An air conditioning system including a four-way valve including a first port, a second port, a third port and a fourth port, at least the first port and the third port are fluidly isolated; a compressor, an output end and an input end of which are in communication with the first port and the third port respectively; a first evaporator, a first end of which is in communication with the third port; a second evaporator and a condenser, first ends of which are in communication with one of the second port and the fourth port respectively; wherein a second end of the condenser, a second end of the first evaporator, and a second end of the second evaporator are in communication at a first node, and a first throttling valve, a second throttling valve and a third throttling valve are respectively disposed between the condenser and the first node.

An air-conditioning apparatus includes a high-pressure side pressure detection device detecting high-pressure side pressure, a low-pressure side pressure detection device detecting low-pressure side pressure, a high-low pressure bypass pipe connecting a pipe on a discharge side of a compressor and a pipe on a suction side of the compressor, a bypass expansion device disposed in the high-low pressure bypass pipe, a high-pressure side temperature detection device detecting high-pressure side temperature, and a low-pressure side temperature detection device detecting low-pressure side temperature; an outdoor unit side controller that detects circulation composition of refrigerant on the basis of the high-pressure side pressure, the low-pressure side pressure, the high-pressure side temperature, and the low-pressure side temperature; and a relay unit side controller performing at least one of a calculation of evaporating temperature and degree of superheat, and a calculation of condensing temperature and degree of subcooling on the basis of the circulation composition.

A computing device calculates an evaporating temperature Te* and a dew-point temperature Tdew* from a quality X, a temperature glide ΔT determined by a difference between a boiling temperature and a dew-point temperature at a predetermined pressure, and a refrigerant temperature detected by second temperature detection device.

An air-conditioning apparatus includes a refrigerant circuit in which a compressor, a heat-source-side heat exchanger, an expansion device, and a refrigerant flow path in at least one intermediate heat exchanger are connected by a refrigerant pipe, and a heat medium circuit in which a pump, a use-side heat exchanger, and a heat-medium flow path in the at least one intermediate heat exchanger are connected by a heat-medium conveying pipe, the heat medium circuit being configured to cause a heat medium to circulate therethrough. The at least one intermediate heat exchanger comprises a plurality of intermediate heat exchangers. The plurality of intermediate heat exchangers are operative in a heating only operation mode, a cooling only operation mode, and a cooling and heating mixed operation mode in which some of the intermediate heat exchangers serve as the condenser and others of the intermediate heat exchangers serve as the evaporator.

When the temperatures of outdoor heat exchangers 23a and 23b detected by outdoor heat exchanger temperature sensors 57a and 57b become equal to or higher than 5 degrees C. and the sucking superheating degrees of compressors 21a and 21b become equal to or lower than 0 degrees C. while an air conditioning apparatus 1 is performing the reverse defrosting operation, the reverse defrosting operation is stopped and the heating dominant operation is resumed. At this time, the total operating times of the compressors 21a and 21b are reset. The sucking superheating degrees of the compressors 21a and 21b are obtained by subtracting the low pressure saturation temperatures calculated from the sucking pressures of the compressors 21a and 21b, from the temperatures of the refrigerants sucked into the compressors 21a and 21b which temperatures are detected by the sucking temperature sensors 54a and 54b.

An air-conditioning apparatus that can prevent freezing of a heat transfer medium even when using a non-azeotropic refrigerant mixture. The air-conditioning apparatus is designed such that when a heat exchanger serves as a cooler that cools a heat transfer medium, it controls a heat medium passage reversing device. This is so that, when a heat transfer medium flowing through a heat medium flow passage will not be frozen, a refrigerant flowing through a refrigerant flow passage and the heat transfer medium flowing through the heat medium flow passage are in counter flow. It is also to control the heat medium passage reversing device so that, when there is a possibility of freezing the heat transfer medium flowing through the heat medium flow passage, the refrigerant flowing through the refrigerant flow passage and the heat transfer medium flowing through the heat medium flow passage are in parallel flow.

When indoor units are performing a cooling operation, an air-conditioning apparatus controls four flow passage switching valves, for example a first solenoid valve, a second solenoid valve, a third solenoid valve, and a fourth solenoid valve, so that a number of intermediate heat exchangers operating as evaporators is greater than in a cooling main operation. During the cooling main operation, a target value for suction pressure or evaporating temperature at a compressor is set equal to or lower than that in a case in which the indoor units are performing the cooling operation, and a frequency of the compressor and a capacity of a heat-source-side heat exchanger are controlled.

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.

When a first temperature difference is the difference between an inlet temperature of a first refrigerant and an outlet temperature of the first refrigerant in the heat exchanger for heating, and a second temperature difference is the difference between an inlet temperature of a second refrigerant and an outlet temperature of the second refrigerant in the heat exchanger for heating, the difference between the first temperature difference and the second temperature difference is held in a predetermined value or less by controlling the opening degree of a second expansion device.

A multi-split system and a medium-pressure controlling method thereof are provided. The multi-split system includes an outdoor unit, a distribution device, and a plurality of indoor units. The distribution device includes a gas-liquid separator, a first heat exchange assembly, a first electronic expansion valve, a second heat exchange assembly and a second electronic expansion valve. The distribution device is configured to perform a routine correction on a medium-pressure control target value of the first electronic expansion valve according to the subcooling degree of the heating indoor unit, the outlet air temperature of the heating indoor unit and the opening of the throttling element in the heating indoor unit, and to correct a current medium-pressure control target value of the first electronic expansion valve according to a preset step when the opening of the throttling element reaches a maximum opening or a minimum opening and lasts for a first preset time.