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How it Works

Geothermal Heat Pumps (also known as Water Source Heat Pumps)


Geothermal heat pumps are similar to air-source heat pumps, but instead of using heat found in outside air, they rely on the relatively constant heat of the earth (thermal energy) to provide heating, air conditioning and, in most cases, hot water. 

While ground-loop and water-loop heat pump systems may be slightly affected by higher temperature fluctuations, they are not as sensitive to temperature changes as air-source heat pumps. The reasons are that ground and water temperatures, a few feet below the Earth’s surface, stay relatively constant throughout the day or year. For this reason, ground loop heat pump systems remain extremely efficient throughout the year in virtually any climate.

How It Works

In winter, geothermal heat pump systems collect the Earth’s natural heat through a series of pipes made of copper or plastic, called a loop, installed below the surface of the ground or submersed in a body of water.  Fluid circulating in the loop carries this heat to the home. There, an electric compressor and a heat exchanger concentrate the Earth's energy and release it inside the home at a higher temperature. Ductwork distributes the heated air to different rooms. In summer, the process is reversed in order to cool the home. Excess heat is drawn from the home, expelled to the loop, and absorbed by the Earth.

Installation


Geothermal heat pump systems are comprised of an indoor unit that is installed in a basement or attic, and some are small enough to fit on a closet shelf. The indoor location also means the equipment is protected from mechanical breakdowns that could result from exposure to harsh weather.

Outdoors, the ground loop systems can be installed in four ways:

  1. Horizontal.  Long trenches are excavated for the loop(s), which require a substantial amount of land.  This is generally the most cost-effective option for homeowners, particularly for new homes where sufficient land is available.
  2. Vertical.  Deep holes are bored into the ground, which require a great deal less land for installation then horizontal loops.  This option is often used for commercial buildings and schools and for homes where land area is limited. 
  3. Pond/Lake.  Trenches are excavated similar to the horizontal installation, but lead to a body of water where coils of pipes sit at the bottom of the lake/pond.  These loops use the water, rather than the ground, for heat transfer.  This is typically the lowest cost option if the site has an adequate body of water.
  4. Open.  Water is drawn from a well, lake, or stream and pumped into the geothermal unit.  The water is then returned to the ground or body of water.  This option is only available if there is an abundant supply of usable water.

 In ARI’s Directory of Certified Geothermal Heat Pumps, performance data on horizontal, vertical, and pond/lake systems is listed under the ground-loop heat pump (GLHP) application.  Performance data on open systems is listed under the ground water heat pump (GWHP) application.  ARI does not certify units that only heat water.   

Environmental Benefit

With nearly 500,000 geothermal heat pumps installed annually, they collectively help reduce U.S. greenhouse gas emissions by preventing more than 1 million metric tons of carbon dioxide from being generated each year.  According to the Environmental Protection Agency (EPA), geothermal heat pumps can reduce energy consumption and related emissions by 23 percent to 44 percent. Compared to residential electrical resistance heating and standard air-conditioning equipment, the EPA finds geothermal heat pumps are up to 70 percent more efficient. In addition, the EPA has found that geothermal heat pumps offer the lowest carbon dioxide emissions and lowest overall environmental cost of all the residential space-conditioning technology readily available today.

Over an average 20-year lifespan, every 100,000 units of nominally sized residential geothermal heat pumps will save more than 24 trillion Btus of electrical energy, and save consumers approximately $500 million in heating and cooling costs at current prices. Over the same period, the EPA estimates these 100,000 units reduce greenhouse gas emissions by almost 1.1 million metric tons of carbon equivalents. Shipments of geothermal heat pumps are on the rise. In 2004, manufacturers shipped 43,806 geothermal heat pumps, a 20 percent increase over the 2003 total of 36,439.

How Much Does It Cost?

Installation costs for geothermal systems are somewhat higher than air-source heat pumps because they require underground connections. On average, a geothermal system costs about $2,500 per ton of capacity, or roughly $7,500 for a 3-ton unit (typical residential size).

In comparison, other systems would cost about $4,000 with air-conditioning.  When included in the mortgage, the homeowner has a positive cash flow from the beginning.  For example, say that the extra $3,500 will add $30 per month to each mortgage payment.  But the energy cost savings will easily exceed that added mortgage amount over the course of each year. 

Installing a geothermal heat pump system in an older home typically means much lower utility bills, allowing the investment to be recouped in two to 10 years.