Monday, November 10, 2008

House Model

This section describes how one uses equivalent wall results to a house model in transient building simulation programs. For the purposes of this example, a simple house design of typical construction is used as a reference, as shown below.

Successful implementation of the equivalent wall approach largely depends on the proper dimensioning of building envelope components. A wall elevation for the house shown above is depicted in below. The wall system is comprised of 2 x 4 steel stud with R-11 insulation, and contains one door and one window. Only one wall is shown here, since it is assumed that the procedure that follows can be applied to construct the remaining walls of the house.

The first step is to list the building envelope sections that exhibit transient and multidimensional effects. The sample wall elevation contains the following sections of dissimilar thermal response: wall/floor, wall/ceiling, corner wall interfaces, window header, window framing, door header and door framing. In this example, the thermal response of the door header and window header are assumed equal. Figure below distinguishes each of these zones by color, with the dimensions of the transient and three-dimensional effects as indicated in the Wall Assembly Information Sheets.

The second step is to determine the building envelope areas for each dissimilar section. As noted previously, it is important not to double-count building envelope areas. The easiest way to avoid this problem is to first calculate the areas of the building envelope that contain three-dimensional effects. These values can then be subtracted from the total building envelope area to determine the clear wall area.

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