[Trace-users] heat pump cut off

[Mark Denyer]

This is how I replied to the very same review comment about heat pump 
operating temps, and elect strip heat.


This screen capture shows the efficiencies of the PTHPs used for the 
baseline. The Unloading curves show that the system is designed to 
calculate efficiencies and capacities as outdoor temperatures vary.

This screen capture shows that the PTHPs will operate down to 17 degrees 
F, and the electric strip heat is the second stage of heating if the 
compressor cannot keep up.

The secondary capacity curve prevents the strip heat from being 
activated when the outdoor temp is above 40 F.



On 8/20/2013 1:11 PM, trace-users-request at lists.onebuilding.org wrote:
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>     1. Heat Pump Cut Off (UNCLASSIFIED) (Eurek, John S NWO)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Tue, 20 Aug 2013 16:56:19 +0000
> From: "Eurek, John S NWO" <John.S.Eurek at usace.army.mil>
> To: "trace-users at lists.onebuilding.org"
> 	<trace-users at lists.onebuilding.org>
> Subject: [Trace-users] Heat Pump Cut Off (UNCLASSIFIED)
> Message-ID:
> 	<E777FD5A41D3B04A83296213737A85D7070018D9 at EIS-MB05WPC.eis.ds.usace.army.mil>
> 	
> Content-Type: text/plain; charset="us-ascii"
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> Classification: UNCLASSIFIED
> Caveats: NONE
>
> How do you have the Heat Pumps use electric heat below 40 degrees and cut off the compressor entirely below 17 degrees?
>
> -Here is the insightful comment from the leed reviewing oracle.
>
> Additionally, ensure that the Baseline heat pumps are modeled according to Section G3.1.3.1, which requires that the electric air?source 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. 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).
>
> Classification: UNCLASSIFIED
> Caveats: NONE
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> End of Trace-users Digest, Vol 57, Issue 1
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-- 
Mark Denyer P.E.   LEED^(TM) AP BD&C
Principal
MFIA, Inc. Consulting Engineers
2007 SE Ash St.
Portland, Oregon 97214
(503) 234-0548
mark.denyer at mfia-eng.com
www.mfia-eng.com

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