Combined air-conditioning and hot-water supply system

A combined air-conditioning and hot-water supply system comprising:

• a refrigeration cycle in which a compressor, an outdoor heat exchanger, an air-conditioning expansion unit, and an indoor heat exchanger are connected to one another in series by using pipes, in which the compressor, the outdoor heat exchanger, a hot-water supply expansion unit, and a refrigerant-side passage of a refrigerant-heat medium heat exchanger are connected to one another in series by using pipes, in which the refrigerant-side passage of the refrigerant-heat medium heat exchanger and the hot-water supply expansion unit are connected in parallel with a bypass path by using pipes, the bypass path including a bypass solenoid valve and bypassing the refrigerant-heat medium heat exchanger, and in which refrigerant circulates;
• a hot-water supply load circuit in which a circulation pump, a heat medium passage of the refrigerant-heat medium heat exchanger, and a hot-water-storing tank are connected to one another in series by using pipes, and in which a heat medium circulates,
• the refrigeration cycle and the hot-water supply load circuit being connected in cascade with each other to perform heat exchange between the refrigerant and the heat medium in the refrigerant-heat medium heat exchanger;
• and
• a controller that controls the air-conditioning expansion unit, the hot-water supply expansion unit, and the bypass solenoid valve,
• the controller controlling
• the bypass solenoid valve and the hot-water supply expansion unit in a defrosting operation, based on a refrigerant temperature on a refrigerant inlet side of the refrigerant-heat medium heat exchanger and a heat medium temperature on a heat medium inlet side of the refrigerant-heat medium heat exchanger, wherein
• the controller calculates a third temperature that is a temperature of the refrigerant at which the heat medium freezes when the heat medium temperature is higher than a first temperature and where a value obtained by subtracting the heat medium temperature from a preset heat medium temperature is lower than a second temperature, and
• the controller closes the bypass solenoid valve and opens the hot-water supply expansion unit if the refrigerant temperature is higher than a value obtained by adding a water freezing margin to the third temperature.