Has anyone installed geothermal air conditioning for their home?

Is it okay if the ground is limestone? How deep do the pipes need to go into the ground? What is the necessary diameter of the pipes? If I have an old, deep water well hole, about 8 inch diameter, could that be made part of a geothermal airconditioning system?

I'm in central Texas, if that matters.

Thanks,

Rick#7

-- Rick (rick7@postmark.net), July 23, 2001

Answers

Rick, Have you tried,http://www.waterfurnace.com/technology.html ? I have installed these in various configrations charles-n-TN

-- charles gentry (cbgentry@mlec.com), July 23, 2001.

Hey, Rick, I'm from Texas, originally, but couldn't stand the humidity of East Texas, so i moved out here to the west coast. I've got a water furnace heat pump, which is also an air conditioner. I've only used it a total of about 15 hours in three summers, though. I can tell you that it only costs 18 cents per hour to run, and requires 4 1/2 gallons of water out of my 52 degree well for its cooling. Same cost for heating. It's a three ton unit, and handles my 3000 foot home no prob.

I happen to have an artesian well, or I'd have drilled return well. Most folks use buried pipe, which requires a lot of deep trenches and pipe. I think they are buried about five feet deep here.

There's also a "closed loop" configuration which would likely work for your "old deep water well hole". Go to water furnace's web site, and they'll either answer your questions more thoroughly, or direct you to a dealer. JOJ

-- jumpoff joe (jumpoff@ecoweb.net), July 23, 2001.

Hey,

The water furnace site is good and there are other resources but sometimes they can be pretty technical. If your burrying your pipes in a horizontal configuration they should be about 5 feet deep. If your going vertical it really doesn't matter. I've seen systems that go down 500 ft. for the average 2 1/2-5 ton residential system 1 1/4" pipe is good. It's highly recommended that you use fusion welded HDPE tubing. Look for the stuff that specifically made for geothermal loops. It a little more expensive but there is a difference. Do not use glue or PVC! If you can't use fusion welding there are accetable compression fittings available.

A fair rule of thumb is about 150' of pipe per ton of capacity but this can vary wildly depending on your geology so if you don't do a thermal capacity test of the ground first I'd start with the 150'/ton and configure it in way that you can add more later if need be. If your pumping the water directly thru your heat exchanger from a well you'll need about 2-3 gallons per minute per ton. For closed loop systems configure your field so that the fluid velocity in the pipe runs 2-3 feet per second. Much faster requires more pump work and much slower and the flow might be laminar and inhibit the heat transfer. This is probably getting too technical but you want turbulent flow in the pipe so you need a Reynolds number above 2000. Anyway, if you don't have pretty extensive technical knowledge to start I'd seek professional help. Unfortuneately, good help is hard to find. The single biggest mistake I've seen are overdesigned systems that drive up the cost and this is something professional help is famous for. The real challenge is to get the system just right with the minimum cost so the the long term economics are the best possible. Some good news is the systems are fairly forgiving and it's not that hard to get something that will work pretty well even if it's not totally optimized.

Good luck.

CQ

-- Carter (chucky@usit.net), July 24, 2001.

I think there was an article about this in Backwoods Home several years ago. They included detailed diagrams if I recall correctly. You might go to their website and access their archives.

-- connie in nm (karrellewis@aol.com), July 24, 2001.

Thanks a lotfor all the advice. I just looked up the past articles in Back Woods Home magazine. I think they will help.

Rick#7

-- Rick#7 (rick7@postmark.net), July 25, 2001.