Building envelope average energy demands

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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?

Best,

Giulio

Giulio Castorina's picture
Joined: 2011-10-02
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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.

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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.
http://www.youtube.com/watch?v=7U91jeksOAw&list=PLF80F250937E2A648&index=38&feature=plpp

And here is a link to COP adjusted end use graphs in Google Documents
https://docs.google.com/spreadsheet/ccc?key=0AhCALIzwiaGPdEI5ZHhaVmpfUHAtdGFDMjg5eW5tT1E&hl=en_US#gid=49

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

Goldwasser, David's picture
Joined: 2011-10-02
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Hi All,

thank you all for your quick response. Actually I don't want to
calculate that value, but just need to cite/reference a source that
gives information about this data.

I found this http://www.sustainablefacility.com/articles/print/86593
where a graph is shown...but not really references fully. It says about
ASHRAE Std 90 - I dont have access to this. Is this a chart inside the
Do you know if it is inside the ASHRAE standards?

In particular I'm looking at expenditure through external vertical
walls/windows - hence facades especially in office buildings.

Best

Giulio

Giulio Castorina's picture
Joined: 2011-10-02
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David,
?
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?
?

John Eurek's picture
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As an engineer reading that article I chuckled thinking "Do they realize 'energy loss' isn't always a bad thing?"
?
In your house, most of the time it is a bad thing.? In an office building it can be a good thing.? I think the answer you are looking for will be difficult to find.? If you make a good energy model you can site yourself.? And you get something like David talked about
?

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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.

Goldwasser, David's picture
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The graph/pie chart is not from ASHRAE 90.1. I believe the author is trying to show the energy savings of a building designed to the requirements of ASHRAE 90.1 as compared to a building not following energy savings design practices.

Reba Schaber Mechanical Engineer, P.E.

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I see.
Do you dataset where I can I at least retrieve construction costs per
building components? Such as a breakdown of Envelope/Energy Plant
Facilities/Plumbing/Elevators etc..?

Giulio Castorina's picture
Joined: 2011-10-02
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Giulio,

I am pretty sure you will ultimately find yourself frustrated if you try
to find "typical" costs (construction or consumption) for specific
building elements - as you may have gathered, the reality of energy cost
breakdowns varies widely even within a specific building type - so
averaged percentages between projects, even if found, may not be of much
practical use.

We can only speculate as to for whom you're asking and why, but I expect
you will find it much easier to cite/source construction and/or derive
consumption costs of a specific envelope for a specific building, which
you can then compare/contrast to the project you're actually discussing
to extrapolate expectations.

Ideally, a perfectly similar building would make for an easy comparison,
but simply make a point to identify the major differences in the
referenced building's makeup/location/equipment/occupant usage so that
you can factor the data to "fit" the project under discussion, as
necessary.

NICK CATON, P.E.

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