[Equest-users] [Bldg-sim] PTHP crankcase heater?

via Equest-users equest-users at lists.onebuilding.org
Fri Sep 2 14:30:22 PDT 2016

Yes, crankcase heaters can be found in any packaged equipment with a
compressor, and more likely with heatpumps (which operate in cool
ambient conditions).


Here's a listing of crankcase heaters for various recognizable heatpump


This sample varies from ~30 - 140 Watts, sometimes varying output on
their own with temperature.


Sometimes these are simply on all the time, other times you'll have
controls that 

*         cutoff operation above a certain temperature 

*         prevent heating while compressor is actually operating

*         vary wattage with temperature

*         energize only during as part of the ON cycle


eQUEST (as an illustrative example) has defaults which assumes crankcase
heating controls reflective of the first two bullets:  

*         50F cutoff, 

*         only when compressor isn't operating,

*         either 50W or 24W per compressor, depending on system type.


If on a data sheet you see the phrasing "low-ambient kit," then a
crankcase heater is likely a part of that option.  Low-ambient kits can
include other features/controls such as a defrost cycle, hoods to
increase condenser fan velocity, etc.   For some manufacturers,
crankcase heaters are standard on packaged AC/HP equipment and won't be
listed as an option you'd otherwise have to specify (particularly as you
move upwards into larger equipment, where the service calls could be
more costly).


In a similar vein, anyone dealing with simulating open cooling towers
(operating at or near freezing temperatures) should seek out the
presence of basin water heaters.  They are very similar to compressor
crankcase heaters in terms of operation, but can be an order of
magnitude more impactful to miss!





Nick Caton, P.E.

  Senior Energy Engineer
  Energy and Sustainability Services
  Schneider Electric

D  913.564.6361 
M  785.410.3317 
E  nicholas.caton at schneider-electric.com
<mailto:nicholas.caton at schneider-electric.com> 
F  913.564.6380

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States




From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf
Of Doug Maddox via Bldg-sim
Sent: Friday, September 02, 2016 1:25 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] PTHP crankcase heater?


Does anyone know whether packaged terminal heat pumps use crankcase
heaters, and if so, what is a typical Wattage?


Doug Maddox

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