window replacement

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Thanks, Carol, for your quick response. I think my question might have
been too specific. My baseline model agrees to within 5% of the actual
gas and electric bills for the building. The exterior walls, especially
north and south elevations, are about 30% windows by area. By replacing
single-paned windows with double-paned, modern windows, I am expecting
about a 23% reduction in energy usage based on simple heat equation
estimations. eQuest is only returning a 5% savings. I suspect I am not
defining the replacement windows correctly, but it seems there must also
be a problem with how eQuest is calculating my heating loads through the
windows. I specified the windows' estimated percent wall area, and also
drew custom windows everywhere to match what the actual building looks
like. What is the best way to approach solving this problem?

Thanks again,
Ben

Ben Pressman's picture
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Ben,

I would first go back to your base model and examine what percentage of the building load is actually coming from the glass. Your LS-C reports will give you your peak load components, and LS-F will give you your Monthly load components - a better indicator of overall energy usage.

Keep in mind this doesn't factor in ventilation loads. You will need to look at the SS-D report to get an overall picture of the loads your system sees, and work backwards from that to get a picture of what the ventilation component is. So for example - if your LS-C shows a peak cooling load of 1000kBTU/hr and your SS-D Shows 1500 kBTU/hr, then your ventilation loads will be 500 kBTU/hr. [eQUEST users - please correct me if I'm wrong here]

So if your glass conductance + Solar is 15% f the overall load, then a 5% savings is pretty significant, however, if its 50% of the load, then there might be a problem with your model.

Hope this helps

Vikram Sami, LEED AP

Sami, Vikram's picture
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Hi Ben,

Vikram makes a good point below - you should check first check to make sure results and expectations are reasonable.

Regarding your original question: in your parametric runs you can set frame width to zero: window/basic specification/frame width. In that way, when you enter your full frame U-factor and full frame SHGC (actually I think you need to enter this as SC) you will no longer have to worry about the U-factor of the base-case frames in your parametric run. There is a lot of concern about putting in one value for U-factor and one value for SHGC. So the alternative is what Carol suggested: to import the window into eQUEST after creating it in WINDOW5 (LBNL's free window tool). The problem with that is that I don't believe that eQUEST imports frame data. So you would need to import the glass, determine the improved frame U-factor (probably around U-1.0 for TB aluminum) and set your parametric run with 2 components: 1 to change the glass, and 2 to change the frame conductance.

Hope this helps!

Cheers,

Alex Krickx

John Dossmith's picture
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Joined: 2011-09-30
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