Installing a geothermal heat pump system can be a smart way to save energy and money. Unlike other types of heating systems which convert fuel to heat, a heat pump is designed to move heat from one place to another. Even at relatively cold outdoor temperatures, a heat pump is able to extract heat from outside to heat the home. In the summer the system reverses the direction of heat movement to cool the home.
In the past, most heat pumps were the air-to-air or air source type. Air source heat pumps rely on outdoor air for their heat source. As outdoor air temperatures fall, the capacity (amount of heat delivered) and efficiency of the system is reduced. Geothermal heat pumps extract heat from the ground or from water below the surface. Because ground and ground water temperatures are typically 50°-55° F. year-round, a geothermal heat pump is not affected by outside air temperature and therefore much more efficient.
There are two basic types of geothermal systems, open loop and closed loop. An open loop system typically uses a conventional well as its heat source. Water is pumped from the well through the heat pump's heat exchanger, where heat is extracted and transferred to a refrigerant system. The heat is then transferred to the air in the home. The water is then returned to a pond, stream, or second well. Local conditions such as quantity and quality of available water can affect the use of this type of system. Local water use and disposal regulations may also limit the use of open loop systems.
Closed loop systems circulate a heat transfer fluid (usually a water/antifreeze solution) through a system of buried plastic piping, arranged either horizontally or vertically. Horizontal loop systems draw their heat from loops of piping buried 6-8 feet deep in trenches or ponds. Vertical loop systems use holes bored 150'-200' deep with U-shaped loops of piping. They work the same as horizontal loop systems, but can be installed in locations where space is limited due to size, landscaping or other factors.
Another type of geothermal heat pump is called a "Direct Exchange" or "DX" system. This type of system uses a much shorter loop of piping buried below ground, through which the refrigerant itself is circulated, replacing the heat transfer fluid used in other geothermal systems. Because the heat is transferred directly between the ground and the refrigerant , the amount of piping can be drastically reduced. This type of system is ideal for situations where the amount of space for the piping loop is very limited.
How the Heat Pump Works
The heat pump operates on the principle that heat can be transferred by a cycle of alternating vaporization and condensation, the same cycle used by refrigerators, freezers and air conditioners. When a liquid vaporizes, heat is absorbed, and when a vapor condenses, heat is released. By alternately pressurizing and depressurizing a substance with a very low boiling point (called a refrigerant), the heat pump can absorb heat from a relatively cool medium and transfer it to a warmer one.
Even though the ground or ground water temperature may be a relatively cool 50° F, the circulating fluid can absorb some heat, and the vapor compression cycle of the heat pump can transfer it to the indoor air.
During the summer, the same refrigerant is circulated through the loop of piping and the heat pump's heat exchanger, but the heat pump's cycle is reversed. Instead of absorbing heat from the refrigerant and transferring it to the indoor air, it now absorbs heat from the indoor air and transfers it to the refrigerant, where it is given off to the ground or ground water. Because of the constant relatively cool temperature of the ground or water, the geothermal system is actually more efficient for cooling than a typical air conditioner, which must reject heat to hot outdoor air.
The geothermal system is a highly efficient and economical year-round space conditioning system. It can save up to 60% on heating costs and up to 30% on air conditioning costs, while providing clean, safe comfort year-round.
