[BLDG-SIM] Heat Pump COP

[Brandon Nichols]

Thanks Xiaobing
 
In reviewing some past heat pump projects, I see that the way we have been doing it is in agreement with modeling the supply fan separately, and using the manufacturer's published EIR/COP values to compute the cooling/heating EIRs without adjustment.  
 
A problem many of us have in supervising modeling projects is backchecking...modifying manufacturer's published data creates a variance in the documentation and backcheck processes that needs to be addressed consistently for every project going forward.  Thus when modifying manufacturer's published heat pump EIR/COP values was suggested to be necessary for LEED compliance, I wanted to go through the justification exercise <http://elcca-exchange.blogspot.com/2007/10/heat-pump-parametrics.html>  of why we generally don't.
 
Dead horse beaten, as far as I'm concerned!
 
Brando
 

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From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Xiaobing Liu
Sent: Tuesday, October 16, 2007 9:12 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Heat Pump COP


Brandon:
 
Thanks for your continuous effort to discuss the issue of heat pump COP and the fan power. Just want to clarify several things cited in your e-mails.
 
1. The fan power included in the EER/COP calculation may not be the same as the fan actually demand when the heat pump runs. For water-source heat pumps, ANSI/ARI/ASHRAE ISO Standard 13256-1:1998 (Water-source heat pumps - testing and rating for performance - Part 1: Water-to-air and brine-to-air heat pump) states following requirements for fan power input in COP/EER calculations
 
4.1.2 Power input of fans for heat pumps without duct connection
In the case of heat pumps which are not designed for duct connection and which are equipped with an integral fan, all power consumed by the fans shall be included in the effective power input to the heat pump.

4.1.3 Power input of fans for heat pumps with duct connection

4.1.3.2 If a fan is an integral part of a heat pump, only the portion of the fan power required to overcome the internal resistance shall be included in the effective power input to the heat pump. The fraction which is to be excluded from the total power consumed by the fan shall be calculated using the following formula: φfa = q x Δp / η

where

φfa is the fan power adjustment, in watts;

η = 0.3 × 103 by convention;

Δp is the measured external static pressure difference, in pascals;

q is the nominal airflow rate, in litres per second.

This value shall be subtracted from the heating capacity and added to the cooling capacity.

The reason for this is that, in a particular heat pump installation, depending on the air flow and external static pressure of the duct work, the fan power is different, which is unknown when the heat pump is tested in the lab. So, to isolate from the unknown effect of the external duct work, only the portion of the fan power required to overcome the internal resistance shall be included in the effective power input to the heat pump if the heat pump is designed for duct connection. Therefore, the fan power in the real operating condition should be specified in the simulation to more accurately predict the fan energy consumption. 

2. The electric consumption of fan depends on not only the fan power (which may be less than 10% of the compressor power) but also the run time of the fan. In the case of mild climate, if fan runs continuously (to provide OA and air circulation in the conditioned space), the electric consumed by fan may be higher than the compressor power since fan runs 8760 hours a year but the cumulative run time of compressor over a year may be less than 1000 hours. Whether the fan power play an important role in energy analysis does not necessarily depends on the size of heat pump, it depends on what the system is (i.e. single small heat pump or multiple small heat pumps connected with a water loop) and how the indoor fan of the heat pump is operated (continuous or intermittently).  For this reason, it is recommended to use DOAS for WLHP system so that the indoor fan of the heat pump can run intermittently to take care the space loads while the DOAS delivers the required amount of OA to the space.

Hope it helps,

Xiaobing

	-----Original Message-----
	From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com]On Behalf Of Brandon Nichols
	Sent: Tuesday, October 16, 2007 12:54 AM
	To: BLDG-SIM at gard.com
	Subject: [BLDG-SIM] Heat Pump COP
	
	
	OK All, 
	 
	Has anyone looked at this lovely document <http://www.eere.energy.gov/buildings/appliance_standards/residential/pdfs/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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