Refrigerators and air conditioners both contain heat pumps. In a refrigerator, heat is moved from the food storage sections and discharged to the kitchen air. Air conditioners work the same way — they move heat from the inside of a building and discharge it to the outside air. Conventional or air source heat pumps differ from those in a refrigerator or air conditioner because they are reversible — they can concentrate heat from the outside air and move it inside to provide warmth, as well as move heat out of the building to provide cooling. To do this, air-source heat pumps (and central air conditioners) need a large outside unit to exchange heat with the outdoor air.
Geothermal Heating and Cooling Systems
In a geothermal heating and cooling system, the heat pump is connected to the building by a distribution system — most commonly air ducts. And the heat pump is connected to the earth through a series of pipes called a “loop” The system exchanges heat with the earth, meaning that no noisy or unsightly outdoor unit is needed.
Vapor Compression Cycle
All heat pumps use a vapor compression cycle to transport heat from one location to another. In heating mode, the cycle starts as the cold liquid refrigerant within the heat pump passes through a heat exchanger (evaporator) and absorbs heat from the low-temperature source (fluid circulated through the earth connection). The refrigerant evaporates into a gas as heat is absorbed. The gaseous refrigerant then passes through a compressor where it is pressurized, raising its temperature to over 180 degrees F. The hot gas then circulates through a refrigerant-to-air heat exchanger where the heat is removed and sent through the air ducts. When the refrigerant loses the heat, it changes back to a liquid. The liquid refrigerant cools as it passes through an expansion valve, and the process begins again. Although heat pumps are complex internally, they are marvels of compact design for reliability. Some include features such as additional heat exchangers for water heating, and microprocessor-based automatic controls and protection devices.