Residential Geothermal Heating & Cooling
Geothermal heating and
cooling systems using heat pumps are one of the most cost efficient
ways of heating and cooling your home. Geothermal systems
consume 25-50% less energy than traditional oil and natural gas
systems, and 70% less than electric heating and air conditioning.
Moreover, using a ground-source heat pump will work in just about any
location in the U.S. The key to this energy approach is that the
temperature a few feet below ground stays at a very stable 45°F (7°C)
to 60°F (16°C). degrees year around depending upon your latitude.
This means that during the winter the ground temperature is usually
warmer than the air temperature and can be used for heating your home.
In the summer the ground temperature is cooler than the air
temperature so the same heat pump can be used to pump hot air out of
your house into the earth in order to cool it.
Geothermal heating systems have been available since the late
1940's and have rapidly risen in popularity as oil and natural gas
heating costs have begun to soar. There are now more than
600,000 geothermal heating units installed in the U.S. and their
implementation has in recent years grown by more than 15% per year. Heat pumps do require electricity to operate but they are extremely
efficient because they are leveraging the temperatures in the earth
rather than air temperature. They are similar to some other
types of energy solutions such as solar energy in that there is a
significant up front cost for putting in the ground-source piping and
for the cost of the heat pumping unit. However, once they are
set up they are relatively trouble free and have an excellent payback
period, usually between 6-10 years.
System life is estimated at 25 years for the inside components and 50+
years for the ground loop.
Components of a Geothermal System
Geothermal heating and cooling systems are not overly complex.
Let's review the components that make up a typical system:
- Heat Pump: The heat pump is the heart of the system. A
heat pumps job is to transfer heat energy from one location to
another. It does this through a process of heat exchange.
- Ground Coils: Typical ground-source heat pumps transfer heat using a network of tubes, called "closed loops." Basically, the loops are filled with either water, refrigerant or an anti-freeze solution. They run through the ground in the vicinity of a building and the liquid absorbs the Earth’s heat energy. Then, this warmed liquid is pumped back through the system into the building. This process provides heat to the building space. Once the fluid passes through the building and transfers its energy, it flows through the loop system back to the Earth and the process repeats itself.
- Heat Exchange Fluid: Basically, the loops are filled with
either water, refrigerant or an anti-freeze solution.
- Heating and Cooling Ducts: There needs to be a system of
ducts to move the heated or cooled air to each room. If you
already used some type of forced air heating or have central air
conditioning then this duct work is probably already in place.
- Thermostat: The heat pump would normally be connected to
the house's thermostat which would turn the pump on or off depending
upon the desired house temperature.
While many parts of the country experience seasonal temperature extremes—from scorching heat in the summer to sub-zero cold in the winter—a few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45°F (7°C) to 75°F (21°C). Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of this by exchanging heat with the earth through a ground heat exchanger.
As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water. Some models of geothermal systems are available with two-speed compressors and variable fans for more comfort and energy savings.
Relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air.
A dual-source heat pump combines an air-source heat pump with a geothermal heat pump. These appliances combine the best of both systems. Dual-source heat pumps have higher efficiency ratings than air-source units, but are not as efficient as geothermal units. The main advantage of dual-source systems is that they cost much less to install than a single geothermal unit, and work almost as well.
Even though the installation price of a geothermal system can be several times that of an air-source system of the same heating and cooling capacity, the additional costs are returned to you in energy savings in 5–10 years. System life is estimated at 25 years for the inside components and 50+ years for the ground loop. There are approximately 40,000 geothermal heat pumps installed in the United States each year.