[Bldg-sim] Loads to Energy Model

Will Mak wmak at epsteinglobal.com
Mon Aug 29 06:17:12 PDT 2011

Thanks for all the great responses!


I guess the main point I was trying to confirm was whether I would save time building the energy model from load calcs. Unfortunately, the way things are set up here, the LEED energy model is completed after 90% Construction Documents and not much preliminary modeling is done during the SD/DD stages.


All of you bring up good points that modeling is much more powerful and can be utilized as a tool to help drive design decisions early on. With the way the economy is, I can see more owners/developers asking why specific decisions are being made and energy modeling can provide some analytical data behind those decisions (rather than just saying, well this was done in the past or hey this looks nice).


Unfortunately, for this project, I just need to complete the LEED energy model the most efficient way which led me to throw out the loads to modeling question in the first place...


William Mak, LEED AP BD+C
Mechanical Design Engineer

600 West Fulton Street
Chicago, Illinois 60661-1259
D: (312) 429-8116


From: Marcus Sheffer [mailto:marcus at energyopportunities.com] 
Sent: Friday, August 26, 2011 7:51 PM
To: 'Nick Caton'; John Eurek; Will Mak; bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] Loads to Energy Model


In my experience the problem with doing the load calculations first and then creating your energy model is that the model is often done too late to have much effect.


Too often the load calculations are not done until the building design is set, maybe end of SD but usually sometime in DD.  Most engineers don't seem to want to do the load calculations more than once.  By this time the vast majority of design decisions that affect energy use are cast in CAD and it is too late to change them.  The only thing you can affect are the details associated with the HVAC design.  Modeling done at the end for LEED points is frankly almost a waste of time.  Modeling done in DD has a marginal affect.  Modeling done from the beginning can guide the full measure of design decisions and help produce a very efficient design (as Nick alludes to below).  This is why we model.


On many of our projects we start modeling at the conceptual design phase to inform the development of the architecture, way before any load calculations are done.


I will second the awesome analogy by John!


Marcus Sheffer

Energy Opportunities/a 7group company

1200 E Camping Area Rd, Wellsville, PA 17365


http://www.energyopportunities.com <http://www.sevengroup.com/> 


From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Friday, August 26, 2011 4:53 PM
To: John Eurek; Will Mak; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Loads to Energy Model


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.  




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... 










Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617



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




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



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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