Homepage › Forums › Technical Discussion › Off-Grid ground source heat pump?
- This topic has 8 replies, 3 voices, and was last updated 10 years, 8 months ago by fotman.
July 12, 2012 at 12:00 am #63149
I have a 700sq/ft camp in rural Nova Scotia. I am currently installing a 400w wind generator to compliment my solar panel. I would like to come up with a method of keeping the camp warm (above freezing) while I’m not there. I have excavating equipment at my disposal and a field area I can dig up to lay pipe. Has anyone had any experience building a system similar to this?July 12, 2012 at 12:00 am #66494pintadaMember
I haven’t actually done it, but have some knowledge … i think
Most of the plans that i’ve seen include wells. The deeper you go, the more heat you will access. Also, i don’t know where the frost line is up there. Here, people bury water lines at least 6 feet deep to keep them from freezing so if the pipelines are not at least 6 feet deep here, you would be building a refrigerator (LOL) not a heater!
I’m in the mountains of southern CO US.
My advice, ask some old fart (a farmer or house builder) how deep to bury a water line, then plan on going much deeper.
Come to think about it, i’m sorry, but i really think you will need wells … to get your heat collection stuff 10 meters or more below ground.July 13, 2012 at 12:00 am #66496
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.July 13, 2012 at 12:00 am #66497
And as far as blowing air underground for cooling/heating I’d consider using metal culvert. I think the corrugated design would make heat transfer more efficient. Though I have heard of using sewer pipe for this as well.
On a side note I once visited a cave in Northern Arkansas USA. This cave was called Zack Blowing cave because if always blew air out its entrance. Some clever folks in the 1800s who wanted to cool and heat their store (supplies and outfitting I assume) ran a cast iron pipe of about 1.5 feet in diameter from the store into the cave as a duct. They walled up the cave with stone a few hundred feet in as to concentrate the blowing air into the pipe. They cemented around the pipe to protect it from rusting I guess. And the front of the cave served as cold storage I guess. There was a concrete frame and wooden door on the front of the cave. This cave was fairly large with a good sized stream and 1000’s of feet of passage if not much more that human’s couldn’t get too.July 13, 2012 at 12:00 am #66499
I will say this however, in solar the win win situation is in using direct solar radiation to heat air. So in the geothermal situation maybe warming air isn’t such a bad way to go. It will require a lot of culvert or pipe though. It will also require active ventilation. If you don’t want musty underground smells and moisture in your dwelling then a heat exchanger would be more ideal.
The question becomes, how much energy is needed to blow or push air through the underground system vs operating an electric heater.July 16, 2012 at 12:00 am #66512
I was sort of thinking about a fluid type system with plumbers antifreeze and a small circ pump. Drilling wells would probably be $10k or more, which doesn’t really fit in the budget. We are contemplating digging a large fish pond (1/2 acre). I know my friends pond only freezes about 12-24″ deep. I wonder if I could do something with that? My camp is all steel construction with only 2″ of insulation in the walls. I had to paint the top white so we aren’t baked out of it in the summer.In the winter there is sometimes 4 or 5 feet of snow on the top.July 16, 2012 at 12:00 am #66513
Well, (a deep subject for such a shallow mind as my grandmother used to say) I suppose water would need antifreeze in it. I’m not sure pure antifreeze is necessary. As for the wells, have you looked into cheaper options for drilling your own wells? There are very small hand operated well drilling equipment on the market available. Also there are point driven wells. These are where pipe is pile driven into the ground. Of course this only works in anything but rock and will only go so deep. There are 3 point hitch drilling rigs for tractors as well. If you couldn’t buy one for $5K then maybe you could rent one.July 16, 2012 at 12:00 am #66514
Do you have any room for stacking several 50 gallon drums of water in this camp? Water is great thermal mass. Think about it. 50 gallons of water is about 400 lbs of water. if that 50 gals looses 1 degree of warmth it gives off 400 BTU’s of heat. On the other hand if it freezes and you are trying to warm the place back up it will cool the same way.July 30, 2012 at 12:00 am #66545
I looked into the three point hitch drill rigs. I can have one landed here for between $7-8k. While this doesn’t fit in the budget, in the end I would have it to sell or use for fun and profit. I will need to check into it more before laying out the cash
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