Patent Description:
Refrigeration systems are often used to provide cooling to temperature controlled display devices (e.g. cases, merchandisers, etc.) in supermarkets and other similar facilities. Vapor compression refrigeration systems are a type of refrigeration system which provides such cooling by circulating a fluid refrigerant (e.g., a liquid and/or vapor) through a thermodynamic vapor compression cycle. In a vapor compression cycle, the refrigerant is typically compressed to a high temperature high pressure state (e.g., by a compressor of the refrigeration system), cooled/condensed to a lower temperature state (e.g., in a gas cooler or condenser which absorbs heat from the refrigerant), expanded to a lower pressure (e.g., through an expansion valve), and evaporated to provide cooling by absorbing heat into the refrigerant. CO<NUM> refrigeration systems are a type of vapor compression refrigeration system that use CO<NUM> as a refrigerant.

CO<NUM> refrigeration system components such as parallel compressors and gas coolers are often selected based on design conditions which takes into account the warmest projected climate to which those components are expected to be subject. While it is important to ensure the system and its components will be able to run in these peak extreme conditions, it can be difficult to predict how these components should be optimally controlled under non-design conditions. The components of the CO<NUM> refrigeration system may be subject to non-design conditions for over <NUM>% of its operation time.

No control information is typically provided for non-design conditions. Instead, a set of generic default setpoints are typically used at the commissioning of the equipment. So long as the system appears to operate successfully under the startup conditions, the setpoint is rarely changed. If the system does not appear to operate successfully, a setpoint either directly or indirectly related may be changed, whether or not it is the correct modification. All changes to setpoints typically require a person to manually observe live or logged historical system performance data and then determine how the setpoints should be adjusted.

<CIT> discloses a method for controlling a vapour compression system comprising an ejector. In the case that a pressure difference between a pressure prevailing in the receiver and a pressure of refrigerant leaving the evaporator decreases below a first lower threshold value, the pressure of refrigerant leaving the heat rejecting heat exchanger is kept at a level which is slightly higher than the pressure level.

<CIT> discloses a method of controlling a condenser fan of a heating, ventilating, and air-conditioning (HVAC) system based on a comparison of a refrigerant flow rate to maintain a valve position of an expansion valve. In the method, a controller modulates the condenser fan to maintain the valve position of the expansion valve at a valve position setpoint when the refrigerant flow rate is higher than the critical flow rate.

<CIT> discloses systems and methods for controlling pressure in a CO<NUM> refrigeration system. The pressure control system includes a pressure sensor, a gas bypass valve, a parallel compressor, and a controller.

This section is intended to provide a background or context to the invention recited in the claims. Therefore, unless otherwise indicated herein, what is described in this section is not prior art and is not admitted to be prior art by inclusion in this section.

According to the invention there is provided a refrigeration system including a gas cooler/condenser, a fan, and a controller. The gas cooler/condenser is configured to remove heat from a refrigerant flowing through the gas cooler/condenser and comprising an outlet through which the refrigerant exits the gas cooler/condenser. The fan is operable to cause airflow across the gas cooler/condenser and configured to operate at multiple different fan speeds to modulate an amount of heat removed the refrigerant flowing through the gas cooler/condenser. The controller is configured to calculate a condenser approach temperature by subtracting the temperature of the airflow caused by the fan from the temperature of the refrigerant exiting the gas cooler/condenser, operate the fan to modulate the amount of heat removed from the refrigerant flowing through the gas cooler/condenser to maintain the condenser approach temperature at or below a condenser approach setpoint, and automatically adjust the condenser approach setpoint in response to the amount of heat removed from the refrigerant being insufficient to maintain the condenser approach temperature at or below the condenser approach setpoint.

Automatically adjusting the condenser approach setpoint includes performing an approach setpoint adjustment process. The approach setpoint adjustment process may include starting a condenser approach subroutine timer, monitoring the condenser approach temperature and a fan speed of the fan after starting the condenser approach subroutine timer, automatically increasing the condenser approach setpoint to an adjusted condenser approach setpoint in response to the condenser approach temperature and the fan speed failing to maintain predetermined conditions for at least a minimum amount of time before the condenser approach subroutine timer expires, and repeating the starting, monitoring, and automatically increasing steps until the condenser approach temperature and the fan speed maintain the predetermined conditions for at least the minimum amount of time before the condenser approach subroutine timer expires.

In some embodiments, the predetermined conditions include at least one of the condenser approach temperature being less than the condenser approach setpoint, the fan speed being less than a fan speed setpoint, and the fan speed being between a low deadband value and a high deadband value.

In some embodiments, the approach setpoint adjustment process includes writing the adjusted condenser approach setpoint as an optimum condenser approach setpoint in response to the condenser approach temperature and the fan speed maintaining the predetermined conditions for at least the minimum amount of time.

In some embodiments, the approach setpoint adjustment process further includes determining whether the adjusted condenser approach setpoint exceeds a maximum approach setpoint after automatically increasing the condenser approach setpoint to the adjusted condenser approach setpoint and restarting the condenser approach subroutine timer in response to the adjusted condenser approach setpoint not exceeding the maximum approach setpoint.

In some embodiments, the approach setpoint adjustment process further includes terminating the approach setpoint adjustment process in response to the condenser approach subroutine timer in response to the adjusted condenser approach setpoint exceeding the maximum approach setpoint.

In some embodiments, the controller is configured to determine whether the gas cooler/condenser is operating in a subcritical mode and execute the approach setpoint adjustment process in response to determining that the gas cooler/condenser is operating in the subcritical mode.

In some embodiments, the controller is configured to obtain a measurement of an ambient air temperature that occurs while automatically adjusting the condenser approach setpoint and store an association between the condenser approach setpoint that results from automatically adjusting the condenser approach setpoint and the measured ambient air temperature.

In some embodiments, the controller is configured to, in response to a current ambient air temperature matching the measured ambient air temperature associated with the condenser approach setpoint, start a condenser approach verification subroutine timer, monitor the condenser approach temperature and a fan speed of the fan, and verify that the condenser approach temperature and the fan speed maintain predetermined conditions for at least a minimum amount of time before the condenser approach verification subroutine timer expires.

