NZ763929B2 - Refrigeration system and method of refrigeration load control - Google Patents

Abstract

method of controlling a refrigeration system including a medium temperature refrigeration load and a low temperature refrigeration load. The method includes selectively bypassing refrigerant between a medium temperature suction group and a low temperature suction group via a bypass line using an electronic valve positioned in the bypass line. The method also includes controlling flow of refrigerant between the medium temperature suction group and the low temperature suction group via a controller communicatively coupled to the valve, and modulating the valve at any position between a closed position and a full open position to vary an amount of refrigerant flow between the medium temperature suction group and the low temperature suction group in response to determining, via the controller, one or both of a state of the medium temperature suction group and a state of the low temperature suction group. lectronic valve positioned in the bypass line. The method also includes controlling flow of refrigerant between the medium temperature suction group and the low temperature suction group via a controller communicatively coupled to the valve, and modulating the valve at any position between a closed position and a full open position to vary an amount of refrigerant flow between the medium temperature suction group and the low temperature suction group in response to determining, via the controller, one or both of a state of the medium temperature suction group and a state of the low temperature suction group.

Description

Attorney Docket No. 047177WO01 REFRIGERATION SYSTEM AND METHOD OF ERATION LOAD CROSS-REFERENCE TO RELATED APPLICATIONS This ation claims priority to U.S. Provisional Application No. 420 filed October 24, 2017, the entire contents of which are hereby incorporated by reference.

BACKGROUND The present invention relates to a refrigeration system and, more specifically, to a method of controlling the eration load of the refrigeration system.

Refrigeration s are well known and widely used in supermarkets, warehouses, and elsewhere to erate product that is supported in a refrigerated space.

Conventional refrigeration systems include a heat exchanger or evaporator, a compressor, and a condenser. The evaporator provides heat transfer between a refrigerant flowing within the evaporator and a fluid (e.g., water, air, etc.) g over or through the evaporator. The evaporator transfers heat from the fluid to the refrigerant to cool the fluid. The refrigerant absorbs the heat from the fluid and evaporates in a refrigeration mode, during which the compressor mechanically compresses the evaporated refrigerant from the evaporator and feeds the superheated refrigerant to the condenser, which cools the refrigerant. From the condenser, the cooled refrigerant is typically fed through an expansion valve to reduce the temperature and pressure of the refrigerant, and then the refrigerant is directed through the evaporator.

Often, retail settings also include one or more enclosed spaces (e.g., open or enclosed merchandisers, walk-in coolers, freezers, etc.) that must be cooled or refrigerated at different temperatures. Some retail gs employ mechanical subcooling in the refrigeration system to cool refrigerant in one portion of the refrigerant circuit using the same refrigerant in another portion of the refrigerant circuit. In these retail settings, liquid refrigerant in one area of the refrigerant t is cooled to approximately 50 degrees Fahrenheit by refrigerant from another n of the same refrigerant circuit before being fed to low temperature loads in the retail g.

Some existing refrigeration systems include medium temperature and low temperature compressor assemblies that are arranged in parallel with each other to condition 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 separate refrigeration loads. In these systems, a check valve can be installed n the low temperature suction header and the medium temperature suction header. If the low temperature suction header pressure rises to a certain pressure (e.g., due to compressor failure) then the check valve will allow flow from the low ature suction header to the medium temperature header. This will allow some level of refrigeration to the low temperature circuits at a higher pressure than normal. However, these existing systems cannot actively monitor the low temperature ssor for failure, and do not modify or adjust the medium temperature circuits to accommodate the shift in refrigeration to the low temperature circuits. More ically, these mechanically-controlled systems cannot adjust or control the setpoints for the medium temperature suction group, and can cannot modulate the amount of erant mass flow to the medium temperature suction group. In addition, existing mechanically-controlled systems do not have the capability to disable the mode in which refrigerant flow is d n the medium and low temperature suction groups.

Control systems for commercial refrigeration systems generally control cooling capacity in response to variations in refrigeration load. Often this involves on/off control of fixed speed compressors and/or variable control of variable speed compressors. When multiple compressors in a parallel arrangement are used to provide refrigerant to multiple ators operating at varying temperatures, suction pressure is generally used as a control variable input to the control system. Often a controller, implementing a proportional-integralderivative control algorithm, processes a sensed suction pressure common to all the compressors in the parallel arrangement and determines a control output for one or more compressors to maintain cooling capacity at a level that closely matches the refrigeration load presented by the evaporators.

Some existing eration systems have a mechanical pressure ting valve installed n the low temperature suction group and the medium ature group. This mechanical re regulating valve attempts to maintain a predetermined pressure in the low temperature suction header and constantly allows refrigerant to flow from the medium temperature suction header to low temperature suction header.

