A method of initiating a defrost cycle using a controller of a heat pump system includes measuring a temperature of an evaporator coil and determining whether the temperature of the evaporator coil is less than a freezing temperature. Responsive to a determination that the temperature of the evaporator coil is less than the freezing temperature, determining whether a current dew point temperature of air is greater than the temperature of the evaporator coil. Responsive to a determination that the current dew point temperature of air is greater than the temperature of the evaporator coil, calculating a frost-collection rate. Determining whether the frost-collection rate is greater than a frost-collection-rate threshold, and, responsive to a determination that the frost-collection rate is greater than the frost-collection-rate threshold, initiating a defrost cycle.

A cooling and heating system for a motor vehicle comprises a heat pump, a controller, a low temperature radiator in thermal communication with the heat pump, a passenger cabin heat exchanger in thermal communication with the heat pump, and a defrost system comprising a bypass coolant loop in selective fluid communication with the low temperature radiator. When in the heating mode, the controller opens a solenoid valve and activates a coolant heater in the bypass coolant loop upon detecting operation of the heat pump outside of a predetermined normal operating range and upon detecting an ambient temperature below a predetermined temperature. The controller de-activates the coolant heater upon detecting operation of the heat pump within the predetermined normal operating range. The controller may also de-activate close the solenoid upon detecting operation of the heat pump within the predetermined normal operating range.

A refrigeration system includes a free cooling system having an air-cooled heat exchanger, where the air-cooled heat exchanger includes a fan configured to move air over coils of the air-cooled heat exchanger to remove heat from a coolant flowing through the air-cooled heat exchanger, and a mechanical cooling system with a refrigerant loop that includes an evaporator, a compressor, and a condenser disposed along the refrigerant loop, where the compressor is configured to circulate a refrigerant through the refrigerant loop, and wherein the evaporator is configured to receive the coolant and transfer heat from the coolant to the refrigerant. The refrigeration system also includes a controller configured to adjust a fan speed of the fan up to a threshold fan speed, to initiate operation of the compressor when the fan speed reaches the threshold fan speed, wherein the fan speed and a compressor speed of the compressor are based at least on an ambient air temperature and a cooling load demand.

An illustrative example refrigerant system includes a compressor configured to pressurize a refrigerant fluid. The compressor includes a sump portion. A heater is situated to heat at least the sump portion. A controller is configured to selectively operate the heater to apply heat to at least the sump portion while the compressor is off and continue operating the heater when the compressor turns on until a temperature of the compressor or a temperature of fluid discharged from the compressor satisfies at least one criterion.

A vapor compression system includes a first conduit fluidly coupling a liquid collection portion of a condenser and an evaporator, where the first conduit is configured to direct a first flow of refrigerant from the condenser to a first inlet of the evaporator and a second conduit fluidly coupling the liquid collection portion of the condenser and the evaporator, where the second conduit is configured to direct a second flow of refrigerant from the condenser to a second inlet of the evaporator via gravitational force, and where the first inlet is disposed above the second inlet relative to a vertical dimension of the evaporator.

A refrigeration system includes a startup mode control module that receives an off time of a compressor and an ambient temperature, determines whether the off time and the ambient temperature indicate that the compressor is in a flooded condition, and selects, based on the determination, between a normal startup mode and a flooded startup mode. A compressor control module operates the compressor in the normal startup mode in response to the startup mode control module selecting the normal startup mode, operates the compressor in the flooded startup mode in response to the startup mode control module selecting the flooded startup mode, and transitions from the flooded startup mode to the normal startup mode after a predetermined period associated with operating in the flooded startup mode.

An air-conditioning apparatus that includes a compressor, a flow switching device, an outdoor heat exchange unit, an expansion section and an indoor heat exchanger, which are connected by pipes, in which the outdoor heat exchange unit includes a first outdoor heat exchanger, a first flow rate control device, a second outdoor heat exchanger, a second flow rate control device, a bypass pipe, the second outdoor heat exchanger, the second flow rate control device, a third flow rate control device, and a flow control device.

Disclosed are an air conditioning system and its pressure ratio control method and device. The method includes acquiring an actual pressure ratio of the compressor every preset time period in operation of the air conditioning system; judging whether the actual pressure ratio is greater than or equal to the first pressure ratio corresponding to a current level; controlling the compressor to downshift one level for operation if the actual pressure ratio is greater than or equal to the first pressure ratio corresponding to the current level; further judging whether the actual pressure ratio is less than the second pressure ratio corresponding to the current level if the actual pressure ratio is less than the first pressure ratio corresponding to the current level; and controlling the compressor to upshift one level for operation if the actual pressure ratio is less than the second pressure ratio corresponding to the current level.

The present invention discloses a refrigerator controlling method and system with a linear compressor. The method comprises: monitoring an environment temperature T of the refrigerator located in the environment comparing the environment temperature T with a preset environment temperature threshold T0; if T is larger than T0, controlling a refrigerating unit and/or a heating unit in the refrigerator such that the refrigerator runs under a first operation condition; and if T is smaller than or equal to T0, controlling the refrigerating unit and/or the heating unit in the refrigerator such that the refrigerator runs under a second operation condition. When the linear compressor runs within predetermined time, a refrigeration amount of the linear compressor under the second operation condition is controlled to be larger than a refrigeration amount of the linear compressor under the first operation condition, such that a compartment of the refrigerator reaches a target temperature.

According to one embodiment, an air conditioning apparatus has one or a plurality of indoor units, an outdoor unit, and a controller. The one or plurality of indoor units have an indoor heat exchanger, and an indoor expansion valve in which a degree of opening is variable. The outdoor unit has an outdoor heat exchanger, a four-way valve, a compressor, and a discharge pressure sensor configured to detect a pressure of a refrigerant discharged from the compressor. When a discharge pressure detected by the discharge pressure sensor is less than a predetermined pressure threshold value while a heating operation is performed, the controller sets a maximum time for continuing a defrosting operation started by a start condition of the defrosting operation being satisfied to be shorter than a maximum time for continuing the defrosting operation when the discharge pressure is equal to or higher than the pressure threshold value.