The foregoing is a summary and thus by necessity contains simplifications, generalizations, and omissions of detail. Consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the invention, which is defined solely by the claims, will become apparent in the detailed description set forth herein and taken in conjunction with the accompanying drawings.

Referring generally to the FIGURES, a CO<NUM> refrigeration system is shown, according to various exemplary embodiments. The CO<NUM> refrigeration system may be a vapor compression refrigeration system which uses primarily carbon dioxide (i.e., CO<NUM>) as a refrigerant. In some implementations, the CO<NUM> refrigeration system is used to provide cooling for temperature controlled display devices in a supermarket or other similar facility.

Referring now to <FIG>, a CO<NUM> refrigeration system <NUM> is shown, according to an exemplary embodiment. CO<NUM> refrigeration system <NUM> may be a vapor compression refrigeration system which uses primarily carbon dioxide (CO<NUM>) as a refrigerant. However, it is contemplated that other refrigerants can be substituted for CO<NUM> without departing from the teachings of the present disclosure. CO<NUM> refrigeration system <NUM> and is shown to include a system of pipes, conduits, or other fluid channels (e.g., fluid conduits <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>) for transporting the CO<NUM> refrigerant between various components of CO<NUM> refrigeration system <NUM>. The components of CO<NUM> refrigeration system <NUM> are shown to include a gas cooler/condenser <NUM>, a high pressure valve <NUM>, a receiver <NUM>, a gas bypass valve <NUM>, a medium-temperature ("MT") subsystem <NUM>, and a low-temperature ("LT") subsystem <NUM>.

Gas cooler/condenser <NUM> is a heat exchanger or other similar device for removing heat from the CO<NUM> refrigerant. Gas cooler/condenser <NUM> is shown receiving CO<NUM> gas from fluid conduit <NUM>. In some embodiments, the CO<NUM> gas in fluid conduit <NUM> may have a pressure within a range from approximately <NUM> bar to approximately <NUM> bar (i.e., about <NUM> psig to about <NUM> psig), depending on ambient temperature and other operating conditions. In some embodiments, gas cooler/condenser <NUM> may partially or fully condense CO<NUM> gas into liquid CO<NUM> (e.g., if system operation is in a subcritical region). The condensation process may result in fully saturated CO<NUM> liquid or a two-phase liquid-vapor mixture (e.g., having a thermodynamic vapor quality between <NUM> and <NUM>). In other embodiments, gas cooler/condenser <NUM> may cool the CO<NUM> gas (e.g., by removing superheat) without condensing the CO<NUM> gas into CO<NUM> liquid (e.g., if system operation is in a supercritical region). In some embodiments, the cooling/condensation process is an isobaric process. Gas cooler/condenser <NUM> is shown outputting the cooled and/or condensed CO<NUM> refrigerant into fluid conduit <NUM>.

In some embodiments, CO<NUM> refrigeration system <NUM> includes a temperature sensor <NUM> and a pressure sensor <NUM> configured to measure the temperature and pressure of the CO<NUM> refrigerant exiting gas cooler/condenser <NUM>. Sensors <NUM> and <NUM> can be installed along fluid conduit <NUM> (as shown in <FIG>), within gas cooler/condenser <NUM>, or otherwise positioned to measure the temperature and pressure of the CO<NUM> refrigerant exiting gas cooler/condenser <NUM>. The CO<NUM> refrigeration system <NUM> includes a condenser fan <NUM> configured to provide airflow across gas cooler/condenser <NUM>. The speed of condenser fan <NUM> can be controlled to increase or decrease the airflow across gas cooler/condenser <NUM> to modulate the amount of cooling applied to the CO<NUM> refrigerant within gas cooler/condenser <NUM>. In some embodiments, CO<NUM> refrigeration system <NUM> also includes a temperature sensor <NUM> and a pressure sensor <NUM> configured to measure the temperature and pressure of the ambient air that flows across gas cooler/condenser <NUM> to provide cooling for the CO<NUM> refrigerant contained therein.

High pressure valve <NUM> receives the cooled and/or condensed CO<NUM> refrigerant from fluid conduit <NUM> and outputs the CO<NUM> refrigerant to fluid conduit <NUM>. High pressure valve <NUM> may control the pressure of the CO<NUM> refrigerant in gas cooler/condenser <NUM> by controlling an amount of CO<NUM> refrigerant permitted to pass through high pressure valve <NUM>. In some embodiments, high pressure valve <NUM> is a high pressure thermal expansion valve (e.g., if the pressure in fluid conduit <NUM> is greater than the pressure in fluid conduit <NUM>). In such embodiments, high pressure valve <NUM> may allow the CO<NUM> refrigerant to expand to a lower pressure state. The expansion process may be an isenthalpic and/or adiabatic expansion process, resulting in a two-phase flash of the high pressure CO<NUM> refrigerant to a lower pressure, lower temperature state. The expansion process may produce a liquid/vapor mixture (e.g., having a thermodynamic vapor quality between <NUM> and <NUM>). In some embodiments, the CO<NUM> refrigerant expands to a pressure of approximately <NUM> bar (e.g., about <NUM> psig), which corresponds to a temperature of approximately <NUM>° F (<NUM>,<NUM>). The CO<NUM> refrigerant then flows from fluid conduit <NUM> into receiver <NUM>.

