[Bldg-sim] Loads to Energy Model

Nick Caton ncaton at smithboucher.com
Fri Aug 26 13:53:06 PDT 2011


Awesome analogies John!

 

I was writing up a response simultaneously and took it into a few other directions specific to LEED... for anyone curious, I'm in full support of John's response as well =).  To add to the hat: our office predominantly sizes up equipment using HAP (with a smattering of Trace), and I'm familiar with tying the load reports for both into energy models under eQuest as a QC measure.  

 

Will:

 

As a general QC practice, after everything is functionally set up and before "fine-tuning" steps like evaluating unmet hours, I will spot check and adjust as necessary to ensure an energy model is in the same ballpark as the designed loads, time permitting.  Zones of notably high occupancy/ventilation/equipment loads get higher priority.  In any model where you're specifying equipment capacities (not autosizing), askew loads are a common suspect for unmet hours.  Oftentimes, an energy model is wrapping up well after design loads are put together, and elements of design may have changed, so the energy model can in some fashion serve as a back-check for the load calcs as well.

 

I chose the word "ballpark" carefully:  Trying to match loads precisely/exactly between different software packages, outside of an academic exercise, wouldn't functionally accomplish much - acknowledging that even the most sophisticated load calculations are built on assumptions, estimations and weather predictions.  I've encountered some model reviewers (outside of LEED, btw) who conceptually miss the fundamental differences of purpose between a load calc and an energy model... but don't let such eye-rollers lead you astray =)!

 

That's not to say one cannot use an energy model to do load calcs (some certainly do), but before going down that path I think it's important to identify the calculations serve two tightly related but necessarily distinct purposes: sizing equipment (balancing "worst case" conditions against expected comfort and applying safety factors for present/future unknowns) and evaluating energy behavior, which means running with a longer set of assumptions (over time), permitting informed decisions for design to save $$$ on energy bills (or rainforests, if that's your metric of choice).  

 

"But Nick, I thought energy modeling was simply for LEED points..."  Well, that's what I thought getting started too, but I've grown to learn energy modeling produces much greater value than a plaque on the wall (hey, where's mine anyway?): it informs better design (which I appreciate as an MEP consultant), while simultaneously saving really big money for our clientele (and the rest of us indirectly paying every month for ever-increasing energy infrastructure).  Any indefinite environmental benefits, however fuzzy, are only icing on the cake.

 

Getting back to the original query:  The energy modeling process for LEED, and specifically for 90.1 Appendix G by design avoids the necessity to sync loads precisely with a load calc - the emphasis is instead on having the elements match the proposed design.  That said, you are expected to have equipment with capacities (heating/cooling/CFM/GPM) equivalent to what's scheduled, so by extension you do want to be in the same ballpark as the designed loads to avoid excessive undercooled/heated hours... 

 

~Nick

 

 

 

 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com 

 

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 3:25 PM
To: Will Mak; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Loads to Energy Model

 

Will

 

Turning a file you used for load calculation and equipment sizing into an energy model is not a quick thing.  Having the loads done is not half way.  You now need to make schedules for lighting, equipment & people, get the 8760 weather file, find out energy cost in the area, input equipment information and a few more quick things as indicated in ASHRAE 90.1.

 

I explain it to people by saying 'Doing load calcs for equipment sizing is like taking 2 pictures, one in the summer and one in the winter.  Making an energy model is like making a full length movie with special effects.' 

 

And don't forget that you need to make 2 full length movies, one which will be build and then spend time on an another pretend building (baseline) to compare it to.

 

Good luck man.  We are here for you.

 

To answer the question, Yes, I use my Trace file I created for equipment sizing as the starting point for the energy model. 





 

From: Will Mak <wmak at epsteinglobal.com>
To: bldg-sim at lists.onebuilding.org
Sent: Friday, August 26, 2011 12:30 PM
Subject: [Bldg-sim] Loads to Energy Model




Have any of you built an energy model for LEED from loads you have created for design? i.e. Trace/HAP load calcs and take it to energy modeling level?

 

William Mak, LEED AP BD+C
Mechanical Design Engineer

EPSTEIN
Architecture
Interiors
Engineering
Construction

Sustainability

600 West Fulton Street
Chicago, Illinois 60661-1259

D: (312) 429-8116
F: (312) 429-8800

E: wmak at epsteinglobal.com
W: www.epsteinglobal.com <http://www.epsteinglobal.com/> 

þ Epstein is a firm believer in sustainability. We ask that you please consider the environment before printing this e-mail.

 


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