[Bldg-sim] Window Film and Building heating

Bishop, Bill bbishop at pathfinder-ea.com
Tue Nov 4 08:40:08 PST 2014

One idea is to check the timing of your heating savings. Maybe you are saving reheat energy?

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

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From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of John Aulbach
Sent: Tuesday, November 04, 2014 11:33 AM
To: bldg-sim at onebuilding.org
Subject: [Bldg-sim] Window Film and Building heating

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
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