Receiver <NUM> collects the CO<NUM> refrigerant from fluid conduit <NUM>. In some embodiments, receiver <NUM> may be a flash tank or other fluid reservoir. Receiver <NUM> includes a CO<NUM> liquid portion <NUM> and a CO<NUM> vapor portion <NUM> and may contain a partially saturated mixture of CO<NUM> liquid and CO<NUM> vapor. In some embodiments, receiver <NUM> separates the CO<NUM> liquid from the CO<NUM> vapor. The CO<NUM> liquid may exit receiver <NUM> through fluid conduits <NUM>. Fluid conduits <NUM> may be liquid headers leading to MT subsystem <NUM> and/or LT subsystem <NUM>. The CO<NUM> vapor may exit receiver <NUM> through fluid conduit <NUM> (i.e., a refrigerant supply line). Fluid conduit <NUM> is shown leading the CO<NUM> vapor to a gas bypass valve <NUM> and a parallel compressor <NUM> (described in greater detail below). In some embodiments, CO<NUM> refrigeration system <NUM> includes a temperature sensor <NUM> and a pressure sensor <NUM> configured to measure the temperature and pressure within receiver <NUM>. Sensors <NUM> and <NUM> can be installed in or on receiver <NUM> (as shown in <FIG>) or along any of the fluid conduits that contain CO<NUM> refrigerant at the same temperature and/or pressure as receiver <NUM> (i.e., fluid conduits <NUM>, <NUM>, <NUM>, or <NUM>).

Still referring to <FIG>, MT subsystem <NUM> is shown to include one or more expansion valves <NUM>, one or more MT evaporators <NUM>, and one or more MT compressors <NUM>. In various embodiments, any number of expansion valves <NUM>, MT evaporators <NUM>, and MT compressors <NUM> may be present. Expansion valves <NUM> may be electronic expansion valves or other similar expansion valves. Expansion valves <NUM> are shown receiving liquid CO<NUM> refrigerant from fluid conduit <NUM> and outputting the CO<NUM> refrigerant to MT evaporators <NUM>. Expansion valves <NUM> may cause the CO<NUM> refrigerant to undergo a rapid drop in pressure, thereby expanding the CO<NUM> refrigerant to a lower pressure, lower temperature two-phase state. In some embodiments, expansion valves <NUM> may expand the CO<NUM> refrigerant to a pressure of approximately <NUM> bar to <NUM> bar. The expansion process may be an isenthalpic and/or adiabatic expansion process.

MT evaporators <NUM> are shown receiving the cooled and expanded CO<NUM> refrigerant from expansion valves <NUM>. In some embodiments, MT evaporators may be associated with display cases/devices (e.g., if CO<NUM> refrigeration system <NUM> is implemented in a supermarket setting). MT evaporators <NUM> may be configured to facilitate the transfer of heat from the display cases/devices into the CO<NUM> refrigerant. The added heat may cause the CO<NUM> refrigerant to evaporate partially or completely. According to one embodiment, the CO<NUM> refrigerant is fully evaporated in MT evaporators <NUM>. In some embodiments, the evaporation process may be an isobaric process. MT evaporators <NUM> are shown outputting the CO<NUM> refrigerant via suction line <NUM>, leading to MT compressors <NUM>.

MT compressors <NUM> compress the CO<NUM> refrigerant into a superheated gas having a pressure within a range of approximately <NUM> bar to approximately <NUM> bar. The output pressure from MT compressors <NUM> may vary depending on ambient temperature and other operating conditions. In some embodiments, MT compressors <NUM> operate in a transcritical mode. In operation, the CO<NUM> discharge gas exits MT compressors <NUM> and flows through fluid conduit <NUM> into gas cooler/condenser <NUM>.

Still referring to <FIG>, LT subsystem <NUM> is shown to include one or more expansion valves <NUM>, one or more LT evaporators <NUM>, and one or more LT compressors <NUM>. In various embodiments, any number of expansion valves <NUM>, LT evaporators <NUM>, and LT compressors <NUM> may be present. In some embodiments, LT subsystem <NUM> may be omitted and the CO<NUM> refrigeration system <NUM> may operate with an AC module or parallel compressor <NUM> interfacing with only MT subsystem <NUM>.

Expansion valves <NUM> may be electronic expansion valves or other similar expansion valves. Expansion valves <NUM> are shown receiving liquid CO<NUM> refrigerant from fluid conduit <NUM> and outputting the CO<NUM> refrigerant to LT evaporators <NUM>. Expansion valves <NUM> may cause the CO<NUM> refrigerant to undergo a rapid drop in pressure, thereby expanding the CO<NUM> refrigerant to a lower pressure, lower temperature two-phase state. The expansion process may be an isenthalpic and/or adiabatic expansion process. In some embodiments, expansion valves <NUM> may expand the CO<NUM> refrigerant to a lower pressure than expansion valves <NUM>, thereby resulting in a lower temperature CO<NUM> refrigerant. Accordingly, LT subsystem <NUM> may be used in conjunction with a freezer system or other lower temperature display cases.

LT evaporators <NUM> are shown receiving the cooled and expanded CO<NUM> refrigerant from expansion valves <NUM>. In some embodiments, LT evaporators may be associated with display cases/devices (e.g., if CO<NUM> refrigeration system <NUM> is implemented in a supermarket setting). LT evaporators <NUM> may be configured to facilitate the transfer of heat from the display cases/devices into the CO<NUM> refrigerant. The added heat may cause the CO<NUM> refrigerant to evaporate partially or completely. In some embodiments, the evaporation process may be an isobaric process. LT evaporators <NUM> are shown outputting the CO<NUM> refrigerant via suction line <NUM>, leading to LT compressors <NUM>.

LT compressors <NUM> compress the CO<NUM> refrigerant. In some embodiments, LT compressors <NUM> may compress the CO<NUM> refrigerant to a pressure of approximately <NUM> bar (e.g., about <NUM> psig) having a saturation temperature of approximately <NUM>°F. In some embodiments, LT compressors <NUM> operate in a subcritical mode. LT compressors <NUM> are shown outputting the CO<NUM> refrigerant through discharge line <NUM>. Discharge line <NUM> may be fluidly connected with the suction (e.g., upstream) side of MT compressors <NUM>.

Still referring to <FIG>, CO<NUM> refrigeration system <NUM> is shown to include a gas bypass valve <NUM>. Gas bypass valve <NUM> may receive the CO<NUM> vapor from fluid conduit <NUM> and output the CO<NUM> refrigerant to MT subsystem <NUM>. In some embodiments, gas bypass valve <NUM> is arranged in series with MT compressors <NUM>. In other words, CO<NUM> vapor from receiver <NUM> may pass through both gas bypass valve <NUM> and MT compressors <NUM>. MT compressors <NUM> may compress the CO<NUM> vapor passing through gas bypass valve <NUM> from a low pressure state (e.g., approximately <NUM> bar or lower) to a high pressure state (e.g., <NUM>-<NUM> bar).

