By Jana J. Madsen
Installed in 650,000 commercial and residential facilities and 650 educational buildings, the installation of geothermal heat pump heating and cooling systems are rising in popularity. Since their introduction into the world of HVAC in the mid-1970s, these systems have been a key component in finding energy-efficient heating and cooling options for commercial and institutional buildings. Endorsed by the U.S. Environmental Protection Agency and Department of Energy, geothermal heat pump systems offer significant energy savings and quick return on investment (usually less than five years).
How and Why They Work
Often referred to as GeoExchange or water source heat pumps, geothermal heat pump (GHP) systems use the earth’s constant temperature to heat and cool a facility. Plastic pipes usually made of high-density polyethylene are buried several feet in the ground (or lake) and connected to a geothermal heat pump located in the facility. A mixture usually containing water and an anti-freeze solution is circulated through the pipes. GHP systems differ from conventional furnaces in that instead of using fuel to create heat, the system takes advantage of the heat created naturally in the earth.
Because the earth maintains a constant temperature (ranging from an average of 45 to 70 degrees F. at approximately six feet deep), the system can be used as a heat source in winter (see Figure 2) and a heat sink in summer, when the process is reversed. According to Conn Abnee, executive director of the Geothermal Heat Pump Consortium, Washington, D.C., “In the wintertime, you’re taking heat from the earth and bringing it back into the building, and in the summertime, you are taking heat from the building and disposing of it back into the earth.”
GHP systems are composed of three major components: the earth connection, which is the piping in the earth; the geothermal heat pump that moves heat from the building to the earth connection (and vice versa); and the distribution system that delivers heating and cooling throughout a facility. The earth (loop) connection can be configured in a number of ways: horizontal or vertical, open or closed, ground or pond/lake, and even as a standing column well system.
The Benefits of GHP Systems
Applicable for both new construction and modernization projects, GHP systems are becoming a global solution for energy shortages and reduced energy consumption. With so many benefits, it’s easy to understand why:
• Energy efficiency. Because there is no fuel to burn for heat generation, the amount of energy used is considerably less. The Geothermal Heat Pump Consortium reports that savings of between 45 and 70 percent can be achieved.
• Reduced maintenance costs. “The maintenance costs are substantially less – somewhere in the neighborhood of around 12 to 15 cents per square foot annually vs. 30 to 35 cents per square foot annually for conventional equipment,” Abnee explains. Less skilled personnel can handle the maintenance of these systems, changing air filters periodically.
• Longevity. Typical life of these systems is 22 years, with many loop manufacturers offering warranties of up to 50 years.
• Simplified building design. Since most GHP systems install unit ventilators in rooms, less space is required for mechanical equipment. “From a construction standpoint, if you don’t have equipment sitting on your roof, you can reduce the structural strength of your roof,” Abnee adds.
The Waterfront Office Building
Perhaps the largest application of geothermal heat pump technology, the owner of Louisville’s Waterfront Office Building knew just how successful and economical the system would be. At the Galt House East Hotel complex that adjoins the 1994 office facility, small, distributed heat pumps had been successfully serving the building’s heating and cooling needs since 1984. The 1,700-ton system cost $1,500 per ton to install. A conventional system, by comparison, would have cost twice this much or more. Reduced energy has resulted in an astounding savings of $25,000 per month at the Galt House East Hotel.
Combined, the Galt House East and Waterfront Office Building have the capacity for more than 4,700 tons of GeoExchangeSM heating and cooling. Approximately 2,700 tons of this is sized for the million-square-foot Waterfront Office Building. “We are fortunate here in Louisville. We have water under most of the city,” explains designer, engineer, and contractor for the complex, Marion Pinckley, Pinckley Engineering Inc., Louisville.
Water from 130-foot-deep wells is pumped into a reservoir, where it is then circulated through heat exchangers, which separate ground water from the buildings’ closed loop circulation system. Water source heat pumps connected to the loops extract heat from the water (or vice versa) and distribute it according to zone requirements. “The logics and physics used to design that system are no different than a 2-ton system for your house,” explains Pinckley.
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This article was written by Jana J. Madsen (firstname.lastname@example.org) senior associate editor at Buildings magazine, with information provided by the Geothermal Heat Pump Association (www.geoexchange.org).