Abstract: Method and device for conditioning of a gas which passes through the treatment zone in a regenerative moisture exchanging apparatus (10, 16) for instance a rotor for exchanging moisture with an absorbing bed in the exchanging apparatus. In order to regenerate the bed, a regenerant gas, such as air is passed through the exchanging apparatus in a further treatment zone which is separated from the first mentioned zone. The regenerant air is passed in a closed circuit (3-7) after the passage through the exchanger apparatus. The circuit comprises an evaporator(E) in a heat pump circuit by means of which the regenerant gas air is cooled and its moisture content is decreased. The regenerant air is then passed over a condenser(K) in the heat pump circuit by means of which the regenerant air is heated before being passed to the regenerating zone of the exchanger apparatus.