GEOTHERMAL

How would you like to have a heating and air conditioning system in your home that can:

  • Save energy and slash electric bills
  • Cut greenhouse gas emissions
  • Rid your yard of unsightly outdoor equipment
  • Reduce the cost of your hot water
  • Reduce maintenance cost - even as it improves the year-round comfort of your home

Sounds to good to be true?  In fact, such units called geothermal systems, offer such a lengthy list of benefits that at first glance they do seem too good to be true.  Once you understand how these systems work, you'll understand how they can bring such an attractive list of benefits to your home.

What geothermal systems do

Geothermal systems provide heating in the winter and cooling in the summer, at efficiencies that are far greater than those for most conventional systems.  Like conventional heat pumps, they are essentially air conditioners that can run in reverse to provide heat in the winter.  The primary difference is geothermal systems rely on the nearly constant temperature of the earth for heat transfer instead of the widely fluctuating temperatures of the outside air. This is the key to the geothermal systems surprising efficiency.

How It All Works

Geothermal systems, like common heat pumps and air conditioners, make use of a refrigerant to help transfer (or pump) heat into and out of your home.  The refrigerant helps the geothermal system take advantage of two primary principles of heat transfer:

  1. Heat energy always flows from areas of higher temperature to areas of lower temperature.
  2. The greater the difference in temperature between two adjacent areas, the higher the rate of heat transfer between them

Conventional heat pumps, while relatively simple, face one major challenge.  Their operating efficiency is lowest when demand is highest; that is, heat pumps have to work hardest when we want the most from them.  A conventional heat pump extracts heat energy from outside air in the winter, and rejects heat to outside air in the summer.  Unfortunately, the colder the outside air, the more difficult it is to extract heat from it, and the hotter the outside air, the harder it is to transfer heat to it.  The temperature difference between the air and the refrigerant is small in both cases, lowering heat transfer rates within the system.  A geothermal system eliminates this dilemma by using the relatively constant earth temperature as a heat source in the winter and a heat sink in the summer, instead of the constantly changing outside air temperature. Throughout most of the U.S., the temperature of the ground below the frost line remains at nearly constant temperature, generally in the 45- 50 degree range in the nothern latitudes, and in the 50- 70 degree range in the south.  So, in the winter, a geothermal unit can extract heat from the ground that is relatively warm compared to the outside air, and in the summer, it can discharge heat to the ground that is relatively cool, compared to the hot outside air.  Since the difference between the refigerant temperature and the ground temperature remains relatively high in both seasons, so do heat transfer rates.  Consequently, the geothermal system operates at a much higher year round efficiency than a conventional heat pump.

Making The Ground Connection

The unique aspect of a geothermal system, and the key to its lengthy list of benifits, is the ground loop.  The ground loop provides the means for tranferring heat to the earth in the summer, and extracting heat from the earth in the winter.  Physically, the "ground loop" consists of several lengths of plastic pipe with the water inside the piping being circulated through the heat exchanger inside the geothermal unit.  In the summer, it absorbs heat from the refrigerant hot zone and carries it to the ground through the ground loop piping.  In the winter, it absorbs heat from the earth through the ground loop, and then transfers that heat to the refrigerant cold zone.  The length of the ground loop is determined by the heating and cooling load, which are determined by the size of your home, the design and construction of your home, the orientation of your home, and the climate in which you live.

Heat Transfer

The unique aspect of a geothermal system, and the key to its lengthy list of benifits, is the ground loop.  The ground loop provides the means for tranferring heat to the earth in the summer, and extracting heat from the earth in the winter.

Vertical Loop

Generally one bore hole for each nominal ton of heating or cooling capacity, typically installed with 15 to 25 feet of spacing.  This approach works best in formations containing clays, silts, sands, and gravels, with lengths ranging from 150 to 250 feet, or more.

Horizontal Loop

Trenches are commonly installed approximately 10 feet apart and up to 150 feet in length per nominal ton of heating or cooling capacity.  The trench width and depth, as well as pipe configuration directly effects the trench design length.

Pond Loop

Loop is typically a 300 foot coil of PE pipe per nominal ton of heating or cooling capacity.  A pond loop requires a minimum pond size of 1/2 acre and a depth of 8 to 10 feet at the driest time of the year.

Open Loop

Utilizes a water supply well to pump raw ground water through the heat pump and then discharging to a reinjection well or designated surface location.  Open loop systems are directly effected by water quantity and quality.