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The Heat Movers
This story is the second of a series that will explore various types of ground heat mining and their campus applications. Also see Universities Lead the Charge to Mine the Heat Beneath our Feet, and look forward to the final piece in December. -Ed.
Beijing’s Bird’s Nest stadium was the focal point of the 2008 Summer Olympics due to its stunning architecture, but the structure was also a demonstration site for a gold-medal renewable energy technology little-known by the public: ground-source heat pumps.
Water pipes buried deep beneath the stadium’s infield provided heating and cooling for the athletes’ locker rooms. “The loop-field is right under the grass where the guys were throwing the javelin,” says engineer Phil Schoen, who consulted with Chinese officials on the design of the ground-source heating system.
Ground-source heat pumps, also called geothermal heat pumps, can shave heating and cooling bills by 50 percent, making them an attractive alternative to traditional furnaces and air conditioners. They tap into the relatively constant temperature just below the earth’s surface. In winter, the systems transport warm water into buildings where the heat is extracted. In summer, the process is reversed: Water pulls heat from inside buildings and dumps it underground.
“We’re just heat movers,” says Jim Bose, executive director of the International Ground Source Heat Pump Association and an engineering professor at Oklahoma State University.
More than a million geothermal heat pumps have been installed in homes and buildings nationwide. The Oklahoma State Capitol is heated and cooled with this technology, as is President Bush’s Crawford, Texas, ranch. Al Gore had a system installed on his Tennessee mansion after the release of the movie “An Inconvenient Truth.” Combined, these systems reduce the nation’s annual fossil fuel use by the equivalent of 21.5 million barrels of oil and cut carbon emissions by 5.8 million metric tons-equal to removing 1.3 million cars from the road, according to industry statistics.
Now, after years of obscurity, ground-source heating and cooling is poised for a rapid expansion. “There is a perfect storm right now with rising energy bills, concerns about energy security and climate change,” says Dan Ellis, president of ClimateMaster, the nation’s largest manufacturer of geothermal heat pumps. The company’s sales have tripled in the last five years.
“We’re growing by leaps and bounds,” says Jack DiEnna, executive director of the Geothermal National and International Initiative. The trade group is pushing the technology worldwide and hopes the industry can capture 30 percent of the market for heating and cooling by 2030. Interest is booming in China, England, Japan, South Korea and Australia, among other nations, DiEnna says.
Domestically, interest is booming thanks to a homeowner tax credit in the federal economic bailout bill approved by Congress in October. The $2,000 Residential Renewable Energy Tax Credit is “a historic milestone” for ground-source heating, says John Kelly, executive director of the Geothermal Heat Pump Consortium. Geothermal heat pumping has lagged behind wind and solar energy in federal support. “Now we’re on a more level playing field,” Kelly says.
All of this is none too soon for Bose, who is sometimes called the “father of ground-source heat pumps in the United States.” He remembers the excitement of first learning about these devices. It was 1974, and the young Oklahoma State professor found an article about the technology in the library. “I was fascinated,” Bose says. “I kept reading and reading and looked up everything I could find out. I thought: ‘Why isn’t this being used?'”
The first ground-source heat pump in North America is believed to have been installed in the 1940s in the home of an employee at Indianapolis Power and Light Company. The technology got a boost during the 1970s energy crisis but federal aid was eliminated in the 1980s and interest languished through the 1990s due to low energy costs. The technology also suffered from a public relations problem: Wind and solar have visible infrastructure (photovoltaic panels and turbines), but most of the hardware on a geothermal heat pump system is buried.
Geothermal heating and cooling should not be confused with geothermal electricity, which taps hot water thousands of feet underground to power electric turbines. (For more on this, see our previous article “The Heat Beneath Our Feet,” about geothermal energy.)
The two main elements of a geothermal heating and cooling system are the heat pumps, located indoors, and the loop field, where the water-filled pipes are buried. Loop fields are either open or closed. Closed-loop systems are completely sealed, and the water inside the pipes often contains a relatively safe anti-freeze such as ethanol. Open-loop systems draw water up from an aquifer, extract the heat and return the water to the aquifer. Large systems typically use vertical loops whose polyethylene pipes can reach down 500 feet or more. Smaller residential systems often have horizontal loop fields buried just six feet underground.
