An air-conditioning apparatus includes a refrigeration cycle circulating refrigerant and connecting a compressor, a heat-source-side heat exchanger, one or more of load-side expansion devices, and one or more of load-side heat exchangers by refrigerant pipes, a bypass having one end connected to a discharge side of the compressor of the refrigeration cycle and the other end connected to a suction side of the compressor of the refrigeration cycle to bypass a portion of the refrigerant discharged from the compressor, a first expansion device depressurizing the refrigerant flowing through the bypass, an auxiliary heat exchanger cooling the refrigerant depressurized at the first expansion device, a second expansion device controlling a flow rate of the refrigerant flowing from the auxiliary heat exchanger to the suction side of the compressor, and a controller controlling an opening degree of the second expansion device.

A multistage compression system uses refrigerant and oil. The multistage compression system includes a low-stage compressor that compresses the refrigerant, a high-stage compressor that further compresses the refrigerant compressed by the low-stage compressor, refrigerant pipes that-introduce the refrigerant compressed and discharged by the low-stage compressor into a suction part of the high-stage compressor, a pressure reducing element disposed between the refrigerant pipes, an accumulator disposed between the refrigerant pipes at a downstream side of the pressure reducing element and at an upstream side of the high-stage compressor, and an oil discharge pipe. The oil discharge pipe discharges the oil in the low-stage compressor. The oil discharge pipe connects the low-stage compressor and a portion of the refrigerant pipes. The portion of the refrigerant pipes is on a downstream side of the pressure reducing element and an upstream side of the accumulator.

A cooling and heating control method of a multi type air conditioner in which a target pressure of a compressor is adjusted based on conditions of respective indoor units so as to reduce power consumption is provided. The cooling control method includes determining the indoor unit desired to execute power saving control, judging whether or not a difference between a temperature of a space in which the indoor unit desired to execute power saving control is located and a set temperature of the indoor unit is less than a reference value, raising a target evaporation temperature of the indoor unit upon judging that the difference is less than the reference value, comparing an evaporation temperature of the indoor unit with the raised target evaporation temperature, and raising an evaporation pressure of a compressor, when the evaporation temperature of the indoor unit is lower than the raised target evaporation temperature.

A heat-pump system may include an outdoor heat exchanger, an expansion device, an indoor heat exchanger, a compressor, and a multiway valve. The expansion device is in fluid communication with the outdoor heat exchanger. The indoor heat exchanger is in fluid communication with the expansion device. The compressor circulates working fluid through the indoor and outdoor heat exchangers. The multiway valve may be movable between a first position corresponding to a cooling mode of the heat-pump system and a second position corresponding to a heating mode of the heat-pump system. The working fluid flows in the same direction through the outdoor heat exchanger in the cooling mode and in the heating mode, and the working fluid flows in the same direction through the indoor heat exchanger in the cooling mode and in the heating mode.

An air-conditioning apparatus includes a controller which calculates a composition ratio of a refrigerant mixture using a high-pressure-side pressure of a refrigerant discharged from a compressor, a low-pressure-side pressure of a refrigerant to be sucked into the compressor, a high-pressure-side temperature of a refrigerant at an inlet side of a second expansion device in a high/low pressure bypass pipe, and a low-pressure-side temperature of a refrigerant at an outlet side of the second expansion device in the high/low pressure bypass pipe and which determines whether to open or close a bypass-channel opening/closing device.

An air conditioner including a hot gas line for receiving a portion of refrigerant compressed in a compressor, an indoor heat exchanger, an outdoor expansion device for expanding the refrigerant having exchanged heat in the indoor heat exchanger, an outdoor heat exchanger functioning as a condenser in a cooling mode while functioning as an evaporator in a heating mode, and a 4-way valve for receiving a remaining portion of the compressed refrigerant, to guide the refrigerant emerging from the compressor to the outdoor heat exchanger in the cooling mode and to the indoor heat exchanger in the heating mode. The outdoor heat exchanger includes a main heat exchanger section functioning as a condenser in the cooling mode while functioning as an evaporator in the heating mode, and an auxiliary heat exchanger for receiving the refrigerant from the hot gas line in a frosting prevention mode.

An air conditioner including an outdoor unit, an air conditioning indoor unit, a showcase indoor unit, and a combination unit. The combination unit includes a first gas control unit connected to the air conditioning indoor unit gas pipe, a second gas control unit connected to the showcase indoor unit gas pipe, a first pipe which connects the outdoor unit liquid pipe and the indoor unit liquid pipe, and a second pipe which connects the first pipe and the second gas control unit. The first gas control unit and the second gas control unit are converged to be connected to the outdoor unit gas pipe, so that the air conditioning indoor unit and the showcase indoor unit can use a single outdoor unit, and heat emitted from the air conditioning indoor unit to a room during a heating operation is used as condensation heat of the showcase indoor unit.

In a heating main operation mode in which a load to be processed by the heating operation is dominant during cooling and heating mixed operation, an air-conditioning apparatus closes an opening and closing valve, and adjust the opening degree of an expansion device in accordance with the evaporating temperature of a load-side unit requesting cooling.

A heat pump system includes a heat source unit having a variable-capacity compressor and a heat-source-side heat exchanger that functions as an evaporator for a refrigerant, and a plurality of usage units connected to the heat source unit and having usage-side heat exchangers that function as radiators for the refrigerant. The operating capacity of the compressor is controlled to bring the discharge pressure of the compressor, or a state quantity equivalent to the discharge pressure, to a first target value. The first target value is determined based on an equivalent target value equivalent to a usage temperature required in individual usage units.

A first circulation channel connects a first heat demand part and first supply heat exchanger with its forward route and return route. Supply and discharge channels are connected to a first heat accumulation tank, which accommodates a second heat medium heated in the first supply heat exchanger and supplied via the supply channel. A heat accumulation switching valve changes over communication of the second heat medium serving as hot heat or cold heat flowing from the first supply heat exchanger and supplied to the first heat demand part without branching to the supply channel or branching to the supply channel and supplied to the first heat accumulation tank. A heat-accumulating hot-water-supplying air conditioner operates at a first temperature when the second heat medium from the first supply heat exchanger branches to the supply channel, and at a second lower temperature when the second heat medium does not branch to the supply channel.