A primary refrigerant circuit allows circulation of a primary refrigerant and includes a primary compressor, a cascade heat exchanger, and a primary heat exchanger. A secondary refrigerant circuit allows circulation of a secondary refrigerant and includes a secondary compressor, the cascade heat exchanger, and a utilization heat exchanger. The primary refrigerant circuit includes a first connecting pipe, a primary first connection pipe, and a liquid connecting pipe connecting the cascade heat exchanger and the primary heat exchanger, a primary suction flow path of the primary compressor, a primary subcooling circuit connecting the liquid connecting pipe and the primary suction flow path, and a primary subcooling expansion valve provided in the primary subcooling circuit.

A cold source unit is connectable to an indoor heat exchanger and is provided for a refrigerant circuit. The cold source unit includes: a compressor; an outdoor heat exchanger having a gas header; an oil return path through which refrigeration oil is returned from the gas header to the compressor; an oil return adjusting unit configured to adjust a flow rate of refrigeration oil flowing through the oil return path; and a controller configured to control the refrigerant circuit. The controller is configured to control the oil return adjusting unit to prevent refrigeration oil from flowing through the oil return path when the compressor is driven at a frequency equal to or higher than a threshold value, and control the oil return adjusting unit to allow the refrigeration oil to flow through the oil return path when the compressor is driven at a frequency lower than the threshold value.

An air-conditioning apparatus includes a main circuit in which a compressor, a flow switching device, an indoor heat exchanger, a pressure reducing device, and a plurality of parallel heat exchangers connected in parallel with each other are connected by pipes, a bypass pipe, a flow control device provided to the bypass pipe and configured to adjust a flow rate of refrigerant flowing through the bypass pipe, an evaporating pressure sensor configured to measure an evaporating pressure of the refrigerant, and a controller. The air-conditioning apparatus is configured to operate in a normal heating operation mode and a heating-defrosting operation mode. When an operation associated with the normal heating operation mode is switched to an operation associated with the heating-defrosting operation mode, the controller adjusts an opening degree of the flow control device using the evaporating pressure in the parallel heat exchanger and a driving frequency of the compressor.

Embodiments relate generally to subcooling control of a heating, ventilation, and air conditioning (HVAC) system. An HVAC system may include a compressor, a first heat exchanger, a refrigerant vessel having an inlet fluidly coupled to a discharge conduit extending from the compressor, and the refrigerant vessel having an outlet fluidly coupled to a liquid conduit, the liquid conduit configured to pass liquid refrigerant between the first heat exchanger and a second heat exchanger. The HVAC system may further include an electronic expansion valve (EEV) fluidly coupled between the discharge conduit and the inlet of the refrigerant vessel, wherein the EEV is configured to modulate and divert a portion of vapor refrigerant flowing through the discharge conduit into the refrigerant vessel to control subcooling (SC) produced by the HVAC system.

Embodiments relate generally to subcooling control of a heating, ventilation, and air conditioning (HVAC) system. An HVAC system may include a first electronic expansion valve (EEV) fluidly coupled to an indoor coil, wherein the first EEV is adjacent to the indoor coil. The HVAC system may also include a second EEV fluidly coupled to an outdoor coil, wherein the second EEV is adjacent to the outdoor coil. A system controller may be configured to control the first and second EEVs to control a flow of refrigerant to control subcooling (SC) produced by the HVAC system. The second EEV remains open during a cooling mode, and the first EEV modulates during the cooling mode. The second EEV modulates during a heating mode, and the first EEV remains open during the heating mode.

A multi-connected heat recovery air conditioning system and a control method thereof. The multi-connected heat recovery air conditioning system includes an indoor unit, an outdoor unit and a hydraulic module, wherein the outdoor unit comprises a compressor, an outdoor heat exchanger, a first four-way valve and a second four-way valve. The multi-connected heat recovery air conditioning system further comprises an indoor unit temperature unit, a water temperature unit, a high-pressure sensor and a low-pressure sensor. The indoor unit temperature unit is arranged in the indoor unit for detecting and obtaining the outlet temperature value of the indoor unit, the water temperature unit is arranged at a heat exchange water tank for detecting and obtaining water temperature, and the high-pressure sensor and the low-pressure sensor are arranged at the output end and the air return end of the compressor respectively.

A refrigeration cycle apparatus includes a compressor, first and second heat exchangers, an expansion valve, a four-way valve, and a controller. The four-way valve is configured to switch a direction of flow of the refrigerant between a first direction and a second direction. The controller is configured to control the four-way valve to switch an operation from a defrosting operation in which the refrigerant flows in the second direction, to a heating operation in which the refrigerant flows in the first direction, to perform a heating preparation control for increasing a degree of superheat of the refrigerant output to the compressor from the second heat exchanger, and thereafter to start the heating operation.

Embodiments relate generally to subcooling control of a heating, ventilation, and air conditioning (HVAC) system. An HVAC system may include a compressor, a first heat exchanger, a refrigerant vessel having an inlet fluidly coupled to a discharge conduit extending from the compressor, and the refrigerant vessel having an outlet fluidly coupled to a liquid conduit, the liquid conduit configured to pass liquid refrigerant between the first heat exchanger and a second heat exchanger. The HVAC system may further include an electronic expansion valve (EEV) fluidly coupled between the discharge conduit and the inlet of the refrigerant vessel, wherein the EEV is configured to modulate and divert a portion of vapor refrigerant flowing through the discharge conduit into the refrigerant vessel to control subcooling (SC) produced by the HVAC system.

Embodiments relate generally to subcooling control of a heating, ventilation, and air conditioning (HVAC) system. An HVAC system may include a first electronic expansion valve (EEV) fluidly coupled to an indoor coil, wherein the first EEV is adjacent to the indoor coil. The HVAC system may also include a second EEV fluidly coupled to an outdoor coil, wherein the second EEV is adjacent to the outdoor coil. A system controller may be configured to control the first and second EEVs to control a flow of refrigerant to control subcooling (SC) produced by the HVAC system. The second EEV remains open during a cooling mode, and the first EEV modulates during the cooling mode. The second EEV modulates during a heating mode, and the first EEV remains open during the heating mode.

Disclosed is a heat pump system for an electric vehicle including an outdoor fan configured to blow air to an outdoor heat exchanger, a coolant temperature sensor installed at a coolant line and configured to detect a temperature of a coolant circulating in a power train module or a battery, an outdoor heat exchange sensor installed on one side of the outdoor heat exchanger and configured to detect an outdoor heat exchanger outlet pressure defined as a pressure of a refrigerant passing through the outdoor heat exchanger, and a compressor inlet sensor installed on an intake side of a compressor and configured to detect a compressor inlet temperature defined as a temperature of the refrigerant flowing into the compressor. Whether frost sticking occurs may be determined based on information detected by the coolant temperature sensor, the outdoor heat exchange sensor, and the compressor inlet sensor.