What The Tech: How do heat pumps work?

Today’s heating supply calls for concepts that are based on renew­able ener­gies and are prof­itable as energy prices increase. A heat pump is a great example for this. It only requires very little elec­trical energy to make the multi­tude of heat avail­able from the ground, ground water or outside air usable.

This is how: In a closed circuit, ambient heat is trans­ferred to a refrig­erant in the evap­o­rator and becomes a gas. In the elec­tric compressor, the gaseous refrig­erant is then compressed, heating it. In the condenser, the hot gas then heats the water in the heating circuit or the hot water tank. The gaseous refrig­erant condenses again and returns to the evap­o­rator via the expan­sion valve and the cycle is repeated. A temper­a­ture of -20 degrees Celsius is suffi­cient for the refrig­erant in air-to-water heat pumps to operate the circuit effi­ciently.

The refrig­er­a­tion circuit described above is the heart of a heat pump. Heat pumps extract about three quar­ters of the required energy from the envi­ron­ment. In the best case, the remaining energy also comes from renew­able energy sources. Systems consisting of a heat pump and photo­voltaic system work largely inde­pen­dently of rising elec­tricity prices and thus save on oper­ating costs. As a rule, the elec­tric compressor requires the most addi­tional energy inside the heat pump. But other compo­nents such as the fan also consume elec­tricity and can there­fore help to save energy and money.

Various fans are used in heat pumps, e.g. axial or centrifugal fans. Centrifugal fans are used for indoor instal­la­tions, as they are suit­able for higher pres­sure require­ments, whereas quiet-running axial fans are used for outdoor instal­la­tion. The low noise level is very impor­tant here. Axial fans that can be oper­ated at low speed thanks to EC motors and that enable quiet oper­a­tion even in partial-load oper­a­tion mean that the heat pump does not have to be switched off at night. If the heat pumps are in the front of a house, the evap­o­rator is a sepa­rate unit outdoors and a refrig­erant pipe leads inside.