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samclem · 11-07-2007, 08:47 PM

It can be a very attractive technology. It saves a lot of energy. There are a few approaches to exchanging heat with the ground :

- Bury a large loop of PEX (plastic pipe) either horizontallly or vertically. These "closed loop" systems require a lot of digging and installation costs can make them prohibitively expensive (payback on the order of tens of years)

- same as above, but the loop rests ont he bottom of a large pond or lake. Far less expensive to install than above, but temps won't be as favorable as deeper ground coupling.

- Pump out well water, exchange the heat, and re-inject the well water in a different well nearby. This can save a lot of money and be a very attractive approach if the water quality is good. Very hard water will cause the heat exchanger to scale up and cost big $$ in maintenence. This approach is not allowed in some areas (due to possibility of contaminating the groundwater used by everyone else.)

- Pump out the well water, exchange the heat, dump it into a river/surface point. Cheaper than above, but illegal/irresponsible unless you are lucky enough to live in an area with tons of extra subterranean water.

- Single casing well exchange (I've forgotten the actual name of this): If you've got a really deep well (typically 500+ feet for the heat/ac needs of an average home) you can take water out of the bottom of a well, exchange the heat, and dump it back into the top. It will heat up/cool off back to ambient temp by the time it reaches the bottom again. This approach is NOT a common one, but it does work and can be done inexpensively (again, if your water quality is good and the well is deep enough).

Also, there are "Direct Exchange" units that don't use water/glycol in the ground loop, they send the actual refrigerant into the ground through a loop. Technically, these are more efficient (one less exchange of heat), but they can be more costly, and I didn't get the feeling that the approach was likely to be as reliable as the more common method using water/glycol earth exchange loop and a flourocarbon-refrigerant loop for the compressor/internal heat exchanger.

The technology of groundsource heat pumps is mature and it works. The biggest problem is that each installation requires site-specific analysis/engineering, so you need a good, qualified dealer/installer. These are not common, and it takes some work to know if the installer reallly knows what he is doing (they all have very glossy brochures and impressive sales pitches). I looked into it, wanted to do it, but I could not find a good local dealer and the cost/payback numbers just didn't work out.

Good luck!

11-07-2007, 08:47 PM	#4
samclem Thinks s/he gets paid by the post Join Date: May 2004 Posts: 4,309	It can be a very attractive technology. It saves a lot of energy. There are a few approaches to exchanging heat with the ground : - Bury a large loop of PEX (plastic pipe) either horizontallly or vertically. These "closed loop" systems require a lot of digging and installation costs can make them prohibitively expensive (payback on the order of tens of years) - same as above, but the loop rests ont he bottom of a large pond or lake. Far less expensive to install than above, but temps won't be as favorable as deeper ground coupling. - Pump out well water, exchange the heat, and re-inject the well water in a different well nearby. This can save a lot of money and be a very attractive approach if the water quality is good. Very hard water will cause the heat exchanger to scale up and cost big $$ in maintenence. This approach is not allowed in some areas (due to possibility of contaminating the groundwater used by everyone else.) - Pump out the well water, exchange the heat, dump it into a river/surface point. Cheaper than above, but illegal/irresponsible unless you are lucky enough to live in an area with tons of extra subterranean water. - Single casing well exchange (I've forgotten the actual name of this): If you've got a really deep well (typically 500+ feet for the heat/ac needs of an average home) you can take water out of the bottom of a well, exchange the heat, and dump it back into the top. It will heat up/cool off back to ambient temp by the time it reaches the bottom again. This approach is NOT a common one, but it does work and can be done inexpensively (again, if your water quality is good and the well is deep enough). Also, there are "Direct Exchange" units that don't use water/glycol in the ground loop, they send the actual refrigerant into the ground through a loop. Technically, these are more efficient (one less exchange of heat), but they can be more costly, and I didn't get the feeling that the approach was likely to be as reliable as the more common method using water/glycol earth exchange loop and a flourocarbon-refrigerant loop for the compressor/internal heat exchanger. The technology of groundsource heat pumps is mature and it works. The biggest problem is that each installation requires site-specific analysis/engineering, so you need a good, qualified dealer/installer. These are not common, and it takes some work to know if the installer reallly knows what he is doing (they all have very glossy brochures and impressive sales pitches). I looked into it, wanted to do it, but I could not find a good local dealer and the cost/payback numbers just didn't work out. Good luck! __________________ "Freedom begins when you tell Mrs. Grundy to go fly a kite." - R. Heinlein Last edited by samclem; 11-07-2007 at 11:44 PM.