the flows in and out of the building. This table provides a number of aids to assist in balancing airflows. The cell in the upper left corner of the table indicates whether the table is balanced by displaying the word balanced or unbalanced. The row headings designate the zones from which the flow is leaving, while the column headings designate the zones to which the flows are entering. In the figure shown, the airflow leaving Zone 3 and entering Zone 2 is 30.4 cubic meters per hour.
The top row in the table provides the sum of flows entering each zone, while the first column provides the sum of flows leaving each zone. When a particular zone is balanced (i.e., the sum entering the zone is equal to the sum leaving the zone), these sums are shaded green. Unbalanced flows are indicated when the cells are shaded red. If all the cells in the first row and first column of the table are green, then the airflows for the building are balanced.
2.4 TEM provides the ability to define multiple Air Flow Regimes and to schedule the use of these flow regimes at specific times or during specific events. For example, you can define a unique set of airflows that will be used during a specific event, such as a shower. To define an additional flow regime, select the button labeled Add/Remove/Edit Flow Regime. After naming a new flow regime, an additional tab is added to the bottom of the Interzonal Airflow Table, which provides a new table creating the new flow regime. The Default Regime Schedule allows you to define the sequence and starting times at which each regime will occur. The first flow regime starts at midnight (i.e., hours=0, minutes=0). The starting time of each subsequent flow should be entered as the hour and minute of the day on a 24-hour clock. Each flow regime will remain active until the subsequent flow regime is set to begin. The Sort Rows button can be used to put the regime schedule in sequential order.
Note that on the Human Activities screen, if you choose to Sample Activity Patterns from a Database, you will be prompted to create Flow Regime Rules that specify certain flow regimes to occur when specific sampled activities occur. The Flow Regime Rules will override the Default Regime Schedule.
3. Select Building from Database
The Select Building from Database approach offers a method for selecting a building based on actual measurements from other U.S. homes. A database of time-averaged air exchange rates and interzonal airflow rates, based on measurements with perfluorocarbon tracers (PFTs), has been compiled by Versar (1990). The PFT measurement technology involves constant release and time-integrated sampling of multiple tracers, with a unique tracer assigned to each zone in a residence (zones are defined by the field team collecting the measurements). Measurements collected in more than 4,000 residences between 1982 and 1987 are summarized in this PFT database. The residences that appear in the database are not a random sample of U.S. homes; rather, they represent a compilation of homes visited in about 100 different field studies, some of which involved random sampling.
Only selected residences from the PFT database are included in TEM. The PFT database has a series of data-quality flags, and these flags were used to select only those cases thought to provide reliable data. For example, PFT measurements can result in estimated airflow rates with negative values, due to measurement uncertainty, even though negative values are physically impossible. Such cases are excluded from TEM. Conditions for each PFT measurement, such as whether exterior doors or windows were open during the measurement period, are not included in the PFT database.
The database of available houses is presented in the lower portion of the screen. Select any house from the database by clicking on the row containing the desired record. After selecting a row, a summary of the house characteristics and interzonal airflows is presented in the upper portion of the screen.
A database query tool is provided to allow you to identify the subset of records that most closely meet the desired conditions. You can execute a query by clicking on the Query Database button and adding the desired criteria to the Defined Query List. To add a criterion to the list, select the desired field, the desired operator, and the desired criterion value. Subsequently, select the Add Query button to add it to the list. For example, if you wish to consider only houses located in the state of New York, select the field "STATE", select the operator "=", enter "NY" in the value field, and then click on the Add Query button. To remove a criterion, select the string you wish to remove from the Defined Query List, and then click on the button Remove Query.
