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Refrigeration heat in vs. heat out

by tinska.h
Tags: heat, refrigeration
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tinska.h
#1
Aug9-14, 04:37 PM
P: 3
Greetings,

I wonder what are the usual thermal efficiency for vapor compressor (refrigeration cycle), and only speaking thermal efficiency. I mean COP describes the heat energy pumped vs. work put in. But since some of the work is converted to mechanical energy and to other forms than heat. Therefore I wonder:

Is there any quantitative benchmark which I should look in to, which describes the heat energy pumped from cold side vs. system's overall produced heat? Or if anyone has knowledge what sort of heat in vs. heat out ratios do modern refrigerator/heat pumps have?


Thanks in advance
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billy_joule
#2
Aug9-14, 05:23 PM
P: 87
I'm not quite sure I understand your question, but anyway..

If you compare the actual COP to the ideal COP you can find the total losses; pipe friction, motor & compressor losses etc etc.
tinska.h
#3
Aug9-14, 06:12 PM
P: 3
I mean COP tells me the work in versus the heat energy being pumped. However since not all work in is converted to heat output, I'm looking for pure number of heat in vs. heat out, neglecting all other losses.

I'm in an understanding that COP just tells you the additional work needed vs. heat energy being pumped. But I'm looking for heat energy in vs. heat energy out.

billy_joule
#4
Aug9-14, 06:59 PM
P: 87
Refrigeration heat in vs. heat out

I'm in an understanding that COP just tells you the additional work needed vs. heat energy being pumped. But I'm looking for heat energy in vs. heat energy out.
conservation of energy tells us that:
Q low + W in = Q high

And we know that:

COP = Q low / W in

So heat in and heat out relate to the COP:

e.g. Q low + Q low/COP = Q high
tinska.h
#5
Aug10-14, 09:32 AM
P: 3
So the work in, means that all energy put in will convert in to heat energy?

The compressor's mechanical work is also heat?
Mech_Engineer
#6
Aug31-14, 12:40 AM
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Quote Quote by tinska.h View Post
So the work in, means that all energy put in will convert in to heat energy?
That would depend on the compressor's efficiency. If a compressor is 80% efficient, 20% of the input energy would be converted to heat.

Can you explain what you're hoping to compare as a metric? If we consider "heat produced" to be the addition of energy to your system boundary (e.g. room) that didn't start as thermal energy, the only "heat produced" by a refrigeration cycle will be the heat losses in the pump, which if I remember correctly is already taken into account in a standard COP calculation. The heat pumped by the refrigeration cycle is not really "heat produced" in the strict sense of the word, because it's really just heat from the environment that leaked into the fridge only to be pumped out again.

http://www.physicsforums.com/showthread.php?t=143647
http://en.wikipedia.org/wiki/Coefficient_of_performance
russ_watters
#7
Aug31-14, 03:15 PM
Mentor
P: 22,312
Quote Quote by tinska.h View Post
So the work in, means that all energy put in will convert in to heat energy?

The compressor's mechanical work is also heat?
All mechanical work eventually becomes heat. So the rejected heat is the heat removed from the fridge plus the mechanical work input.


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