Geothermal Heat Pump Heating
The main reason for the high installation cost of ground-source heat pumps is the long run of tubing required to transfer heat to and from the ground.
Growing interest in improving home energy efficiency has put geothermal heat pumps in the spotlight. Also known as "ground-source" heat pumps, this type of system provides a home with heat, air conditioning (cooling) and —in some cases—even hot water. The big news is that a ground-source heat pump can accomplish these tasks more efficiently and thus less expensively than most other HVAC options.
The Environmental Protection Agency estimates that a geothermal heat pump can reduce energy consumption up to 44% compared to air-source heat pumps and up to 72% compared to an HVAC system that combines electric resistance heat with standard central air-conditioning.
How geothermal systems work
A ground-source heat pump works just like an air-source heat pump. It uses electricity to pump a refrigerant through compression and expansion cycles and thus "pump" heat from one location to another.
The main difference is that a ground-source heat pump relies on the consistent temperature of the earth (6ft. or more below the ground level) rather than the ambient air temperature as its heat source and heat sink. Six feet or more below ground level, the earth's temperature will be between 45 and 75 degrees, no matter what time of year it is or where your house is located. An air-source heat pump becomes inefficient at supplying heat when outside temperatures drop below freezing. This never happens with a ground-source heat pump, which can work at very high efficiency all year long.
If you invest in a geothermal heat pump system, you can expect reliable long-term performance. There are very few moving parts in this type of HVAC system, and they're all located inside the house where they're protected and easily accessible.
The two main "cons" with geothermal heat pumps are cost and installation requirements. Long runs of plastic tubing are required to transfer heat to and from the earth in a geothermal system. In a horizontal installation, the tubing is buried in trenches, as shown in the drawing. Alternatively, it can extend vertically into deep holes bored in the ground. It can also extend along the bottom of a pond or lake. All of these options are expensive, and a horizontal installation requires a certain amount of land. The type of tubing installation is best determined by an experienced geothermal heat pump contractor after a site visit. In any case, excavation (or drilling) can cost anywhere from $10,000-$30,000, and the geothermal heat pump itself will be about twice as expensive as an air-source heat pump —in the $4,000 range for an average house.
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