An air conditioner unit includes a variable speed compressor for circulating refrigerant through an outdoor heat exchanger and an indoor heat exchanger, an indoor fan, and an outdoor fan. A controller obtains an indoor temperature using an indoor temperature sensor and operates the variable speed compressor, the indoor fan, and the outdoor fan at a first capacity level to adjust the indoor temperature toward a target temperature. The controller determines that a rate of change of the indoor temperature is below a predetermined rate threshold and operates the variable speed compressor, the indoor fan, and the outdoor fan at a second capacity level.

A method and system for improving energy efficiency of a refrigeration system include system components such as a condenser, one or more expansion valves, an evaporator, one or more compressors, and a system controller electrically coupled to the one or more of the system components, according to one embodiment. The system controller is configured to selectively actuate, directly or indirectly, the one or more expansion valves, the condenser, and/or the one or more compressors, at least partially based on temperatures and/or pressures of the system fluid at various points of the system, to control a temperature of a refrigerated area.

The disclosed technology includes systems and methods of reducing frost accumulation on a heat pump evaporator coil. The disclosed technology can include a heat pump assembly having an evaporator coil, a fan configured to direct air across the evaporator coil, a temperature sensor, and a controller configured to energize the fan to direct air across the evaporator coil when the temperature of the evaporator coil is below a threshold temperature.

In other features, a refrigeration system is provided and includes a compressor motor, an inverter, a converter and a control module. The inverter is configured to convert a direct current (DC) bus voltage to an alternating current (AC) voltage and supply the AC voltage to the compressor motor. The converter is configured to convert a DC input voltage to the DC bus voltage. The control module is configured to obtain a parameter and in response to the parameter exceeding a predetermined threshold, reduce the DC bus voltage and at least one of (i) reduce a switching frequency, (ii) increase an amount of negative d-axis current of the compressor motor, or (iii) reduce a speed of the compressor motor.

A vector control system is used to control a vapor compression circuit. The vector control system may monitor the vapor compression circuit and adjust the speed of one or more motors to increase efficiency of the system by taking into account the torque forces placed on a compressor motor.

A refrigeration cycle device includes a third refrigerant passage connecting a utilization heat exchanger to a first expansion valve, a fourth refrigerant passage connecting the first expansion valve to a receiver, a fifth refrigerant passage connecting the receiver to a second expansion valve, a sixth refrigerant passage connecting the second expansion valve to an air heat exchanger, a hot-gas bypass passage connecting a discharge passage to the sixth refrigerant passage, a hot-gas bypass valve, an internal heat exchanger to exchange heat between the liquid refrigerant inside the receiver and the refrigerant passing through the suction passage, a liquid bypass passage including an inlet portion connected to the fourth refrigerant passage, the fifth refrigerant passage, or a lower portion of the receiver, and an outlet portion connected to the suction passage upstream of the internal heat exchanger, and a liquid bypass valve.

Disclosed is a CO.sub.2 based refrigeration system including a condenser for transferring heat from a CO.sub.2 refrigerant of the refrigeration system to an air stream. The system further includes a metering device downstream of the condenser and a bypass arrangement. The metering device is configured to create a pressure drop so that part of the refrigerant liquifies, when received in a supercritical state, from the condenser such that a liquid component and a flash gas component are generated. The bypass arrangement includes a valve and a bypass line to allow the refrigerant to bypass the metering device.

A method, which is for controlling a temperature of a refrigerating compartment, includes cooling the refrigerating compartment, cooling the freezing compartment, determining a temperature of the refrigerating compartment, and based on the temperature of the refrigerating compartment, controlling the refrigerating compartment to a constant temperature range by controlling opening and closing of first and second passages of a three-way valve of the refrigerator to alternate cooling the refrigerating compartment and cooling the freezing compartment.

Devices, systems, and methods are disclosed for cooling using both air and/or liquid cooling sub circuits. A vapor compression cooling system having both an air and liquid cooling sub circuit designed to service high sensible process heat loads that cannot be solely cooled by either liquid or air is provided.

A thermal management system that include an electronic circuit boards having at least two circuit boards with a space in between and further includes one or more air tubes or conduits. The electronic circuit board and air tubes are configured for drawing air into the space to facilitate cooling of the electronic circuit board concurrent with cooling of a heat sink of a heat pump connected with the electronic circuit board. The system can further include a partition to isolate airflow from the heat sink from airflow through the electronics circuit board, and can further include one or more interface components for maintaining isolation and control of air flow, improving air intake and/or supporting auxiliary components.