Heat pump

A heat pump comprising:

• an electric motor driven by input electric power;
• a first compressor mechanically connected to the electric motor and compresses air;
• a water supply pipe configured to supply water;
• a first heat exchanger performing heat exchange between compressed air produced by the first compressor and the water supplied from the water supply pipe;
• a first hot water outlet through which the water heated by heat exchange in the first heat exchanger is taken out;
• an expander driven by the compressed air produced by the first compressor;
• a power generator mechanically connected to the expander;
• a second heat exchanger performing heat exchange between air expanded by the expander and the water from the water supply pipe;
• a cold water outlet through which the water cooled to ordinary temperature or lower by the heat exchange in the second heat exchanger and supplied from the water supply pipe is taken out;
• and
• a first accumulator storing the compressed air produced by the first compressor, wherein
• the expander is driven by the compressed air supplied from the first accumulator,
• the power generator is driven by the expander to generate electric power,
• a switch configured to switch a supply destination of the electric power generated by the power generator between the electric motor and a demander.