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Differences in results between EnergyPlus 9.3 and 9.4

asked 2021-06-30 06:34:35 -0500

Bárbara Torregrosa's avatar

updated 2021-06-30 07:42:20 -0500

I found significant differences in the results of energy use of a simple building between EnergyPlus 9.3 and 9.4. The differences are related with the windows, since the same building without windows shows negligible differences between versions. I use the WindowMaterial:SimpleGlazingSystem, so I guess the differences come from this issue (

My building is just a 10x10m square containing an Ideal Loads Air System. The "District Heating energy use" decreases from version 9.3 to 9.4 between 0.7% and 8.8% depending on the size, orientation and shading of the windows. While the "District Cooling energy use" increases between 0.8 and 3.8%. Differences are bigger when the building "gets more sun" (= south-facing windows, larger windows, less shading). When I add a WindowShadingControl with the option ExteriorShade, there are practically no differences in the results, as in the case without windows.

My question is: is this the expected behavior of the WindowMaterial:SimpleGlazingSystem after the fix #8001? Or should I change any parameters related to the windows to keep them working as before? I used the transition tool to get the idf files for both versions 9.3 and 9.4, from version 9.1 (I was actually comparing v9.1 with v9.5 but I located the relevant differences between versions 9.3 and 9.4).

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answered 2021-06-30 09:23:26 -0500

This is expected as, prior to the fix, the SimpleGlazingSystem could have negative absorptance at certain angles of incidence. For an Ideal Loads Air System, I would only expect to see heating loads decrease because of the fix (which is consistent with what you are seeing). There is now a check in the source code that ensures the calculated absorptance is never outside of 0.0-1.0, so you couldn't change the parameters to give consistent results even if you wanted to.

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Asked: 2021-06-30 06:34:35 -0500

Seen: 151 times

Last updated: Jul 01 '21