[Bldg-rate] LEED+90.1 Process/Plug Loads Conundrum

Kevin Kyte KKyte at watts-ae.com
Fri Apr 30 13:05:58 PDT 2010

In my experience, I have generally included plug loads to the extent of the owner/ architect basis of design.  Any additional process required to reach 25% is included as an internal load directly on the meter with no contribution to internal gains.  I have not identified, as of yet, anything that would instruct me to do otherwise but I have not taken a very close look at G-2007 yet.


From: bldg-rate-bounces at lists.onebuilding.org [mailto:bldg-rate-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Friday, April 30, 2010 1:55 PM
To: bldg-rate at lists.onebuilding.org
Subject: [Bldg-rate] LEED+90.1 Process/Plug Loads Conundrum

Something new occurred to me this week and I'd love to hear others' thoughts!

LEED prescribes baseline/proposed energy models to follow ASHRAE 90.1 with a caveat:  the "process energy costs" must total 25% of the baseline energy costs.  By extension, 90.1 requires the same loads/schedules be applied to the proposed model as they have to match.  As an aside, the LEED EAc1 templates appear to calculate/check this using process energy consumption (not cost), but that's not what I'm getting at...

I just had a typical case where I had to inflate the baseline internal miscellaneous equipment loads to get to 25%.  These additional loads were substantial enough that when applied to the proposed model/design, I ran into many unmet cooling hours for the equipment capacities entered.

Then I realized:  We can define additional equipment electricity loads but simultaneously apply a multiplier (in eQuest anyway - I expect this is feasible other programs also) to reduce/negate the corresponding heat load contributions.  This results in the energy consumption/costs showing up correctly in the final results/reports, but does not artificially inflate the internal loads that the baseline/proposed systems must handle.

Would this practice (which incidentally can be a time saver) of accounting for extra process/miscellaneous loads without extra thermal contributions be in line with the intent of ASHRAE/USGBC?  It would still normalize the otherwise unstandardized process consumption/costs of the baseline/proposed models between different building types...

On the other hand, if it really is the intent of USGBC to add arbitrary additional internal heat loads to our models that our actual designs were not designed and sized for, does it follow that we should allow the proposed models to autosize cooling equipment/fan capacities and not specify them (this would seem incongruous with 90.1 to me)?


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