Heat Pumps

[jaybee]

Question:

Can an old fridge be used to extract heat from a sub-terranean coil and then dump the heat into a hot water tank.

It's a CFC free fridge if that's the worry and the cause of the deletion of this post.

[bob g]

yes it can be used that way, but

most refrigerator compressors aren't capable of many btu's, probably less than a few hundred btu at most.

also the size of the tubing used in the subterrainian strata will likely not be able to pick up much heat for very long, before the area in contact with the tubing will become frozen or not have alot of heat to harvest.

perhaps in a well or pond you might do better

there are refrigeration guru's on this board, perhaps they will weigh in on your idea

bob g

[Ungrounded Lightning Rod]

Also:  Fridges are optimized to work at lower temperatures than you'll have.  You might want to look into building something from heat-pump heating/air conditioning equipment instead.

Isn't the usual method to use water to connect to the underground heat source/sink stratum, either by pumping up, using, and re-injecting ground water or by buring pipes?  (Then the water goes to a heat-exchanger to interface with the freon replacement in the heat pump.)

[Volvo farmer]

Average refrigerator compressors are 800-1100 BTU. I just checked my gas range. The burners on the top of my range are rated at 9000 btu. So if you get it all hooked up it will heat water ten times slower than the burner on top of a gas range. I'd be concerned about corrosion of the underground coil too.

I've got more old free refrigerators than I can shake a stick at. I've also got a EPA CFC license and the tools to do a job like this but the seat of my pants tells me it's not a worthwhile endeavor.

 

[maker of toys]

I would add that it doesn't seem like it'd be worth-while if you're trying to get anything more than a little bit of luke-warm water- remember that the efficiency of a heat pump varies inversely with the temperature differential.

ie, you can expect much better performance if the ground is at 20'c and the water only has to be 30'c, than if the ground is 15'c and the desired water temperature is 50'c.

into the bargain, the higher the output temperature, the faster your compressor will wear.

for the same electrical input power, I'd expect more hot water from a pump and some solar collectors; of course, if you're dealing with home-owners limitations or other appearance concerns. . .