Quote:
Originally Posted by theoldwizard1
If the specs on my GSHP showed CoP falling off below 4C, I would surely want a field that could produce above 4C !
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Dear Wiz,
If someone gave you the impression that COP falls off (like a buffalo falling off a cliff) at some particular temperature, they have seriously misled you.
The truth is that in a heat pump situation, COP depends on the temperature of the SOURCE, no matter if it is air, or water, or concrete.
When the temperature of the source declines to any extent, so does the COP.
EDIT: I went to the Carnot Efficiency page of Wikipedia, and generated a graph that will best indicate what I am trying to say... the legends are bogus, but the shape is right.
When your source temperature goes down at all, so does your COP, and it will continue to do so at an increasing rate.
The actual problem is really an economic issue, because there will be a point when the electricity to run the unit, is worth more in watts of heat than your heat pump can deliver.
Now, it is possible that you could build a loop field so vast, that you would no longer be able to notice any temperature drop (and COP decrease)... and that is because you are old and your eyes are not those of an Olympian god so you would not be able to see it.
-AC