Ground source heat pumps

Ground source heat pumps are designed to heat and cool

Ground source heat pumps can be used for heating and cooling buildings virtually anywhere. To understand how ground source heat pumps work, keep in mind that heat always flows spontaneously from warmer to cooler regions. A heat pump is designed to reverse the process. It "pumps" thermal energy from a cooler region to a warmer region—reversing the natural flow of heat.

The technology is like a refrigerator, moving thermal energy from a cooler region (the freezer) to a warmer region. Ground source heat pumps work the same way, except that its heat source is the warmth of the earth. The process of elevating low-temperature heat to over 100°F and transferring it indoors involves a cycle of evaporation, compression, condensation and expansion. A refrigerant is used as the heat-transfer medium which circulates within the heat pump. The cycle starts as the cold, liquid refrigerant passes through a heat exchanger (evaporator) and absorbs heat from the low-temperature source (fluid from the ground loop).

The refrigerant evaporates into a gas as heat is absorbed. The gaseous refrigerant then passes through a compressor where the refrigerant is pressurized, raising its temperature to more than 180°F. The hot gas then circulates through a refrigerant-to-air heat exchanger where heat is removed and pumped into the building at about 100°F. When it loses the heat, the refrigerant changes back to a liquid. The liquid is cooled as it passes through an expansion valve and begins the process again. To work as an air conditioner, the system's flow is reversed.

The geothermal loop

The component that is unique to a geothermal heat pump is a large loop of piping that is buried beneath the ground. Fluid, usually a water and antifreeze solution, circulates through the piping. When ground source heat pumps are used to heat the house cool fluid is circulated through the loop. As the fluid passes through the loop, thermal energy flows from the warmer ground to the cooler fluid because thermal energy spontaneously flows from warmer to cooler regions.

By the time the fluid has circulated throughout the loop it is at roughly the same temperature as the soil. This warmed fluid is pumped inside the building, where a refrigerator-like piece of machinery extracts thermal energy from the fluid and transfers it to the air in the building. Extracting thermal energy from the fluid in the loop causes the temperature of the fluid to drop. Finally, the cooled fluid is pumped back through the loop in order to absorb more thermal energy from the ground.

During the summer months, most ground source heat pumps can extract thermal energy from the air inside a building and move the energy into the ground outside via the same loop of circulating fluid.

Ground source heat pumps provide significant energy savings

Savings of more than 75 percent when compared to electric baseboard heating and between 30 and 60 percent relative to other methods of heating and cooling. The most serious disadvantage of ground source heat pumps is that they tend to be more expensive to install than more conventional heating and air conditioning units. The extra expense can be amortized in as little as 3 or 4 years for some systems though most installations carry a longer pay-off period. Eventually all geothermal heat pumps provide savings that accrue as lower-than-normal utility bills. As energy prices continue to rise, however, that difference will become less significant.

Ground source heat pumps copyright 2011