Geothermal heating and cooling

Very cool idea finally starting to gain traction. (I have seen articles about it from 20 years ago but only now seeing systems being installed). From the NY Times:

Heat From the Earth to Warm Your Hearth
Russ Root made an efficient move last year - to a new home he had built in Goshen, Conn. While it is considerably bigger than his former house, in Chenango Forks, N.Y., it will cost far less to cool and to heat. That is because he did something he had thought about ever since he built his last house, 15 years earlier: he installed a geothermal system instead of an oil-guzzling boiler.

Now all the heat to warm his house is supplied by the earth beneath him. It's pumped up, through plastic piping, in water circulating in his backyard six feet underground - where the temperature stays at about 45 degrees - and distributed by a fan through the house's ductwork as air warmed to around 95 degrees.

The bill for Mr. Root's geothermal pump, its ground loop of piping and the house's ductwork was just over $21,500. While a geothermal system, including labor, typically costs more than a comparable furnace and air-conditioning system, the price was about the same for Mr. Root, because the extra expense of digging and looping - $1,500 in his case - was more than offset by a $2,000 rebate from Connecticut Light and Power.

"I was in the black from the day I moved in," said Mr. Root, who is a lineman for the utility, which treated him as it would any customer.

The water circulates through the geothermal pump over coils containing refrigerant, which absorbs its heat. The refrigerant is then raised to the higher temperature under pressure by a compressor. In the summer, the method is reversed. His home is cooled by circulating hot air out of the house - a process that is similar to the operation of a refrigerator, an appliance that his basement pump resembles.

The system is quiet, clean and odorless, and uses little electricity. Maintenance consists of cleaning a filter every few months; the pipes are guaranteed to last 50 years. There are virtually no moving parts other than the pump. After living for more than a year in the 2,900-square-foot home, a third bigger than his old house, Mr. Root finds that his energy costs are running about 20 percent less than the $2,700 he used to spend, or about 40 percent less per square foot.

Very cool -- this is a version of what is called a Heat Pump. Unlike an Air Conditioner or Refrigerator that move heat from one area to another, Heat Pumps can be reversed and used for heating and air conditioning. Since you are not using the electricity to create heat, only to move it, they are very economical to run. Since there is more work pumping 10 degrees up to 70 than there is in pumping 45 degrees up to 70, it makes more sense to start at the higher temperature. Ditto when it is hot inside and hot outside, pumping heat into a net sink takes less energy that trying to pump it into an area that is just as hot.