[Bldg-sim] EUI calculation using ECB Method and PRM Method

Paul Erickson perickson at aeieng.com
Fri Jun 8 10:11:30 PDT 2012


Forecasting an EUI with energy models is a risky proposition to begin with, though many of us are asked to do so on a regular basis.  Hopefully all modelers realize that modeling is best used for making relative comparisons rather than predicting absolutes.  That said, a model can give you a much better idea of an EUI for a particular building/program than just pulling a value from the air.  Hopefully folks are looking to benchmark data to help confirm the reasonableness of their findings.

To your point about which to use, ECB or Appendix G, I would say neither.  If you're trying to determine EUI it should be based on the most representative model you can develop, not necessarily restricted by anything dictated by 90.1.  To Arpan's point about tracking cost intensities, that makes sense if LEED is part of the project or the owner is concerned with cost.  As engineers/analysts we should be thinking about energy and cost, and in some cases CO2e as well.  The final decision making metric very much depends on the goals of your client.

The challenge on many projects is a tension between energy and energy cost savings.  We have countless projects that save significant amounts of energy but score terribly in energy cost savings (using 90.1 or not as the reason to look at cost), especially with low gas prices these days.  This highlights the importance of the client's goal...if it's about saving energy, the necessary design strategies to do so may or may not also save a proportional amount of energy cost.  Thus the conundrum, energy cost as a metric is not indicative of the energy savings potential of a design path, but it is likely indicative of the likelihood for strategies to provide an economic return on investment.

Shanta, we've seen that it's good to use 90.1 App G for code and LEED modeling, and keep track of those Base and Proposed EUI's, but also consider the EUI of a "typical baseline" design that the owner/market would build and a "proposed" model that is as reflective of our actual design as possible.  It's a lot to track, especially when you add in the cost numbers for each, but it allows us to paint a more complete picture of the options and their outcomes.

Not sure if that resonates with others but would be interesting to hear what others are doing if something different.


Paul Erickson  LEED(r) AP BD+C

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From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Arpan Bakshi
Sent: Friday, June 08, 2012 9:19 AM
To: Shanta Tucker
Cc: bldg-sim at onebuilding.org
Subject: Re: [Bldg-sim] EUI calculation using ECB Method and PRM Method

In our work we are also leaning towards using cost intensities based on a model rather than energy intensities to "LEED-proof" our early design comparisons.

Arpan Bakshi, LEED AP BD+C

On Fri, Jun 8, 2012 at 10:14 AM, Shanta Tucker <shanta.tucker at atelierten.com<mailto:shanta.tucker at atelierten.com>> wrote:
Hello modeling community,
I've always thought that when trying to forecast an EUI for a building with a whole building energy model, the better approach would be to use 90.1 appx G PRM over Section 11 ECB. While I realize that neither one is intended for energy use predictions per se, I am curious what folks think about using Section 11. Thoughts? Pros/Cons?


Shanta Tucker, PE, LEED AP BD+C, BEMP

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