Abstract: Embodiments of the invention relate to a heat pump system comprising a heat pump so arranged as to permit the taking up of thermal energy from outdoor air and the giving off of thermal energy to another medium, and an external space adapted to permit heating of the outdoor air by the use of solar radiation, the system being so arranged as to conduct the outdoor air to the heat pump via the external space. The invention is characterized in that the heat pump system comprises means for regulating the flow of the outdoor air to the external space.