Gas bypass valve <NUM> may be positioned along fluid conduit <NUM> (i.e., a refrigerant supply line) or fluidly coupled to fluid conduit <NUM> such that gas bypass valve <NUM> is arranged in series with MT compressors <NUM> (upstream of MT compressors <NUM>). Gas bypass valve <NUM> can be operated to control a flow of gas refrigerant from fluid conduit <NUM> into suction line <NUM>. Gas bypass valve <NUM> may be operated to regulate or control the pressure within receiver <NUM> (e.g., by adjusting an amount of CO<NUM> refrigerant permitted to pass through gas bypass valve <NUM>). For example, gas bypass valve <NUM> may be adjusted (e.g., variably opened or closed) to adjust the mass flow rate, volume flow rate, or other flow rates of the CO<NUM> refrigerant through gas bypass valve <NUM>. Gas bypass valve <NUM> may be opened and closed (e.g., manually, automatically, by a controller, etc.) as needed to regulate the pressure within receiver <NUM>.

In some embodiments, gas bypass valve <NUM> includes a sensor for measuring a flow rate (e.g., mass flow, volume flow, etc.) of the CO<NUM> refrigerant through gas bypass valve <NUM>. In other embodiments, gas bypass valve <NUM> includes an indicator (e.g., a gauge, a dial, etc.) from which the position of gas bypass valve <NUM> may be determined. This position may be used to determine the flow rate of CO<NUM> refrigerant through gas bypass valve <NUM>, as such quantities may be proportional or otherwise related.

In some embodiments, gas bypass valve <NUM> may be a thermal expansion valve (e.g., if the pressure on the downstream side of gas bypass valve <NUM> is lower than the pressure in fluid conduit <NUM>). According to one embodiment, the pressure within receiver <NUM> is regulated by gas bypass valve <NUM> to a pressure of approximately <NUM> bar, which corresponds to about <NUM>°F. Advantageously, this pressure/temperature state may facilitate the use of copper tubing/piping for the downstream CO<NUM> lines of the system. Additionally, this pressure/temperature state may allow such copper tubing to operate in a substantially frost-free manner.

In some embodiments, the CO<NUM> vapor that is bypassed through gas bypass valve <NUM> is mixed with the CO<NUM> refrigerant gas exiting MT evaporators <NUM> (e.g., via suction line <NUM>). The bypassed CO<NUM> vapor may also mix with the discharge CO<NUM> refrigerant gas exiting LT compressors <NUM> (e.g., via discharge line <NUM>). The combined CO2 refrigerant gas may be provided to the suction side of MT compressors <NUM>.

In some embodiments, the pressure immediately downstream of gas bypass valve <NUM> (i.e., in suction line <NUM>) is lower than the pressure immediately upstream of gas bypass valve <NUM> (i.e., in fluid conduit <NUM>). Therefore, the CO<NUM> vapor passing through gas bypass valve <NUM> and MT compressors <NUM> may be expanded (e.g., when passing through gas bypass valve <NUM>) and subsequently recompressed (e.g., by MT compressors <NUM>). This expansion and recompression may occur without any intermediate transfers of heat to or from the CO<NUM> refrigerant, which can be characterized as an inefficient energy usage.

Still referring to <FIG>, CO<NUM> refrigeration system <NUM> is shown to include a parallel compressor <NUM>. Parallel compressor <NUM> may be arranged in parallel with MT compressors <NUM> and arranged in series with LT compressors <NUM>. Although only one parallel compressor <NUM> is shown, any number of parallel compressors may be present. Parallel compressor <NUM> may be fluidly connected with receiver <NUM> and/or fluid conduit <NUM> via a connecting line <NUM>. Parallel compressor <NUM> may be used to draw non-condensed CO<NUM> vapor from receiver <NUM> as a means for pressure control and regulation. Advantageously, using parallel compressor <NUM> to effectuate pressure control and regulation may provide a more efficient alternative to traditional pressure regulation techniques such as bypassing CO<NUM> vapor through bypass valve <NUM> to the lower pressure suction side of MT compressors <NUM>.

In some embodiments, parallel compressor <NUM> may be operated (e.g., by a controller <NUM>) to achieve a desired pressure within receiver <NUM>. For example, controller <NUM> may receive pressure measurements from a pressure sensor <NUM> monitoring the pressure within receiver <NUM> and may activate or deactivate parallel compressor <NUM> based on the pressure measurements. When active, parallel compressor <NUM> compresses the CO<NUM> vapor received via connecting line <NUM> and discharges the compressed gas into discharge line <NUM>. Discharge line <NUM> may be fluidly connected with fluid conduit <NUM>. Accordingly, parallel compressor <NUM> may operate in parallel with MT compressors <NUM> by discharging the compressed CO<NUM> gas into a shared fluid conduit (e.g., fluid conduit <NUM>).

Parallel compressor <NUM> may be arranged in parallel with both gas bypass valve <NUM> and with MT compressors <NUM>. CO<NUM> vapor exiting receiver <NUM> may pass through either parallel compressor <NUM> or the series combination of gas bypass valve <NUM> and MT compressors <NUM>. Parallel compressor <NUM> may receive the CO<NUM> vapor at a relatively higher pressure (e.g., from fluid conduit <NUM>) than the CO<NUM> vapor received by MT compressors <NUM> (e.g., from suction line <NUM>). This differential in pressure may correspond to the pressure differential across gas bypass valve <NUM>. In some embodiments, parallel compressor <NUM> may require less energy to compress an equivalent amount of CO<NUM> vapor to the high pressure state (e.g., in fluid conduit <NUM>) as a result of the higher pressure of CO<NUM> vapor entering parallel compressor <NUM>. Therefore, the parallel route including parallel compressor <NUM> may be a more efficient alternative to the route including gas bypass valve <NUM> and MT compressors <NUM>.

