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Good point Fred, for larger unitary packages and for
dialing-in energy savings rebate studies. I did say 'arguably', and
yours is an insightful observation. Scanned all 90.1-2004 but didn't
see the reference you alluded to -- if you can be more specific please
advise.
Given the small heatpumps my firm is
accustomed to installing, coupled with the fuzzy level of design at which we're
doing our preliminary energy studies, the simplification of discounting fan
operation when compressors aren't running I think is well within the error bars
of the overall study.
Which doesn't provide any comfort from the realization that
this business gives one plenty of cause to ask where picking the
theoretical flyspecs out of manufacturer's published pepper has crossed a
threshold of mind-numbingly diminished returns!
Regards
Brandon Nichols,
PE, LEED®
AP
Mechanical
HARGIS ENGINEERS
600 Stewart Street Suite 1000 Seattle, WA 98101 www.hargis.biz d | 206.436.0400 c | 206.228.8707 o | 206.448.3376 f | 206.448.4450 From: BLDG-SIM@xxxxxxxx [mailto:BLDG-SIM@xxxxxxxx] On Behalf Of Fred Porter Sent: Friday, October 12, 2007 3:31 PM To: BLDG-SIM@xxxxxxxx Subject: [BLDG-SIM] Heat Pump COP The method cited below
only gives correct results if the heat pump fan operates intermittently on a
call for heat/cool, and if the fan as installed runs at its ARI-tested power.
Otherwise this method greatly under-estimates fan energy, at least for constant
speed fans. This is mentioned specifically for App G/ECB models either in the
Standard itself or in the UM. -- Fred
From: Brandon
Nichols [mailto:BrandonN@xxxxxxxxxx] Good point, John -- but there may
be an arguably easier way to not double-count fan energy...following is a
reprint from the DOE2 documentation: COOLING-EIR
The Electric Input Ratio (EIR), or
1/(Coefficient of Performance), for the cooling unit at ARI rated conditions.
The program defines EIR to be the ratio of the electric energy input to
the rated capacity, when both the energy input and rated capacity are expressed
in the same units. This EIR is at ARI rated conditions, i.e., without correction
for different temperature or part load. Note: If you include fan electric
energy consumption in your value of COOLING-EIR, then you should set SUPPLY-KW/FLOW to zero (and SUPPLY-STATIC, SUPPLY-EFF and
SUPPLY-DELTA-T should be omitted). Otherwise, the supply fan electrical energy
will be double counted. For commercial systems the default value
of COOLING-EIR includes compressor and outdoor fan energy, but not indoor fan
energy. HEATING-EIR
Electric Input Ratio, or 1/(heating Coefficient of
Performance), for the heat pump. This EIR is at ARI rated conditions, i.e.,
without corrections for temperature or part load. The program-calculated HEATING-EIR
does not include fan power and heat. This keyword is appropriate only to HP,
RESYS, and PTAC systems. Mysteriously, the HEATING-EIR documentation
makes no mention of the fan energy double counting issue. But if you're
consistent and use 3.41 divided by the manufacturers published EER for the
cooling EIR, the inverse of the published COP for the heating EIR,
and zero-out the supply fan energy as described in the
documentaion ... then Bob's your uncle, right?
FWIW, that's the way we do
it... Brandon Nichols,
PE, LEED® AP Mechanical HARGIS
ENGINEERS www.hargis.biz d
| 206.436.0400
c |
206.228.8707 o
| 206.448.3376
f |
206.448.4450 From:
BLDG-SIM@xxxxxxxx [mailto:BLDG-SIM@xxxxxxxx] On Behalf Of Fred Porter Yes and no. The energy is "removed," but
the COP improves because the fan heat had a COP of 1.0, and is included in the
rated gross kW in and Btuh out. I think the T24 ACM may have a "method" or
formula. From:
Aulbach, John Folks: In eQuest, the Energy
Input Ratio (EIR) can be derived from EER or COP given for a unit or from a
Standard. To correctly model such a unit, one must subtract the fan energy for
the unit to obtain the EER (EIR) of the compressor only. This improves the input
from, say, a COP of 12.3 to 15. What about in the case
of the heat pump heating COP? Must one subtract out the fan energy here as well,
thus "worsening" the COP for the heating side? I cannot find anything
written on this subject. Thanks. John R. Aulbach, PE,
CEM Project
Manager Nexant,
Inc. 100 North Barranca, Phone:
626-430-9054 Fax:
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