Mining the Earth for Heat

Americans usually rely on two familiar systems to heat homes or buildings:

  • fuel-powered furnaces or boilers (which burn gas, oil, or propane) and electric-powered air-source heat pumps or baseboard radiant heat. However, these traditional systems present two drawbacks.
  1. First, even highly efficient models pollute the environment because fuel must be burned to produce heat.
  2. Second, energy prices are rising.

Accordingly, people want cost-effective long-term heating and cooling options.

  • Geothermal systems are one such option, they are being installed in homes, businesses, and schools across the country.

Geothermal 101

What is a “geothermal” system?

  • It’s a system takes advantage of the Earth’s ability to store vast amounts of heat in the soil (“geo” means earth and “thermal” refers to heat).
  • This heat energy is maintained at a constant temperature (50°F to 70°F depending on latitude) in the soil and near-surface rocks.
  • In Ohio, the soil maintains a 50°F temperature beginning approximately four feet down, well past the winter frost line.
  • Geothermal heating systems, also called ground-source heat pumps, “capture” this steady supply of heat energy and “move” it from the Earth and through a home or building. Basically, once installed, a home or building owner will use much less energy, save money each month, and reduce the amount of pollution produced by fossil fuel systems. In Ohio, for example, many area schools & colleges recently began installing geothermal systems. Schools across Ohio and the country have faced skyrocketing energy bills and they are searching for cost-effective alternatives.
  • Geothermal systems represent a proven option.
  • They can heat and cool your home and heat the water.
  • In addition, they utilize a renewable energy source—the Earth’s naturally-occurring heat energy.

What’s Wrong With Good, Old-Fashioned Combustion?

  • Traditional heating systems rely on combustion (the burning of fuel) either on site or at the power plant. Fuel-powered heating units, such as gas and boiler systems, burn fuel at the site to produce heat energy. Electric-powered heating and cooling systems do not require combustion at the site of the furnace; instead, it occurs at power plants. In 1998, approximately 80% of U.S. electricity was produced by burning fossil fuels. Only nuclear, wind, and hydroelectric plants do not burn fossil fuels.
  • The problem with combustion systems is that the by-products they produce contain harmful emissions. These emissions degrade air quality and contribute to other environmental problems including acid rain and the greenhouse effect. For the health of individuals and communities throughout the world, it makes sense to develop heating and cooling technologies that reduce or eliminate fossil fuel combustion.

How Ground Source Heat Pumps Work

  • A heat pump is a mechanical device that transfers heat from one source to another. Ground-source units pull heat from the earth and transfer it to homes or buildings. Heat pumps (despite their name) can provide both heating and cooling. The cooling process is simply the reverse of the heating process: heat is taken out of a building and returned to the Earth.
  • 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.
  • In the summertime, these systems “reverse” into cooling mode. Technically, the system does not “run backwards.” Instead, a series of valves enables the system to switch the “hot” side and the “cold” side. The heat from the building is transferred to the liquid in the loop and this liquid is pumped back into the ground. When the ground source heat pump is in cooling mode, it usually has an excess of warmed liquid in the system. This liquid can heat water for the building and basically eliminate the use of the hot water heater during the summer months.

Saving Energy

  • Ground-source heat pumps can use 25%-70% less electricity than conventional electric heating and cooling systems. First, in winter heating mode, a ground-source heat pump uses energy from the Earth to provide heat, whereas air-source heat pump try to extract the last bits of heat energy out of cold winter air. For example, because of the long, cold Wisconsin winters, air-source heat pumps are not effective or efficient, and the same goes for Ohio during bitter cold snaps.
  • Second, ground-source heat pumps are more energy efficient than conventional electric heaters because they maximize the thermodynamic advantage of a heat transfer fluid. This benefit enables the ground source heat pump to produce more heat energy output than electric energy input. Conventional electric heaters on the other hand don’t quite produce as much heat output as electric input. (Under some conditions, a ground source heat pump cannot meet the required heating needs. In these cases, supplemental heat must be provided from another source–usually conventional electric units.)
  • Third, during the summer, the ground source heat pump “reverses” into cooling mode. This fact makes the ground-source heat pump more energy efficient for cooling than a traditional air conditioner.
  • Finally, when a desuperheater is installed, energy from the ground source heat pump can be transferred to the hot water tank. As a result, building occupants receive “free” hot water in the summer and very low-cost hot water in the winter. bullet Most of a ground-source heat pump’s electrical energy requirement (70% to 80%) is consumed by the compressor and pump that combine to move heat energy to or from the ground, through the loop system, and into or out of a building. The remaining 20% to 30% of the electricity is used for fan(s) and controls to distribute the conditioned air throughout the building.