G3.1.2.2 Equipment Capacities

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I made the comment below a while back on equest-users. Has anyone gotten any LEED comments that either confirm or challenge my interpretation?
Thanks,
Bill

My understanding has always been that the G3.1.2.2 oversizing requirement should be met by setting the COOL-SIZING-RATI to 1.15, the HEAT-SIZING-RATI to 1.25 and the SYSTEM:SIZING-RATIO to 1.00 for all baseline systems. The system sizing ratio acts as a multiplier on airflows as well as a multiplier on the cool and heat sizing ratios, so you could accomplish the cooling and heating oversizing by setting system sizing ratio to 1.15, the cool sizing ratio to 1.00 and the heat sizing ratio to 1.09. However, you would then be oversizing the airflow as well. While earlier versions of ASHRAE 90.1 did not elaborate on what exactly should be multiplied, 90.1-2010 specifically says "system coil capacities" shall be oversized. So we should be leaving the system sizing ratio at 1.00 and only oversizing via the cool and heat sizing ratios.

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

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Bill Bishop's picture
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Bill,

Every LEED model I've created employs the first method mentioned below, 'COOL-SIZING-RATI to 1.15, the HEAT-SIZING-RATI to 1.25 and the SYSTEM:SIZING-RATIO to 1.00' and I've never had a LEED reviewer call me out on it.

I'm curious how this questions came about. Did a LEED reviewer comment on it?

Sincerely,
David Griffin

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Another modeler in the office attended some training where they were recommending the second method described below (system sizing ratio to 1.15), as it would increase the baseline fan energy and therefore improve the energy savings calculation.

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Hmmmm...

I would like to know the name of the trainer, so I can make sure I don't take any of his/her courses (unfortunately this is not allowed on the list sever - don't mention name). Diviating from standard modeling practice to make the energy model numbers 'look' better is a horrible idea for many reasons!

I'm sure you are aware of them which is why you posted the question in the first place.

Yet another reason why energy modeling methodologies should be standardized.

Thanks for posting.

Sincerely,
David Griffin
ETC Group, LLC

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For your base case would you just save as a new model or would you do a parametric run? I need to build my energy model for LEED as well and trying to get away with doing a parametric run instead of 2 different models in case I need to make changes later. Also wondering if the sizing ratio is all that is required or do you have to manually change any cooling/heating capacities to any equipment (ie. baseboard heaters?)

Thanks,

-John

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