A refrigeration system includes an expansion valve downstream of one or more medium temperature compressors. The expansion valve is configured to decrease pressure of a portion of refrigerant output by the one or more medium temperature compressors. When defrost operation of an evaporator is indicated, the refrigerant with decreased pressure from the expansion valve is provided to the evaporator for at least a period of time sufficient to defrost the evaporator.

The disclosed technology includes devices, systems, and methods for heat pump systems configured to operate in low ambient temperatures. The disclosed technology can include a heat pump water heater system having an evaporator, a first compressor configured to compress refrigerant to a first pressure, and a second compressor configured to compress the refrigerant to a second pressure. The second pressure can be greater than the first pressure. The heat pump water heater system can include a preheater configured to receive the refrigerant at the first pressure and heat water and a condenser configured to receive the refrigerant at the second pressure and heat water. The water can be passed through the preheater before being passed through the condenser.

Systems and methods are provided and include first and second case controllers for first and second refrigeration cases. The first case controller receives a first air temperature value of the first refrigeration case and communicates the first air temperature value to the second case controller. The second case controller receives a second air temperature value, determine an evaporator saturated suction temperature (SST) value, controls an evaporator pressure regulator based on a comparison of the evaporator SST value with an evaporator SST setpoint, determines an air temperature control value, determines whether the air temperature control value is within a predetermined range of an air temperature setpoint, and adjusts the evaporator SST setpoint in response to the air temperature control value being outside of the predetermined range of the air temperature setpoint.

Systems and methods are provided and include first and second case controllers for first and second refrigeration cases. The first case controller receives a first air temperature value of the first refrigeration case and communicates the first air temperature value to the second case controller. The second case controller receives a second air temperature value, determine an evaporator saturated suction temperature (SST) value, controls an evaporator pressure regulator based on a comparison of the evaporator SST value with an evaporator SST setpoint, determines an air temperature control value, determines whether the air temperature control value is within a predetermined range of an air temperature setpoint, and adjusts the evaporator SST setpoint in response to the air temperature control value being outside of the predetermined range of the air temperature setpoint.

A Heating, Ventilation, and Air Conditioning (HVAC) system that is configured to receive a refrigerant from a condenser at a fixed expansion device and a variable expansion device. The system is further configured to output a first portion of the refrigerant to a first downstream HVAC component at a fixed flow rate using the fixed expansion device. The system is further configured to sense a temperature of an evaporator using a sensing bulb and to apply a first force to a pin of the variable expansion device based on the sensed temperature. The system is further configured to apply a second force to a valve of the variable expansion device via the force applied to the pin and to output a second portion of the refrigerant to a second downstream HVAC component at a variable flow rate based on the second force using the valve of the variable expansion device.

A Heating, Ventilation, and Air Conditioning (HVAC) system that is configured to receive a refrigerant from a condenser at a fixed expansion device and a variable expansion device. The system is further configured to output a first portion of the refrigerant to a first downstream HVAC component at a fixed flow rate using the fixed expansion device. The system is further configured to sense a temperature of an evaporator using a sensing bulb and to apply a first force to a pin of the variable expansion device based on the sensed temperature. The system is further configured to apply a second force to a valve of the variable expansion device via the force applied to the pin and to output a second portion of the refrigerant to a second downstream HVAC component at a variable flow rate based on the second force using the valve of the variable expansion device.

In a refrigeration cycle apparatus, a refrigerant pipe is connected to a compressor, a first heat exchanger, an expansion valve, a second heat exchanger, a heat absorber, and the compressor sequentially in this order. R290 is used as refrigerant flowing through the refrigerant pipe. The heat absorber is provided in a portion of the refrigerant pipe between the compressor and the first heat exchanger or the second heat exchanger serving as an evaporator. The heat absorber is disposed in contact with an electric component. A branch pipe is connected in parallel with the portion provided with the heat absorber in the refrigerant pipe. The branch pipe is provided with a flow rate regulating valve.

A HVAC system that includes a compressor comprising a suction port and a discharge port. Also included is a refrigerant circulating throughout the HVAC system and through the compressor. Further included is a pressure equalization valve fluidly coupling the discharge port of the compressor with the suction port of the compressor, the pressure equalization valve configured to open while the compressor is operating.

A HVAC system that includes a compressor comprising a suction port and a discharge port. Also included is a refrigerant circulating throughout the HVAC system and through the compressor. Further included is a pressure equalization valve fluidly coupling the discharge port of the compressor with the suction port of the compressor, the pressure equalization valve configured to open while the compressor is operating.

A cooling system is designed to generally allow for one or more compressors to be bypassed when ambient temperatures are low. The system includes a bypass line and valve that opens when ambient temperatures are low and/or when the pressure of the refrigerant in the system is low. In this manner, the refrigerant can flow through the bypass line instead of through one or more compressors. These compressors may then be shut off. To supply any needed pressure to cycle the refrigerant, the system may include a pump that turns on when the bypass line is open. When ambient temperatures are extremely low, thermosiphon may be used to cycle the refrigerant.