The Bunsen Unit is a solar powered heat pump. There are other types of heat pumps – Air source use the temperature from the air, Ground source us the temperature from the ground. The Bunsen uses the two external hot water panels which transfer heat from the air temperature, wind, rain, sunlight or even snow. All our natural elements have a contributing effect.
The job of the Bunsen Unit, is to extract the heat from the refrigerant gas as it returns from the solar collector panels, and transfer it to the water which is circulated from the hot water cylinder to take the heat away.