Geo-Exchange
A geo-exchange system is a central heating and/or air
cooling system that actively pumps heat to or from the shallow ground several
meters deep, where temperatures remain moderate all year (Hanova and
Dowlatabadi 2007). Geo-exchange technology takes advantage of the cave-like conditions
under the soil, using it as alternately a heat source or heat sink throughout
the year. Geo-exchange, in contrast to utilities-scale geothermal power, does
not rely chiefly on heat from true geological sources (Rafferty 1997) but draws
energy from the sun-warmed ground to boost heating and cooling efficiency far
above that of electrical heating (it may be combined with solar heating to
create a geosolar system with even greater efficiency; see “Solar”). In a
geo-exchange system, a pump circulates
water or antifreeze through several hundred feet of pipes that have been buried
in the ground (vertically or horizontally) or, alternatively, submerged in a
pond or lake. The tubes of fluid serve both to supplement heat (with relatively
warm fluid in winter) and to cool (with relatively cool fluid in summer) a
structure. Using an electrically-driven compressor and heat exchangers, warm or
cool air or fluid is pumped into either an air duct system or to radiant
flooring.
The U.S. EPA has called ground-source heat pumps the most energy-efficient, environmentally clean, and cost-effective space conditioning system available (EPA 1993). It has significant potential to reduce GHG emissions if employed widely. Geo-exchange produces zero emissions, provided electrical power to run the system is supplied by some renewable source. Natural gas furnaces may be a more sound heating choice on balance, depending on the GHG intensity of the local electricity supply. One barrier to employing geo-exchange is the high up-front cost, but the difference can be made up in energy cost savings in three to ten years, (http://en.wikipedia.org/wiki/Geothermal_heat_pump) and the system can last 30 to 50 years (http://apps1.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12640).
In Sonoma County, the Sonoma County Water Agency is studying the feasibility of using recycled water to heat and cool buildings using geo-exchange principles in a project called the Regional Geo-exchange Energy Efficiency Project (http://scwa2.computergrafixco.com/eNews/index.asp?issue=1/1/2009&campaign=Enews&article=2029).
Citations:
Environmental Protection Agency (EPA). 1993. Space Conditioning: The Next Frontier. Report 430-R-93-004. Washington, D.C.
Hanova, J. and H. Dowlatabadi. 2007. Strategic GHG reduction through the use of ground source heat pump technology. Environmental Research Letters 2: 04400, 8 pages.
Rafferty, K. 1997. An information survival kit for the prospective residential geothermal heat pump owner. Geo-Heat Centre Quarterly Bulletin 18(2): 1-11. Oregon Institute of Technology, Klamath Falls, Oregon.
