I have several projects coming up dealing with window film savings on large glass area buildings. I need a primer to some of the results i am seeing.

Logically, if you install window film on glass, you will reduce the cooling load in that space, but would expect the heating load to rise. This, by the way, is in the temperate So Ca climate.

In BOTH cases, my improvement with window film does a killer job in reducing cooling. But is also saves about 7% heating !! I am going from a Shading Coefficient (SC) of 0.75 to an SC of 0.36.

Experiment. I reduced the SC to 0.01. AS boatload of cooling, but a 22% INCREASE in heating.

Then I tried a SC of 0.18. A median between the other two runs in space cooling savings, but now virtually NO change in space heating.

Why is there a balance point in heating? System is VAV w/RH.

This BTW was double glass.

I tried another building with single glass curtain wall. SC = 0.29. 3% reduction in cooling. Tried SC = 0.14. -1$ in heating. System is DDVAV.

Can ANYONE enlighten me as to what is going on?

John R. Aulbach, PE