The GHP takes advantage of these more favorable temperatures to become high efficient by exchanging heat with the earth through a ground heat exchanger. As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water. Some models of geothermal systems are available with two-speed compressors and variable fans for more comfort and energy savings. Relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air.
A dual-source heat pump combines an air-source heat pump with a geothermal heat pump. These appliances combine the best of both systems. Dual-source heat pumps have higher efficiency ratings than air-source units, but are not as efficient as geothermal units.
The main advantage of dual-source systems is that they cost much less to install than a single geothermal unit, and work almost as well. Even though the installation price of a geothermal system can be several times that of an air-source system of the same heating and cooling capacity, the additional costs may be returned in energy savings in 5 to 10 years, depending on the cost of energy and available incentives in your area. There are approximately 50, geothermal heat pumps installed in the United States each year.
Watch how geothermal heat pumps heat and cool buildings by concentrating the naturally existing heat contained within the earth -- a clean, reliable, and renewable source of energy. There are four basic types of ground loop systems. The fourth type of system is the open-loop option. Several factors such as climate, soil conditions, available land, and local installation costs determine which is best for the site. All of these approaches can be used for residential and commercial building applications.
Most closed-loop geothermal heat pumps circulate an antifreeze solution through a closed loop -- usually made of a high density plastic-type tubing -- that is buried in the ground or submerged in water. A heat exchanger transfers heat between the refrigerant in the heat pump and the antifreeze solution in the closed loop. One type of closed-loop system, called direct exchange, does not use a heat exchanger and instead pumps the refrigerant through copper tubing that is buried in the ground in a horizontal or vertical configuration.
Direct exchange systems require a larger compressor and work best in moist soils sometimes requiring additional irrigation to keep the soil moist , but you should avoid installing in soils corrosive to the copper tubing. Because these systems circulate refrigerant through the ground, local environmental regulations may prohibit their use in some locations. This type of installation is generally most cost-effective for residential installations, particularly for new construction where sufficient land is available.
It requires trenches at least four feet deep. The most common layouts either use two pipes, one buried at six feet, and the other at four feet, or two pipes placed side-by-side at five feet in the ground in a two-foot wide trench. Large commercial buildings and schools often use vertical systems because the land area required for horizontal loops would be prohibitive.
Vertical loops are also used where the soil is too shallow for trenching, and they minimize the disturbance to existing landscaping. It may also be possible to include the purchase of a GHP system in an "energy-efficient mortgage" that would cover this and other energy-saving improvements to the home. Banks and mortgage companies can provide more information on these loans. There are also special financing and incentives available to help offset the cost of adding a GHP to your home. These provisions are available from federal , state, and local governments; power providers; and banks or mortgage companies that offer energy-efficient mortgage loans for energy-saving home improvements.
Be sure the system you're interested in qualifies for available incentives before you make your final purchase. Shallow ground temperatures are relatively constant throughout the United States, so geothermal heat pumps GHPs can be effectively used almost anywhere. Factors such as the composition and properties of your soil and rock which can affect heat transfer rates require consideration when designing a ground loop.
For example, soil with good heat transfer properties requires less piping to gather a certain amount of heat than soil with poor heat transfer properties. The amount of soil available contributes to system design as well -- system suppliers in areas with extensive hard rock or soil too shallow to trench may install vertical ground loops instead of horizontal loops.
Ground or surface water availability also plays a part in deciding what type of ground loop to use. Depending on factors such as depth, volume, and water quality, bodies of surface water can be used as a source of water for an open-loop system, or as a repository for coils of piping in a closed-loop system. Ground water can also be used as a source for open-loop systems, provided the water quality is suitable and all ground water discharge regulations are met.
Antifreeze fluids circulated through closed-loop systems generally pose little to no environmental hazard. The amount and layout of your land, your landscaping, and the location of underground utilities or sprinkler systems also contribute to your system design. Horizontal ground loops generally the most economical are typically used for newly constructed buildings with sufficient land. Specialized technical knowledge and equipment is needed to properly install the piping, so a GHP system installation is not a do-it-yourself project.
To find a qualified installer, contact your local utility company, the International Ground Source Heat Pump Association , or the Geothermal Exchange Organization for their listings of qualified installers in your area.
Installers should be certified and experienced. Ask for references from owners of systems that are several years old, and check them. The ground heat exchanger in a GHP system is made up of a closed or open loop pipe system. Most common is the closed loop, in which high density polyethylene pipe is buried horizontally at 4 to 6 feet deep or vertically at to feet deep.
In the winter, the fluid in the pipes extracts heat from the earth and carries it into the building. In the summer, the system reverses and takes heat from the building and deposits it to the cooler ground. Ductwork in the home distributes the heated or cooled air through the house, just like conventional systems.
The box that contains the indoor coil and fan is sometimes called the air handler because it moves house air through the heat pump for heating or cooling. The air handler contains a large blower and a filter just like conventional air conditioners.
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