[Equest-users] Heat pump COP curves

[Bishop, Bill]

Matt,



I believe a sufficient response to your reviewer’s comment would be to verify/set the MIN-HP-T and MAX-HP-SUPP-T in the System -> Heating -> Supp Heat/Defrost tab.  Minimum HP Heat Temp (MIN-HP-T) should be 17°F and Maximum HP Supp Temp (MAX-HP-SUPP-T) should be 40°F. I don’t know how to model the requirement that auxiliary (supplemental) heat “only energizes on the last thermostat stage”. I’ll assume that eQUEST does that automatically, giving preference to the compressor and only adding supplemental heat as necessary to meet the loads.



[Madjid HP.jpg]



Regards,

Bill



William Bishop, PE, BEMP, BEAP, LEED AP | Pathfinder Engineers & Architects LLP

Senior Energy Engineer



134 South Fitzhugh Street                 Rochester, NY 14608

T: (585) 325-6004 Ext. 114            F: (585) 325-6005

bbishop at pathfinder-ea.com           www.pathfinder-ea.com

   Sustainability – the forest AND the trees.



-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Madjid Madjidi
Sent: Tuesday, September 24, 2013 11:49 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Heat pump COP curves





Dear experts,



how can I modulate the COP of a heat pump in eQUEST in relation to outdoor dry bulb temperature, outdoor wetbulb temperature and partial load. I see that I can enter the value for electricity input ratio (BTU/BTU)  in a box (e.g. 0.3) and there are two different fraction curves available which can be defined as linear or quadratic or else functions. But it is unclear to me how these curves are linked to the EIR value (e.g. EIR x frac1 x frac 2 ?) and furthermore, how the supplemental heater could be considered. I have this problem with the baseline case for a LEED project and the reviewer has sent to me the following comment:



It is unclear if the packaged rooftop heat pumps in the Baseline model were modeled according to Section G3.1.3.1, which requires that the electric airsource heat pumps are modeled with electric auxiliary heat that only energizes on the last thermostat stage and when the outdoor air temperature is less than 40 degrees F. Per ASHRAE Interpretation 90.1-2007-09, this means that the heat pump and auxiliary heat should operate together at low temperature conditions, with the compressor as the lead machine. The outside air cutoff temperature for the compressor must be no greater than the temperature associated with the low-temperature heating efficiency requirements of Table 6.8.1B (17 degrees F). Note that for packaged heat pump units smaller than 65,000 Btuh and packaged terminal heat pumps, the HSPF rating accounts for electric auxiliary operation, and includes test conditions at 17 degrees F.



The interesting aspect is that there is no cop curve specified in ASHRAE 90.1. There are only two different values for the COP defined (3,3  and 3,22).

So it seems that for the reference model (baseline) the value could be set to constant and I just have to consider three different situations:



toutdb < 17 F --> COP = 1

toutdb = 17 F --> COP = 2,25

toutdb > 40 F --> COP = 3,3



Is this true ? How should I model that in EQUEST ? Any friendly advise is welcome.



Thank you in advance and with best regards



Matt

_______________________________________________

Equest-users mailing list

http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org

To unsubscribe from this mailing list send  a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG<mailto:EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20130924/808a0b54/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.jpg
Type: image/jpeg
Size: 44044 bytes
Desc: image002.jpg
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20130924/808a0b54/attachment-0002.jpg>