Need info on geothermal heat pumps... PV's viable?

[austi012]

Hey,

I'm designing the house that will go on my land.

I want to be off the grid if I can manage it.

I am very intrigued by ground source heat pumps. These things run a big coil of antifreeze-filled tubing under the ground. In the winter, they use a heat pump to extract the heat for the house. In the summer, the heat pump runs "in reverse" and puts het in the ground, cooling the house.

I read some case studies on my local utility's web site. In one case, a fellow put up a 4500 square foot house with a geothermal pump. He heats and cools that beast for 30 bucks a month... the cost of the electricity to run the heat pump.

My question: does anybody make a Geothermal Heat pump that runs on 12V Dc or 24V DC current, such as you'd get from a wind generator or an array of Photovoltaics? It would be too sweet to have a house that heated and cooled itself for 0 dollars a month, after the initial investment in the equipment.

If anybody can point me to info, I'd be obliged.

cheers

Thaddeus

[AndyF]

Why do you need to have the heat pump run on 12/24 V DC? You can install an inverter and get 110/220 AC out of your array pretty easily and then use standard components for your heating system.

[austi012]

Don't -have- to, but there's a conversion loss I wouldn't want to incur. Waste not, want not.

[rbhollabaugh]

Have you looked at homepower.com?
They have a wonderful magazine but I don't think I've ever seen a low voltage conversion of a heat pump.
Once you know how many BTU the unit needs to produce you can size a 12 or 24 volt motor and compressor. Use a car compressor. The Sanden SD508 is one of the most common and reliable compressors around. It takes a couple horsepower to run a car compressor and that ain't chump change when running off batteries for an hour at a time. I would also want to know the heat loss/gain of your building at 0 degrees F and 100 degrees F. I suspect that the amount of energy to run a heat pump would be substantial and would cause your battery bank to be extremely large and expensive.
When we built we could have gone with a heat pump for backup heat/AC but we got estimates around $15k. The electric backup coil cost $500 + installation. The AC cost us $5k at a later date but would have been half that if I did it myself.
I hope you find a way to do it.
Rich