In some embodiments, gas bypass valve <NUM> is omitted and the pressure within receiver <NUM> is regulated using parallel compressor <NUM>. In other embodiments, parallel compressor <NUM> is omitted and the pressure within receiver <NUM> is regulated using gas bypass valve <NUM>. In other embodiments, both gas bypass valve <NUM> and parallel compressor <NUM> are used to regulate the pressure within receiver <NUM>. All such variations are within the scope of the present invention.

Referring now to <FIG>, a block diagram illustrating controller <NUM> in greater detail is shown. Controller <NUM> receives signals from one or more measurement devices (e.g., pressure sensors, temperature sensors, flow sensors, etc.) located within CO<NUM> refrigeration system <NUM>. For example, controller <NUM> is shown receiving temperature and pressure measurements from sensors <NUM>-<NUM> and <NUM>-<NUM>, a valve position signal from gas bypass valve <NUM>, and a fan speed signal from condenser fan <NUM>. Controller <NUM> may use the input signals to determine appropriate control actions for controllable devices of CO<NUM> refrigeration system <NUM> (e.g., compressors <NUM> and <NUM>, parallel compressor <NUM>, condenser fan <NUM>, valves <NUM>, <NUM>, <NUM>, and <NUM>, flow diverters, power supplies, etc.). For example, controller <NUM> is shown providing control signals to parallel compressor <NUM>, gas bypass valve <NUM>, and condenser fan <NUM>.

In some embodiments, controller <NUM> is configured to operate gas bypass valve <NUM> and/or parallel compressor <NUM> to maintain the CO<NUM> pressure within receiving tank <NUM> at a desired setpoint or within a desired range. In some embodiments, controller <NUM> operates gas bypass valve <NUM> and parallel compressor <NUM> based on the temperature of the CO<NUM> refrigerant at the outlet of gas cooler/condenser <NUM>. In other embodiments, controller <NUM> operates gas bypass valve <NUM> and parallel compressor <NUM> based a flow rate (e.g., mass flow, volume flow, etc.) of CO<NUM> refrigerant through gas bypass valve <NUM>. Controller <NUM> may use a valve position of gas bypass valve <NUM> as a proxy for CO<NUM> refrigerant flow rate. In some embodiments, controller <NUM> operates high pressure valve <NUM> and expansion valves <NUM> and <NUM> to regulate the flow of refrigerant in system <NUM>.

Controller <NUM> may include feedback control functionality for adaptively operating the various components of CO<NUM> refrigeration system <NUM>. For example, controller <NUM> may receive a setpoint (e.g., a temperature setpoint, a pressure setpoint, a flow rate setpoint, a power usage setpoint, etc.) and operate one or more components of system <NUM> to achieve the setpoint. The setpoint may be specified by a user (e.g., via a user input device, a graphical user interface, a local interface, a remote interface, etc.) or automatically determined by controller <NUM> based on a history of data measurements. In some embodiments, controller <NUM> includes some or all of the features of the controller described in PCT Patent Application No. <CIT>, published as <CIT>.

Controller <NUM> may be a proportional-integral (PI) controller, a proportional-integral-derivative (PID) controller, a pattern recognition adaptive controller (PRAC), a model recognition adaptive controller (MRAC), a model predictive controller (MPC), or any other type of controller employing any type of control functionality. In some embodiments, controller <NUM> is a local controller for CO<NUM> refrigeration system <NUM>. In other embodiments, controller <NUM> is a supervisory controller for a plurality of controlled subsystems (e.g., a refrigeration system, an AC system, a lighting system, a security system, etc.). For example, controller <NUM> may be a controller for a comprehensive building management system incorporating CO<NUM> refrigeration system <NUM>. Controller <NUM> may be implemented locally, remotely, or as part of a cloud-hosted suite of building management applications.

Still referring to <FIG>, controller <NUM> is shown to include a communications interface <NUM> and a processing circuit <NUM>. Communications interface <NUM> can be or include wired or wireless interfaces (e.g., jacks, antennas, transmitters, receivers, transceivers, wire terminals, etc.) for conducting electronic data communications. For example, communications interface <NUM> may be used to conduct communications with gas bypass valve <NUM>, parallel compressor <NUM>, compressors <NUM> and <NUM>, high pressure valve <NUM>, various data acquisition devices within CO<NUM> refrigeration system <NUM> (e.g., temperature sensors, pressure sensors, flow sensors, etc.) and/or other external devices or data sources. Data communications may be conducted via a direct connection (e.g., a wired connection, an ad-hoc wireless connection, etc.) or a network connection (e.g., an Internet connection, a LAN, WAN, or WLAN connection, etc.). For example, communications interface <NUM> can include an Ethernet card and port for sending and receiving data via an Ethernet-based communications link or network. In another example, communications interface <NUM> can include a Wi-Fi transceiver or a cellular or mobile phone transceiver for communicating via a wireless communications network.

Processing circuit <NUM> is shown to include a processor <NUM> and memory <NUM>. Processor <NUM> can be implemented as a general purpose processor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a group of processing components, a microcontroller, or other suitable electronic processing components. Memory <NUM> (e.g., memory device, memory unit, storage device, etc.) may be one or more devices (e.g., RAM, ROM, solid state memory, hard disk storage, etc.) for storing data and/or computer code for completing or facilitating the various processes, layers and modules described in the present application. Memory <NUM> may be or include volatile memory or non-volatile memory. Memory <NUM> may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described in the present application. According to an exemplary embodiment, memory <NUM> is communicably connected to processor <NUM> via processing circuit <NUM> and includes computer code for executing (e.g., by processing circuit <NUM> and/or processor <NUM>) one or more processes or control features described herein.

