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Geothermal Energy
In this section we will explore geothermal energy systems.  This includes high temperature systems which pull energy directly from the earth's core as well as low temperature systems which leverage the difference between air temperature and the temperature of the earth.

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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 45F (7C) to 60F (16C). 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:

  1. 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.
  2. 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.
  3. Heat Exchange Fluid: Basically, the loops are filled with either water, refrigerant or an anti-freeze solution.
  4. 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.
  5. 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 45F (7C) to 75F (21C). 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.

 

 

Finding the Best

One of the services we want to provide our EB members is a listing of Recommended Geothermal Heating Contractors.  If you have used a heating and cooling contractor to put a ground source heat pump into your home or business and were happy with their work please provide us their contact info by clicking here and we will do the rest. As soon as we have a sufficient list together we will publish it on the site.  Thanks! --Editor

Geothermal Facts
As early as 10,000 years ago, Native Americans used hot springs water for cooking and medicine. For centuries the Maoris of New Zealand have cooked "geothermally," and, since the 1960s, France has been heating up to 200,000 homes using geothermal water.
More Facts

In snow covered Idaho they raise alligators using ponds heated by geothermal energy.

Geothermal Books

Most books on the topic of geothermal energy are really targeted for energy professionals and are not of much value to the average consumer.  An exception is the book Geothermal Heat Pumps by Karl Oschner.  See this book and others in our book section.

 
 

 

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