Loads to Energy Model

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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

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Will
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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.
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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.'
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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.
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Good luck man.? We are here for you.
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To answer the question, Yes, I use my Trace file I?created for equipment sizing as the starting point for the energy model.?

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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 CATON, P.E.

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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

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I've had some personal experiences and plenty of time to develop some opinions regarding the concerns Marcus raised. This may help others trying to get a handle of some realities that can make energy modeling tricky for non-technical reasons:

1. LEED is set up in its present state as a form of purely prescriptive, compliance modeling. Fundamentally, this sort of modeling does not inform design well or at all - but rather targets a different role: benchmarking. That's important to recognize, as LEED models have proven to be easily misconstrued in purpose.

2. Many of us in time have come to realize that "informed design" grows from a non-prescriptive sort of modeling which isn't defined by LEED, 90.1 or any other "compliance" standards set by states and local govt's. In my experience, such SD/DD stage models are often not "the LEED model" at an early stage, but rather something much more abstract and element-specific - tools custom-crafted on the fly to explore and answer project-specific queries. Not all building owners and design teams recognize the value such modeling services bring to the table, but it's an understandably hard sell from the designers' perspective without positive direct experience to relate with.

3. Some select 'enlightened' mechanical, envelope and electrical designers who I have the pleasure of working with make a point to allow energy modeling to inform their respective design work from the earliest to latest stages. This sort of behavior is not spontaneous or natural... but it is encouraged by taking a few minutes during and after a big project to show individuals the impact they personally make with specific decisions (preferably the good ones!). I recall one colleague's eyes bugging out when he learned a subtle choice of CFL lamping for a large project's can fixtures had an positive impact on the building's energy consumption measureable in full LEED points.

4. I find designers of all backgrounds and trades can be fairly easy to "sway" in this regard, but only if they have the inclination to learn and improve themselves - that's more of a personality issue no energy model can tackle. Better to recognize when that's in play and focus your efforts towards individuals on the design team who will gain more from the knowledge you can share (perhaps outside of your office).

5. We can't always get the best combination of clients or colleagues to work with for a given project - you sometimes just have to play the hand that's dealt for the next great opportunity to roll around - chin up =)!

NICK CATON, P.E.

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