Still referring to <FIG>, controller <NUM> is shown to include a pressure controller <NUM>. Pressure controller <NUM> can be configured to control the pressure within receiver <NUM> by operating gas bypass valve <NUM> and/or parallel compressor <NUM>. Pressure controller <NUM> may use parallel compressor <NUM> to control the pressure within receiver <NUM> when the amount of CO<NUM> refrigerant gas being produced by CO<NUM> refrigeration system <NUM> is sufficient to sustain the operation of parallel compressor <NUM>. However, if CO<NUM> refrigeration system <NUM> does not produce enough CO<NUM> refrigerant gas to sustain the operation of parallel compressor <NUM>, pressure controller <NUM> may regulate the pressure within receiver <NUM> by directing the CO<NUM> refrigerant gas through gas bypass valve <NUM> to be compressed by MT compressors <NUM>. If CO<NUM> refrigeration system <NUM> begins producing enough CO<NUM> refrigerant gas to sustain the operation of parallel compressor <NUM>, pressure controller <NUM> may close gas bypass valve <NUM> and activate parallel compressor <NUM>.

Pressure controller <NUM> may determine whether CO<NUM> refrigeration system <NUM> produces enough CO<NUM> refrigerant gas to sustain the operation of parallel compressor <NUM> by comparing a process variable to a switchover setpoint. The process variable may be any variable received as a feedback from CO<NUM> refrigeration system <NUM> including, for example, the pressure of the CO<NUM> refrigerant within receiver <NUM>, the flow rate of the CO<NUM> refrigerant through gas bypass valve <NUM>, or the position of gas bypass valve <NUM>. Once the process variable exceeds the switchover setpoint for a predetermined amount of time, pressure controller <NUM> may close gas bypass valve <NUM> and activate parallel compressor <NUM>. Advantageously, the switchover setpoint may be determined automatically by switchover optimizer <NUM> (described in greater detail with reference to <FIG>). In order to transition back to the use of MT compressors <NUM> to compress the CO<NUM> refrigerant gas from receiver <NUM>, pressure controller <NUM> may compare the pressure within receiver <NUM> to a pressure setpoint. The pressure setpoint may be the same as the switchover setpoint or may be different from the switchover setpoint. Once the pressure of the CO<NUM> refrigerant gas within receiver <NUM> drops below the pressure setpoint, pressure controller <NUM> may deactivate parallel compressor <NUM> and operate gas bypass valve <NUM> to control the pressure within receiver <NUM>.

Still referring to <FIG>, controller <NUM> is shown to include a condenser approach controller <NUM>.

Condenser approach controller <NUM> is configured to operate condenser fan <NUM> to maintain the condenser approach temperature at or below an approach setpoint. The condenser approach temperature is defined as the difference between the temperature of the CO<NUM> refrigerant exiting gas cooler/condenser <NUM> (i.e., the temperature measured by temperature sensor <NUM>) and the temperature of the ambient air used to provide cooling for the CO<NUM> refrigerant in gas cooler/condenser <NUM> (i.e., the airflow controlled by operating condenser fan <NUM>). The temperature of the ambient air may be measured by temperature sensor <NUM>. If the condenser approach temperature is greater than the approach setpoint, condenser approach controller <NUM> increases the speed of condenser fan <NUM> to provide more cooling for the CO<NUM> refrigerant in gas cooler/condenser <NUM>. However, if the approach temperature is less than or equal to the approach setpoint, condenser approach controller <NUM> may maintain condenser fan <NUM> at its current speed. Advantageously, the approach setpoint is determined automatically by condenser approach optimizer <NUM> (described in greater detail with reference to <FIG>).

Referring now to <FIG> and <FIG>, controller <NUM> is shown to include a switchover optimizer <NUM>. Switchover optimizer <NUM> can be configured to determine an optimal value for the switchover setpoint provided to pressure controller <NUM>. In some embodiments, switchover optimizer <NUM> performs process <NUM> (shown in <FIG>) to determine the optimal value for the switchover setpoint.

Process <NUM> begins when the optimization subroutine is executed by a user (step <NUM>) and the user initiates the optimizing control logic (step <NUM>). Switchover optimizer <NUM> may determine whether appropriate temperature and pressure readings (measured by sensors <NUM>-<NUM> and <NUM>-<NUM>) are present for parallel compression to start (step <NUM>). Appropriate temperature and pressure readings should fall within min and max operating values in order for parallel compressor <NUM> to successfully start.

If the temperature and pressure readings do not fall within the min and max operating values (i.e., the result of step <NUM> is "no"), switchover optimizer <NUM> may generate a notification that the optimization cannot execute until temperatures and pressures are within min and max boundaries (step <NUM>). Switchover optimizer <NUM> may then exit the optimization subroutine and signal "Optimization NOT Complete" to the user (step <NUM>). CO<NUM> refrigeration system <NUM> may then resume normal operation. If at any point during process <NUM>, the temperature and pressure readings in the system fall out of the min and max operating values, the optimization subroutine may stop and exit, notifying the user that the system has not completed the optimization routine but the system will operate as normal.

If the temperature and pressure readings fall within the min and max operating values (i.e., the result of step <NUM> is "yes"), switchover optimizer <NUM> may determine whether the process variable (e.g., pressure within receiver <NUM>, position of gas bypass valve <NUM>, refrigerant flow rate through gas bypass valve <NUM>, etc.) exceeds a switchover setpoint value (step <NUM>). Initially, the switchover setpoint value may be set to a default or initial value, which can be optimized by performing the subsequent steps of process <NUM>. If the process variable does not exceed the switchover setpoint value (i.e., the result of step <NUM> is "no"), switchover optimizer <NUM> may wait until the criterion in step <NUM> is satisfied. However, if the process variable does exceed the switchover setpoint value (i.e., the result of step <NUM> is "yes"), switchover optimizer <NUM> may switch the receiver pressure control from gas bypass valve <NUM> to parallel compressor <NUM> (step <NUM>). Step <NUM> may include closing gas bypass valve <NUM> and activating parallel compressor <NUM>. Upon activating parallel compressor <NUM>, switchover optimizer <NUM> may start a parallel compressor run delay timer (step <NUM>) and determine whether a shutdown of parallel compressor <NUM> occurs before the run delay timer expires (step <NUM>). A shutdown of parallel compressor <NUM> may occur when the amount of CO<NUM> refrigerant gas being produced by CO<NUM> refrigeration system <NUM> is insufficient to sustain the operation of parallel compressor <NUM>. For example, pressure controller <NUM> may shutdown parallel compressor <NUM> when the pressure within receiver <NUM> drops below a pressure setpoint.

