Geothermal heating and cooling is having another revival due to rising energy and oil costs. Geothermal heating utilizes the natural temperature of the ground at about 10 feet and below which averages about 68 degrees Farenhiet. Trenches are dug or holes are drilled and plastic tubing is placed in them. The tubing is then filled with a circulating fluid, usually just water and heated to the temperature of the ground during circulation. The fluid then goes to a heat exchanger where the heat of the fluid is exchanged to the air, which in turn circulates through the house to warm it. This eliminates the need for a compressor in a heat pump, which uses a lot of energy to compress a substance like refrigerants into a liquid. On average, a geothermal heat pump saves about 7 out of ten energy units that would go into operating a standard heat pump. The main additional cost of adding a geothermal heat pump is in the installation of the tubing in the trenches or holes, which can be expensive because it requires special machinery like a large excavator or drill rig. The average added cost is about $5K-10K, but can be payed back within a few years depending on energy costs in your area.
You have to google this one to get a decent explanation of how it works, because it is kind of extensive. The basic premise is that tubes of glycol are circulated in about 1000 feet of tubing to pick up the heat of the earth which is about 55 degrees in the northern areas of the country all the time. This glycol is circulated thru the condenser of the air conditioner/heat pump to make the refrigerant 55F instead of relying on the air temperature. Heat pumps that get their heat from the air don't work well when the air temperature drops to below 40F, so this is where geothermal shines because it doesn't drop below 55F and the cooling fluid is a liquid instead of a gas, like air , so it transfers heat much better. Heat pumps get more energy from the glycol earth heat than it takes to run the compressor. So if your compressor uses 2 kwh of power it might be able to get 8 kwh of heat from the ground temperature. That is the big attraction. A normal electric heater would use 2 kwh of electricity to make 2 kwh of heat. A geothermal heat pumps works by using the earth heat of 55F to boil the refrigerant which boils at maybe -40F. So the temp of the earth at 55F looks downright balmy. When the refrigerant is boiled it is compressed and condensed which releases the heat of the compression plus the heat from the earth. The downside is the expense. At a minimum, for a small house it is about $7000 dollars as opposed to an air heat pump which would be about $3500. Big systems for large houses can run close to $20000
