CBS Newsletter
Fall 1997
pg. 5

THERM: Two-Dimensional Building Heat-Transfer Modeling

For more information and to download THERM, please visit our website:

The Windows and Daylighting Group's two-year-old computer program THERM 1.0 is a state-of-the-art tool for modeling two-dimensional heat-transfer effects in building components. The thermal property information THERM provides is important for the design and application of building components such as windows, walls, foundations, roofs and doors. This Microsoft Windows-based program has great potential to users such as building component manufacturers, educators, students, architects, engineers and others who are interested in assessing the heat-transfer properties of single products, product interactions, or integrated systems. THERM identifies thermal short circuits in components, allowing designers to make more effective insulation technologies and insulating designs.

THERM 1.0 uses a two-dimensional conduction heat-transfer analysis methodology based on the finite-element method, which can model the complicated geometries of building products. A graphic interface allows the user to draw the cross section to be analyzed. The user can trace imported files in DXF or bitmap format or input the product's geometry from known dimensions. The cross section is represented by a combination of polygons, with material properties defined for each polygon. The user introduces the environmental conditions to which the component is exposed by defining the boundary conditions surrounding the cross section. Once the model is created, the remaining analysis is user-transparent. Results from THERM can be viewed in terms of U-factors, isotherms, heat-flux vectors and local temperatures.

Figure 1: Greenhouse windows, such as this one, and other projecting fenestration products can now be modeled more accurately with THERM 2.0.

Figure 2: (Upper Left) Greenhouse window vertical cross-section defined with THERM 2.0. Shaded areas define a radiation enclosure; radiation view factors for all elements on the boundary are calculated. (Lower Right) Detail of the greenhouse window cross-section shown after heat transfer analysis; isotherms show constant temperature contours.

New Version Under Development

An update to THERM 1.0 is in the final stages of development. THERM 2.0 is a 32-bit application that will take advantage of new developments in personal computer operating systems. This release will include several new technical and user interface features-most significantly, a radiation view-factor algorithm. This feature increases the accuracy of calculations in cases where nonplanar surfaces at different temperatures exchange energy through radiation heat transfer. This heat-transfer mechanism is important in greenhouse windows and in hollow cavities.

THERM is a module of the WINDOW+5 program being developed at Berkeley Lab. THERM's results can be used with WINDOW's center-of-glass optical and thermal models to determine total window product U-factors and Solar Heat Gain Coefficients. These in turn will be used with the RESFEN module, which calculates total annual energy requirements in typical residences throughout the U.S.

—Dariush Arasteh

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Dariush Arasteh
Building Technologies Program

This work is supported by DOE's Office of Building Technology, State and Community Programs.

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