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View Full Version : O.T. Ground Source Heat Pump



Duffy
11-04-2008, 12:36 PM
Thought someone would be interested. In the next block they are building a new house.
Driller showed up at 7.00 AM, started drilling about 8.00. He is drilling a 6" hole 375 feet, installing a 750 foot loop of 1 1/4" polyethylene pipe and grouting it all in with a "high conductivity" silica sand proprietary grout. I was just talking to the drill boss, and they were adding stem to the rig. he was at 200 feet and said he would complete the hole in about an hour. He will have the whole job done and be gone by quitting time!
Cost is $19.00/ft of finished hole plus $5.00/ft from well to furnace. Including taxes, it will be about $8300.00. Who knows what the furnace will cost-I know that it is only a 2 1/2 ton heat pump, probably with a 15 Kw booster heater, so it SHOULD cost about $2500.00. BUT this is REALLY a "State-of-the-Art, Energy, Efficient Greenhouse Gas Reducing Domestic Climate-Control Device" and the owner will probably pay in excess of $10,000.00. The Government will give about $7000.00 subsidy on this little project--aint life grand? Duffy

aostling
11-04-2008, 12:47 PM
I don't think there is anything O.T. about heat pumps. http://en.wikipedia.org/wiki/Geothermal_heat_pump gives a good overview of geothermal heat pump systems. The one in your neighborhood may be unusual in involving such a deep hole. Where is it?

Duffy
11-04-2008, 01:48 PM
I live in Gatineau Quebec, just across the river from Ottawa. There are at least four systems within two blocks of me. One, two houses down, uses two wells, each over 250 feet, both with closed loops. That is a large house, and indoor pool, hence the need for deep wells. The design figure that is being used around here is ABOUT 125 ft of well per ton. This area is shallow soil,(about 2 feet,) over layered limestone and shale. Interestingly, there is lots of groundwater, usually at about 125 feet. The driller told me this morning that he hit water at that depth and the flow was about 20 gpm. That would be LOTS of water for a heat pump, although they would have to drill another well the same depth, to get rid of the chilled water. Such a system would have been MUCH cheaper, since there would only be 250 ft of well @$18.00/ft, (yes, a dollar a foot LESS for water wells-no grout,) against the additional cost of a good-sized submersible pump, and the heat pump is the same.
One consideration with an open loop system is that you have to determine the direction of flow of the groundwater, and ensure that you extract upstream and discharge downstream to prevent thermal short circuits. That way you can place the two wells as close as 75 feet, i.e. on a small residential city lot. Here the lots are what some would call "large" lots, about 10,000 square feet, and separation should not be a problem. all of that gets sorted out by a hydrogeological engineer- one hopes.