What is a Geoexchange System?
Geoexchange systems use geothermal energy, the energy that is naturally stored as heat in the earth's surface, in oceans and large water bodies. Almost everywhere in the world, the earth's surface under the frost line maintains a nearly constant temperature between 10¡ã C and 16¡ã C (50¡ã F and 60¡ã F), remaining warmer than the air above it in the winter and cooler in the summer. A geoexchange, or geothermal heat pump, system takes advantage of this constant temperature by transferring heat stored in the earth or in ground water into a building during the winter, and transferring it out of the building and back into the ground during the summer. The ground acts as a heat source in winter and a heat sink in summer.
A geoexchange system consists of three main parts: pipes buried in the ground, a heat exchanger, and ductwork to distribute heat into the building. The series of pipes, commonly called a "loop," is buried in the ground, either vertically or horizontally, near or beneath the building. The loop circulates a fluid (water, or a mixture of water and antifreeze) that absorbs heat from, or relinquishes heat to, the surrounding soil, depending on whether the building requires heating or cooling.
For heating, heat is removed from the fluid in the loop system, concentrated in the heat exchanger and transferred to the building. This process is controlled by a heat pump that regulates the temperature level. For cooling, the process is reversed. In essence, the system works like an air conditioner, only its sink is underground.
In addition to space conditioning, a geoexchange system can provide hot water heating, using a "desuperheater," which transfers excess heat from the heat pump's compressor to the building's hot water tank. This is very common in residential geothermal heat pump applications.
Typically, heat pump systems reduce heating and cooling costs by 25 to 40 per cent, compared with conventional systems. At McMath Secondary School in Richmond, for example, this translates into savings of $20,000 a year.
"Although the initial cost for the geoexchange system was higher than that for a conventional system, the cost will be quickly offset by lower energy bills," says Eric Thorleifson, Energy and Projects Manager of Richmond School District.
Increase the scope of the installation, and you increase the savings. In Lincoln, Nebraska, four elementary schools recently installed geoexchange systems. Compared to natural gas HVAC systems that were installed in two other schools at the same time, the four schools had a total energy cost saving of 57 per cent.
A major advantage of geoexchange systems for schools is their ability to heat or cool individual classrooms or areas. With zone control, each room can be kept as warm or cool as needed, rather than heating or cooling the entire building uniformly. In addition to being more energy efficient, this boosts occupant comfort.
This has certainly been the case at Paint Lick Elementary School in Kentucky, the first newly constructed school in the state to be heated and cooled by a geoexchange system. Thirty-five separate heat pumps throughout the school allow the library, cafeteria, offices, gymnasium and each classroom to have individual thermostats and zone control. Kentucky now has over 40 schools with geoexchange systems.
Environmental and social benefits
Geoexchange systems work by concentrating naturally existing heat, rather than by producing heat through the combustion of fossil fuels. By displacing electricity, they reduce associated greenhouse gas emissions, resulting in less air pollution.
Obviously, the best time to install a geothermal system is at the construction stage. However, a heat pump system may also be added during a building retrofit, to replace an HVAC system.
In moderate climates, during some parts of the year, and for some building types, heat removed from spaces requiring cooling is recovered and reused for heating. For example, community centres can recover heat removed from cooling an ice rink and use it to heat a pool. This heat recovery capability proves effective even in larger systems such as the one provided in West Vancouver Community Centre (see diagram).
Heat Flow Diagram for West Vancouver Community Centre courtesy Stantec
BC Hydro's Role
BC Hydro is currently co-funding a demonstration project at the GVRD Water Treatment Plant in North Vancouver. We are also inviting applications for one or two additional innovative applications for heat pumps especially where electric resistance heating would normally be used. School districts, hospitals, municipalities, sports arenas and similar Power Smart Partner customers may qualify for demonstration funding incentives for geoexchange applications. Funding is also available for qualified incentive applications under BC Hydro's Power Smart Partner program, which is available to business customers.
BC Hydro is co-hosting an international GeoExchange conference and trade show in Vancouver on March 17 and 18, 2005, providing an opportunity for both novices and professionals to learn about the many aspects of this emerging technology. The event website provides further information on how to register for the conference and describes sessions dedicated to sustainability, innovative design, successful field installations, market potential and financial considerations.
BC Hydro has been involved in the Canadian Geoexchange Coalition which, under a 2.5-year contract with Natural Resources Canada, has contributed partial funding for activities in promoting the geoexchange industry in B.C. One of the outcomes of this collaboration has been BC Hydro's involvement with the GeoExchange BC, a non-profit organization that promotes the industry in B.C. Currently, BC Hydro's funding is primarily directed to education and promotion, and organizing a community-based involvement in geoexchange.
For more information, see the geoexchangebc.ca website, where BC Hydro will advertise available opportunities for involvement in geoexchange initiatives.
The case study examples cited in this article are adapted from articles prepared by the US Department of Energy and the Canadian GeoExchange Coalition.