Components of a Heat Pump
The four main components of a heat pump are the compressor, condenser, expansion valve, and evaporator.
Each component has its own importance and their strategic placement can used to build various applications like refrigerators, etc. (One interesting application of heat pump technology are the new hybrid heat pump/heating element water heaters entering the market. Please see the link in the next section for an informative article.)
Compressors act on the carrying medium (refrigerants) in order to change its pressure level, i.e. from low pressure to high pressure. The change in pressure helps in the absorption or the release of the thermal energy from the refrigerant.
The condenser re-condenses the refrigerant or the medium enabling it to release or absorb the thermal energy and return to a liquid state.
The expansion valve is the pressure reducing device. When high-pressure, medium-temperature refrigerant goes through the expansion valve, its pressure quickly reduces and the temperature drops. The refrigerant is then in a mixed liquid and gaseous state.
The evaporator is normally the sink where the thermal energy collected from the source, i.e. the condenser (in the case of a heat pump), is dumped.