 a machine that moves heat from a location to another location, using mechanical work

 Compressor: This increases the pressure of the refrigerant so that it will accept the maximum amount of heat from the air.  Condenser: Coils that move heat to or from the outside air.  Evaporator: Coils that move heat to or from the air inside the home.  Air handler: Fan that blows the air into the ducts of the home. Components 1, 2, 3 and 4 are found in all standard air conditioners.  Reversing valve:Changes the heat pump from air conditioning to heating, and vice versa. This is not part of the thermostat.

 a heat pump which extracts heat from ground or water.

 The engineering and scientific communities prefer the terms "geoexchange" or "ground source heat pumps" because geothermal power traditionally refers to heat originating from deep in the earth's mantle. Ground source heat pumps harvest a combination of geothermal power and heat from the sun when heating, but work against these heat sources when used for air conditioning.

 An antifreeze solution is circulated through plastic pipes buried beneath the ground for closed loop systems. The fluid gathers heat from the earth and circulates it through the system and into the building. During the summer, the system reverses itself and pulls heat from the structure and places it in the ground. This process creates free hot water in the summer and produces a considerable savings on hot water in the winter.

 The COP for a heat pump in a heating or cooling application, with steady-state operation, is:  where  ΔQ cool is the amount of heat extracted from a cold reservoir at temperature T cool,  ΔQ hot is the amount of heat delivered to a hot reservoir at temperature T hot,  ΔA is the compressor's dissipated work.  All temperatures are in absolute units

 Heat pumps are always more efficient at heating than pure electric heaters, even when extracting heat from cold winter air. But unlike an air-source heat pump, which transfers 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 more stable than air temperatures through the year. Seasonal variations drop off with depth and disappear below seven meters due to thermal inertia.

 Ground source heat pumps, which are also confusingly referred to as Geothermal heat pumps, typically have higher efficiencies than air-source heat pumps. This is because they draw heat from the ground or groundwater which is at a relatively constant temperature all year round below a depth of about eight feet (2.5 m). This means that the temperature differential is lower, leading to higher efficiency. Ground- source heat pumps typically have COPs of at the beginning of the heating season, with lower COPs as heat is drawn from the ground. The tradeoff for this improved performance is that a ground-source heat pump is more expensive to install due to the need for the digging of wells or trenches in which to place the pipes that carry the heat exchange fluid. When compared versus each other, groundwater heat pumps are generally more efficient than heat pumps using heat from the soil.

 geothermal heat pump (extracts heat from the ground or similar sources) › geothermal–air heat pump (transfers heat to inside air) › geothermal–water heat pump (transfers heat to a tank of water);  Closed-loop system-horizontal, vertical and lake/pond;  Open-loop system

 The setup costs are higher than for conventional systems, but the difference is usually returned in energy savings in 3 to 10 years. System life is estimated at 25 years for inside components and 50+ years for the ground loop. As of 2004, there are over a million units installed worldwide providing 12 GW of thermal capacity, with an annual growth rate of 10%.If deployed on a large scale, this technology may help alleviate energy costs and global warming.

 Two geothermal heat pumps used at the College of Southern Idaho.