Heat pump for simultaneously cooling and heating

The device has a coolant circuit with a compressor (1), a first heat exchanger (2) as a liquefier, an expansion valve (6) and a second heat exchanger (5). A third heat exchanger (4) between the first and second heat exchangers near the expansion valve operates alternately as a liquefier and as an evaporator. The expansion valve is downstream or upstream of the third heat exchanger when operating as a liquefier and as an evaporator respectively.