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Old 04-01-2009, 01:53 PM   #9 (permalink)
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Join Date: Mar 2009
Location: oregon
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> ...what if I got a small window-mount heat pump unit,
> detached its exterior coil and built a water box around that?
> Then just circulate your heat exchanger water from the
> ground loops into the water box.

I think it would really improve the efficiency of the unit, you should do this!

I actually considered making a water box around the air heat exchangers also for my project, but I intend to use this to heat my house, so I took the route I took.

A couple of things you might consider, the amount of tubing and fins, etc that the air exchanger uses is way bigger than you need, it will still work, though. I've been looking for some rule-of-thumb that I could use to make a switch from air to water, so I'd know where to start. I seem to recall that I saw on some boat refitting blog, someone saying there was a 50:1 difference between tubing in air and tubing in water. A buddy of mine is fitting a small refrig into his boat and using a condenser that is actually in contact with the ocean water. He said the condenser tube was only a few inches long for his refrig. So maybe the 50:1 ratio is close.

Another thing is that if you plan to use this unit for a long time you could get stuff growing between the fins, in which case you might need to carefully remove the fins all together, to prevent fouling.

Another suggestion is that your unit, however big or small it is will be putting out a surprising amount of heat, so you'll need to have sufficient pipe in the ground to absorb all the heat. The rule of thumb where I live is that a 200 foot hole is required to transfer 12000 btu per hour. Look on your AC to see what the BTU rating is. If, for instance it is 8000 btu, the equation would be:

Required Hole Depth= (8000/12000) * 200

So your hole would need to be at least 133 feet deep.

You could also use 10 holes, each 13 feet deep. They should be separated by at least 8 feet each.

The earth has a lot of heat to give or, in your case, to absorb. But it does it slowly on a per foot basis. So you need more feet of pipe in the ground to get the heat flow rate you desire.

But it definitely sounds like a worthy experiment that we can all learn from.

I'm currently working on a detailed post, spelling exactly how to convert an Air Conditioner or De-Humidifier to a working heat pump.

So stay tuned...

And best luck on Eco-Modding your AC,


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