Introduction - Heat pumps technology has been around for over 100 years. Actually, they use very similar principles to an ordinary home air conditioner when operated in "reverse cycle" (e.g. when run over winter as a heater).
Essentially, a heat pump "soaks-up" heat from the surrounding air and transfers this heat to your pool's water. Even below 10 degrees Celsius, air still has heat that can be collected by the heat pump.
Further detail - The description below refers to the diagram above provides a fuller description of what actually happens:
Overall - A heat pump is basically two recirculating systems. One for the refrigerant gas (that collects heat from the air), another for the pool water (that receives that collected heat).
Stage 1- Liquid refrigerant moves through an Expansion Valve. The liquid is expanded, turns to a gas and drops to a very low temperature (typically less than minus 20oC).
Stage 2 - This super-cold refrigerant gas passes through the evaporator coil. A fan draws warmer air across the evaporator. The cold refrigerant now absorbs heat from the passing air.
Stage 3 - The warmed refrigerant is then compressed by the Condenser. Compressing a substance raises (or concentrates) its temperature (e.g., to even greater than 100oC).
Stage 4 - The intensely hot gas passes through a coil inside the heat exchanger. Cool water circulates outside the coil absorbing heat from the hot gas inside. The now heated water then returns to the pool.
Stage 5 - As the refrigerant loses its heat, it returns to a liquid state (having lost this heat to the pool cater). The refrigerant now circulates back to the expansion valve and the process repeats.
How Heat Pumps Work
