Geothermal

What is Geothermal?

Geothermal Heat Pump

A geothermal heat pump (GHP) system is a central heating and/or air conditioning system that actively pumps heat to or from the shallow ground. It uses the earth as either a source of heat in the winter, or as a coolant in the summer. This design takes advantage of moderate temperatures in the shallow ground to boost efficiency and reduce operational costs. It may be combined with solar heating to form a geosolar system with even greater efficiency.
Geothermal heat pumps are also known by a variety of other names, including geoexchange, earth-coupled, earth energy, ground-source or water-source heat pump. The engineering and scientific community tend to prefer the terms “geoexchange” or “ground-source heat pumps”[1] because geothermal power generally refers to heat originating from deep geologic sources. Ground-source heat pumps harvest a mixture of genuine geothermal power[2] and heat from the sun, or they may work against these heat sources when used for air conditioning.
Like a refrigerator or air conditioner, these systems use a heat pump to
force the transfer of heat. Heat pumps can capture heat from a cool area and transfer it to a warm area, against the natural direction of flow, or they can enhance the natural flow of heat from a warm area to a cool one. The core of the heat pump is a loop of refrigerant pumped through a vapor- compression refrigeration cycle that moves heat. Heat pumps are always more efficient than pure electric heating, even when extracting heat from air.
But unlike an air-source heat pump, which extracts or exhausts heat to or from the outside air, a ground-source heat pump exchanges heat with the ground. This is much more energy-efficient because underground temperatures are relatively stable through the year. Seasonal variations drop off with depth and disappear below 10 m due to thermal inertia.[2] Like a cave, the shallow ground temperature is warmer than the air above during the winter and cooler than the air in the summer. A ground-source heat pump extracts that ground heat in the winter (heating) and exhausts heat back into the ground in the summer (cooling). Some systems are designed to operate in one mode only, heating or cooling, depending on climate.

Get the latest Flash Player to see this player.

Get the latest Flash Player to see this player.

Building distribution

Liquid-to-air heat pump

The heat pump is the central unit that becomes the heating and cooling plant for the building. Some models may cover space heating, space cooling, (space heating via conditioned air, hydronic systems and / or radiant heating systems), domestic or pool water preheat (via the desuperheater function, demand hot water, and driveway ice melting all within one appliance with a variety of options with respect to controls, staging and zone control. The heat may be carried to its end use by circulating water or forced air. Almost all types of heat pumps are produced for commercial and residential applications.
Liquid-to-air heat pumps (also called water-to-air) output forced air, and are most commonly used to replace legacy forced air furnaces and central air conditioning systems. There are variations that allow for split systems,
high-velocity systems, and ductless systems. Heat pumps cannot achieve as high of a fluid temperature as a conventional furnace, so they require a higher volume flow rate of air to compensate. When retrofitting a residence, the existing duct work may have to be enlarged to reduce the noise from the higher air flow.

Liquid-to-water heat pump

Liquid-to-water heat pumps (also called water-to-water) are hydronic systems that use water to carry heating or cooling through the building. Systems such as radiant underfloor heating, baseboard radiators, conventional cast iron radiators would use a liquid-to-water heat pump. These heat pumps are preferred for pool heating or domestic hot water pre-heat. Heat pumps can only heat water to ~50°C (120°F) efficiently, whereas a boiler normally reaches 65–95°C. (150–200°F) Legacy radiators designed for these higher temperatures may have to be doubled in numbers when retrofitting a home. A hot water tank will still be needed to raise water temperatures above the heat pump’s maximum, but pre- heating will save 25-50% of hot water costs.
Ground-source heat pumps are especially well matched to underfloor heating and baseboard radiator systems which only require warm temperatures (40°C) to work well. Thus they are ideal for open plan offices. Using large surfaces such as floors, as opposed to radiators, distributes the heat more uniformly and allows for a lower water temperature. Wood or carpet floor coverings dampen this effect because the thermal transfer efficiency of these materials is lower than that of masonry floors (tile, concrete). Underfloor heating cannot be used for cooling because atmospheric humidity would condense on the floor.
Combination heat pumps are available that can produce forced air and circulating water simultaneously and individually. These systems are largely being used for houses that have a combination of air and liquid conditioning needs, for example central air conditioning and pool heating.