The invention relates to a process and apparatus (1) for transferring heat from a first relatively cold medium to a second relatively hot medium, comprising a gastight rotor (4) rotatably mounted in a frame (2), and, mounted inside the rotor (4), a compressor (10), a first heat exchanger (8) for transferring heat from the fluid to the second medium and located relatively far from the axis of rotation of the rotor (4), an expansion chamber (11) for expanding the fluid, and a channel (14) for conveying the expanded fluid from the expansion chamber (11) to the compressor (10), wherein the first heat exchanger (8) is thermally insulated from the channel (14).