A preheater for a compressor that is capable of heating a lubricant oil efficiently with smaller power is provided. A preheater for a compressor includes: a capacitive oil surface sensor that is provided at a compressor used in a refrigerating cycle, and detects an oil surface of a lubricant oil A in the compressor; and a power supply unit that applies high-frequency voltage to the oil surface sensor.

A preheater for a compressor that is capable of heating a lubricant oil efficiently with smaller power is provided. A preheater for a compressor includes: a capacitive oil surface sensor that is provided at a compressor used in a refrigerating cycle, and detects an oil surface of a lubricant oil A in the compressor; and a power supply unit that applies high-frequency voltage to the oil surface sensor.

A water heater appliance includes a first heat exchanger that is coupled to a tank. The water heater appliance also includes a caloric heat pump system that is configured for heating liquid within the tank via the first heat exchanger. The caloric heat pump system includes a plurality of caloric material stages. A field generator is positioned such that the caloric material stages are moved in and out of a field of the field generator during operation of the caloric heat pump system.

A water heater appliance includes a first heat exchanger that is coupled to a tank. The water heater appliance also includes a caloric heat pump system that is configured for heating liquid within the tank via the first heat exchanger. The caloric heat pump system includes a plurality of caloric material stages. A field generator is positioned such that the caloric material stages are moved in and out of a field of the field generator during operation of the caloric heat pump system.

An air-conditioning and hot water supplying composite system includes a heat source unit and a heat source-side heat exchanger, an indoor heat source unit, a hot water supply unit connected to the heat source unit and including a hot water supply-side heat exchanger and a hot water supply-side expansion device, and a controller that controls the heat source unit. The controller includes a mode switching unit that switches a control mode of the air-conditioning and hot water supplying composite system between a hot water supply control mode, a hot water supply preheating mode, and a condensing temperature control unit. The condensing temperature control unit determines the target condensing temperature according to a temperature of a heat medium subjected to heat exchange by the hot water supply unit, in the hot water supply control mode.

An air-conditioning and hot water supplying composite system includes a heat source unit and a heat source-side heat exchanger, an indoor heat source unit, a hot water supply unit connected to the heat source unit and including a hot water supply-side heat exchanger and a hot water supply-side expansion device, and a controller that controls the heat source unit. The controller includes a mode switching unit that switches a control mode of the air-conditioning and hot water supplying composite system between a hot water supply control mode, a hot water supply preheating mode, and a condensing temperature control unit. The condensing temperature control unit determines the target condensing temperature according to a temperature of a heat medium subjected to heat exchange by the hot water supply unit, in the hot water supply control mode.

A water heating system for a domestic hot water tank, the system including: a heat pump adapted to provide heat energy; and a heat exchanger comprising a coil of thermally conductive material arranged such that a diameter of the coil is approximately between five and six times greater than a diameter of the thermally conductive material and the heat exchanger is adapted to be installed in the domestic hot water tank and operationally coupled to the heat pump.

A thermal storage and exchange heating apparatus includes: a thermal storage tank that stores a heated heat medium; a circulation channel connected to high and low temperature sides of the thermal storage tank, and through which the heat medium circulates; a heat exchanger provided to the circulation channel and configured to exchange heat between the heat medium and a heating object, to heat the heating object; a circulation direction switch configured to switch circulation of the heat medium in the circulation channel between a forward direction from the high-temperature side to the low-temperature side and a reversed backward direction; and a controller configured to cause the heat medium to circulate in the forward direction by switching the circulation direction switch in a heating operation and causing the heat medium to circulate in the backward direction by switching the circulation direction switch after a stop of the heating operation.

A thermal storage and exchange heating apparatus includes: a thermal storage tank that stores a heated heat medium; a circulation channel connected to high and low temperature sides of the thermal storage tank, and through which the heat medium circulates; a heat exchanger provided to the circulation channel and configured to exchange heat between the heat medium and a heating object, to heat the heating object; a circulation direction switch configured to switch circulation of the heat medium in the circulation channel between a forward direction from the high-temperature side to the low-temperature side and a reversed backward direction; and a controller configured to cause the heat medium to circulate in the forward direction by switching the circulation direction switch in a heating operation and causing the heat medium to circulate in the backward direction by switching the circulation direction switch after a stop of the heating operation.

The present disclosure relates to a method and a system for preventing freezing when a four-way valve in a heat pump water heater is failed, which includes following acts: In act S1, it is judged that whether current water temperature T is lower than a preset minimum temperature T.sub.min , for the water tank, if yes, perform act S2; if no, perform act S1 again. In act S2, it is judged that whether a cooling rate Td of the current water temperature T is greater than or equal to a preset rate ΔT; or, it is judged that whether the current water temperature T satisfies T<T.sub.min−a and whether T<T.sub.min−a stands for a first time period t1, in which a is a limit value of a temperature difference; if at least one yes, perform act S3, otherwise, return to act S1. In act S3, a heat pump system is controlled to stop and an electric auxiliary heating system is started. By judging whether a cooling rate Td of the current water temperature T is greater than or equal to a preset rate ΔT; or by judging whether the current water temperature T satisfies T<T.sub.min−a and whether T<T.sub.min−a stands for a first time period t1, it may be judged precisely that whether the four-way valve is failed, which avoids a misjudgment.