If the shutdown of parallel compressor <NUM> occurs before the run delay timer expires (i.e., the result of step <NUM> is "yes"), switchover optimizer <NUM> may switch the receiver pressure control from parallel compressor <NUM> to gas bypass valve <NUM> (step <NUM>). Switchover optimizer <NUM> may then modify (increase) the switchover setpoint value (step <NUM>) and process <NUM> may return to step <NUM>. Increasing the switchover setpoint value in step <NUM> will require a greater value of the process variable to trigger a switchover to parallel compressor <NUM> in step <NUM>. Accordingly, it will be less likely that the amount of CO<NUM> refrigerant gas being produced by CO<NUM> refrigeration system <NUM> is insufficient to sustain the operation of parallel compressor <NUM> for at least the duration of the compressor run delay timer next time steps <NUM>-<NUM> are performed. Steps <NUM>-<NUM> can be repeated as many times as necessary to cause parallel compressor <NUM> to remain active for at least the duration of the run delay timer in step <NUM>.

If the shutdown of parallel compressor <NUM> does not occur before the run delay timer expires (i.e., the result of step <NUM> is "no"), switchover optimizer <NUM> may wait until the run delay timer expires (step <NUM>) and write the switchover setpoint value as the optimum switchover setpoint (step <NUM>). Switchover optimizer <NUM> may then exit the optimization subroutine and signal "Optimization Complete" to the user (step <NUM>). CO<NUM> refrigeration system <NUM> may then be ready for optimized operation.

Referring now to <FIG> and <FIG>, controller <NUM> is shown to include a condenser approach optimizer <NUM>. Condenser approach optimizer <NUM> is configured to determine an optimal value for the approach setpoint provided to condenser approach controller <NUM>. In some embodiments, condenser approach optimizer <NUM> performs process <NUM> (shown in <FIG>) to determine the optimal value for the condenser approach setpoint.

Process <NUM> begins when the optimization subroutine is executed by a user (step <NUM>) and the user initiates the optimizing control logic (step <NUM>). Condenser approach optimizer <NUM> may determine whether appropriate temperature and pressure readings (measured by sensors <NUM>-<NUM> and <NUM>-<NUM>) are present for subcritical operation to start (step <NUM>). Appropriate temperature and pressure readings should fall within min and max operating values in order for gas cooler/condenser <NUM> to operate in a subcritical mode.

If the temperature and pressure readings do not fall within the min and max operating values (i.e., the result of step <NUM> is "no"), condenser approach optimizer <NUM> may generate a notification that the optimization cannot execute until temperatures and pressures are within min and max boundaries (step <NUM>). Condenser approach optimizer <NUM> may then exit the optimization subroutine and signal "Optimization NOT Complete" to the user (step <NUM>). CO<NUM> refrigeration system <NUM> may then resume normal operation. If at any point during process <NUM>, the temperature and pressure readings in the system fall out of the min and max operating values, the optimization subroutine may stop and exit, notifying the user that the system has not completed the optimization routine but the system will operate as normal.

If the temperature and pressure readings fall within the min and max operating values (i.e., the result of step <NUM> is "yes"), condenser approach optimizer <NUM> starts a condenser approach subroutine timer (step <NUM>). Condenser approach optimizer <NUM> then checks whether several conditions <NUM>-<NUM> are maintained continuously for at least a minimum amount of time Tmin (step <NUM>). In various embodiments, the minimum amount of time Tmin may be shorter than the duration of the condenser approach subroutine timer or equal to the duration of the condenser approach subroutine timer. Condition <NUM> is satisfied if the measured approach (i.e., the measured difference between the temperature of the CO<NUM> refrigerant exiting gas cooler/condenser <NUM> and the ambient air temperature) is less than an approach setpoint. The temperature of the CO<NUM> refrigerant exiting gas cooler/condenser <NUM> may be measured by temperature sensor <NUM>, whereas the ambient air temperature may be measured by temperature sensor <NUM>. Initially, the approach setpoint has a default or initial value, which can be optimized by performing the subsequent steps of process <NUM>. Condition <NUM> is satisfied if the actual speed of condenser fan <NUM> is less than a fan speed setpoint. The fan speed setpoint may be defined by a user or otherwise provided as an input to process <NUM>. Condition <NUM> is satisfied if the actual speed of condenser fan <NUM> is between a low deadband fan speed value and a high deadband fan speed value.

If any of conditions <NUM>-<NUM> are not continuously maintained (i.e., any of conditions <NUM>-<NUM> become false) before the condenser approach subroutine timer has expired (i.e., the result of step <NUM> is "no"), condenser approach optimizer <NUM> may wait until all of conditions <NUM>-<NUM> are satisfied and repeat step <NUM>. Step <NUM> may be repeated as many times as necessary until either all of conditions <NUM>-<NUM> are maintained for at least the minimum amount of time Tmin or the condenser approach subroutine timer has expired.

If the condenser approach subroutine timer expires (step <NUM>) before all of conditions <NUM>-<NUM> are maintained for at least the minimum amount of time Tmin, condenser approach optimizer <NUM> increases the approach setpoint value (step <NUM>) and check whether the approach setpoint value exceeds a maximum approach setpoint (step <NUM>). If the maximum approach setpoint is exceeded (i.e., the result of step <NUM> is "yes"), condenser approach optimizer <NUM> exits the optimization subroutine and signals "Optimization NOT Complete" to the user (step <NUM>). CO<NUM> refrigeration system <NUM> may then resume normal operation. However, if the maximum approach setpoint is not exceeded (i.e., the result of step <NUM> is "no"), condenser approach optimizer <NUM> returns to step <NUM>. Steps <NUM>-<NUM> may be repeated as many times as necessary until either all of conditions <NUM>-<NUM> are maintained for at least the minimum amount of time Tmin in step <NUM> or the maximum approach setpoint is exceeded in step <NUM>.