Another existing mechanical system includes a hot gas bypass valve oned between the compressor rge and the suction and hot gas bypass line to add a false load to the low temperature compressor to force the ssor to run. A disadvantage of this type of system is that the system is not controlled and will continue to bypass refrigerant to the 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 low temperature compressor at times when not required.

Still other systems attempt to control the flow of refrigerant between low and medium temperature suction groups by adding additional compressors to provide capacity staging on the medium temperature suction group, but this setup disadvantageously incorporates more complex control associated with the added compressors and does not ively manage the load on the low temperature suction group. In addition, adding compressors does not provide for load shedding or management of refrigerant capacity between the different medium temperature compressors.

SUMMARY OF THE INVENTION The ion provides in one aspect, a refrigeration system including a medium temperature refrigeration load, a low temperature refrigeration load, a medium temperature n group ing a n header and at least one medium temperature compressor, a low temperature suction group including a suction header and at least one low temperature compressor, a bypass line positioned between and selectively fluidly connected to the medium temperature suction group and the low temperature suction group, and an electronic valve positioned in the bypass line. A controller is in ication with the electronic valve to control the position of the valve between a closed position and a full open on, wherein control of the electronic valve ively provides refrigerant flow between the medium temperature suction group and the low temperature suction group.

In another aspect, the ion provides a method of controlling a refrigeration system including a medium temperature refrigeration load and a low ature refrigeration load, the refrigeration system further including a medium temperature n group including a suction header and at least one medium temperature compressor, and a low temperature suction group including a suction header and at least one low temperature compressor. The method includes selectively ing refrigerant between the medium temperature suction group and the low temperature suction group via a bypass line using an electronic valve oned in the bypass line, and controlling a flow of refrigerant between the medium temperature suction group and the low temperature suction group to maintain minimum run time for the low temperature compressor, emergency redundant control, or incremental staging capacity for the medium temperature compressor. 18446809_1 ters) P113510.NZ Attorney Docket No. 047177WO01 [0011A] In yet another aspect, the invention provides a method of lling a refrigeration system including a medium temperature refrigeration load and a low temperature refrigeration load, the refrigeration system r including a medium temperature suction group having a suction header and a medium ature compressor assembly operable at a first n pressure setpoint in a normal refrigeration mode, and a low temperature suction group having a suction header and a low temperature compressor ly operable at a second suction pressure setpoint in a normal refrigeration mode, the method comprising: ively bypassing refrigerant between the medium temperature suction group and the low temperature suction group via a bypass line using an electronic valve positioned in the bypass line; controlling flow of refrigerant between the medium temperature suction group and the low temperature suction group via a controller communicatively coupled to the onic valve, the controller further communicatively coupled to a first sensor in communication with the medium temperature suction group to detect a medium temperature suction pressure of refrigerant contained in the medium temperature suction group, and a second sensor in communication with the low ature suction group to detect a low temperature suction pressure of refrigerant contained in the low temperature suction group; and modulating the electronic valve at any on between a closed position and a full open position to vary an amount of refrigerant flow between the medium temperature suction group and the low temperature suction group in response to determining, via the controller, one or both of a state of the medium temperature n group and a state of the low temperature suction group using one or both of the first sensor and the second sensor. [0011B] In yet another aspect, the invention provides a refrigeration system comprising: a medium temperature refrigeration load; a low temperature refrigeration load; a medium temperature suction group including a suction header and a medium temperature compressor assembly operable at a first suction pressure setpoint in a normal refrigeration mode; a low temperature suction group including a suction header and a low temperature compressor assembly operable at a second suction re setpoint in a normal eration mode; a first sensor in communication with the medium temperature n group to detect a medium ature suction pressure of refrigerant contained in the medium temperature suction group; a second sensor in communication with the low temperature suction group to detect a low temperature suction pressure of refrigerant contained in the low temperature n group; a bypass line positioned between and selectively fluidly connected to the 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 medium temperature suction group and the low temperature suction group; an electronic valve positioned in the bypass line to control flow of refrigerant between the low temperature suction group and the medium temperature suction group; and a ller in communication with the electronic valve, each of the medium temperature compressor assembly and the low temperature compressor assembly, and the first and second sensors, the controller programmed to modulate the electronic valve at any position between a closed position and a full open position based on one or both of a state of the medium temperature suction group and a state of the low temperature suction group ined by the ller via one or both of the first sensor and the second sensor, wherein control of the onic valve by the controller selectively provides varying amounts of refrigerant flow between the medium temperature suction group and the low temperature suction group in response to determining the state of the medium temperature n group and the low temperature suction group.

