How It Works
Homeowners in virtually every region of the United States are enjoying a high level of comfort and significantly reducing their energy use today with GeoExchange (geothermal) heating and cooling.
This marvelous technology relies primarily on the Earth’s natural thermal energy, a renewable resource, to heat or cool a house or multi-family dwelling. The only additional energy GeoExchange systems require is the small amount of electricity they employ to concentrate what Mother Nature provides and then to circulate high-quality heating and cooling throughout the home.
Homeowners who use GeoExchange systems give them superior ratings because of their ability to deliver comfortably warm air, even on the coldest winter days, and because of their extraordinarily low operating costs. As an additional benefit, GeoExchange systems can provide inexpensive hot water, either to supplement or replace entirely the output of a conventional, domestic water heater.
GeoExchange heating and cooling is cost effective because it uses energy so efficiently. This makes it very environmentally friendly, too. For these reasons, federal agencies like the Environmental Protection Agency and the Department of Energy, as well as state agencies like the California Energy Commission, endorse it.
Owners of GeoExchange systems can relax and enjoy high-quality heating and cooling year after year. GeoExchange systems work on a different principle than an ordinary furnace/air conditioning system, and they require little maintenance or attention from homeowners. Furnaces must create heat by burning a fuel--typically natural gas, propane, or fuel oil. With GeoExchange systems, there’s no need to create heat, hence no need for chemical combustion. Instead, the Earth’s natural heat is collected in winter through a series of pipes, called a loop, installed below the surface of the ground or submersed in a pond or lake. Fluid circulating in the loop carries this heat to the home. An indoor GeoExchange system then uses electrically-driven compressors and heat exchangers in a vapor compression cycle--the same principle employed in a refrigerator--to concentrate the Earth’s energy and release it inside the home at a higher temperature. In typical systems, duct fans distribute the heat to various rooms.
In summer, the process is reversed in order to cool the home. Excess heat is drawn from the home, expelled to the loop, and absorbed by the Earth. GeoExchange systems provide cooling in the same way that a refrigerator keeps its contents cool--by drawing heat from the interior, not by injecting cold air.
GeoExchange systems do the work that ordinarily requires two appliances, a furnace and an air conditioner. They can be located indoors because there’s no need to exchange heat with the outdoor air. They’re so quiet homeowners don’t even realize they’re on. They are also compact. Typically, they are installed in a basement or attic, and some are small enough to fit atop a closet shelf. The indoor location also means the equipment is protected from mechanical breakdowns that could result from exposure to harsh weather.
GeoExchange works differently than conventional heat pumps that use the outdoor air as their heat source or heat sink. GeoExchange systems don’t have to work as hard (which means they use less energy) because they draw heat from a source whose temperature is moderate. The temperature of the ground or groundwater a few feet beneath the Earth’s surface remains relatively constant throughout the year, even though the outdoor air temperature may fluctuate greatly with the change of seasons. At a depth of approximately six feet, for example, the temperature of soil in most of the world’s regions remains stable between 45 F and 70 F. This is why well water drawn from below ground tastes so cool even on the hottest summer days.
In winter, it’s much easier to capture heat from the soil at a moderate 50o F. than from the atmosphere when the air temperature is below zero. This is also why GeoExchange systems encounter no difficulty blowing comfortably warm air through a home’s ventilation system, even when the outdoor air temperature is extremely cold.2 Conversely, in summer, the relatively cool ground absorbs a home’s waste heat more readily than the warm outdoor air.
Studies show that approximately 70 percent of the energy used in a GeoExchange heating and cooling system is renewable energy from the ground. The remainder is clean, electrical energy which is employed to concentrate heat and transport it from one location to another. In winter, the ground soaks up solar energy and provides a barrier to cold air. In summer, the ground heats up more slowly than the outside air.
Making Hot Water
GeoExchange systems can also provide all or part of a household’s hot water. This can be highly economical, especially if the home already has a GeoExchange system, hence a ground loop, in place.
One economical way to obtain a portion of domestic hot water is through the addition of a desuperheater to the GeoExchange unit. A desuperheater is a small, auxiliary heat exchanger that uses superheated gases from the heat pump’s compressor to heat water. This hot water then circulates through a pipe to the home’s water heater tank. In summer, when the GeoExchange system is in the cooling mode, the desuperheater merely uses excess heat that would otherwise be expelled to the loop. When the GeoExchange unit is running frequently, homeowners can obtain all of their hot water in this manner virtually for free. A conventional water heater meets household hot water needs in winter if the desuperheater isn’t producing enough, and in spring and fall when the GeoExchange system may not be operating at all.
Because GeoExchange systems heat water so efficiently, many manufacturers today are also offering triple function GeoExchange systems. Triple function systems provide heating, cooling and hot water. They use a separate heat exchanger to meet all of a household’s hot water needs.
The Earth Connection
Once installed, the loop in a GeoExchange system remains out of sight beneath the Earth’s surface while it works unobtrusively to tap the heating and cooling nature provides. The loop is made of a material that is extraordinarily durable but which allows heat to pass through efficiently. This is important so it doesn’t retard the exchange of heat between the Earth and the fluid in the loop. Loop manufacturers typically use high-density polyethylene, a tough plastic. When installers connect sections of pipe, they heat fuse the joints. This makes the connections stronger than the pipe itself. Some loop manufacturers offer up to 50-year warranties. The fluid in the loop is water or an environmentally safe antifreeze solution that circulates through the pipes in a closed system.
To ensure good results, the piping should be installed by professionals who follow procedures established by the International Ground Source Heat Pump Association (IGSHPA). Installers should be certified by IGSHPA or be able to show equivalent training by manufacturers or other recognized authorities at a recognized institution, such as one of the many regional GeoExchange training centers located throughout the United States.
The length of the loop depends upon a number of factors, including the type of loop configuration used; a home’s heating and air conditioning load; soil conditions; local climate; and landscaping. Larger homes with larger space conditioning requirements generally need larger loops than smaller homes. Homes in climates where temperatures are extreme also generally require larger