Air-conditioning apparatus

An air-conditioning apparatus comprising:

• an outdoor unit equipped with a compressor that compresses a heat source side refrigerant, and a heat source side heat exchanger that exchanges heat between outdoor air and the heat source side refrigerant;
• a heat medium relay unit equipped with a heat exchanger related to heat medium that exchanges heat between the heat source side refrigerant and a heat medium, an expansion device that depressurizes the heat source side refrigerant, and a pump that pumps the heat medium by pressure;
• an indoor unit equipped with a use side heat exchanger that exchanges heat between indoor air and the heat medium;
• a concentration determining device that detects and computes a refrigerant concentration;
• and
• a plurality of shutoff devices that shut off a flow of the heat source side refrigerant on the basis of the refrigerant concentration computed by the concentration determining device,
• wherein the compressor, the heat source side heat exchanger, a refrigerant flow path in the heat exchanger related to heat medium, and the expansion device are connected by refrigerant pipes to form a refrigerant circuit through which the heat source side refrigerant circulates,
• a heat medium flow path in the heat exchanger related to heat medium, the pump, and the use side heat exchanger are connected by heat medium pipes to form a heat medium circuit through which the heat medium circulates, and
• a leakage rate of heat source side refrigerant from each of the shutoff devices is 1.0×10−6 [m3/s] or less when the shutoff devices shut off the flow of the heat source side refrigerant,
• one of the shutoff devices is installed on the refrigerant pipe that flows the heat source side refrigerant into the heat medium relay unit, and another of the shutoff devices is installed on the refrigerant pipe that flows the heat source side refrigerant out of the heat medium relay unit,
• the concentration determining device outputs a control signal indicating whether or not the refrigerant concentration is dangerous, on the basis of the computed refrigerant concentration,
• a controller that outputs a driving signal to the shutoff devices to control the operation thereof, on the basis of the control signal received from the concentration determining device is provided, and
• the shutoff devices are installed such that the installation distance, being the distance to the heat medium relay unit, satisfies
• (heat medium relay unit connecting pipe volume [m3/m]×installation distance [m]×average refrigerant density [kg/m3]/indoor volume [m3])+(heat medium relay unit volume [m3]×average refrigerant density [kg/m3]/indoor volume [m3])<leakage concentration limit [kg/m3],
• wherein the concentration determining device includes
• a detecting unit in which an electrical resistance changes in accordance with the refrigerant concentration,
• a concentration detecting device configured to output the control signal, and
• a computing device that computes the refrigerant concentration of a plurality of types of heat source side refrigerants on the basis of correlation information between a resistance value of the detecting unit and the refrigerant concentration near the detecting unit,
• wherein the correlation information is a calibration curve in which the higher the refrigerant concentration, the lower the resistance value becomes.