Heat pump apparatus

A heat pump apparatus to supply a heat medium to a tank unit including a water heat exchanger to exchange heat between the heat medium and water stored in a hot water storage tank, the heat pump apparatus comprising:

• a compressor to compress refrigerant;
• a heat medium heat exchanger to exchange heat between the refrigerant and the heat medium;
• a heat transfer performance determiner to determine heat transfer performance of the water heat exchanger;
• and
• a compressor controller to adjust a rotation speed of the compressor during a hot water storage operation, which is an operation for increasing a temperature of the water in the hot water storage tank,
• wherein the compressor controller is configured to adjust the rotation speed of the compressor during the hot water storage operation such that the rotation speed of the compressor when the heat transfer performance of the water heat exchanger is determined to be relatively low is higher than the rotation speed of the compressor when the heat transfer performance of the water heat exchanger is determined to be relatively high.