[Bldg-sim] Energy Model from Green Star (LEED) to predictive model

Sami, Vikram Vikram.Sami at perkinswill.com
Tue Jan 29 12:29:54 PST 2013


Morgan - 10% is pretty damn close - well done!

That being said - I would like to respond to the second part of your email. Personally I think it is possible to be slightly inaccurate, but still correct.

In my experience it is when you are in the early stages (when there is a huge margin of error) that the modeling is actually at its most useful. Very often it's the early on normative modeling that leads to good design decisions. For example when modeling a VAV system versus a chilled beam system, I might not have the exact BTU number, but if I can get the usage patterns appropriately represented (cooling, heating, fans & reheat) then the result might not be 'accurate', but correct. Your overall numbers might go up and down with occupancy and weather, but the decision still remains a good one. This is where having the experience and the backing of a good database of comparable buildings is invaluable. CBECS is good for overall usage, but it's even better to be able to look at how the BTUs are spent over the year. Investing the time to collect utility bills for your building type is worth a lot.

Often we worry about the accuracy of our results to the nth degree before making recommendations, but by the time we come up with the magic number its too late - the design has morphed, or been finalized so your numbers are either outdated or redundant (in some cases both).


Vikram Sami, LEED AP BD+C
Sustainable Design Analyst
1315 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462    f: 404.892.5823       e: vikram.sami at perkinswill.com   www.perkinswill.com<http://www.perkinswill.com/>
Perkins+Will.  Ideas + buildings that honor the broader goals of society


From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Morgan Heater
Sent: Thursday, January 24, 2013 5:17 PM
To: 'Kapil Upadhyaya'; 'Jason Quinn'; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Energy Model from Green Star (LEED) to predictive model

I've been getting within 10% without calibration on the last five or six buildings I've done where I've tracked the bills afterwards.  The key is to be thorough and careful.  If you're not getting reasonably close, how can you justify your recommendations for energy efficiency measures?


Morgan Heater, P.E.
BEMP, LEED AP
morgan at ecotope.com<mailto:morgan at ecotope.com>
206-322-3753
206-596-4709 Direct

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Kapil Upadhyaya
Sent: Thursday, January 24, 2013 2:08 PM
To: Jason Quinn; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Energy Model from Green Star (LEED) to predictive model

Get utility bills (if you can), or Use Energy Star or CBECs for a reference building (CBECs median may be higher than a 1930 building !); based on these, you can present a range between 'simulated' savings and 'estimated' savings.

Kapil Upadhyaya, LEED AP
Associate
Kirksey | Architecture

From: Jason Quinn [mailto:jason.e.quinn at gmail.com]
Sent: Wednesday, January 23, 2013 9:38 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Energy Model from Green Star (LEED) to predictive model

I've ALWAYS avoided predictive modeling (telling a client your energy usage will be below X) as I've been scared. Now I'm pretty deep into a project performing Green Star energy modeling and my client has popped the question.

We've discussed "why it is hard" and the big three un-knowns: Infiltration, Occupant behavior!!, and Actual Weather. They still want me to go forward and are willing to put a bunch of caviates and an agreed margin on the results.

This is an old 1930's building 200,000 sq ft with original metal window frames (single pane) that will not be replaced (heritage). We're insulating the roof and basement ceiling and a completely new HVAC system. Is there a standard process I can follow or specific suggestions the community could offer?

So far my idea is to try and guesstimate infiltration, box in comfort behavior with lease agreements and a survey, and put some margin on weather.

--
Jason
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