Ask Focus on Energy

There are many factors to consider with ground-source (geothermal) heat pumps.

Ground-source (geothermal) heat pump systems consist of a series of underground tubes, other heat exchangers, electric heat pump units and ductwork or hydronic tubes that run throughout the building. The underground heat-transfer tubes are assembled in either a horizontal or vertical configuration, offering flexibility for space issues. Heat is transferred through the tubes, taking advantage of the fairly constant temperature beneath the earth’s surface. In winter, circulating fluid in the tubes absorbs heat from the earth and delivers it to the heat pumps inside your home. Then the heat pump boosts the temperature of the fluid, which heats your home. In summer, the process is reversed. Refrigerant in the heat pumps absorbs excess heat from the building then transfers it into fluid which is circulated through tubes in the ground where the heat is expelled. Ponds and lakes can also be used as stable heat sources and heat sinks.

Ground-source (geothermal) heat pumps circulate water, or a refrigerant through: piping in the ground (often called a ground loop), piping in a pond, lake or stream (often called a pond loop) or from a well (often called a pump and dump). As the refrigerant circulates through the piping it can either pick up heat from the surrounding material to heat the home or reject heat to cool the home. Because the temperature of the surrounding material remains the same throughout the year geothermal can be very effective at heating and cooling. Electricity is required to pump the refrigerant and to operate a compressor that boosts the effectiveness of the system. Ground-source (geothermal) systems can be used to replace a forced air system, a radiant heat system or both. In addition the ground-source (geothermal) system is often used to supplement domestic hot water production.

These systems can be an efficient, effective and inexpensive way to heat and cool your home; however, many factors need to be considered to determine if it is the right option for your home.

• The upfront costs of the ground-source (geothermal) heat pump and the associated ground excavation for underground tubes (also called field loops) are significantly higher than a conventional furnace and air conditioner system. However, the daily operational costs will likely be much lower with a ground-source (geothermal) heat pump, especially if the system is sized correctly and you were previously relying on high electric-consumption equipment to heat your home, such as electric baseboard heat.
• You should also consider that most ground-source (geothermal) heat pump systems require a loop field to be excavated near your home, which may not be practical for all existing homes, especially if you have a small city lot.
• Almost all residential ground-source (geothermal) heat pumps require backup heat during the coldest winter months, which is most often gained through electric heaters. Depending on your utility's rate structure, this additional electric use may cause your utility bills to go up, thereby cutting into the money savings that you should be seeing from the ground-source (geothermal) heat pump. In those cases, consider using an efficient gas furnace for supplemental heat.
• The most important thing to remember when considering a ground-source (geothermal) heat pump system is to work with a qualified, experienced contractor and loop installer.

Published Thursday, April 16, 2009