Heat pumps are dependent on compressors and refrigerants to transfer energy to and from the ground loop. However, not all geothermal systems rely on heat pumps. One such system, popular in Europe and quickly gaining traction in North America, is deep-water source cooling (DWSC).

Cornell University uses a DWSC system to cool its classrooms in Ithaca, New York. A 2-mile-long intake pipe located about 250 feet below the surface of nearby Lake Cayuga delivers 39-degree Fahrenheit water into onshore heat exchangers located in a special utility building. A second, closed loop running through the heat exchangers brings chilled water to campus at about 47 degrees Fahrenheit. Warmer water is rejected through a 500-foot-long diffuser pipe closer to the lake's surface. The chilled water is piped directly through the classrooms, eliminating the school's previous chillers, which ran on ozone-depleting refrigerants.

Cornell's system, designed for 20,000 tons, allows the $58-million investment to reach a COP of 25 and reduce overall cooling energy by 86 percent. Cornell estimates that the cost premium over conventional methods is on track to pay for itself in an estimated 10 to 13 years from its 2000 completion date, a payback that is now not too far away.

"The savings is on the order of 25 million kWh," says William S. "Lanny" Joyce, Cornell's senior manager of engineering, planning, and energy. "That's almost 10 percent of our campus electrical use." The local community also benefits, he notes, from reduced peak loading on the electrical grid.

Because the loops never mix, this is a type of closed-loop, geothermal system that does not rely on heat pumps. A more typical, closed-loop system that uses heat pumps can be found in Elgin, Illinois, but the size of the system is anything but typical.

There, Sherman Health, owner of a 255-bed hospital going up in the Chicago suburb, plans to save more than $1 million a year by tapping into a 15-acre, 17-foot-deep geothermal pond-one of the world's largest-which will provide heating and cooling for the 650,000-square-foot facility. Sherman knew that it needed to build a 5-acre stormwater-detention pond on its 154-acre site, so it tripled the size to accommodate a geothermal loop.

While in planning, the owner figured that its loop would cost $4.5 million to install. Add to that $1.6 million for the land, and the hospital was looking at a $6.1-million investment. At a savings of over $1 million per year, though, it wouldn't take long to pay off. The system sports 150 miles of tubing, 175 underwater heat exchangers, and 750 heat pumps. A nontoxic methanol solution flows through the loop, essentially turning the lake into a 15-acre cooling tower.

GROUND SOURCES

All GSHPs are closed loops arranged in either a vertical or horizontal fashion. The arrangement depends on real-estate constraints, and all the tubing is buried at least below the frost line to prevent damage.

Heat pumps generally do not cost more than conventional furnaces, but the ground loops are an added cost. They require expensive, shallow trenching, more expensive deep drilling, or a combination of both. Installation equates to a few dollars per foot and on up to $25 per foot, according to government statistics. Heat pumps are flexible, though. Users can tailor them to their regional needs; some are even designing "hybrid" systems to take advan-tage of local power, geology, and climate.

One such system, designed for airline company WestJet's headquarters in Calgary, Alberta, incorporates heat sinks into the six-story, 314,000-square-foot building's foundations. By looping tubes inside 105 bored piles, "we reduced the capital cost," says Jim Bererton, senior project engineer for consulting engineer Stantec. This method is more mature in Europe, where foundations commonly double as heat exchangers.

Because geothermal systems are still relatively new, the unexpected often arises during installation. WestJet lost 30 percent of its loop due to pier-construction problems, requiring it to drill 20 additional, small-diameter boreholes 350 feet deep.

Normally, the building would have needed 200 holes drilled to 300 feet, so the owner still saved more than $700,000 in installation and is expected to save $200,000 per year in energy. Part of the savings is due to the
unusual addition of a conventional chiller and condensing boiler. The "secret sauce" is a computer controller that takes into account daily costs of electricity and natural gas and cycles the systems on and off accordingly
to deliver the best bang for the buck.

Drilling equipment is another low-hanging fruit ripe for innovation. In Chicago, a homebuilder whose friend, and now wife, convinced him to build her a greener home is leading the charge to cut costs for vertical-well construction in tight, urban environments. David Dwyer, president of American Renewable Energy and author of Green Power Blue Collar, helped local-physician Toni Bark design her green home in Evanston, Illinois. The 4,700-square-foot home has 16 wells drilled to 125 feet and two heat pumps that play a part in holding their utility bills under $100 per month.

Both LEED-accredited professionals, they are pushing for more homes-which make up a significant portion of the building stock-to go geothermal. Both are aware of the high costs, too, so Dwyer has built what he calls the first geothermal drill designed for urban jobsites. While reluctant to showcase his system just yet, he described it as a three-wheeled machine that weighs about 2,500 pounds, or 10 times less than a typical, truck-mounted rig.

"Our cost of drilling is about half of what our competitors' [costs] are," Dwyer says. Stantec's Bererton also has worked with a rig called a "SpiderPlow," which simultaneously digs a shallow trench and lays HDPE pipe in a horizontal fashion, further shaving costs off the more expensive vertical construction. As the world goes geothermal, more advances will continue to drive down the cost of these systems.