A system and method are described that help to alleviate pressure and strain spikes in and around dead tubes or frontiers between stages in a multi-stage condenser coil. Instead of cycling a fan off and on, fans associated with the condenser are kept running at a low speed instead of being turned off. Preventing the fans from turning off completely helps to even out the pressure and strain spikes. The present teachings can be especially beneficial in aluminum-based coils. The present teachings include both a unit controller that carries out the teachings, and a system based on temperature and/or pressure switches connected to a fan controller.

In some embodiments, an air-cooled ammonia refrigeration system comprises: a plurality of air-cooled condensers, each having a heat exchanger and at least one axial fan and having a first operating state capable of condensing vaporous ammonia to form liquid ammonia; an evaporator coupled to the air-cooled condenser; a subcooler positioned between the air-cooled condenser and the evaporator; a compressor coupled to the evaporator; an oil cooler coupled to the compressor; and a plurality of valves coupled to the plurality of air-cooled condensers and having a first configuration corresponding to the first operating state of the plurality of air-cooled condensers, and a second configuration corresponding to a second operating state of one or more of the plurality of air-cooled condensers such that the one or more of the plurality of air-cooled condensers functions as an evaporator capable of evaporating liquid ammonia to form vaporous ammonia.

A method for controlling a variable capacity ejector unit (7) arranged in a refrigeration system (1) is disclosed. An ejector control signal for the ejector unit (7) is generated, based on an obtained temperature and an obtained pressure of refrigerant leaving a heat rejecting heat exchanger (3), or on the basis of a high pressure valve control signal for controlling an opening degree of a high pressure valve (6) arranged fluidly in parallel with the ejector unit (7). The ejector control signal indicates whether the capacity of the ejector unit (7) should be increased, decreased or maintained. The capacity of the ejector unit (7) is controlled in accordance with the generated ejector control signal. The power consumption of the refrigeration system (1) is reduced, while the pressure of the refrigerant leaving the heat rejecting heat exchanger (3) is maintained at an acceptable level.

A refrigeration cycle device includes a refrigeration cycle formed by connecting a compressor, a condenser, an expansion valve and an evaporator to each other. As a refrigerant in the refrigeration cycle, a working fluid containing 1,1,2-trifluoroethylene (R1123) and difluoromethane (R32) is used. A degree of opening of the expansion valve is controlled such that the refrigerant has two phases at a suction portion of the compressor.

A refrigeration system includes an evaporator within which a refrigerant absorbs heat, a gas cooler/condenser within which the refrigerant rejects heat, a compressor operable to circulate the refrigerant between the evaporator and the gas cooler/condenser, a high pressure valve operable to control a pressure of the refrigerant at an outlet of the gas cooler/condenser, and a controller. The controller is configured to automatically generate a setpoint for a measured or calculated variable of the refrigeration system based on a measured temperature of the refrigerant at the outlet of the gas cooler/condenser. The setpoint is generated using a stored relationship between the measured temperature and a maximum estimated coefficient of performance (COP) that can be achieved at the measured temperature. The controller is configured to operate the high pressure valve to drive the measured or calculated variable toward the setpoint.

A system based on temperature and/or pressure switches connected to a fan controller. An HVAC circuit includes at least one condenser coil with a plurality of tubes, one or more stages coupled to one or more compressors, at least one temperature sensor, at least one fan configured to provide airflow across the plurality of tubes, and a controller. Instead of cycling the fan off and on, fans associated with the condenser are kept running at a low speed.

An air-conditioning apparatus includes heat-source-side units each including a compressor and a heat-source-side heat exchanger, a load-side heat exchanger and a load-side expansion device, a first header, a second header, bypass expansion devices, circuit switching units, discharge pressure sensors, bypass pressure sensors, and a controller configured to control, in a heat-source-side unit in defrosting mode, the circuit switching unit in such a manner that a portion of refrigerant discharged from the compressor flows into the heat-source-side heat exchanger and configured to control, in the heat-source-side unit in defrosting mode, an opening degree of the bypass expansion device in the heat-source-side unit in such a manner that a value representing a difference between a value obtained by the discharge pressure sensor and a value obtained by the bypass pressure sensor is equal to or greater than a predetermined value.

In some embodiments, an air-cooled ammonia refrigeration system comprises: a plurality of air-cooled condensers, each having a heat exchanger and at least one axial fan and having a first operating state capable of condensing vaporous ammonia to form liquid ammonia; an evaporator coupled to the air-cooled condenser; a subcooler positioned between the air-cooled condenser and the evaporator; a compressor coupled to the evaporator; an oil cooler coupled to the compressor; and a plurality of valves coupled to the plurality of air-cooled condensers and having a first configuration corresponding to the first operating state of the plurality of air-cooled condensers, and a second configuration corresponding to a second operating state of one or more of the plurality of air-cooled condensers such that the one or more of the plurality of air-cooled condensers functions as an evaporator capable of evaporating liquid ammonia to form vaporous ammonia.

A control system controls the output capacity of a compressor to avoid surge conditions in the compressor. The control system determines a capacity control output for the compressor and then modifies the capacity control output in view of any output limiters or overrides as determined by system operating parameters and to maintain a minimum frequency of operation for the compressor.

In various implementations, an air conditioner may include one or more compressors, more than one expansion device, and/or a microchannel condenser. High pressure events may occur during operation of the air conditioner and may be identified. When a high pressure event is identified a bypass operation may be allowed.