[BLDG-SIM] Heat Pump COP

[Brandon Nichols]

OK All, 
 
Has anyone looked at this lovely document
<http://www.eere.energy.gov/buildings/appliance_standards/residential/pd
fs/cac_tp_101105.pdf> , which is the Department of Energy's test
procedure for air conditioners and heat pumps to determine EER and SEER?
To this I turned to answer the burning question "what is the standard
external fan static pressure drop specified to calculate EER and SEER?"
 
Seems to me after wading through the swamp of equations in the back of
the document that fan energy in EER and SEER calculations is specified
at a 0.05 inch external static pressure drop.
 
So then I started digging around for data to support my intuitive
feeling that fan energy is going to be something like 1/10th that of
compressor energy on small heat pumps.
 
In the process I ran across this nifty DOE/ORNL Heat Pump Design Model
<http://www.ornl.gov/~wlj/hpdm/doehpdm.shtml> .  Now we're cooking...
see this post
<http://elcca-exchange.blogspot.com/2007/10/heat-pump-parametrics.html>
for a 3D plot of parametric runs (did I say 'nifty'?), varying supply
airflow and static pressure, from 600 to 4200 and 0.05 to 0.65
respectively.
 
I'm standing by my assertion that supply fan energy does not need to be
subtracted from heat pump EER as SEER and the new number recalculated --
playing those kinds of games can lead to an exercise in futility.
<http://www.ornl.gov/~wlj/hpdm/doehpdm.shtml>  
Best regards,
 
 
Brandon Nichols, PE, LEED(r) 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: Fred Porter [mailto:fporter at archenergy.com] 
Sent: Friday, October 12, 2007 5:22 PM
To: BLDG-SIM; Brandon Nichols
Subject: RE: [BLDG-SIM] Heat Pump COP



G3.1.2.1 Equipment Efficiencies. All HVAC equipment

in the baseline building design shall be modeled at the minimum 

efficiency levels, both part load and full load, in accordance 

with Section 6.4. Where efficiency ratings, such as EER 

and COP, include fan energy, the descriptor shall be broken 

down into its components so that supply fan energy can be 

modeled separately. 

  

G3.1.2.4 Fan System Operation. Supply and return fans 

shall operate continuously whenever spaces are occupied and 

shall be cycled to meet heating and cooling loads during unoccupied 

hours. If the supply fan is modeled as cycling and fan 

energy is included in the energy-efficiency rating of the equipment, 

fan energy shall not be modeled explicitly. 

  

-- 

Fred 

  

  

  _____  

   

From: Brandon Nichols [mailto:BrandonN at Hargis.biz] 
Sent: Friday, October 12, 2007 6:14 PM
To: Fred Porter; BLDG-SIM at gard.com
Subject: RE: [BLDG-SIM] Heat Pump COP 

  

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(r) 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 at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Fred
Porter
Sent: Friday, October 12, 2007 3:31 PM
To: BLDG-SIM at gard.com
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 at Hargis.biz] 
Sent: Friday, October 12, 2007 3:47 PM
To: Fred Porter; BLDG-SIM at gard.com
Subject: RE: [BLDG-SIM] Heat Pump COP 

  


  


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(r) 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 at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Fred
Porter
Sent: Friday, October 12, 2007 10:23 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Heat Pump COP 

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
Sent: Thu, 10/11/2007 3:25pm
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Heat Pump COP 

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, Suite 820 

West Covina, CA 91791 USA 

Phone: 626-430-9054 

Fax: 626-430-9060 

email: jaulbach at nexant.com 

  

 
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