Water circulates through the loop field and is pumped into a home or building, where one or more heat pumps extract and concentrate the heat, which is then circulated through ductwork as in any central heating or cooling system. In summer, heat pumps reverse this process. They extract heat from indoor air and transfer it to the water, which dumps the heat underground. Some systems also provide hot water for showers and sinks.
The technology is fairly simple. In fact, most homes already have heat pumps–refrigerators and air conditioners. Both of these pump heat from one place (inside the refrigerator or home) and move it to another (outside). These air-to-air heat pumps are less efficient than air-to-water geothermal systems, however, because water is a superior medium for heat transfer. The principal drawback to geothermal heat pumps is the up-front cost. Drilling the loop field and installing the underground pipes can add two-thirds to the cost of installing a traditional HVAC (heating, ventilation and air conditioning) system.
However, geothermal systems can pay for themselves in several years due to lower heating and cooling bills. Tax credits and other government incentives can shave the costs even more. New York’s Hamilton College added a geothermal system to its historic Skenandoa House residence hall in 2003. The 21,000-square-foot building now uses 40 percent less energy than a similar hall on campus. “This is the most efficient building we have in terms of energy use,” says Steve Bellona, associate vice president for facilities and planning. Thanks to a state rebate, the system cost the college just $32,000–paying for itself in less than three years.
“The challenge is to get more colleges and universities to understand the value of this,” says Lynn Stiles, a physics professor at New Jersey’s Richard Stockton College, which installed a system in 1994. “This was a wise investment for us.” The system has cut electricity use about 25 percent, natural gas use by 70 percent and saved the school more than $300,000 per year in energy costs. It cost $5.8 million to install, though the school would have paid $4.2 million to install a traditional HVAC system, so the additional cost was just $1.6 million-much of which was covered by state and utility grants.
Stiles says geothermal heat pump systems have low maintenance costs once they are built. The high-density polyethylene pipe used in loop fields is made to flex and resist breaking. This is the same material often used in natural gas pipelines. “You rarely hear about problems,” Stiles says. The loop fields are typically built to last 50 years. That is comparable to the life-span of any well-built heating and cooling system. The heat pumps themselves are located indoors and have similar maintenance costs as any space-heating or cooling device.
While the amount of electricity used to run the pumps is different for every building, some studies indicate ground-source heat pumping is most economical in areas with high natural gas prices. A study conducted by the Department of Energy on four schools in Kansas with geothermal heat pumps found this technology to be the most efficient choice with the lowest life-cycle cost for heating and cooling the schools. A 1993 Environmental Protection Agency study likewise found ground-source heating and cooling to be the most environmentally sound, efficient and cost-effective space-conditioning system available. Even so, more study is needed to pinpoint their overall efficiency. Federal funding for research has been limited over the past decade.
But ground-source heat pumps are no panacea. The pumps and ventilation systems require electricity to run. This is why some projects include photovoltaic panels, though this adds to the cost. Proper design is also crucial: Large installations must be carefully engineered so they do not heat up the ground or groundwater, harming micro-biota and diminishing the ability of the soil to absorb heat over time. “You want to maintain thermal balance,” Stiles says. Closed-loop systems also occasionally leak.
“Geothermal heat pumping only achieves the best efficiency if you design the building appropriately,” says Tony Grahame, director of residential building technology at Arizona’s Yavapai College, whose AgriBusiness and Science Center has a geothermal system with a closed-loop field consisting of 32 vertical wells drilled 300 feet deep to access an underground aquifer. “If you didn’t design the building efficiently then you don’t get the savings you could.” Grahame says he is unaware of the energy savings because the building’s energy use is lumped in with other campus buildings. “It’s hard to separate out the savings because they didn’t put in separate monitoring systems.”
Geothermal heat pumps are one piece of the energy puzzle, advocates say. Buildings and homes use 40 percent of the nation’s energy. Using heat in the ground dramatically reduces the need for fossil fuels. “The dynamics have never been better for our industry,” says Schoen, who consulted on the Bird’s Nest. His company, Geo-Enterprises, is growing about 20 percent per year.
For college students facing a tough economy, tapping the low-grade heat below promises good job growth. “We need young engineers to be taught this technology,” DiEnna says. “Engineers are the key.”