Intro to Geothermal Energy

Geothermal heating and cooling systems work on a different principle than an ordinary furnace/air conditioning system. Furnaces must create heat by burning a fuel such as natural gas, propane, or fuel oil. With geothermal heating 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 geothermal heat pump (GHP) then uses electrically-driven compressors and heat exchangers in a vapor compression cycle 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. GHP systems provide cooling in the same way that a refrigerator keeps its contents cool -- by drawing heat from the interior and moving it to an outside space.

Geothermal heat pump 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.

Geothermal heat pumps work differently than conventional heat pumps that use the outdoor air as their heat source or heat sink. GHP 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 50 F. than from the atmosphere when the air temperature is below zero. This is also why GHP systems encounter no difficulty blowing comfortably warm air through a home’s ventilation system, even when the outdoor air temperature is extremely cold. 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 geothermal 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

GHP systems can also provide all or part of a household’s hot water. One economical way to obtain a portion of domestic hot water is through the addition of a desuperheater to the GHP 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 GHP 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 system may not be operating at all.

Because GHP systems heat water so efficiently, many manufacturers today are also offering triple function 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.

Click here to learn how East Shore Mechanical can put geothermal energy to work for you.