Embodiments of the present disclosure are directed to a controller for a heating, ventilation, and/or air conditioning (HVAC) system. The controller is configured to operate in a first defrost mode or a second defrost mode, determine that feedback from a first sensor of the HVAC system is unavailable, receive feedback from a second sensor of the HVAC system, and operate the HVAC system in the second defrost mode instead of the first defrost mode in response to unavailability of the feedback from the first sensor and based on the feedback from the second sensor.

A refrigerating and air-conditioning system includes a plurality of independent refrigerating and air-conditioning apparatuses each including a refrigerant circuit and a defrosting unit, and further includes a system controller managing the apparatuses in an integrative manner. The system controller includes a defrosting operation control unit. When a time interval between an estimated defrosting start time calculated for a given refrigerating and air-conditioning apparatus and a subsequent estimated defrosting start time calculated for another refrigerating and air-conditioning apparatus is less than or equal to a predetermined target start time interval, the defrosting operation control unit transmits a defrosting start instruction signal to the defrosting unit of the given refrigerating and air-conditioning apparatus.

Provided is a refrigeration apparatus capable of reducing the leakage of a refrigerant even when a refrigerant leak occurs in a defrosting operation of a usage-side heat exchanger. When a refrigerant leak situation around a usage-side heat exchanger satisfies a predetermined leak condition in performing a defrosting operation with a connection state of a four-way switching valve brought into a defrosting connection state in which a heat source-side heat exchanger functions as an evaporator for a refrigerant and a usage-side heat exchanger functions as a radiator for the refrigerant, a controller performs density lowering control to lower a refrigerant density in the usage-side heat exchanger while maintaining the four-way switching valve at the defrosting connection state.

A system and method for controlling a refrigeration system is disclosed. The system includes a cooled compartment, at least one heat source selectively activated to provide heat, at least one sensor, and a controller. The sensor detects a temperature and a relative humidity of ambient air that surrounds the cooled compartment. The controller is in communication with the at least one heat source and the at least one sensor. The controller includes logic for calculating a dew point temperature based on the temperature and the relative humidity. The controller also includes logic for selecting a region of operation based on at least one of the dew point temperature and the relative humidity, where the region of operation is representative of ambient conditions that surround the cooled compartment. The controller further includes logic for determining if the at least one heat source is activated based on the region of operation.

A refrigeration system includes a first compressor system, a second compressor system, a first conduit, a heat exchanger, a second conduit, and a third conduit. The first compressor system includes a plurality of first compressors. The second compressor system includes a plurality of second compressors. The first conduit is configured to provide refrigerant from the first compressor system to the second compressor system. The second conduit is fluidly coupled to the first conduit and configured to provide the refrigerant from the first compressor system to the heat exchanger. The third conduit is configured to provide the refrigerant from the second compressor system to the heat exchanger.

A refrigeration cycle apparatus including a refrigerant circuit including a compressor, an indoor heat exchanger, an expansion device, an outdoor heat exchanger, an outside air temperature sensor, and a controller configured to perform a hot gas defrosting operation and a reverse-defrosting operation based on a temperature obtained by the outside air temperature sensor. In the hot gas defrosting operation, hot gas discharged from the compressor without passing through the indoor heat exchanger is supplied to the outdoor heat exchanger. In the reverse-defrosting operation, refrigerant passing through the indoor heat exchanger is supplied from the compressor to the outdoor heat exchanger. The controller has at least a mixed defrosting operation mode in which the hot gas defrosting operation and the reverse-defrosting operation are performed in sequence. The controller is configured to start the mixed defrosting operation mode when the temperature obtained by the outside air temperature sensor satisfies a preset condition.

A continuous heating control system and method, and an air-conditioning device. The system includes a defrosting solenoid valve (1) arranged on a bypass pipeline, wherein one end of the bypass pipeline is connected to an oil separator (2), and the other end of the bypass pipeline is connected to an outdoor heat exchanger (3); and a heating structure which is arranged at the bottom of a gas separator (4) and used for heating the gas separator (4).

Embodiments of the present disclosure are directed to a controller for a heating, ventilation, and/or air conditioning (HVAC) system. The controller is configured to operate in a first defrost mode or a second defrost mode, determine that feedback from a first sensor of the HVAC system is unavailable, receive feedback from a second sensor of the HVAC system, and operate the HVAC system in the second defrost mode instead of the first defrost mode in response to unavailability of the feedback from the first sensor and based on the feedback from the second sensor.

An outdoor unit control unit has a defrosting operation condition table that defines an activation rotational speed based on the total sum of the rated capacity of indoor units and a refrigerant pipe length that is the length of a liquid pipe or of a gas pipe. The outdoor unit control unit uses the total sum of the rated capacity of the indoor units and refers to the defrosting operation condition table, so as to determine the activation rotational speed, and then the outdoor unit control unit activates a compressor at the determined activation rotational speed when starting a defrosting operation, maintains this activation rotational speed for a predetermined time (one minute) from the start of the defrosting operation, and drives the compressor.

An air conditioner and a method for controlling an air conditioner are provided that inject a refrigerant into a compressor to perform a defrosting operation. The air conditioner may include a compressor; an outdoor heat exchanger; an indoor heat exchanger; a first injection module that injects a refrigerant flowing from the indoor heat exchanger to the outdoor heat exchanger into the compressor during a heating operation and that does not inject a refrigerant flowing from the outdoor heat exchanger to the indoor heat exchanger into the compressor during a defrosting operation; and a second injection module that injects a refrigerant flowing from the indoor heat exchanger to the outdoor heat exchanger into the compressor during the heating operation and that injects a refrigerant flowing from the outdoor heat exchanger to the indoor heat exchanger into the compressor during the defrosting operation.