Other features and aspects of the invention will become nt by consideration of the ing detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view of an exemplary refrigeration system embodying the invention.

Fig. 2 is a flowchart rating an exemplary process for shifting load from the medium temperature suction group to the low temperature suction group to support the low temperature compressor group.

Fig. 3 is a flowchart illustrating an exemplary process for emergency redundant l to support the low temperature load.

Fig. 4 is a flow chart rating an exemplary s for incremental capacity control for the medium temperature compressors.

Before any embodiments of the present ion are explained in detail, it should be understood that the invention is not limited in its application to the details or construction and the arrangement of components as set forth in the following description or as illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. It should be understood that the description of specific 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. WO01 embodiments is not intended to limit the sure from covering all modifications, equivalents and alternatives falling within the spirit and scope of the disclosure. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as ng.

DETAILED DESCRIPTION Fig. 1 illustrates an exemplary refrigeration system 10 that ates a refrigerant to condition several interior spaces (e.g., product display areas of medium temperature merchandisers and low temperature merchandisers). As shown, the refrigeration system 10 includes a medium temperature ("MT") compressor assembly 15 and a low temperature ("LT") compressor assembly 20 that circulate refrigerant through the refrigeration system 10.

In an exemplary embodiment, the MT compressor assembly 15 can include one or more compressors, and is associated and in ication with one or more medium temperature display cases (not shown) via a medium temperature suction main 25. The LT compressor assembly 20 can include one or more compressors (e.g., fixed capacity scrolls or other types of compressors) and is associated and in fluid communication with one or more low temperature display cases via a low ature suction main 30.

Each of the medium and LT compressor assemblies 15, 20 is coupled to a discharge header 35, which is y coupled to a condenser assembly (not shown) directly or through a separator 40. As is well known, the condenser assembly includes one or more condensers and ges heat from the refrigerant circulating through the condenser with another nment (e.g., an ambient environment) to cool the refrigerant. Each condenser es a condenser coil and receives a flow of fluid (e.g., air or liquid) to cool the refrigerant. The ser assembly can be located on a rooftop of a commercial setting, or elsewhere, to discharge energy from the refrigerant in the refrigerant system to the outside, ambient environment.

The refrigeration system 10 also includes a receiver line 45 and a fluid main or liquid line 50 that is fluidly coupled to a liquid header 60. The receiver line 45 is in fluid communication with the condenser assembly and a receiver 65 to direct cooled refrigerant from the condenser assembly to the receiver 65. The fluid main 50 is in fluid ication 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 with the receiver 65 and the medium and low temperature display cases via the liquid header 60 to direct cooled refrigerant to respective evaporators in the display cases. While Fig. 1 illustrates a filter-drier 55 in the fluid main 50, it may be omitted from the eration system 10 in some examples.

The evaporator(s) of the medium temperature display cases are fluidly coupled to the MT ssor assembly 15 via the medium ature suction main 25. The medium temperature suction main 25 includes a medium temperature suction header 70 (e.g., accumulator) and a medium temperature suction line 75 that is disposed downstream of the medium temperature suction header 70 to direct refrigerant to the MT compressor assembly . The medium temperature suction line 75 fluidly interconnects the medium temperature suction header 70 and the MT compressor assembly 15. The evaporator(s) of the low temperature display cases are fluidly coupled to the LT compressor assembly 20 via the low temperature suction main 30. The low ature suction main 30 includes a low temperature suction header 80 (e.g., accumulator) and a low temperature suction line 85 that is disposed downstream of the low temperature suction header 80 to direct refrigerant to the LT compressor assembly 20. The low temperature suction line 85 fluidly interconnects the low temperature suction header 80 and the LT compressor assembly 20. For purposes of description, the medium temperature suction header 70, the suction line 75, and the compressor assembly 15 will be ed to as the medium temperature suction group.

Similarly, the low temperature suction header 80, the suction line 85, and the low temperature ssor assembly 20 will be ed to as the low temperature suction group.

