LEED modeling for Appendix G-Air to Air heat pump with auxiliary heat

2 posts / 0 new
Last post

Hello All,

I have a LEED project modeling for the baseline of air-to-air heat pump system with electrical auxiliary heat. In G3.1.3.1 of ASHRAE 90.1-2007, the requirement is "The systems are controlled
with multistage space thermostats and an outdoor air thermostat activate
electric heat only on the last thermostat stage and the outdoor air temperature
is 40 oF and below.".

In my DOE2.2 model, the electrical heat is activated only when the outdoor air temperature is below 40 oF. But meanwhile is the air-to-air heat pump system still running or turned off? From the description above we cannot find proof whether it is still running or shut off. I looked up other materials such as the ASHRARE 90.1-2007 user manual or Advanced Energy Modeling For LEED Technical Manual and none mentioned the heat pump is continuously run when the outdoor air temperature is below 40 F.

Does anyone have any good insight on this? Thanks for you help.

Regards,

David

Zhen Tian's picture
Offline
Joined: 2011-10-02
Reputation: 0

David---

This is an issue we've tried to resolve as well as it doesn't appear to be explicitly addressed in 90.1. To complicate issues, it is hard to find this data from many manufacturers. As a result we have applied standard practice to the baseline model which says that a typical heat pump can operate to about 5?F (-15?C) before its COP is equivalent to just electric resistance heating. So if you are using eQUEST, you can set the Maximum HP Supp Temp to 40?F and the Minimum HP Temp to 5?F and the heat pump will ramp down between the two set points. There is a pretty informative article provided by Natural Resources Canada that details out some of these parameters (http://oee.nrcan.gc.ca/publications/infosource/pub/home/heating-heat-pump/asheatpumps.cfm)

Regards,

Andrew Craig EIT, LEED AP

Andrew Craig2's picture
Offline
Joined: 2011-10-02
Reputation: 0