Heat pump
Also known as: heat pump system, reverse-cycle unit
Short definitionA refrigeration machine used for heating. It collects heat from a cool source such as outdoor air, well water, the ground or waste heat, raises its temperature and delivers it where it is needed.
In a refrigeration unit the heat leaving the condenser is thrown away. In a heat pump that heat is exactly what is wanted; the evaporator side is only the source. Performance is described by the COP, which is between 3 and 5 for most units, so a third or a fifth of the electricity a resistance heater would use is enough. The warmer the source and the lower the required temperature, the better the COP.
For a cold store contractor the opportunity is the plant’s own condenser heat. With condenser water at 25–35 °C as the source, water at 60–80 °C is produced and the COP reaches 4–6; dairy, meat and beverage plants use it for washing and pasteurising. Before quoting, ask for the water temperature required, how much heat is needed at which hour of the day, and the coldest state of the source. An air-source unit loses output in hard frost; with −10 °C outside only 60–70% of its capacity may remain.