Geothermal is an increasingly attractive heating and cooling option. Here’s what builders and developers need to know to offer and install it.

The vast majority of people in the United States and Canada heat and cool their homes by burning fuel (oil or gas) or by using electricity created by generators that burn fuel. It’s no secret that fuel prices will continue to rise due to availability and the cost of extraction, infrastructure, and delivery. Fuel availability is in question—most of us would probably wager that the price of oil will be at $100/barrel within two years.

Infrastructure must be continually improved and defended at great cost, and energy delivery costs will inevitably rise over time. Aside from these financial concerns, the “carbon footprint” of a home—how much carbon dioxide (a greenhouse gas) a home contributes to the atmosphere—has come into sharp focus with concerns about global warming. To heat and cool a home, the carbon dioxide (CO2) contributed by a typical U.S. household can reach 60 tons each year, according to the EPA. That’s the equivalent pollution created by 11,000 cars driving 1,000 miles a month. With about 75 million households just in the United States, the combined effect of that much CO2 is dramatic.

Geothermal Comes of Age

To mitigate these risks and reduce the carbon footprint of a typical home, there has been renewed and increasing interest in ground-source geothermal or geoexchange heating-andcooling systems. Indeed, there are 1 million of these residential units installed and working in the United States today. Geothermal systems do not depend on commodity fuels (oil or gas), and they depend only minimally on electricity. The name geothermal derives from the fact that the units use the moderating temperature of the earth to help condition the air of a home. (Residential geothermal should not be confused with drilling to find ultra-hot water sources below the earth.) Through a heat-pump cycle of evaporation, compression, condensation, and expansion, the geothermal system in summer concentrates heat from the house and emits it into the earth, while returning cool air. In winter, the geothermal system concentrates that ground heat to well over 100°F and circulates it back into the house using traditional forced-hot-air, hydronic, or radiant heating systems. With geothermal units (just as with a refrigerator, which is a mini heat pump), a coiled loop contains refrigerant under pressure, but the geothermal coil is not strapped to the back of the unit. Instead, the coil, or loop, is run through the ground, below frost depth. A pump and compressor located above ground drive the system to circulate the refrigerant and deliver hot or cold air to the home, depending on the demands of the season. The EPA found that geothermal can reduce energy consumption by over 40% compared with air-source heat pumps and by over 70% compared with electric resistance heating or standard air-conditioning equipment. (Industry sources claim that geothermal units are, on average, 48% more efficient than the best gas furnaces, over 75% more efficient than oil furnaces, and they outperform the best gas technology— gas heat pumps—by an average of 36% in heating mode and 43% in cooling mode.) Geothermal systems are widely considered highly reliable, require little maintenance, and have long service lives. As for homeowner comfort, surveys by utility companies cited on leading trade association Web sites show a higher level of consumer satisfaction for geothermal than for conventional HVAC systems: 95% of all geothermal customers would recommend such systems to a family member or friend. The EPA, the DOE, and state agencies like the California Energy Commission all endorse geothermal. President Bush’s house in Texas is heated and cooled with a geothermal unit.

With the number of U.S. installations at 1 million, geothermal technology has clearly matured to the point where it is risk free for the builder or developer, if the units are sized and installed properly. The manufacturers of geothermal units are well organized, and they offer remarkably long warranties on the above-ground and below-ground aspects of the systems (50+ years). A leading trade association, Geoexchange (Geoexchange.org), offers excellent resources, including contractor locators, marketing materials, case studies, even a brief educational movie that can assure the most skeptical homeowner.

How Geothermal Works l Accessing ground-source heat. Everywhere in the world, just below frost depth, the earth maintains a constant average temperature between 45°F and 70°F. (In the United States, the average is 50°F–55°F.) To generate heat in the winter and cold in the summer, geothermal systems use a loop of copper or plastic piping buried in the earth, hence the origin of the term ground-source geothermal. The loop contains ecologically friendly refrigerant, which is circulated through the loop under pressure. In the winter, the loop collects the relative warmth from the ground and delivers it to the home’s traditional forced-hot-air system through a pressure-reduction and heat-exchange system. In the summer, the refrigerant collects heat from the house and emits it through the same loop back into the earth, while distributing cooler air like a conventional air-conditioning system (see whole-house schematics, previous page). The compressor and heat exchanger needed to run a typical system require electricity, which can be supplied through photovoltaic panels or from traditional AC power. Geothermal systems emit no gases, so they can be located indoors, even in a closet. They are also notoriously quiet.

_{Thank you to www.zerofootprint.net for their permission to use this article. Please check out their website for more articles on green energy. This article can be found here: http://www.zerofootprint.net/ideas/291 Copyright © 2007}