With continued reference to Fig. 1, the refrigeration system 10 further includes a bypass line interconnecting the medium temperature suction main 25 and the low temperature suction main 30 (e.g., fluidly connecting the suction s 70, 80, or the suction lines 75, 85). An onic crossover or bypass valve 90 is positioned in the bypass line to control crossover flow between the medium and low temperature n headers 70, 80 and, therefore, control crossover flow to the medium and LT compressor assemblies. The illustrated ver valve 90 can be a stepper valve, an electronic pressure-regulating valve, or a solenoid valve that can be onically controlled by a ller 95. As explained in detail below, the controller 95 can control or modulate the valve 90 between an open position and a closed position (and any partially open position) to i) provide load shifting to maintain load distribution across the MT and LT compressor assemblies (e.g., shift load to the LT 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 compressor assembly 20 to maintain minimum run time on the LT compressor assembly 20), ii) provide redundant emergency backup control when the LT compressor assembly 20 is shutdown (e.g., due to failure detected by a current sensing relay, or other reasons), and/or iii) provide an incremental capacity step (capacity modulation) for the MT compressor assembly . More generally, the valve 90 can be modulated based on various conditions experienced by one or more components of the refrigeration system 10, including the medium and LT compressor assemblies.

I. Crossover Valve as Load Shifting Valve; Supporting LT ssor When the load on the low temperature suction group has diminished to the point where the LT compressor is oversized, there are ions where it is necessary to keep a single LT compressor running. The time period to keep the LT compressor running is defined as the minimum run time for the LT compressor. In one e, and with reference to Fig. 1, the refrigeration system 10 includes a single LT compressor and two suction transducers 100 (e.g., s) connected to the low temperature suction header 80 and the medium temperature suction header 70 (it will be appreciated that the ucers 100 can be coupled to the suction lines 75, 85 in another embodiment). Referring to Fig. 2, when the LT compressor turns on (Step 200), the ller 95 monitors the pressure in the low temperature suction header 80 (Step 205). If the controller 95 determines that the minimum run time has not d ("No" at Step 210), the controller 95 determines whether the low temperature suction header pressure drops below the setpoint dead band (Step 215). If the suction header pressure has not d below the setpoint dead band ("No" at Step 215), the process returns to Step 210. If the controller 95 determines that the suction header pressure has dropped below the setpoint dead band ("Yes" at Step 215), the controller 95 modulates the crossover valve 90 open to shift refrigerant load to the low temperature suction group (Step 220). The crossover valve 90 modulates between fully closed (0%) to fully open (100%) to allow the LT compressor the appropriate load to continue running while within the minimum run time. In this example, the amount of refrigerant mass flow to the LT ssor can be modulated or terminated when not needed.

Upon reaching the cut-in pressure nt and the minimum off time has been reached, the LT ssor will start and run until the minimum run time has expired. The crossover valve 90 can be controlled (e.g., ted) by the controller 95 to shift medium temperature capacity to the LT compressor to ensure the LT compressor has adequate load to 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 prevent pulling the low temperature suction pressure too low and hitting the cutout point on the low pressure control, and to avoid putting the system in an undesirable vacuum state. The controller 95 continues to monitor the suction pressure at Step 215 prior to expiration of the minimum run time ("No" at Step 200) to determine whether the suction re is below the setpoint. After the minimum run time has expired ("Yes" at Step 225), the ller 95 adjusts the crossover valve 90 back to being a capacity control valve for the MT compressor assembly 15 (Step 230). The controller 95 can close the crossover valve 90 if demands of the refrigeration system 10 require closure to maintain normal refrigerating operation (refrigeration mode). If the suction pressure on the low temperature suction group s a desired or predetermined cutout setpoint ("Yes" at Step 235), the controller 95 cycles off the LT compressor and starts the minimum off time count (Step 240). The controller 95 prevents restarting of the LT compressor ("No" at Step 245) until the minimum off time has expired ("Yes" at Step 245). The minimum off time can be overridden by the controller 95 if the LT compressor is in an alarm state. After the minimum off time has expired (or when the LT compressor is in an alarm state), the controller 95 repeats the process by g on the LT compressor based on refrigerant demand in the low temperature display ).

Returning to Step 210, if the controller 95 determines that the m run time has expired ("Yes" at Step 210), the controller 95 determines whether the cutout pressure setpoint has been reached (Step 235). If the cutout pressure setpoint has not been reached ("No" at Step 235), the controller 95 continues to operate the LT compressor (Step 250).

When the controller 95 determines that the cutout pressure setpoint has been reached ("Yes" at Step 235), the controller 95 shuts down the LT compressor (Step 240).

During a defrost cycle, the controller 95 can control the crossover valve 90 to ensure the LT compressor has adequate load to prevent pulling the low temperature suction re to or below the low pressure control setpoint anytime the LT compressor is within the ermined minimum run time. After the minimum run time has d, the crossover valve 90 will no longer provide load ng and the compressor will be allowed to cycle off based on erant demand. Refrigeration using the LT compressor assembly 20 resumes after t has terminated. uing with this example, the MT compressor assembly 15 includes a lead or primary MT compressor (e.g., a digital compressor) and a secondary MT compressor, each of which has a minimum run time and a minimum off time. In this example, it is preferred that 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 the primary MT compressor is the first compressor turned on by the controller 95 and the last compressor turned off by the controller 95.

