Geothermal Heating & Cooling

Choosing a heating and cooling system for a new or existing home can be a very difficult and confusing task.

There is one alternative to a conventional gas or oil-fired furnace that is more economical, completely safe and is ecologically sound. This system provides total comfort all year long by using an inexhaustible energy source. This system is the geothermal closed-loop heat pump, which provides both heating and cooling for the home.

The geothermal closed-loop heat pump (geothermal system) takes advantage of energy stored within the earth. This stored energy is collected from the sun’s energy striking the earth. This solar energy is absorbed by the ground around your house all year long. The geothermal system uses this huge mass of stored energy to heat and cool our homes and businesses.

How is heat exchanged?

There are two main components to the geothermal system: the buried closed-loop (a loop of pipe buried in the ground) and the indoor unit which is tied into a proper ductwork system. There is no outdoor unit used with this system as you would find with a conventional heat pump system.

Heat is exchanged with the earth by using a buried earth loop and a small circulating pump. Only two types of pipe are acceptable for the earth loop – polybutylene and high-density polyethylene pipe. This earth loop must be installed by a certified contractor. The loop is carefully assembled on location using “heat fusion” to join the pipes where necessary. Once this is done, the loop system becomes “one piece” of pipe with parallel circuits. The integrity of this loop is such that a virtual lifetime of trouble-free use can be expected. Installation by any other means may cause a failure of the pipe because of the unique conditions below the ground.

Water, with an antifreeze solution, is circulated through the earth loop. In the heating mode, the indoor unit extracts heat from the solution in the loop, and with a refrigeration process, intensifies that heat and delivers it through the duct system at temperatures ranging from 95 to 105 degrees F. Since heat is being transferred – not produced – the geothermal system is delivering over three units of energy for every unit of energy it consumes. This is possible due to the fact that it takes advantage of below ground temperatures that are warmer in the winter and cooler in the summer than the outdoor air. Since the earth loop is buried in the ground, where temperatures are constant, the outdoor temperature does not adversely affect the high efficiency of the geothermal system.

In the cooling mode, the indoor unit extracts heat from the air inside the home, and transfers that heat into the solution circulating through the loop. The heat is then rejected to the earth. It is much easier to transfer heat into the cooler earth than trying to transfer it into the 90-100 degree F outdoor air.

Types of Earth Loops

The earth loop can be installed in a horizontal or vertical configuration and a pond or lake can be utilized under the right conditions. All three types have similar performance characteristics and, when designed properly, each will operate as efficiently as the next. The choice will depend upon the installation cost, geographic location, land area availability and local codes.

Horizontal loops are generally installed in a two-pipe design. The trench length is approximately 250 feet long with the bottom pipe at 5-6 feet deep and the top pipe at 3-4 feet deep. A total of 500 feet of pipe per trench will furnish enough heat for one ton (one ton = 12,000 Btu/hr.) of capacity.

The average size home requires three tons of capacity. For this home, there needs to be three trenches 250 feet long, at least eight feet apart, with two small pipes buried in each trench. A “header” system of pipe will tie the three pair of trench pipes together, bringing just two larger pipes into the home. When space is limited, a four or six pipe configuration in a wider trench can dramatically shorten the trench length. Such wider trenches generally require a backhoe rather than a chain trencher for excavation.

Vertical loops can be installed almost anywhere and are ideal when land surface area is minimal. Drilling equipment is used to bore small diameter holes 100 to 200 feet deep. Approximately 150 feet of bore is usually required per ton. A typical three-ton system will have three holes bored at 150 feet each. Two pipes are joined with a U-bend and are inserted into each hole. A “header” system connects these pipes to two larger pipes that are brought into the structure.

Pond or lake loops are simply coils of pipe placed in a lake or pond. The pond/lake loop eliminates much of the excavating in horizontal or vertical installations. Heat is exchanged between the body of water and the submerged loop in the same manner as the earth loop. In most cases, one-fourth to one-half acre surface area with an eight foot depth is required. (Circulation of pond/lake water itself into the geothermal system is not acceptable.)

In all three installations, loop lengths must be determined after sizing the geothermal system. Unit selection is based on the heating and cooling requirements of the building. Sized properly, the geothermal system will provide almost all of the heating requirements of the home, thus little or no supplementary heat is required. In most applications, a low wattage electric heater is installed with the geothermal system to provide supplemental heat if needed.

Domestic Hot Water

Most manufacturers offer an option, which is becoming a standard, that produces a large percentage of the annual hot water requirements. A “Desuperheater” is installed with a small circulating pump between the existing water heater and the geothermal system. During the winter, when the geothermal system is operating in the heating mode, hot water is being produced at the same high efficiency. In the summer, the heat that is being rejected by the geothermal system is transferred to the water heater at little or no cost.

Geothermal Alliance of Illinois

The Geothermal Alliance of Illinois (GAOI) is THE source for information about geothermal heating and cooling. GAOI members are:

• Certified installer-dealers of geothermal equipment
• Designer engineers of geo systems
• Manufacturers of geo equipment
• Loop installers
• Utilities
• Others related to the industry

Adams Electric is a member of the Geothermal Alliance of Illinois. To learn more, visit www.gaoi.org.