How does a heat pump water heater work?

A heat pump is essentially a vapour compression cycle, similar to an air conditioning unit. However, instead of the cycle being used for air cooling purposes with the associated heat as a by-product, a heat pump utilizes the heat generated in the cycle to heat water.

In brief; energy is extracted from the ambient air using a finned-coil heat exchanger, also known as an evaporator, using a refrigerant at low pressure and temperature as the working fluid inside the tubes. This refrigerant is then compressed to a high pressure and temperature by an electrically driven compressor. The high pressure refrigerant is then circulated through a refrigerant-to-water heat exchanger, also known as a condenser. Here energy is exchanged with water, at a lower temperature, thus heating the water to temperatures in the region of 60°C. The refrigerant leaving the condenser is then expanded back to a low pressure by using an expansion valve before it enters the evaporator to start the cycle once more.

This is a continuous process, and the only electrical energy used is to drive i) the compressor, ii) a pump to circulate water through the refrigerant-to-water condenser, and iii) fan power to cycle air through the finned air-to-refrigerant evaporator.

This cycle typically consumes 1 unit of electrical energy for every 3 units of heating produced; i.e. only 33kWhelectrical is used to produce 100kWhthermal. Therefore on average two thirds (67%) of the electrical energy consumption can be saved compared to conventional electrical resistance heating.

Enerflow Heat Pumps

Dr. Martin van Eldik
+27 (0)18 297 0326
mve@mtechindustrial.com