When the primary MT compressor ramps down to 10% capacity, the controller 95 will operate the primary MT compressor on a delay (e.g., for a predetermined delay time) to prevent prematurely staging off the ssor. Minimum off times are over-ridden by the controller 95 if there is an alarm state. For example, the primary MT compressor can be controlled by the controller 95 using a minimum off time that is limited to two minutes.

The controller 95 controls operation of the y MT compressor through a digital pulse-width modulation (PWM) cycle. In one embodiment, the primary MT compressor is controlled for a predetermined PWM cycle (e.g., a twenty second al started in the de-energized or loaded state, ending in an energized or unloaded state with a proportional–integral–derivative (PID) loop rate. For example, the rate can be approximately between a 10 second window, +/- 5 seconds. The change in capacity per step should be limited to 25% per PWM cycle. For e, if the last cycle is at 50%, (10 seconds loaded/10 second unloaded), the next cycle is limited to a min of 25% (5 seconds loaded /15 second unloaded) or 75% (15 second loaded / 5 seconds unloaded). An exception to this cycling may occur when an additional compressor comes online.

The primary MT compressor ramp-up is controlled by the controller 95 through a filter suction re and PID loop based on the dead band set point for the medium ature suction group. The primary MT compressor will be allowed to run down to 10% capacity. Any ty below 10% will cycle off the primary MT compressor for the minimum time off. If the average capacity falls below the primary compressor minimum ty for more than the primary MT compressor low capacity m time, the primary MT ssor will turn off and time out for the compressor minimum time off. Under normal staging, the secondary MT compressor will not start unless the primary MT compressor is either running or in an alarm state.

When the primary MT compressor reaches 100% capacity and is not within the setpoint dead band, the controller 95 will first try to utilize the crossover valve 90 to provide some incremental ty before determining to turn on the secondary compressor. To e for the stage, the primary MT compressor ramps down to 10% capacity just prior to starting or initializing the secondary compressor. The primary MT compressor will remain at 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 % for a time period (e.g., 1 minute) to allow for the medium temperature suction group to stabilize. After that, the primary MT compressor is ramped up by the controller 95 as needed to meet the refrigerant demand. If the primary MT compressor runs, on average, below the primary compressor low capacity setpoint for more than the primary compressor low capacity max time, or goes below 10%, the ller 95 will turn off the secondary MT compressor and ramp up the primary MT compressor to 100%. If the ary ssor has not reach the secondary compressor minimum run time, the secondary compressor will continue to run with the primary MT compressor at 10% until the ary compressor minimum run time has expired.

After the setpoint has been reached, the primary MT compressor will begin ramping down. After the demand reaches a point approximately at or below 10%, the controller 95 will cycle off the secondary compressor. Thereafter, the primary MT compressor will immediately ramp to 100% (e.g., for a period of 1 ) to allow for the system to stabilize, and then the primary MT compressor will be ramped down as needed based on the requirements of the refrigeration system 10. The secondary compressor will remain off for the minimum off time unless the primary MT ssor enters an alarm state.

When the primary MT compressor ramps down to 10%, the controller 95 will delay for the primary MT compressor minimum ty delay time to prevent prematurely staging off a compressor.

The controller 95 manages the medium temperature suction group such that minimum run times will be ignored when the system goes into defrost mode and the medium temperature suction pressure drops below the suction pressure setpoint. Normal g strategy will be followed otherwise. If only the primary MT compressor is running when the medium temperature defrost occurs and the load is below 30%, the controller 95 will turn off the primary MT compressor, open the capacity crossover valve 90, and run the refrigeration system 10 using the low temperature suction group. The LT compressor must be in operation to perform this function.

The minimum run time load shifting provides a lled way to ensure adequate run time on the LT compressor under light load or transient ions. In circumstances when the LT compressor is brought online and the load to too light to support the compressor mass flow or ty at the given condition, which can be ted by the suction pressure dropping beyond a threshold outside the set point dead band, the controller 95 will begin to 09_1 (GHMatters) P113510.NZ Attorney Docket No. WO01 open the crossover valve 90. Opening the crossover valve 90 bleeds over high pressure from the medium temperature suction group. The controller 95 will open the ver valve 90 incrementally until the suction pressure is brought back within the setpoint dead band. After the suction pressure is within the setpoint dead band, the controller 95 will maintain the crossover valve 90 in the incremental open position until the minimum run time limit has expired. Upon expiration of the run time limit, the controller 95 closes the ver valve 90, which s the low temperature suction pressure to react solely to the mass flow of the LT ssor. If the suction pressure goes outside the setpoint dead band, the LT compressor is cycled off by the controller 95. The controller 95 will t LT compressor from restarting until the minimum off time has been reached.

