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NC-2009 EAp2:Minimum Energy Performance

Appendix G - Number and type of chillers

Hi! I have a doubt related to Appendix G, concerning the number and type of chillers and I think you may help me. In item G.3.1.3.7, it is specified that the number and type of chiller for the baseline model are a function of building peak cooling load. In item G.3.1.2.2, it is specified that the baseline's equipment efficiency shall be oversized by 15% (cooling) and by 25% (heating). So, in order to define the number and type of chillers, may I use the oversized capacity or the non- oversized one? Thanks!

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Tue, 09/11/2012 - 18:54

This is a good question! What I have always done is to 1st set the oversizing factors, then perform a simulations with auto-sized equipment, then use the results to determine the number of chillers.

Tue, 09/11/2012 - 21:43

But actually the building cooling load is not affected by the sizing of the equipment!
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Marcus Sheffer
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7group / Energy Opportunities
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Wed, 09/12/2012 - 13:13

G3.1.3.7 indicates the size should be based on the peak cooling load which is different than the equipment size as Santiago mentions. So the number and type of chiller should be based on the peak cooling load. The baseline equipment size is then based on the cooling load plus 15%.

Thu, 09/20/2012 - 14:27

Marcus, I ask this because I've asked some ASHRAE members and, at their view (I didn't get a formal interpretation), I shoud select the number and type based on equipment size. Maybe they were not sure as me... =) Do you know if, in the market, people have adopted the methodology you mentioned? Thanks.
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Marcus Sheffer
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Thu, 09/20/2012 - 15:39

The language in the standard clearly says peak cooling load, not final equipment size. The 15% over-sizing is related to equipment capacity, not peak cooling load. The peak load is the load, not the over-sized equipment capacity. This is how we do it in our models and how the LEED reviewers would expect it to be done in our opinion. I do not know how most modelers do it as this information is generally not provided in a LEED review. Anyone else have an opinion on this one?

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