Embodiments relate generally to subcooling control of a heating, ventilation, and air conditioning (HVAC) system. An HVAC system may include a first electronic expansion valve (EEV) fluidly coupled to an indoor coil, wherein the first EEV is adjacent to the indoor coil. The HVAC system may also include a second EEV fluidly coupled to an outdoor coil, wherein the second EEV is adjacent to the outdoor coil. A system controller may be configured to control the first and second EEVs to control a flow of refrigerant to control subcooling (SC) produced by the HVAC system. The second EEV remains open during a cooling mode, and the first EEV modulates during the cooling mode. The second EEV modulates during a heating mode, and the first EEV remains open during the heating mode.

A refrigeration system includes at least one refrigeration circuit 2. The refrigeration circuit 2 includes a compressor 10, a first heat rejecting heat exchanger 6, a second heat rejecting heat exchanger 8, an expansion valve 12 and a heat absorbing heat exchanger 4. The refrigeration circuit 2 further includes a heat recovery control valve 14 for controlling flow of the compressed refrigerant fluid between the first heat rejecting heat exchanger and the second heat rejecting heat exchanger. The first heat rejecting heat exchanger 6 is for receiving compressed refrigerant fluid from the compressor 10 and exchanging heat between the compressed refrigerant fluid and a second fluid to increase the temperature of the second fluid, for example for heat recovery by heating water. The second heat rejecting heat exchanger 8 is for receiving the compressed refrigerant fluid and exchanging heat with ambient air to cool the compressed refrigerant fluid.

A dual reclaim coil with a smart control application is provided that allows the refrigerant inlet to the HVAC unit switch between the two sides of the condenser for heat reclaim for refrigerants such as CO.sub.2 which have a relatively low critical temperature compared to hydrofluorocarbon refrigerants. Heat reclaim after the exit of gas from the condenser utilizes the high temperature and pressure of the condenser/gas cooler outlet while a CO.sub.2 refrigerant system is operating above critical point. This occurs in hot ambient conditions, when the need for heating in the space is not as great as in the wintertime and the available heat at the condenser/gas cooler's outlet is sufficient to satisfy the heating load. When the CO.sub.2 refrigerant system is operating below the critical point, heat reclaim is carried out at the compressor discharge.

A heat exchange system including a first heat exchanger and a second heat exchanger arranged in parallel with the first heat exchanger with respect to flow of refrigerant through the heat exchange system. A flow control assembly is at an outlet of the first heat exchanger. The flow control assembly is configured to allow refrigerant to flow out of the first heat exchanger through the flow control assembly, and restrict refrigerant that has passed through the second heat exchanger from flowing through the flow control assembly and into the first heat exchanger.

An air-conditioning apparatus includes a refrigerant circuit including first and second load-side heat exchangers, a first flow switching unit located upstream of the second load-side heat exchanger, and a second flow switching unit located downstream of the second load-side heat exchanger, wherein the first flow switching unit is configured to be switched between a first state in which refrigerant communication between a compressor and the second load-side heat exchanger is blocked and a second state in which the compressor is in refrigerant communication with the first and second load-side heat exchangers, and the second flow switching unit is configured to be switched between a third state in which refrigerant communication between the second load-side heat exchanger and a heat-source-side heat exchanger is blocked and a fourth state in which the first load-side heat exchanger is in refrigerant communication with the second load-side heat exchanger and the heat-source-side heat exchanger.

In one embodiment, an HVAC system includes an indoor unit having an indoor blower, an outdoor unit having a compressor and a condenser, an isolation valve coupled to the outdoor unit, and a sensor to detect a refrigerant leak. The HVAC system further includes one or more controllers operable to generate an alarm in response to the sensor detecting the refrigerant leak, operate the indoor blower in response to generating the alarm, close the isolation valve in response to generating the alarm, and operate the compressor to pump down the refrigerant to the condenser in response to generating the alarm.

A refrigeration system includes a gas cooler/condenser configured to remove heat from a refrigerant, a temperature sensor configured to measure a temperature of the refrigerant leaving the gas cooler/condenser, a pressure sensor located along the high pressure conduit and configured to measure a pressure of the refrigerant leaving the gas cooler/condenser, a pressure control valve operable to regulate the pressure of the refrigerant leaving the gas cooler/condenser, and a controller. The controller is configured to determine whether the refrigerant leaving the gas cooler/condenser is in a subcritical region based on at least one of the measured temperature of the refrigerant or the measured pressure of the refrigerant. If the refrigerant leaving the gas cooler/condenser is not in the subcritical region, the controller is configured to add a pseudo-subcooling temperature value to the measured temperature of the refrigerant to calculate a summed temperature, calculate a supercritical pseudo-saturated pressure as a function of the summed temperature, and operate the pressure control valve to drive the pressure of the refrigerant leaving the gas cooler/condenser to the supercritical pseudo-saturated pressure corresponding to the summed temperature.

In one embodiment, an HVAC system includes an indoor unit having an indoor blower, an outdoor unit having a compressor and a condenser, an isolation valve coupled to the outdoor unit, and a sensor to detect a refrigerant leak. The HVAC system further includes one or more controllers operable to generate an alarm in response to the sensor detecting the refrigerant leak, operate the indoor blower in response to generating the alarm, close the isolation valve in response to generating the alarm, and operate the compressor to pump down the refrigerant to the condenser in response to generating the alarm.

A refrigeration system includes a gas cooler/condenser configured to remove heat from a refrigerant, a temperature sensor configured to measure a temperature of the refrigerant leaving the gas cooler/condenser, a pressure sensor located along the high pressure conduit and configured to measure a pressure of the refrigerant leaving the gas cooler/condenser, a pressure control valve operable to regulate the pressure of the refrigerant leaving the gas cooler/condenser, and a controller. The controller is configured to determine whether the refrigerant leaving the gas cooler/condenser is in a subcritical region based on at least one of the measured temperature of the refrigerant or the measured pressure of the refrigerant. If the refrigerant leaving the gas cooler/condenser is not in the subcritical region, the controller is configured to add a pseudo-subcooling temperature value to the measured temperature of the refrigerant to calculate a summed temperature, calculate a supercritical pseudo-saturated pressure as a function of the summed temperature, and operate the pressure control valve to drive the pressure of the refrigerant leaving the gas cooler/condenser to the supercritical pseudo-saturated pressure corresponding to the summed temperature.

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.