II. Crossover Valve for Emergency Redundant Control to support LT Load With reference to Fig. 3, the controller 95 prioritizes control of the crossover valve 90 so that the crossover valve 90 provides emergency ant control for the low temperature suction group. If emergency redundant control is not required ("No" at Steps 300, 305 in Fig. 3), the valve 90 can provide load shift capability to maintain minimum run time on the LT compressor(s) (see Fig. 2), or incremental capacity control (see Fig. 4).

Referring to Fig. 3, in the event the LT compressor is offline and in an alarm state ("Yes" at Step 300), or if the suction pressure reaches a corresponding pressure above the emergency redundant control suction pressure setpoint ("Yes" at Step 305), the controller 95 manipulates the crossover valve 90 so that it is 100% open (Step 310 or Step 315, respectively). In addition, the suction pressure setpoint on the medium temperature suction group is reset by the controller 95 to an emergency redundant control suction pressure setpoint (Step 320). This mode is only used in emergency situations and the LT compressors should be serviced within 24 hours.

The system recovers in the ing exemplary scenarios. In one scenario, if the LT ssor is off and in an alarm state ("Yes" at Step 300), then any LT compressor that recovers from alarm and is able to run ("Yes" at Step 325) will provide for recovery (Step 330). In another scenario, if the controller 95 determines that the low temperature suction re reaches the emergency redundant l suction pressure setpoint to enter redundant control mode ("Yes" at Step 305), then the system is run at the emergency redundant control suction re setpoint for the emergency redundant l maximum 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. WO01 time (Step 335). After the maximum time has been exceeded ("Yes" at Step 340), the suction pressure setpoints are adjusted back to normal operation and the crossover valve 90 is closed (Step 345). The ncy redundant control initiation logic in the controller 95 will be disabled at this point. The logic in the controller 95 that initiates the emergency redundant control mode is tiated when the low temperature suction re reaches the low temperature suction setpoint.

In l, the controller 95 will prioritize ncy redundant l over, and disable, the minimum run time load shift operation ibed in section I above) and incremental capacity stage operation (described in n III below). The minimum run time load shift initiates when the low temperature suction pressure drops below the lower dead band of the low temperature suction pressure set point and the minimum run time timers for all running LT compressors have not expired. The system recovers when the minimum run time timers have expired for all LT compressors. Incremental capacity staging for the medium temperature n group is bypassed via l from the controller 95 during the minimum run time load shift. Furthermore, the controller 95 disables the minimum run time load shift when emergency redundant control is needed.

III. Crossover Valve and Incremental MT Compressor Control The crossover valve 90 can be controlled by the controller 95 to e a small or incremental capacity step between the first MT compressor and the second MT compressor through load shedding to the low ature suction group. With reference to Fig. 4, the controller 95 monitors the pressure of each suction group and the staging of each MT compressor (Step 400). In the event the primary MT compressor (e.g., a digital compressor) is running at 100% capacity and the low temperature suction group is in a state where it can accept additional load ("Yes" at Step 405), the controller 95 modulates the crossover valve 90 to an open position to allow crossflow to the LT suction group (Step 415) subject to the medium temperature suction pressure relative to the setpoint dead band (Step 410). That is, some of the medium temperature load shifts from the medium temperature suction group to low temperature suction group. The load shifting decreases the medium temperature load on the medium temperature suction group an incremental amount, which alleviates the need to stage the secondary MT compressor to meet the medium temperature load requirements. 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 The ller 95 initiates incremental control in the medium temperature suction group by providing an incremental capacity step between the primary MT compressor and the secondary ssor. When the primary MT compressor reaches 100% capacity and medium temperature suction pressure is not above the setpoint dead band ("Yes" at Step 410), the controller 95 will first e the ver valve 90 to provide incremental capacity via the low temperature suction group before determining whether to initiate or turn on the ary compressor ("Yes" at Step 420). In this control situation, the LT ssor must be in the on position to support the incremental capacity stage for the medium temperature suction group. The controller 95 does not force the LT compressor to turn on to provide ental capacity. That is, if the LT compressor is off, additional capacity is provided by the secondary compressor (Step 425).

The incremental staging or control initiates when the medium temperature suction group has only the y MT compressor on and running at 100%, and the medium temperature suction pressure is above the medium temperature suction pressure setpoint upper dead band limit after the minimum run time expires for the primary MT compressor.

