Cooling effeciency

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Modeling a 30 story hotel with PTACs (9.54 EER) vs. WSHP (12 EER) I am
expecting to see a large cooling energy reduction. Since the envelopes
are the same I'm expecting to see the full 26% improvement, however I
only see an 11% improvement in cooling energy comparing the BEPS report.
I would expect part load performance to maintain an almost constant
efficiency spread of 25% through the whole part load curve. But maybe
for some unkown reason to me the efficiency spread decreases
dramatically through part load? Also is there any way to check overall
building cooling efficiency like divide overall cooling loads into
energy? Cooling energy can be found on BEPS, but total building cooling
load varies from LS-F and LS-D to SS-D.

Tobias, Mike's picture
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PTACs usually have the ability to run an economizer and WSHPs do not. I am
not sure if you modeled it this way, you would need to check the inputs.
This would account for a drop in savings, but not sure it would account for
everything. Also, I would expect an increase in pump energy use for the
WSHP system. In regards to the part load efficiency curves, I have not
studied WSHP and PTACs next to each other. You might want to make sure that
your curves are normalized to EERs you are inputting.

--
Karen

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Joined: 2011-09-30
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Mike,

I look at PS-C for overall efficiency calcs. EER = Cooling Load (MBTU) *
1000 / Elec Use (kWH).

Jay Keazer, EI

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