Abstract: A method and apparatus for transferring energy in an absorption system according to the heat pump principle to improve the cycle efficiency thereof, in which the selected working medium is vaporized in an evaporator by heat exchange with heat source of ambient pressure and passed into a sorption station where it is brought into contact with an absorbent solution with consequent release of heat of absorption and heat of condensation. The mixture of absorbent solution and absorbed working medium is passed from the sorption station into a pressurized separating station, where the absorbent is separated from the working medium by diffusing the mixture under pressure through a semi-permeable membrane defining a zone of relatively high pressure and a zone of relatively low pressure higher than the ambient pressure, the concentrated absorbent solution being collected in the high pressure zone and the solution of working medium being received in the low pressure zone by virtue of the resultant reverse osmotic flow.