Systems and methods are provided for controlling compressor systems to ensure sufficient pressure differentials to provide cooling. A compressor system includes a compressor, a suction pressure sensor at a suction of the compressor, a discharge pressure sensor, a condenser, an expansion device, a liquid line, a liquid line pressure sensor, an evaporator, a condenser blower and a controller. The method includes determining a pressure target based on an intermediate pressure within the compressor and a threshold cooling differential pressure value, determining a pressure ratio setpoint based on the pressure target and a liquid line pressure measured by the liquid line pressure sensor, controlling the condenser blower to operate based on the determined pressure ratio setpoint, determining a subcooling setpoint based on the pressure target and the liquid line pressure in the compressor system, and controlling the expansion device to operate based on the subcooling setpoint.

An HVAC system with a reheat coil is described, the system includes a compressor, a micro-channel condenser and an evaporator. A reversing valve is connected to the compressor, the micro-channel condenser and the reheat coil. The reversing valve is used to direct the refrigerant from the compressor to the micro-channel condenser in a normal mode, and to direct the refrigerant from the compressor to the reheat coil in a reheat mode. The reversing valve can be switched from normal mode to reheat mode when a high pressure condition is detected at an input to the micro-channel condenser, and switched back from reheat mode to normal mode when the high pressure condition has resolved or an amount of time has passed. In the normal mode the refrigerant is returned from the reheat coil into a refrigerant line between the evaporator and the compressor through a restrictor.

A heating, ventilation, and/or air conditioning (HVAC) unit includes a refrigerant circuit including a reheat coil and a condenser system, a first valve disposed along the refrigerant circuit and configured to modulate refrigerant flow to the reheat coil and to the condenser system, and a second valve disposed along the refrigerant circuit downstream of the first valve relative to a direction of the refrigerant flow through the refrigerant circuit. The condenser system includes a first condenser coil and a second condenser coil, and the second valve is configured to be actuated to control refrigerant flow to the second condenser coil.

An HVAC system with a reheat coil is described, the system includes a compressor, a micro-channel condenser and an evaporator. A reversing valve is connected to the compressor, the micro-channel condenser and the reheat coil. The reversing valve is used to direct the refrigerant from the compressor to the micro-channel condenser in a normal mode, and to direct the refrigerant from the compressor to the reheat coil in a reheat mode. The reversing valve can be switched from normal mode to reheat mode when a high pressure condition is detected at an input to the micro-channel condenser, and switched back from reheat mode to normal mode when the high pressure condition has resolved or an amount of time has passed. In the normal mode the refrigerant is returned from the reheat coil into a refrigerant line between the evaporator and the compressor through a restrictor.

Systems and methods are provided for controlling compressor systems to ensure sufficient pressure differentials to provide cooling. A compressor system includes a compressor, a suction pressure sensor at a suction of the compressor, a discharge pressure sensor, a condenser, an expansion device, a liquid line, a liquid line pressure sensor, an evaporator, a condenser blower and a controller. The method includes determining a pressure target based on an intermediate pressure within the compressor and a threshold cooling differential pressure value, determining a pressure ratio setpoint based on the pressure target and a liquid line pressure measured by the liquid line pressure sensor, controlling the condenser blower to operate based on the determined pressure ratio setpoint, determining a subcooling setpoint based on the pressure target and the liquid line pressure in the compressor system, and controlling the expansion device to operate based on the subcooling setpoint.

A refrigeration device includes a refrigerant circuit sequentially connecting a compressor, a condenser, a reservoir, and a subcooling coil via refrigerant pipes in series, an injection circuit configured to inject part of refrigerant flowing from the condenser to an intermediate pressure part of the compressor, and an injection expansion valve configured to reduce a pressure of refrigerant branched on a downstream side of the subcooling coil. The refrigeration device includes a temperature measurement unit, a pressure measurement unit, and a controller configured to identify a type of refrigerant on the basis of a measured value of the temperature measurement unit and a measured value of the pressure measurement unit, and control at least one of an operating frequency of the compressor, a rotation frequency of a condenser fan, and an opening degree of the injection expansion valve.

An exemplary heat pump includes: a compressor configured to compress a refrigerant; a first heat exchanger configured to condense the compressed refrigerant; a flow rate adjustment valve configured to adjust a flow rate of the condensed refrigerant; an expansion valve having an adjustable opening and configured to decompress the refrigerant having passed the flow rate adjustment valve; a second heat exchanger configured to cool a temperature control target by using the refrigerant decompressed by the expansion valve; and a control device configured to control the opening of the expansion valve based on a difference between the temperature of the refrigerant flowing into the second heat exchanger and the temperature of the refrigerant flowing out from the second heat exchanger, and to control the opening of the flow rate adjustment valve based on the flow rate of the refrigerant to be supplied to the second heat exchanger.

An air-conditioning apparatus includes a refrigerant circuit including first and second load-side heat exchangers, a first flow switching unit located upstream of the second load-side heat exchanger, and a second flow switching unit located downstream of the second load-side heat exchanger, wherein the first flow switching unit is configured to be switched between a first state in which refrigerant communication between a compressor and the second load-side heat exchanger is blocked and a second state in which the compressor is in refrigerant communication with the first and second load-side heat exchangers, and the second flow switching unit is configured to be switched between a third state in which refrigerant communication between the second load-side heat exchanger and a heat-source-side heat exchanger is blocked and a fourth state in which the first load-side heat exchanger is in refrigerant communication with the second load-side heat exchanger and the heat-source-side heat exchanger.

A refrigeration cycle apparatus is provided with a refrigerant circuit, a refrigerant tank circuit, and a degassing pipe. The refrigerant circuit is configured by connecting a compressor, a flow path switching apparatus, a first heat exchanger, a decompressing apparatus, and a second heat exchanger. The refrigerant tank circuit is connected to the first and second heat exchangers in parallel with the decompressing apparatus. The degassing pipe has a first end and a second end. The flow path switching apparatus is configured to switch a flow of refrigerant discharged from the compressor to any of the first and second heat exchangers. The refrigerant tank circuit contains a refrigerant tank. The degassing pipe has the first end connected to the refrigerant tank and has the second end connected to at least any of the refrigerant circuit and the refrigerant tank circuit.

A method of controlling a refrigeration system having a compressor, a condenser, an evaporator, and a variable speed condenser fan is provided. The method includes determining if a change in an ambient temperature or a compressor suction pressure is greater than a predetermined threshold, determining a near-optimal condensing pressure/temperature if the change in the ambient temperature or the compressor suction pressure is above the predetermined threshold, setting a condensing pressure setpoint based on the determined near-optimal condensing pressure/temperature, and setting a speed of the variable speed condenser fan based on the condensing pressure setpoint.