Abstract: A pump installation has a first heat exchanger for heating a fluid, a compressor unit connected to the first exchanger and having static mechanical means for pre-compression and temperature increase of the fluid, a motor-driven compressor connected to the compressor unit, for compressing the fluid, and a second heat exchanger for passing heat from the fluid to a working circuit fluid. A first valve passes fluid from the outlet of the compressor to the second exchanger selectively directly or indirectly through the compressor unit, and a second valve passes fluid from the outlet of the second exchanger to an expansion means for feeding the fluid back to the first exchanger selectively directly or indirectly through the compressor unit.