Heat pump systems are quite similar to air conditioning systems and can either heat or cool the air passing through it. Because heat pumps merely extract heat from the air and transfer the energy, they can be highly efficient because limited amounts of energy are used in the process. In climates where the air is already a moderate temperature, a heap pump can be a cost-effective alternative to a traditional furnace. However, before deciding if a heat pump or furnace is the best solution for a given space or application, understanding the mechanics behind them is key.
Although there are varying types of heat pumps, they all depend on heat transfer to function. Because heat naturally flows from higher altitudes to lower altitudes, heat transfer effectively reverses this pattern—by extracting heat from air in lower temperature realms and moving it to a higher temperature realm—and uses the extracted heat to warm the air in the given heat pump system.
Air-Source Heat Pumps
An air-source heat pump, also called an air-air heat pump, uses heat transfer to draw exterior air into the heat pump. Once inside the pump, the cooler air is passed through coils with refrigerant, where the refrigerant absorbs heat from the air and generates vapor. Next, the vapor is channeled through a compressor where both the temperature and pressure of the vapor is increased. The refrigerant and the vapor are separated—the refrigerant reforms into liquid and is returned to the coils where it can collect more heat—and the vapor is passed on into an air-duct system, where it is then released into the designated space (such as a home or a factory).
Because the compressor in an air-source heat pump features a reverse valve—which, in this case, uses refrigerant to extract heat from the air—the process can be reversed. Instead of trapping heat, the system can be altered to operate in the opposite direction, so that warm air is removed from the environment and released outside. Essentially, the system functions as a basic air conditioner, removing heat to cool the inside environment.
Ground-Source Heat Pumps
In the same way air-source heat pumps extract heat from the air, ground-course heat pumps extract heat from the ground via underground coils. Refrigerant courses through these coils in order to extract heat from the surrounding ground. The refrigerant can then be re-circulated repeatedly, as in a closed-loop system, or can be returned to its natural source (when water is used instead of refrigerant, a local lake can serve as a source), as in an open-loop system. In other regards, ground-source heat pumps function the same way as air-source heat pumps.
Absorption Heat Pumps
Absorption heat pumps are actually a kind of air-source heat pumps, but they do not depend on electricity to power them. Instead, gas, solar power, or heated water is used as a main power source. Additionally, refrigerant isn’t used at all in the process. To extract heat, an absorption pump absorbs ammonia into water. Next, the water and ammonia mixture is pressurized to induce boiling, and the ammonia is boiled off.