Air-conditioning apparatus

An air-conditioning apparatus, including

• a compressor, a refrigerant flow switching valve, a heat source side heat exchanger, a first expansion valve, and an intermediate heat exchanger, where the compressor, the refrigerant flow switching valve, the heat source side heat exchanger, the first expansion valve, and the intermediate heat exchanger are connected via refrigerant pipes, that constitutes a refrigerant circuit, and
• a heat medium circuit, constituted by a pump, the intermediate heat exchanger, and a use side heat exchanger, where the pump, the intermediate heat exchanger, and the use side heat exchanger are connected via pipes, the air-conditioning apparatus comprising:
• a second expansion valve provided between an upstream side of the heat source side heat exchanger and a downstream side of the first expansion valve during a heating operation;
• an accumulator configured to accumulate excess refrigerant provided on an upstream side of the compressor;
• a suction injection pipe, having one end connected on an upstream side of the second expansion valve during the heating operation, and another end connected to a flow channel between a suction side of the compressor and the accumulator;
• a third expansion valve provided to the suction injection pipe;
• a discharge refrigerant temperature detector configured to detect a discharge refrigerant temperature of the compressor;
• a suction pressure detector configured to detect a pressure (Ps) of the refrigerant suctioned into the compressor;
• a medium pressure detector configured to detect a refrigerant pressure or a refrigerant saturation temperature at a position between an upstream side of the second expansion valve and the downstream side of the first expansion valve or the intermediate heat exchanger during the heating operation;
• and
• a controller configured to control an opening degree of the second expansion valve based on a detection result (PM) of the medium pressure detector, and to control an opening degree of the third expansion valve based on a detection result of the discharge refrigerant temperature detector, the detection result (PM) of the medium pressure detector and a detection result (Ps) of the suction pressure detector;
• wherein,
• a refrigerant having a higher discharge refrigerant temperature than R410A is circulated as refrigerant inside the refrigerant pipes,
• the controller computes a quality of the refrigerant suctioned into the compressor based on the opening degree of the second expansion valve, the opening degree of the third expansion valve, the detection result (PM) of the medium pressure detector, and the detection result (Ps) of the suction pressure detector,
• in a case where the third expansion valve is controlled at a first opening degree that is based on the detection result of the discharge refrigerant temperature detector, when the quality becomes less than a predetermined value, the controller decreases the opening degree of the third expansion valve to a second opening degree that is smaller than the first opening degree such that refrigerant having the quality equal to or greater than 0.9 and less than or equal to 0.99 is suctioned into the compressor, and
• the controller is configured to
• obtain, by using a table expressing a refrigerant pressure to enthalpy relationships, an enthalpy H1 that corresponds to the detection result (Ps) and an enthalpy H2 that corresponds to the detection result (Ps), and
• calculate the quality Xs according to the following formulas,
• G1∝LEVa√{square root over (PM−Ps,)}
• G2∝LEVb√{square root over (PM−Ps,)}
• G1×H1+G2×H2=(G1+G2)×H3,
• H
• ⁢
• ⁢
• 3
• =
• 1
• LEVa
• +
• LEVb
• ⁢
• (
• LEVa
• ×
• H
• ⁢
• ⁢
• 1
• +
• LEVb
• ×
• H
• ⁢
• ⁢
• 2
• )
• ,
• Xs=(H3−H2)/(H1−H2)
• where LEVa is the opening degree of the second expansion valve,
• LEVb is the opening degree of the third expansion valve,
• G1 is a refrigerant flow rate flowing out from the accumulator,
• H1 is an enthalpy of refrigerant flowing out from the accumulator,
• G2 is a refrigerant flow rate passing through the third expansion valve,
• H2 is an enthalpy of refrigerant passing through the third expansion valve,
• G3 is a refrigerant flow rate suctioned into the compressor,
• H3 is an enthalpy of refrigerant suctioned into the compressor,
• PM is the detection result of the medium pressure detector,
• Ps is the detection result of the suction pressure detector, and
• Xs is the quality.