[Equest-users] Appendix G System 4 PSZ-HP Supplemental Electric Heat ( Section G3.1.3.1)

[Bishop, Bill]

Dan,
 
To meet the Appendix G requirement for baseline HP, I would set the Maximum HP Supp Temp to 40°F and use either proportional or reverse-action thermostats. From the help menu description for the Minimum HP Heat Temp, the heat pump will shut off below this temperature. I would leave this at the default value (or copy your proposed value if you are using heat pumps that shut down below a certain temperature) since Appendix G doesn't specifically address the shut off temperature. I suspect that the heat pump is at such a reduced capacity at low OAT that it would not affect the modeled energy consumption much by playing with this number (since your heat is mostly from the supplemental source), but you could always plot out the capacity curve, or do parametric runs, to find out.
 
Regards,
Bill
 
William Bishop, PE, BEMP, LEED® AP | Pathfinder Engineers & Architects LLP
Mechanical Engineer
 
134 South Fitzhugh Street
Rochester, NY 14608
T: (585) 325-6004 Ext. 114
F: (585) 325-6005
wbishop at pathfinder-ea.com
www.pathfinder-ea.com
P Sustainability - less is more.
________________________________

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Dan Russell
Sent: Thursday, July 29, 2010 6:41 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Appendix G System 4 PSZ-HP Supplemental Electric Heat ( Section G3.1.3.1)
 
My LEED baseline model is HVAC system type 4 - PSZ-HP and Section G3.1.3.1 states:
 
"Electric air-source heat pumps shall be modeled with electric auxiliary heat.  The systems shall be controlled with multistage space thermostats and an outdoor air thermostat wired to energize auxiliary heat only on the last thermostat stage and when outdoor air temperature is less than 40degF."
 
So, the auxiliary heat remains off until the heat pump can no longer do its job and is activated only if the OA temp is less than 40degF.  Is the intention to allow the heat pump to continue running simultaneously with the auxiliary heat?  Or, at the moment the heat pump can no longer handle the space heating requirement does it shut off and allow the auxiliary heat to do the entire job by itself?  If it is intended that both functions operate simultaneously is there an OA temperature limit where the heat pump should be turned off?
 
Does anyone have some insight as to what eQUEST is doing for the control sequence of this system type?  Is it meeting the criteria of this Appendix section inherently or do I need to fiddle with the values in the screenshot below to make it compliant?
 
The eQUEST heat pump supplemental heat window looks like this:
 
 
 
There appears to be only two inputs:
*         Minimum HP Heat Temp (Turns heat pump off when OA temp is below this temperature.)
*         Maximum HP Supp Temp (OA temp at which supplemental heat becomes available.)
 
The latter, seems to match with the intended 40 deg OA setpoint specified in the Appendix G section above.
What's more unclear to me is how the Minimum HP Heat Temp input should be utilized.    
 
Thanks,
 
Dan Russell
 
 
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