Absorption heat pump

An absorption heat pump (AHP) is a heat pump driven by thermal energy such as combustion of natural gas, steam solar-heated water, air, or geothermally heated water, unlike a compression heat pump, which is driven by mechanical energy. AHPs are more complex and require larger units than compression heat pumps. In particular, the electricity demand of such heat pumps is only for pumping liquid and often powering fans, so is much lower than that of compression heat pumps. AHPs' applications are restricted to those cases when electricity is extremely expensive or a large amount of unutilized heat at suitable temperatures is available and when the cooling or heating output has a greater value than heat input consumed. Absorption refrigerators work on the same principle, but are not reversible and cannot serve as a heat source.