Sustainable By Design: Heating And Cooling Sourced From The Earth
By Anne Vazquez
Published in the January 2008 issue of Today’s Facility Manager
In 2005, renewable sources provided 7% of the energy consumed in the U.S., according to figures from the Energy Information Administration; geothermal energy made up just 5% of that figure. The tiny portion of energy supplied by geothermal sources is not for lack of potential, but rather lack of infrastructure, feasible financing, and adoption. As more facilities look into the possibilities of geothermal, perhaps it will help to foster the market for this renewable energy source.
Geothermal energy—heat derived from the earth—has the potential to provide heating and cooling in buildings. By drawing this heat from the ground for these purposes, a facility reduces the amount of energy it derives from fossil fuel sources.
Of course, there are a variety of factors to consider when determining if a geothermal system is a good fit. Geography, site characteristics, and first costs for installation all play a part.
The scope of the application depends on the type of geothermal system installed. These types can be divided into two broad categories: direct use and geothermal heat pumps. Direct use involves harnessing the heat in groundwater directly (without a heat pump) and generally requires resource temperatures between 100°F and 300°F.
In the U.S., direct use is most often found in the west due to higher ground temperatures. Explains John Lund, director of the Geo-Heat Center in Klamath Falls, OR, “In most areas, the heat [from the earth] reaches the surface in a very diffuse state. However, due to a variety of geological processes, some areas, including substantial portions of many western states, are underlain by relatively shallow geothermal resources.”
While direct use systems are used only to provide heating, a system that applies geothermal heat pumps is capable of both heating and cooling a building. This is because geothermal heat pumps (sometimes referred to as geo-exchange or ground source heat pumps) use the groundwater as a heat source in winter and a heat sink in summer by transferring the heat from one place to another.
And because this type of system can function with lower groundwater temperatures (between 40°F and 100°F), the geographical potential for these is greater than direct use systems. Notes Lund, “Accurate data is not available on the current number of these systems. However, the rate of installation [for commercial and residential combined] is estimated to be between 10,000 and 40,000 per year.”
In discussing geothermal heat pumps, Lund points out that air source heat pumps offer another option, not to be confused with geothermal heat pumps. “Air source heat pumps are less energy efficient than geothermal pumps,” he explains. “This type of pump takes heat from the air or puts heat out into the air, and the unit sits outside and is exposed to the weather while geothermal pumps are not. When it’s cold and the pump needs to heat, there is not very much heat in the air, so these usually have some backup electric resistance heating to kick in to get them where they need to be. And it’s vice versa in hot weather. So these pumps use more power to do their job.”
Some projects incorporate air source heat pumps, however, to save money. Systems with geothermal heat pumps require a number of deep holes to be drilled in the ground, which can be costly (possibly as much as $10 per foot, according to Lund). Air source heat pumps are an option for tighter budgets, while still providing a system to reduce greenhouse gas emissions when compared to “traditional” electric consumption.
While the western U.S. offers the widest breadth of geothermal sources, facilities all around the country can install such a system, if the factors are aligned for success. In New Jersey, for instance, The Richard Stockton College of New Jersey has been heating and cooling its campus with a geothermal heat pump system since 1993.
Dr. Lynn F. Stiles, Ph.D., professor of Physics and coordinator of energy studies at the college, helped with the research and installation. On the Stockton Web page dedicated to the project, Stiles explains the decision to consider geothermal arose from a number of circumstances: “We’ve been interested in energy conservation in buildings since the early 1970s. We studied geothermal designs in the 1980s.” Then, in 1990, a new vice president, Dr. Charles Tantillo, expressed interest in reducing overhead expenses. At the same time, the school was planning a replacement of its fleet of multizone rooftop HVAC units, and plans for several new classroom and dormitory facilities were also underway.
The single closed loop geothermal HVAC system on the campus totals 1,741 tons of installed geothermal heating and cooling capacity. The project contains 400 heat exchange wells located in boreholes drilled to a depth of 425′. In total, the loop system is comprised of 64 miles of heat exchange pipe. These were installed in a three and a half acre area that included a parking lot and a portion of adjacent open space. Upon completion, the area was once again used for parking.
It was estimated that the geothermal system would reduce electric consumption on campus by 25% and natural gas consumption by 70%. Stiles says, “Based on an extensive monitoring study, this turned out to be quite accurate.” He notes that savings were studied very carefully for the first three years of operation, but “it is impossible to know the savings now, since the operation of the buildings has been changed so significantly. But we are confident of the persistence of savings.”
Alice Gitchell, a member of the Natural Sciences and Mathematics staff involved in studying and sharing project information, also reports on the Stockton Web page that “the project has substantially contributed to a calculated 13% overall reduction in the college’s carbon dioxide emissions during a period of significant growth on the campus.”
The viability of a geothermal system depends on geography, financial resources, and site characteristics. But, if the conditions are right, facility managers may want to consider this renewable energy source.
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