Absorption heat pumps use an ammonia-h2o absorption cycle, as an alternative to a vapor-compression cycle, to transfer heat. Ammonia may be the refrigerant, and water may be the absorber. The ammonia condenses at one of many system’s coils to release heat and evaporates at one other coil to absorb heat. https://purethermal.co.uk/media-news/can-gas-absorption-heat-pumps-provide-an-alternative-heat-pump-option-in-2025/