Frame Cavity Emissivities

Software/Versions Affected:

• THERM›6
• THERM›7

There are some circumstances where the program will assign frame cavity surface emissivities based on the emissivities of the glazing system layers, rather than the emissivities of the surrounding surfaces. This problem occurs only with frame cavities using the advanced radiation model or the iso model, and is partly based on the geometry of the frame cavity as it relates to the glazing system. It is hard to predict when it will happen, and so the best way to make sure this is not happening in a particular file is to print out the Report for the file (File/Report), and examine the emissivities of all the frame cavities to see if there are any that do not seem to make sense.

If some questionable values are found, it is possible to then example the frame cavity in question (the Polygon ID is listed in the report in the first column, and that polygon can be selected in the THERM file by using the Edit/Select Special menu and then typing the Polygon ID number in the ID field). Once the problem polygon is selected, double click on each frame cavity surface and the emissivity of that surface will be displayed. In general, unless overridden by the user, these emissivities should be the emissivities of the materials the surface is touching. If these emissivities are found to be incorrect (if the problem is from this bug, the emissivities will be set to one of the glass layer emissivities, so it should be obvious if that is the problem), then the emissivity can be changed by inputting the correct value into this dialog box, and rerunning the file.