The incremental staging by the controller 95 recovers (Step 430) when the secondary compressor is turned on due to the medium temperature suction pressure being above setpoint dead band for 30 continuous seconds after the capacity staging has ed (Step 425), or if the medium temperature suction re drops below the medium temperature suction pressure setpoint upper dead band limit for 30 continuous seconds ("Yes" at Step 435). The incremental staging is disabled by the ller 95 when the minimum run time load shift is needed (see section I), or when the controller 95 determines that emergency redundant control is needed (see section II). In general, the controller 95 forces the crossover valve 90 closed in the event of any suction transducer failure.

Although the ion is described with reference to its application in refrigerated ndisers, it will be appreciated that the refrigeration system 10 and method of control described herein will have other applications. Also, it should be appreciated that the controller 95 can include and implement different processes and logic to achieve the functionality bed herein.

The refrigeration system 10 with the electronic crossover valve 90 positioned in bypass line between medium temperature and low temperature suction headers 70, 80 es control of synchronization between the medium temperature and low temperature 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 suction groups, and reduces or eliminates the need for adjustments after prolonged operation and to accommodate seasonal weather changes. The bypass control also controls shortcycling of the medium and LT compressors, provides additional staging for the medium temperature portion of the refrigeration system 10, supports ncy redundant capacity, minimizes wide pressure swings during operation under light loads, improves design load flexibility, and ates expensive digital ssors that are common in existing systems.

As described in detail above, in the event of a failure of the LT compressor (e.g., detected by a current sensing relay), the low temperature load is shifted over to the medium temperature suction group to allow some level of refrigeration to the low temperature circuit.

At the same time, the pressure setpoint for the medium temperature suction group is set lower by the controller 95 to better maintain the temperature in the low temperature circuit.

In l, the controller 95 actively monitors the LT compressor for failure, and adjusts the setpoint for the medium temperature suction group to a lower setting when additional ty is needed in the low temperature suction group. In addition, the amount of erant mass flow to the medium temperature suction group can be ted and controlled via the controller 95 and the crossover valve 90, and after a period of time (e.g., 24 hours), the eration system 10 can recover from this mode and run again with a normal suction pressure setpoint and the emergency redundant logic disabled. ed to existing mechanically-controlled systems, the electronically- controlled system described herein provides better load matching capability based on the responsiveness of the electronic crossover valve 90 and the variable load distribution and ability to change the pressure setpoint that can be accomplished by the crossover valve 90.

In addition, the controller 95 and, in particular, control of the crossover valve 90 es emergency redundant control when one of the suction groups experiences a failure, and incremental staging for the MT compressors when .

Various features and advantages of the ion are set forth in the ing claims. 18446809_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01

Claims (16)

1. A method of controlling a refrigeration system including a medium temperature refrigeration load and a low temperature refrigeration load, the refrigeration system further including a medium temperature suction group having a suction header and a medium temperature compressor assembly operable at a first suction pressure setpoint in a normal refrigeration mode, and a low temperature suction group having a suction header and a low temperature compressor assembly operable at a second suction pressure setpoint in a normal refrigeration mode, the method comprising: selectively ing refrigerant between the medium temperature suction group and the low temperature suction group via a bypass line using an electronic valve positioned in the bypass line; controlling flow of erant between the medium temperature suction group and the low temperature suction group via a controller communicatively coupled to the electronic valve, the controller r communicatively coupled to a first sensor in communication with the medium temperature suction group to detect a medium ature suction re of refrigerant contained in the medium temperature suction group, and a second sensor in communication with the low temperature suction group to detect a low temperature suction pressure of refrigerant contained in the low temperature n group; and modulating the electronic valve at any position between a closed position and a full open position to vary an amount of refrigerant flow between the medium temperature suction group and the low temperature suction group in response to determining, via the controller, one or both of a state of the medium ature suction group and a state of the low ature suction group using one or both of the first sensor and the second sensor.

2. The method of claim 1, wherein modulating the electronic valve via the controller provides refrigerant from the medium ature suction group to the low ature compressor assembly to achieve a minimum run time for the low temperature compressor in response to a pressure in the suction header of the low temperature n group below a nt dead band, to achieve emergency redundant control of the low ature compressor assembly in response to an emergency situation associated with the low temperature compressor assembly, or to achieve incremental staging capacity for the medium temperature compressor assembly in response to a primary compressor of the medium 09_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 temperature compressor ly operating at full capacity and the medium temperature suction pressure above a medium temperature suction re nt.

3. The method of claim 1, further comprising: monitoring the low temperature suction pressure; determining that a minimum run time associated with the low temperature compressor assembly has not expired; determining that the low temperature suction pressure has dropped below a setpoint dead band; and modulating the electronic valve one or more open ons to shift refrigerant load to the low temperature suction group.

