Geothermal heat pumps are becoming popular for provided heat and cooling for both residential and commercial buildings. Geothermal systems can be installed in new structures and in some older building, with system installation generally limited by lot size. The extraction of heat from the ground or a water source is possible with temperatures commonly in the range of 45 to 55 degrees. The ground temperature remains consistent throughout the year when measured a few feet below frost line. In areas of the country that experience cold winter weather, the soil freezes to a certain depth, and geothermal piping is generally placed 2 to 4 feet below that depth to take advantage of the ground temperature.
There are several different methods of obtaining heat from the ground or a water source with either an open or closed loop system. Open loop systems pull water directly from a well, lake or pond and discharge the used water back into the water source, or if a well, generally into another well. The drilled wells should be at least 135 feet apart and the producing well must be adequate to supply the heat pump system with continuous water supply of approximately 5 gallons per minute for most systems. In lakes or ponds, the intake and discharge are placed as far apart as is feasible.
The closed loop system is a piping system buried in the ground below frost line. As the loop must extend a significant distance to efficiently absorb ground temperatures, space may be limited on small lots. With small lots, often a series of wells are drilled and the piping is lowered down into the well but the piping is not open ended. The piping continues to form a loop. In doing so, the loop absorbs temperature from the water source in the series of wells. Another method of a closed loop systems is the placement of coils of piping dropped deep within a large pond, lake or other source of water. The heat extraction would alter small pond temperature and reduce the efficiency of the system so the water source must be rather large. The fluid source in a closed loop system is generally a mix of non toxic antifreeze and water while open loop systems are the water source itself.
As the fluid is drawn into the heat pump furnace, it is pumped through a system of copper tube piping. There are two sets of copper tubing wound tightly and closely together and then insulated. The source of one set of the piping is the water or fluid circulated from the ground or water source into the system and back out to complete one loop. The other copper pipe is a loop filled with a gas that is also circulated into a compressor and then into a heat exchanger before returning. As the tightly wound piping exchange temperature, the gas absorbs about 10 degrees of temperature from the water as it flows through the piping. That gas that is heated 10 degrees is then sent to the compressor. The compressor compresses the gas and that function increases the temperature of the gas dramatically, to approximately 110 degrees. The heated and compressed gas continues through this loop to be circulated through a heat exchanger in the furnace. A heat exchanger in a geothermal furnace resembles a car radiator, a component installed directly in the air stream. The air in the home is forced through this heat exchanger and pushed (the feed) into the different rooms through a ducting system. As the air cools in the rooms, it is drawn back into separate ducting and forced back through the heat exchanger to be re-heated (the return). As the cooled gas exits the heat exchanger, it is circulated back to the copper tubing bundle to repeat the cycle. In the summer the process is reversed, removing warm temperature from the house and dumping it into the ground. As the home is cooled in the summer, it also dehumidifies the conditioned air.
Initially, years ago, many horror stories were circulated about how expensive and inefficient the geothermal heat systems were. This was due to inexperienced craftspeople installing system that were not completely understood. As a result most manufacturers started education programs for the heating and cooling technicians, excavators and well drillers to better understand the systems function and components. With an experienced company performing the installation, savings of 50% and more, over conventional fuel sources, may be achieved. With options that electric companies are offering with electricity being provided from green sources, this is difficult challenge to beat.
