Sidebar by Allen Best
Energy – February 2008 – Colorado Central Magazine
While hot water underground can produce electricity, another type of ground-source heat is warming — and, counterintuitively, cooling — homes.
The technology, often called geo-exchange, is decades old, but because natural gas and other fossil fuel energies in the West have cost so little to consumers, it has not been broadly deployed.
Still, a million such systems have been installed in the United States since 1980. It is also gaining favor in Colorado. One firm based in Grand Junction has installed about 500 such systems. The technology, in modified fashion, is also in use at the Snowmass Club, where both the heat and coolness from a small pond are alternatively used in winter and summer.
Geoexchange is premised on the fact that below about 8 to 12 feet, the earth has a constant temperature of 55 to 60 degrees F for hundreds of feet.
To draw upon this heat, wells up to about 400 feet are drilled. Another technique –less expensive given current drilling prices –is to dig trenches about 8 to 12 feet deep. In these wells or trenches, coiled pipe is inserted or laid.
The same mechanics are used with the pond at the Snowmass Club.
Into these pipes either water or glycol is run. The warmth is transferred through the pipe and into the fluid, which is routed to a building’s mechanical room, where the heat is exchanged into a gas, which is compressed, producing greater heat. That heat is then used to heat water. This hot water can then be distributed through the house in either a forced-heat system or in radiant heating.
The process uses some of the same technology as a refrigerator, which uses a gas to help suck the heat out of a box.
A study by the Delta-Montrose Electric Association finds that a 2,000-square-foot home kept to a constant 70 degrees year-round would cost $724 if done by geoexchange. In contrast, natural gas would cost $1,021, propane $2,474, and electrical $2,640.
Geoexchange has a much higher up-front cost than any other system of heating and cooling, but has a rapid pay-back period of 3 to 5 years for commercial applications and 5 to 7 for residential units.
Conventional ground-source heat pump technology is best installed with new buildings. Retrofits, partly because of the damage to landscaping, tend to get expensive.
However, new hybrid technology now being deployed, allowing the outdoor air to also be used, somewhat the same way that an air conditioner operates, will make retrofits more cost-effective. Analyst Tom Konrad of Denver expects the new technology to substantially expand the market for heat pumps.
