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30-11-2009, 04:58 AM #1
Heat-pump mass charge determination
Below is a picture of a typical mass charge determination run for an a/c system.
I have superimposed on the evaporator power & compressor power, the condenser output power curve (in red).
For a heat-pump system, which mass charge would you select, & why?
Last edited by desA; 30-11-2009 at 05:02 AM.
Engineering Specialist - Cuprobraze, Nocolok, CD Technology
Rarefied Technologies ( SE Asia )
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30-11-2009, 06:09 AM #2
Re: Heat-pump mass charge determination
The original test data.
Engineering Specialist - Cuprobraze, Nocolok, CD Technology
Rarefied Technologies ( SE Asia )
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30-11-2009, 11:13 PM #3
Re: Heat-pump mass charge determination
Taking this a step further.
There are, for an a/c system, two 'logical' points to consider:
1. At COP maximum;
2. At maximum evaporator performance (Q'e,max).
For a heat-pump, the condenser output performance (Q'c) seems to continue rising as refrigerant mass charge rises.
Where should the heat-pump cut-off come?Engineering Specialist - Cuprobraze, Nocolok, CD Technology
Rarefied Technologies ( SE Asia )
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30-11-2009, 11:25 PM #4
Re: Heat-pump mass charge determination
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30-11-2009, 11:38 PM #5
Re: Heat-pump mass charge determination
Thanks Gary.
Not according to the chart shown (or in practice, for that matter). It seems that the decision for a heat-pump may not be to cut-&-dried as for an a/c. This is what makes it more difficult.
Things like condenser SC & evap SH seem to become limiting factors, for consideration, well before a Q'c peak can be observed.
What makes matters even more complicated is that the performance of the system changes across the heating range. So, practically, a set of these curves needs to be developed at each stage along the heating cycle. For the purposes of this thread, we can take it that the curve shown represents the hottest condition for the heat-pump.Last edited by desA; 30-11-2009 at 11:48 PM.
Engineering Specialist - Cuprobraze, Nocolok, CD Technology
Rarefied Technologies ( SE Asia )
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01-12-2009, 04:40 AM #6
Re: Heat-pump mass charge determination
It looks as if the condenser output, power input, discharge pressure and subcooling are all going up in unison.
It would seem there must be some point at which they part ways. In particular I would expect the subcooling to cause a reversal in condenser output as the liquid backs up into the condenser.
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01-12-2009, 04:58 AM #7
Re: Heat-pump mass charge determination
What I've observed practically, is that towards the top end of this mass-charge scale, the condenser pushes back by raising approach & SC as well. There must obviously be some limit, somewhere, but this seems to be moving towards an unsafe region in terms of compressor operation, for no obvious benefit, as it is already past the point of maximum COP.
What also happens is that Te,sat rises at the same time - releasing more mass-flow, further feeding into the problem.
Its like these systems don't have a self-regulating mechanism within reasonable pressure bounds.Engineering Specialist - Cuprobraze, Nocolok, CD Technology
Rarefied Technologies ( SE Asia )
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01-12-2009, 05:09 AM #8
Re: Heat-pump mass charge determination
Where is the point of maximum COP?
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01-12-2009, 05:27 AM #9
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