A refrigeration system includes a heat exchanger configured to place a cooling fluid in a heat exchange relationship with a working fluid, a free-cooling circuit having a pump configured to circulate the working fluid through the heat exchanger and a condenser, a flow control valve configured to control a flow rate of the working fluid to the condenser, a condenser bypass valve configured to control a flow rate of the working fluid that bypasses the condenser, and a controller configured to adjust a position of the flow control valve, a position of the condenser bypass valve, a speed of a fan of the condenser, a speed of the pump, and a temperature of a heater based on an ambient temperature, a temperature of the working fluid leaving the condenser, the position of the flow control valve, the position of the condenser bypass valve, or a combination thereof.

An apparatus evaluation system includes a first evaluation unit that evaluates a first air conditioning apparatus, and a first air conditioning control unit that controls a second air conditioning apparatus. The first evaluation unit performs a first evaluation process to evaluate the first air conditioning apparatus based on a first evaluation index obtained in a first operation performed as a first evaluation operation at a time of installation, and a second evaluation process to evaluate the first air conditioning apparatus based on the first evaluation index obtained in a second operation performed as the first evaluation operation after the first evaluation process. The control unit operates the second air conditioning apparatus before at least one of the first and second operations of the first air conditioning apparatus is performed, and/or while at least one of the first and second operations of the first air conditioning apparatus is being performed.

The disclosure describes a system that includes an evaporator, an accumulator downstream of the evaporator, a centrifugal compressor downstream of the accumulator, a first heat exchanger stage downstream of the centrifugal compressor, and a second heat exchanger stage downstream of the first heat exchanger stage. The evaporator is configured to cool a conditioned air stream using a refrigerant. The accumulator is configured to store excess refrigerant. The centrifugal compressor is configured to compress the refrigerant. The first heat exchanger stage is configured to cool the refrigerant using environmental air. The second heat exchanger stage is configured to cool the refrigerant from the first heat exchanger stage using a portion of the excess refrigerant from the accumulator.

A method of controlling an HVAC circuit, comprises allowing refrigerant to circulate within the HVAC circuit, wherein the HVAC circuit comprises an evaporator coil, a condenser coil, at least one fan configured to provide airflow to the condenser coil, at least one expansion valve, and at least one compressor. The method continues by receiving a temperature measurement and determining based on the temperature measurement, a minimum fan speed configured to avoid pressure spikes within the condenser coil. The method concludes by sending a signal to the at the least one fan to direct the at least one fan to spin at a rate greater than or equal to the minimum fan speed when the measured temperature is less than a predetermined temperature, wherein, when the refrigerant circulates through the condenser coil, the minimum fan speed is greater than zero rotations per minute.

A refrigeration system includes a receiver, a gas bypass valve, a parallel compressor, and a controller. The gas bypass valve and the parallel compressor are fluidly coupled to an outlet of the receiver in parallel and configured to control a pressure of a gas refrigerant in the receiver. The controller is configured to switch from operating the gas bypass valve to operating the parallel compressor to control the pressure of the gas refrigerant in the receiver in response to a value of a process variable crossing a switchover setpoint. The value of the process variable depends on an amount of the gas refrigerant produced by the refrigeration system. The controller is configured to automatically adjust the switchover setpoint in response to the amount of the gas refrigerant produced by the refrigeration system being insufficient to sustain operation of the parallel compressor.

A performance degradation diagnosis system includes a determining unit, and control unit. A refrigeration cycle apparatus includes a refrigerant circuit having a compressor, heat-source-side heat exchanger, and use-side heat exchanger. The determining unit determines, based on an index indicating an operation state of the refrigeration cycle apparatus, performance degradation of the refrigeration cycle apparatus with respect to each of a plurality of performance degradation factors. In a case in which the determining unit determines performance degradation, the control unit grasps an operation condition of the refrigeration cycle apparatus which is operating. In a case in which the operation condition of the refrigeration cycle apparatus is not suitable to determine performance degradation with respect to a performance degradation factor of a determination target, the control unit controls the operation condition of the refrigeration cycle apparatus so that the operation condition of the refrigeration cycle apparatus becomes an appropriate operation condition.

A system or method can be used to monitor operations of a heat exchanger, such as a condenser of an air conditioning system, that includes a header plate. A temperature sensor can be secured to the header plate to measure a temperature of the header plate as a proxy for a temperature or a pressure of a working fluid of the heat exchanger.

A system for controlling or optimizing the performance of a vapor compression system by modifying the actuator commands via an output interface, that realizes thermofluid property functions and their derivatives as spline functions which are represented in a coordinate system that is aligned with a fluid saturation curve. The system includes an interface configured to receive measurement data from sensors, a memory configured to store thermofluid property data and computer-executable programs including a B-spline method, and a processor for performing the computer-implemented method. The processor is configured to take as input two thermofluid property variables, and compute a coordinate transformation in which one axis of the coordinates is aligned with the liquid and vapor saturation curves. In the saturation-curve aligned coordinates, a spline function represents the thermofluid property function, with coefficients and knots stored in memory. The spline function is constructed in a manner such that derivatives of the thermofluid property function may be discontinuous across the saturation curve.

A heat exchanger includes: a gas-refrigerant pipe; a header connected to the gas-refrigerant pipe; and heat transfer tubes connected to the header. The header includes: a first plate member; and a second plate member that is stacked on the first plate member in a plate-thickness direction. The first plate member includes a first opening that constitutes an internal space of the header. The second plate member includes a second opening that, together with the first opening, constitutes the internal space of the header. The internal space of the header communicates with the heat transfer tubes. A first direction is perpendicular to both the plate-thickness direction and a direction in which the heat transfer tubes are arranged. A width of a part of the first opening in the first direction is different from a width of the second opening in the first direction.

The disclosed technology includes systems and methods for controlling an air conditioning system. The method of controlling the air conditioning system can include receiving air temperature data from an air temperature sensor and determining that the air conditioning system should operate in a reheat mode based on the air temperature being less than a threshold air temperature. The method can include outputting a control signal to a first electronic expansion valve to close and thereby prevent refrigerant to flow through an outdoor condenser coil. The method can also include outputting a control signal to a second electronic expansion valve to open and thereby permit refrigerant to flow through a reheat coil.