Off Grid Home Forums Technical Discussion Off-Grid ground source heat pump? Re: Off-Grid ground source heat pump?


Well, I’ll chime in.. Haven’t done any of that but I’ve thought a lot about it. I’d say its far more efficient to simply locate your camp underground, or under earth (above grade). Think about root cellars here.

You are trying to escape the cold which seems off topic this time of year here in the USA. Geothermal options include blowing air underground, and pumping water or maybe oil underground I suppose. Let the ground normalize the temps to ground temps and then bring the air/liquid back up trough a heat exchanger maybe. Geothermal wells around here are made using some kind of thermal grout. I suppose a hold is bored up to 400 feet deep, two pipes with a U at the bottom are dropped in, and grout is filled in around them.

A system like this is an active system. I don’t know of a passive geothermal system. (Passive is where you build the living space well below ground, or make good use of solar radiation or thermal mass and ventilation as well as moveable insulation) This means you are using electricity for fans or pumps. Then the point becomes comparing energy used per BTU added or removed for geothermal vs a standard heater or air conditioner.

I’d like to do some testing with geothermal myself, not sure when I’ll get money or time though. 1 BTU is the amount of heat needed to raise 1 pound of water 1 degree F. As I state in one of my articles on the blog, a 10’x10’x10′ area is 1000 cubic feet. raise that 1 degree F and you added approx. 20 BTUs

drop that 1 degree and you lost 20 BTUs. In your case you are loosing BTUs and having to put then back. Now the question becomes, how fast are you loosing

those BTUs and how fast can you put them back.

We need a way to measure these BTUs for various experiments. This is simple we can simply record the temperature of a volume of air or water over time intervals. Note the change over time and calculate BTU’s lost or gained. We need to know how much energy was used to operate this active system during the same time, to see what cost where per BTU for the transfer of the heat. For anything electrical a watt meter might come in handy. Then you would need to

know cost per kw hour (in the USA anyway). Of course you can do all this using metric if you really want too and that might be the more scientific way.