Although many parts of the country experience seasonal temperature extremes -- from scorching heat in the summer to sub-zero cold in the winter—a few feet below the earth's surface the ground remains at a relatively constant temperature.
Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. 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.
The heat within the refrigerant is then extracted using heat exchangers and passed through a system of ducts or pipes throughout the home. The last step is usually done with air handling units if the air is used to distribute the heat. This process is reversed in the summer months. With geothermal cooling, the refrigerant absorbs heat from the indoors and rejects it to the ground through the underground loops.
As with ducted air conditioning systems, geothermal systems also employ a system of ductworks. This makes geothermal systems especially suitable for renovation projects in homes with ductwork already installed. The existing ducts can then be utilized for this purpose. This holds for systems that transfer heat throughout the building using air, called liquid-to-air systems.
Air handling units, which are big fans, move large volumes of air across ducts. Water-to-water systems can also be used as water heaters for domestic use. A geothermal heat pump can keep the running water at a cozy o F, which is less than the required o F achieved through boilers.
But pre-heating the water through a geothermal system results in energy savings with the boiler. Water-to-water arrangements are a popular option for water distribution systems for heating and cooling. Loops are embedded underneath the flooring or within the walls. These loops remain out of sight and do not make any noise while still providing heating and cooling.
Another choice is to use baseboard heating systems in conjunction with geothermal systems. But be careful with this option, and consult a professional for proper sizing of your home and the heating requirements. Geothermal systems present a higher upfront initial investment than contemporary home heating and cooling systems though these costs are gradually decreasing.
The exact amount depends upon the soil characteristics, area to be dug up, whether it is a vertical loop or horizontal loop system, conditioning area within the home, prior ductwork, and installation quality. Higher-end versions can cost even more than this. In addition, the choice between water-to-air and water-to-water can also have a bearing on the cost.
Water-to-air heat pumps are the more economical choice between the two. Drilling and digging can amount to more than half of the total cost of installation of a geothermal system. Geothermal heat pump installation for the whole system can also be costly.
As far as efficiency is concerned, geothermal heating and cooling systems far outscore conventional air conditioning. The main reason for that is that a geothermal heat pump system is not ejecting heat to a hot outdoor environment, rather transferring it into a cool environment. This can seem like a Godsend in the hot summer months.
This is in part due to the high Energy Efficiency Ratios of geothermal systems, reaching as high as 25, as compared to 15 for conventional systems. Geothermal cooling can hence have a major impact on your summer bills. A geothermal system does not have many parts to be taken care of, like a conventional HVAC system.
There are no ducts; there are no dampers or louvers; no fuel needs to be kept in check. In some regions, tectonic and volcanic activity can bring higher temperatures and pockets of superheated water and steam much closer to the surface. Geothermal energy is considered a renewable resource. Ground source heat pumps and direct use geothermal technologies serve heating and cooling applications, while deep and enhanced geothermal technologies generally take advantage of a much deeper, higher temperature geothermal resource to generate electricity.
A ground source heat pump takes advantage of the naturally occurring difference between the above-ground air temperature and the subsurface soil temperature to move heat in support of end uses such as space heating, space cooling air conditioning , and even water heating. A ground source or geoexchange system consists of a heat pump connected to a series of buried pipes. One can install the pipes either in horizontal trenches just below the ground surface or in vertical boreholes that go several hundred feet below ground.
The heat pump circulates a heat-conveying fluid, sometimes water, through the pipes to move heat from point to point. A commercial-scale ground source heat pump system. This example is a demonstration project at a university.
Credit: Craig Miller Productions, NREL If the ground temperature is warmer than the ambient air temperature, the heat pump can move heat from the ground to the building.
The heat pump can also operate in reverse, moving heat from the ambient air in a building into the ground, in effect cooling the building. Four to six feet below ground, temperatures remain relatively constant year-round. That takes place on the scale of utilities and uses different processes, normally by heating water to boiling. The pipes that make up an earth loop are usually made of polyethylene and can be buried under the ground horizontally or vertically, depending on the characteristics of the site.
The indoor unit compresses the heat to a higher temperature and distributes it throughout the building, as if it were an air conditioner running in reverse. Unlike ordinary heating and cooling systems, geothermal HVAC systems do not burn fossil fuel to generate heat; they simply transfer heat to and from the earth. Geothermal heat pumps, as well as all other types of heat pumps, have efficiencies rated according to their coefficient of performance, or COP.
Most geothermal heat pump systems have COPs of 3. This means for every unit of energy used to power the system, three to five units are supplied as heat.
Geothermal systems require little maintenance. When installed properly, which is critical, the buried loop can last for generations. Usually, periodic checks and filter changes and annual coil cleaning are the only required maintenance. They work with nature, not against it, and they emit no greenhouse gases. Geothermal HVAC systems are becoming common features of eco-friendly homes as part of the growing green building movement.
Green projects accounted for 20 percent of all newly built homes in the U. But a lot of information out there on geothermal heating and cooling is based on outdated information, or outright myths.
Geothermal HVAC systems are not considered a renewable technology because they use electricity. Fact: Geothermal HVAC systems use only one unit of electricity to move up to five units of cooling or heating from the earth to a building. Photovoltaic and wind power are more favorable renewable technologies when compared to geothermal HVAC systems.
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