October • 2014
Geothermal Heat Pumps and Sustainable HVAC Technology
As most people who have visited an underground cave understand, the temperature under the ground remains a fairly constant 45 to 75 degrees or so all year long, no matter how cold or hot the air above may be. That natural phenomenon is the science behind a source of efficient and renewable energy known as geothermal energy. Even in extreme desert climates like Palm Springs, air temperature fluctuations between daytime and nighttime do not exist only 4 or 5 feet under the surface of the ground. By using a geothermal heat pump (GHP), commercial, industrial and even residential buildings can take advantage of the constant earth temperature to heat and cool their interiors.
When daytime temperatures reach 100+ degrees in the summer, the cooling efficiency of a GHP can make indoor spaces cool and comfortable. The up-front investment in a GHP may be higher than a traditional HVAC system, but the payback in reduced energy costs is even greater.
GHP technology relies on the fairly constant temperature of the earth to pull heat out of your home in the summer and move heat back into your home in the winter. With a GHP, a closed loop system is buried under the ground. In the winter, it absorbs heat. It then makes contact with a heat exchanger filled with a refrigerant and transfers the heat it has absorbed from the ground into the above-ground part of the HVAC system. The refrigerant is alternately condensed into a liquid and then evaporated into a gas as it moves through the system, which warms the building.
When cooling is needed, the heat pump works the same way, pulling warm out of the building air into the refrigerant and then transferring it into the closed loop to be expelled back into the ground.
Because the ground temperature is constant, a GHP does not have to work as hard as an ordinary heat pump, which takes heat from the ever-changing air temperature. Geothermal energy is considered renewable because the heat that is removed from the ground in the winter and used to warm the interiors of buildings is then replaced during the cooling cycle in the summer. Up to 70% of the energy created by a GHP is renewable.
GHPs operate more efficiently and quietly than other types of HVAC systems. Some estimates by the United States Department of Energy put the efficiency of a GHP at up to 600% on even the coldest nights in winter. In comparison, a regular heating or cooling system may only achieve an efficiency of 200% even on moderate days.
It is true that GHPs cost more to install than ordinary HVAC systems because they involve digging into the ground to lay piping and because the equipment is more expensive. But a well-built, correctly installed GHP can last 50 years for the underground components and will generally start paying for itself in as little as five years. Studies estimate that energy bills are lower in GHP systems than traditional systems by as much as 30 to 40%.