Heat pump systems
Heat pumps use mechanical energy to transfer thermal energy from a source at a lower temperature to a sink at a higher temperature. Electrically driven heat pump heating systems have two advantages compared to electric resistance heating or expensive fuels. The heat pump’s COP is high enough to yield 11 to 15 MJ of heat for each kW h of energy supplied to the compressor , which saves on purchase of energy, and usefulness for air conditioning in the summer. Water-to-air heat pumps, which use solar heated water from the storage tank as the evaporator energy source, are an alternative auxiliary heat source. Use of water
involves freezing problems which need to be taken into consideration. Solar heating systems using liquids will operate at lower temperatures than conventional hydronic systems and will require more baseboard heater area to transfer heat into the building.