Air-conditioning apparatus

An air-conditioning apparatus, comprising:

• an outdoor unit including a compressor for compressing and conveying a refrigerant, a first refrigerant flow switching device for switching passages conveying the refrigerant, and a heat source side heat exchanger for exchanging heat between an air and the refrigerant;
• a plurality of indoor units each including a use side heat exchanger for exchanging heat between air and a heat transfer medium, the heat transfer medium flowing in the use side heat exchangers;
• and
• a relay unit disposed between the outdoor unit and the indoor units, for exchanging heat between the refrigerant conveyed from the outdoor unit and the heat transfer medium,
• the relay unit including
• a main relay unit including a gas-liquid separator for separating the refrigerant conveyed from the outdoor unit into gas and liquid, a main-unit expansion device arranged at a liquid refrigerant outlet side passage from the gas-liquid separator and a returning refrigerant passage through which the refrigerant returning to the outdoor unit flows, the main relay unit being connected to the outdoor unit with refrigerant piping, and
• a plurality of sub relay units connected to the main relay unit through each of a gas refrigerant outlet side passage from the gas-liquid separator, the liquid refrigerant outlet side passage from the gas-liquid separator, and the returning refrigerant passage, the plurality of sub relay units including:
• a plurality of heat exchangers related to heat medium each for exchanging heat between the refrigerant and the heat transfer medium;
• a plurality of second refrigerant flow switching devices each for switching passages of the refrigerant conveyed from the main relay unit;
• a plurality of sub-unit expansion devices respectively disposed in refrigerant passages corresponding with the heat exchangers related to heat transfer medium;
• a plurality of heat transfer medium conveying devices each for conveying the heat transfer medium that has exchanged heat with the refrigerant in the corresponding heat exchanger related to heat transfer medium to the indoor units, which are connected to the plurality of heat transfer medium conveying devices through heat transfer medium piping;
• a plurality of heat transfer medium flow switching devices each disposed in a counter position to the inlet side and outlet side of the corresponding indoor unit in which the heat transfer medium flows, the heat transfer medium flow switching devices each for selecting a passage of the heat transfer medium, which flows in the indoor unit, among the heat exchangers related to heat transfer medium;
• and
• a plurality of heat transfer medium flow control devices each disposed in a counter position to the inlet side or the outlet side of the corresponding indoor unit in which the heat transfer medium flows, the heat transfer medium flow control devices each controlling a flow rate of the heat transfer medium, wherein
• a first bypass passage is branched between the liquid refrigerant outlet side passage from the gas-liquid separator and the plurality of heat exchangers related to heat transfer medium and is connected to the returning refrigerant passage and a first bypass expansion device controlling amount of the refrigerant that flows through the first bypass passage is disposed on the first bypass passage.