If all of conditions <NUM>-<NUM> are continuously maintained (i.e., all of conditions <NUM>-<NUM> remain true) for at least the minimum amount of time Tmin before the condenser approach subroutine timer has expired (i.e., the result of step <NUM> is "yes"), condenser approach optimizer <NUM> may write the condenser approach setpoint value as the optimum condenser approach setpoint (step <NUM>). Condenser approach optimizer <NUM> may then exit the optimization subroutine and signal "Optimization Complete" to the user (step <NUM>). CO<NUM> refrigeration system <NUM> may then be ready for optimized operation.

Referring now to <FIG>, a flowchart of a process <NUM> for monitoring and verifying condenser approach is shown. Process <NUM> may be performed by controller <NUM> after condenser approach optimization process <NUM> is performed to ensure that CO<NUM> refrigeration system <NUM> continues to operate as expected. When process <NUM> has been successfully completed, controller <NUM> may record the optimized approach setpoint and the corresponding values for the fan speed (i.e., the optimized fan speed) and the fan power (i.e., the optimized fan power). Such variables can be stored in memory and used during process <NUM>. Process <NUM> may be performed when CO<NUM> refrigeration system <NUM> is operating normally and continuously (condition <NUM>) and when the ambient temperature matches the ambient temperature recorded when performing condenser approach optimization process <NUM> (condition <NUM>).

When both conditions <NUM>-<NUM> are satisfied, controller <NUM> may start a condenser approach verification subroutine timer (step <NUM>). Controller <NUM> may then check whether several conditions <NUM>-<NUM> are maintained continuously for at least a minimum amount of time Tmin (step <NUM>). The temperature of the CO<NUM> refrigerant exiting gas cooler/condenser <NUM> may be measured by temperature sensor <NUM> and the ambient air temperature may be measured by temperature sensor <NUM>. Condition <NUM> is satisfied if the measured approach (i.e., the measured difference between the temperature of the CO<NUM> refrigerant exiting gas cooler/condenser <NUM> and the ambient air temperature) is maintained at the optimal condenser approach setpoint plus or minus a predetermined percentage of the approach setpoint (i.e., (Setpoint - % value) < measured approach < (setpoint + % value)). Condition <NUM> is satisfied if the measured fan speed is maintained at the optimal fan speed plus or minus a predetermined percentage of the optimal fan speed (i.e., (optimized fan speed - % value) < fan speed < (optimized fan speed + % value)). Condition <NUM> is satisfied if the measured fan speed is maintained at the optimal fan power plus or minus a predetermined percentage of the optimal fan power (i.e., (optimized fan power - % value) < fan power < (optimized fan power + % value)).

If any of conditions <NUM>-<NUM> are not continuously maintained (i.e., any of conditions <NUM>-<NUM> become false) before the condenser approach verification subroutine timer has expired (i.e., the result of step <NUM> is "no"), controller <NUM> may wait until all of conditions <NUM>-<NUM> are satisfied and repeat step <NUM>. Step <NUM> may be repeated as many times as necessary until either all of conditions <NUM>-<NUM> are maintained for at least the minimum amount of time Tmin or the condenser approach verification subroutine timer has expired. If all of conditions <NUM>-<NUM> are continuously maintained (i.e., all of conditions <NUM>-<NUM> remain true) for at least the minimum amount of time Tmin before the condenser approach subroutine timer has expired (i.e., the result of step <NUM> is "yes"), controller <NUM> may exit the verification subroutine (step <NUM>).

If the condenser approach verification subroutine timer expires (step <NUM>) before all of conditions <NUM>-<NUM> are maintained for at least the minimum amount of time Tmin, controller <NUM> may increment an approach verification counter (step <NUM>) and check whether the approach verification counter is less than a threshold (step <NUM>). If the approach verification counter is less than the threshold (i.e., the result of step <NUM> is "yes"), controller <NUM> may exit the verification subroutine (step <NUM>). However, if the approach verification counter is not less than the threshold (i.e., the result of step <NUM> is "no"), controller <NUM> may exit the verification subroutine (step <NUM>) and perform the condenser approach optimization subroutine (i.e., process <NUM>) to update the optimized values used in conditions <NUM>-<NUM>.

The construction and arrangement of the CO<NUM> refrigeration system as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention, as defined by the appended claims.

As utilized herein, the terms "approximately," "about," "substantially", and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims.

The terms "coupled," "connected," and the like as used herein mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another.

Claim 1:
A refrigeration system (<NUM>) comprising:
a gas cooler/condenser (<NUM>) configured to remove heat from a refrigerant flowing through the gas cooler/condenser (<NUM>) and comprising an outlet through which the refrigerant exits the gas cooler/condenser (<NUM>);
a fan (<NUM>) operable to cause airflow across the gas cooler/condenser (<NUM>) and configured to operate at multiple different fan speeds to modulate an amount of heat removed the refrigerant flowing through the gas cooler/condenser (<NUM>);
characterized by a controller (<NUM>) configured to:
calculate a condenser approach temperature by subtracting a temperature of the airflow caused by the fan (<NUM>) from a temperature of the refrigerant exiting the gas cooler/condenser (<NUM>);
operate the fan (<NUM>) to modulate the amount of heat removed from the refrigerant flowing through the gas cooler/condenser (<NUM>) to maintain the condenser approach temperature at or below a condenser approach setpoint; and
automatically adjust the condenser approach setpoint in response to the amount of heat removed from the refrigerant being insufficient to maintain the condenser approach temperature at or below the condenser approach setpoint;
wherein automatically adjusting the condenser approach setpoint includes performing an approach setpoint adjustment process comprising:
starting a condenser approach subroutine timer;
monitoring the condenser approach temperature and a fan speed of the fan (<NUM>) after starting the condenser approach subroutine timer;
automatically increasing the condenser approach setpoint to an adjusted condenser approach setpoint in response to the condenser approach temperature and the fan speed failing to maintain predetermined conditions for at least a minimum amount of time before the condenser approach subroutine timer expires; and
repeating the starting, monitoring, and automatically increasing steps until the condenser approach temperature and the fan speed maintain the predetermined conditions for at least the minimum amount of time before the condenser approach subroutine timer expires.