Space conditioning goes underground to beat operating costs

Space conditioning goes underground to beat operating costs

THERE ARE BENEFITS to visiting an old fine wine cellar besides the wine, and one is the temperature. The temperature of a wine cellar is nearly always the same, held steady by the earth’s temperature. The wine likes that consistent environment And most people do, too.

While moving offices underground may not be a good idea, building owners can move their HVAC systems there with ground-source geothermal heat pump technology. Called GeoExchange systems by the Geothermal Heat Pump Consortium, geothermal heat pump systems have been growing at 20 percent a year, making strong inroads in the commercial and institutional markets. The reasons for such growth are the technology’s energy efficiency, simplicity and life-cycle cost savings.

A Low-Tech Process

There are several different types of ground-source geothermal heat pump systems but two general categories: open loop and closed loop. The most popular system is a closed-loop system where a heat exchange fluid is circulated through polyethylene pipes that are laid underground or at the bottom of a large body of water and returned to heat pumps located within the facility. Open loops draw water from underground or aboveground.

The system is simple and efficient. The heart of the system is in the heat exchange process. The heat exchange fluid – water or water with glycol – absorbs heat from or transfers it to the earth.

The fluid returns to the heat pumps, which utilize a refrigerant cycle to take the fluid’s low quality heat and concentrate it; the process is reversed for cooling. Air passing over coils is distributed by fans. The heat pumps tend to be rather small – one- to three-ton capacity pumps are typical, with the largest around 50 tons.

One of the largest systems in the United States is the Great River Medical Center in West Burlington, Iowa. The new 650,000-square-foot complex uses about 1,400 tons of cooling for its three main buildings. The center’s 768 heat pumps range in size from 1.5 to 5 tons. The center’s heat exchange field is a 14-acre, 13-foot-deep pond.

A positive experience with geothermal systems in the past had a strong influence on Steve Leavitt, director of development. A projected 60 percent energy savings and significant maintenance savings made the decision to choose one for the center easy. A $2 million utility rebate was a bonus.

A Balance of Costs

Because geothermal heat pump systems are energy efficient, typically 25 to 50 percent more efficient than most conventional HVAC systems, they use less electricity and reduce the amount of air pollution and global warming gases emitted by utilities. And because the system is relatively low tech and maintenance costs are low compared to conventional systems, the life-cycle cost of the system is also lower.

There is a first cost premium. Costs vary geographically but can range from $1,800 to $2,800 per ton. A large percentage of the cost of the system is in the construction of the heat exchange field. These costs do not proportionally increase after 50 tons, however. There is little difference in costs between vertical and horizontal exchange fields.

Energy costs and indoor comfort were key to Steve Bob, finance manager of the threeyear-old West Philadelphia Enterprise Center, a 32,000-square-foot business incubator in the heart of the city’s downtown. The system consists of 66 wells, 300 feet deep under the center’s parking lot. Excellent temperature control and electric costs of $1.25 to $1.33 per square foot – for everything, including the geothermal system – has made Bob a happy CFO.

“In three years, we’ve had a couple of compressor problems, and we had to change filters,” he says. “That’s really been our costs.”

About the biggest obstacle to greater adoption of the systems is education, says Cone Abnee, executive director of the Geothermal Heat Pump Consortium. Abnee says some people are still thinking of the systems from the ’50s and ’60s, which have had problems, such as pipe-joint failures. End users also confuse air-source heat pumps that don’t work in northern climates with ground-source pumps.

And some in the marketplace also think of geothermal systems as new construction options, Abnee says. “Retrofit may be a larger market now than new construction,” he says.

These systems can more than pay for themselves over the years, avoiding costs on maintenance and roof repairs, because the equipment can last so long. “The energy savings are really the icing on the cake,” Abnee says.

E-mail comments to Geothermal Heat Pump Consortium

The Geothermal Heat Pump Consortium was created in 1994 to advance the market for ground-source, heat pump technology. It is supported by the U.5 Department of Energy and Environmental Protection Agency as well as the private sector.

The consortium ( counts among its members electric utilities, equipment manufacturers, architects, builders and Electric Power Research Institute.

Copyright Trade Press Publishing Company Aug 2000

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