[Bldg-sim] Building envelope average energy demands

Goldwasser, David David.Goldwasser at nrel.gov
Fri Aug 26 14:50:29 PDT 2011

In a way it is really the demand the thermostat setpoints put on heating  and cooling that along with lighting and equipment loads are responsible for all of the energy. Of course the role that the envelope and lighting/plug loads, people and ventilation play in altering a zones temperate. Take some responsibility, but as you suggest, you can’t just assign the energy to one building component or another. I tired that as well, and it isn’t as easy as splitting up end uses.

From: John Eurek [mailto:redmodeler at yahoo.com]
Sent: Friday, August 26, 2011 3:25 PM
To: Goldwasser, David; Giulio Castorina; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Building envelope average energy demands


I did the same thing with one of my buildings.  I made "perfect insulation" which in Trace is simple deleting all the walls.  The result was an increase of energy use.  Since the internal loads were so high, too much insulation wouldn't allow the heat out.  (I compare it to a wrestler running around in plastic trying to cut weight.  It may be winter, but you get real hot real quick.)

So in the case of the super insulation increasing the energy use, what % of the total energy usage can I contribute to the skin load?  Would it be a negative percentage?

From: "Goldwasser, David" <David.Goldwasser at nrel.gov>
To: John Eurek <redmodeler at yahoo.com>; Giulio Castorina <artitecture at gmail.com>; "bldg-sim at lists.onebuilding.org" <bldg-sim at lists.onebuilding.org>
Sent: Friday, August 26, 2011 4:06 PM
Subject: RE: [Bldg-sim] Building envelope average energy demands

Maybe not quite what you are looking for, but we have a video  tutorial showing an envelope elimination parametric. In this example we used a full service restaurant but you can do this with any model. The approach is to run a baseline simulation and then to switch all exterior and ground exposed surfaces to an adiabatic boundary condition. Next remove all fenestration surfaces. Then re-run the model. Due to the load driven nature of this project the maximum savings through envelope improvements was just over 3%, but maybe would be 15-20% for an office. Of course it depends where the project is located; the harsher the climate, the more potential savings through envelope improvements. And it depends on the quality of the envelope that you use as a starting point; building activity, and mechanical system efficiency.

Here is a link to the video.

And here is a link to COP adjusted end use graphs in Google Documents

This doesn’t mean that only 3% of the energy is due to the envelope, but it does show potential savings for retrofits on various elements. You could get more specific and just isolate the roof, or even solar gain from the windows. Or run create an elimination run for plug loads where you set loads to nothing.


David Goldwasser, LEED AP
National Renewable Energy Laboratory

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of John Eurek
Sent: Friday, August 26, 2011 2:36 PM
To: Giulio Castorina; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Building envelope average energy demands

I don't know if this answers your question, but I have tried to determine the % of energy use due to the envelope on a recent building by running multiple energy models.  What I found was the energy balance in complex.

An example is a perfect balance on a cold day
"People" + "Lighting" + "Plug Loads" - "Loss through Wall" = 0

So if the insulation was higher, your loss though the wall would be less and the A/C power usage would be increased.

You could hand calculate the envelope energy demand for an empty unoccupied building, but with internal loads it gets foggy.

The energy model will show you what you can expect from various R-values, but I have not found a way to say x% of energy is due to the envelope.

From: Giulio Castorina <artitecture at gmail.com>
To: bldg-sim at lists.onebuilding.org
Sent: Friday, August 26, 2011 2:52 PM
Subject: [Bldg-sim] Building envelope average energy demands

Hi All,

Can anyone advise a good resource (article, webpage, book, etc..) which states what is the average energy demands (construction+running costs) due to Envelopes only in buildings? I would need just a figure in percentage over the whole energy demands of a typical office building. Is this data somehow available?


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