ENERGY EFFICIENT
HEAT Pumps Richmond School District 38 had a decision to make in designing the new Robert McMath Secondary School. Should the district install a conventional heating and cooling system for an annual energy cost of $120,000? Or should it install a geoexchange heat pump system that would cost less than $100,000 a year in operating costs? The decision was easy: McMath Secondary is now home to a groundcoupled heat pump system that is designed to supply at least 80 per cent of the school's heating needs. On very cold winter days, additional heat is provided by a high-efficiency natural gas condensing boiler. In addition to reduced operating costs, the school district is also enjoying the environmental benefits of less energy use, and a more comfortable indoor environment for students, teachers and staff. A Smart Choice for Schools Heating and cooling account for the largest portion of a school's energy costs (approximately 70 %) and a significant part of overall operating costs. Because of their lower operating and maintenance costs, energy efficiency and comfort, schools in Canada and the United States are increasingly turning to geoexchange systems as an alternative to conventional HVAC systems. How Do Heat Pumps Work? Geoexchange systems use geothermal energy, or the energy that is naturally stored as heat in the earth's surface, in the oceans or large water bodies. Almost everywhere in the world, the earth's surface under the frost line maintains a nearly constant temperature between 10 C and 16 C (50 F and 60 F), remaining warmer than the air above it in the winter and cooler in the 10 School Plant Officials Association of B.C.
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. In other words, 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, very common in residential geothermal heat pump applications. Benefits Electricity savings Typically, heat pump systems reduce heating and cooling costs by 25 to 40 per cent, compared with conventional systems. At McMath Secondary, 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. Enhanced comfort 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. And at Swan Lake First Nations School in Brandon, Manitoba, during a winter cold snap, when the outside temperature plunged to -35 C for two days in a row, the auxiliary electric baseboard heaters were not needed.