4. The method of claim 3, wherein the electronic valve is modulated until a minimum run time associated with the low temperature compressor assembly has expired.

5. The method of claim 3, further comprising shutting off the low temperature compressor assembly in response to the controller determining that a cutout pressure setpoint has been reached after expiration of the minimum run time.

6. The method of claim 3, further comprising closing the electronic valve in response to the ller determining that the medium temperature load requires additional refrigeration.

7. The method of claim 1, further comprising: determining that the low temperature ssor ly is e and in an alarm state or ining that the second suction re has reached a pressure above a first emergency redundant control n pressure setpoint; modulating the electronic valve to the full open position in response to either determination; and resetting the first suction pressure setpoint to a second emergency redundant control suction re setpoint.

8. The method of claim 7, further comprising: determining that a maximum time has been exceeded for emergency redundant control; and resetting the first second suction pressure setpoints to normal operation; and disabling emergency redundant control via the controller. 18446809_1 (GHMatters) P113510.NZ ey Docket No. 047177WO01

9. The method of claim 1, wherein the medium temperature compressor ly includes a primary compressor and a secondary compressor, the method further comprising: determining, via the controller, that the primary compressor is at 100% capacity and the low temperature suction group is at less than 100% capacity; ining that the medium temperature suction pressure is above a first suction pressure setpoint upper dead band limit after a minimum run time expires for the primary compressor; modulating the electronic valve to a variable open position to allow crossflow of refrigerant from the medium temperature suction group to the low temperature suction group to decrease a load on the medium temperature n group an incremental amount.

10. The method of claim 9, initiating the secondary compressor when the primary compressor is at 100% capacity only in response to i) the low temperature suction group being unable to take on onal capacity, or ii) the low temperature suction group is

11. A refrigeration system comprising: a medium temperature eration load; low temperature refrigeration load; a medium temperature suction group including a suction header and a medium temperature compressor ly operable at a first suction pressure setpoint in a normal eration mode; a low temperature suction group including a suction header and a low temperature compressor assembly le at a second suction pressure setpoint in a normal refrigeration mode; a first sensor in communication with the medium temperature suction group to detect a medium temperature suction pressure of refrigerant contained in the medium temperature suction group; a second sensor in ication with the low temperature suction group to detect a low temperature suction pressure of refrigerant contained in the low temperature suction group; a bypass line positioned between and selectively fluidly connected to the medium temperature suction group and the low temperature suction group; 09_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01 an electronic valve positioned in the bypass line to control flow of refrigerant between the low temperature suction group and the medium ature suction group; and a controller in communication with the electronic valve, each of the medium temperature compressor assembly and the low temperature compressor ly, and the first and second sensors, the controller programmed to modulate the electronic valve at any position between a closed position and a full open position based on one or both of a state of the medium ature suction group and a state of the low temperature suction group determined by the controller via one or both of the first sensor and the second sensor, wherein control of the electronic valve by the controller selectively provides varying amounts of refrigerant flow between the medium temperature suction group and the low temperature suction group in response to determining the state of the medium temperature suction group and the low temperature suction group.

12. The refrigeration system of claim 11, wherein the controller is programmed to open the electronic valve to the full open position in response to the controller determining the at least one low temperature compressor is in an alarm state and offline.

13. The refrigeration system of claim 11, n the controller is programmed to open the electronic valve to the full open position in response to the controller determining the suction pressure has reached a pressure associated with an ncy redundant control suction pressure setpoint, and wherein the ller is mmed to adjust the first suction pressure setpoint to a lower setpoint.

14. The refrigeration system of claim 13, wherein controller is programmed to override the second suction pressure setpoint and to operate the at least one low temperature ssor at the emergency redundant control suction pressure setpoint for a maximum run time, and wherein the controller resets the low temperature compressor to the second suction pressure setpoint upon expiration of the maximum run time.

15. The refrigeration system of claim 11, further sing an emergency redundant l mode, a m run time load shift mode, and an incremental capacity stage mode, and wherein the controller is mmed to prioritize the emergency redundant control mode. 09_1 (GHMatters) P113510.NZ Attorney Docket No. 047177WO01

16. The method of claim 1, wherein the modulating step includes crossover flow of refrigerant between the medium temperature n group and the low temperature suction group. 18446809_1 (GHMatters) P113510.NZ WO 83558 --------- 1O {333$}??? HEIRS»? Turn on LT Compressor 205 245 “”0”"? LT Operate LT ”Minimum off tlmé‘»\\\\\