Guide to Geothermal Heat Pumps Geothermal heat pumps are among the most efficient and comfortable heating and cooling technologies available because they use the earth’s natural heat to provide heating, cooling, and often, water heating.
About Geothermal Heat iStockphoto #’s 117086265 and 12333446 117086265 iStockphoto #’s Pumps Geothermal heat pump systems, consisting of the heat exchanger (left) and the heat pump (right), heat and While many parts of the country cool a home by transferring heat to and from the earth. experience seasonal temperature extremes – from scorching heat How Geothermal Heat Pumps Work in the summer to sub-zero cold in the winter – a few feet below the Using a heat exchanger, a geothermal heat pump can move heat from one space earth’s surface the ground remains a to another. In summer, the geothermal heat pump extracts heat from a building relatively constant temperature. The and transfers it to the ground for cooling. In winter, the geothermal heat pump natural ground temperature is cooler takes natural heat from the ground and transfers it to the home or building for than the natural air temperature in heating. summer, and warmer than the natural Installing a geothermal heat pump system can be the most cost-effective and air temperature in winter. While the energy-efficient home heating and cooling option. Geothermal heat pumps are margin of variation is small, seasonal a particularly good option if you are building a new home or planning a major changes in ground temperature give renovation to an existing home by replacing, for example, an HVAC system. geothermal heat pumps a dependable and permanent wintertime heat source and summertime heat sink. Geothermal vs. Air-Source Heat Pumps While geothermal heat pumps operate similarly to the far more common Geothermal heat pumps, also known air-source heat pump (ASHP), geothermal heat pumps are substantially more as ground source heat pumps, geoex energy-efficient than even ASHPs because they take advantage of the relatively change, water-source, earth-coupled, consistent ground temperatures, which are far more uniform than air tempera- and earth energy heat pumps, take tures. Geothermal systems can reduce energy consumption by approximately advantage of this resource and 25% to 50% compared to air source heat pump systems. Geothermal heat represent one of the most efficient pumps reach high efficiencies (300%-600%) on the coldest of winter nights. and durable options on the market to heat and cool your home. As with any heat pump, geothermal heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water. Some models of geothermal systems Many heating, ventilation, and air are available with two-speed compressors and variable fans for more comfort conditioning systems use some sort of and energy savings. Relative to ASHPs, they are quieter, last longer, need little heat pump for heating and cooling. maintenance, and do not depend on the temperature of the outside air.
continued > A dual-source heat pump combines an systems can be more expensive, but $4,000, but the energy costs could ASHP with a geothermal heat pump. they use less land and also mini- easily equate to the extra cost of These appliances simultaneously mize disturbance to the existing installing a geothermal heat pump. provide the consumer with a more landscape. Additionally, geothermal heat pump efficient alternative to the ASHP, and systems installed in new or existing a more affordable alternative to the • Pond/Lake: If the site has an homes by Dec. 31, 2016 are eligible geothermal heat pump. Dual-source adequate water body, this may be for a 30% federal tax credit. See the heat pumps have higher efficiency the least expensive option. A supply Financial Incentives box for more ratings than air-source units, but are line pipe runs underground from information. not as efficient as geothermal units. the building to the water and coils The main advantage of dual-source into circles at least eight feet under Geothermal heat pump systems have systems is that they cost much less to the surface to prevent freezing. The an average 20+ year life expectancy install than a single geothermal unit, coils should only be placed in a for the heat pump itself and 25 to 50 and work almost as well. water source that meets minimum years for the underground infrastruc- volume, depth, and quality criteria. ture. Additionally, they move between three and five times the energy they Types of Geothermal Heat Open-Loop System consume between a building’s interior Pumps This type of system uses well or sur- space and the ground. Geothermal heat pumps come in face body water as the heat exchange To determine the energy efficiency four types of loop systems that loop fluid that circulates directly through of a geothermal heat pump, look for: the heat to or from the ground and the geothermal heat pump system. the Energy Efficiency Ratio (EER), your house. Three of these – hori- Once it has circulated through the and the Coefficient of Performance zontal, vertical, and pond/lake – are system, the water returns to the (COP). The cooling capacity is closed-loop systems. The fourth type ground through the well, a recharge indicated by the EER while the of system is the open-loop option. well, or surface discharge. This op- heating capacity is indicated by the Choosing the one that is best for tion is practical only with an adequate COP. To find current ENERGY STAR your site depends on the climate, soil supply of relatively clean water, and requirements and ratings, please see conditions, available land, and local if all local codes and regulations the ENERGY STAR link below. installation costs at the site. regarding groundwater discharge are met. Closed-Loop Systems Further Resources • Horizontal: This type of installa- Energy-Efficient and Cost- DOE Energy Savers: Geothermal Heat tion is generally most cost-effective Effective Pumps for residential installations, Although installing a geothermal heat www.energysavers.gov/ particularly for new construction geothermal_heat_pumps where sufficient land is available. It pump system is more expensive than requires trenches at least four feet installing an air source system of the Energy 101: Geothermal Heat Pumps deep. same heating and cooling capacity, www.eere.energy.gov/multimedia/ you can recoup the additional costs video_geothermal_heat_pumps.html • Vertical: This is often used for in energy savings in 5 to 10 years. larger scale geothermal systems An average geothermal heat pump (such as in commercial buildings) system costs about $2,500 per ton of Financial Incentives where land is limited, or where capacity. If a home requires a 3-ton Tax credits, incentives, and rebates may be the soil is too shallow to bury the unit, then it would cost about $7,500 available in your area. Please visit horizontal loops in the trenches (plus installation and drilling costs). www.energysavers.gov/taxcredits for more and some form of drilling into the A comparable ASHP system with information. bedrock is necessary. Vertical loop air conditioning would cost about
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