US20070022767A1 - Method and apparatus for refrigeration system control having electronic evaporat or pressure regulators - Google Patents

Abstract

A method and apparatus for refrigeration system control includes a control system operable to modulate a suction pressure of each of the refrigeration circuits by controlling an evaporator pressure regulator respectively associated with each of the refrigeration circuits independently of evaporator refrigerant superheat to meet cooling demand. A sensor assembly provides refrigeration case temperature and evaporator pressure regulator valve position data to the control system to determine cooling demand.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a divisional of U.S. patent application Ser. No. 11/128,811 filed on May 13, 2005, which is a continuation of U.S. patent application Ser. No. 10/621,625 filed on Jul. 17, 2003 (now U.S. Pat. No. 6,983,618), which is a continuation of U.S. patent application Ser. No. 10/146,848 filed on May 16, 2002 (now U.S. Pat. No. 6,601,398), which is a divisional of U.S. patent application Ser. No. 10/061,703 filed on Feb. 1, 2002 (now U.S. Pat. No. 6,449,968), which is a divisional of U.S. patent application Ser. No. 09/539,563 filed on Mar. 31, 2000 (now U.S. Pat. No. 6,360,553), which are hereby incorporated by reference.
FIELD OF THE INVENTION
• The present invention relates to a method and apparatus for refrigeration system control and, more particularly, to a method and apparatus for refrigeration system control utilizing electronic evaporator pressure regulators and a floating suction pressure set point at a compressor rack.
BACKGROUND OF THE INVENTION
• A conventional refrigeration system includes a compressor that compresses refrigerant vapor. The refrigerant vapor from the compressor is directed into a condenser coil where the vapor is liquefied at high pressure. The high pressure liquid refrigerant is then generally delivered to a receiver tank. The high pressure liquid refrigerant from the receiver tank flows from the receiver tank to an evaporator coil after it is expanded by an expansion valve to a low pressure two-phase refrigerant. As the low pressure two-phase refrigerant flows through the evaporator coil, the refrigerant absorbs heat from the refrigeration case and boils off to a single phase low pressure vapor that finally returns to the compressor where the closed loop refrigeration process repeats itself.
• In some systems, the refrigeration system will include multiple compressors connected to multiple circuits where a circuit is defined as a physically plumbed series of cases operating at the same pressure/temperature. For example, in a grocery store, one set of cases within a circuit may be used for frozen food, another set used for meats, while another set is used for dairy. Each circuit having a group of cases will thus operate at different temperatures. These differences in temperature are generally achieved by using mechanical evaporator pressure regulators (EPR) or valves located in series with each circuit. Each mechanical evaporator pressure regulator regulates the pressure for all the cases connected within a given circuit. The pressure at which the evaporator pressure regulator controls the circuit is adjusted once during the system start-up using a mechanical pilot screw adjustment present in the valve. The pressure regulation point is selected based on case temperature requirements and pressure drop between the cases and the rack suction pressure.
• The multiple compressors are also piped together using suction and discharge gas headers to form a compressor rack consisting of the multiple compressors in parallel. The suction pressure for the compressor rack is controlled by modulating each of the compressors on and off in a controlled fashion. The suction pressure set point for the rack is generally set to a value that can meet the lowest evaporator circuit requirement. In other words, the circuit that operates at the lowest temperature generally controls the suction pressure set point which is fixed to support this circuit.
• There are, however, various disadvantages of running and controlling a system in this manner. For example, one disadvantage is that the requirement for the case temperature generally changes throughout the year. This requires a refrigeration mechanic to perform an in-situ change of evaporator pressure settings, via the pilot screw adjustment of each evaporator pressure regulator, thereby further requiring re-adjustment of the fixed suction pressure set point at the rack of compressors. Another disadvantage of this type of control system is that case loads change from winter to summer. Thus, in the winter, there is a lower case load which requires a higher suction pressure set point and in the summer there is a higher load requiring a lower suction pressure set point. However, in the real world, such adjustments are seldom done since they also require manual adjustment by way of a refrigeration mechanic.
• What is needed then is a method and apparatus for refrigeration system control which utilizes electronic evaporator pressure regulators and a floating suction pressure set point for the rack of compressors which does not suffer from the above mentioned disadvantages. This, in turn, will provide adaptive adjustment of the evaporator pressure for each circuit, adaptive adjustment of the rack suction pressure, enable changing evaporator pressure requirements remotely, enable adaptive changes in pressure settings for each circuit throughout its operation so that the rack suction pressure is operated at its highest possible value, enable floating circuit temperature based on a product simulator probe, and enable the use of case temperature information to control the evaporator pressure for the whole circuit and the suction pressure at the compressor rack. It is, therefore, an object of the present invention to provide such a method and apparatus for refrigeration system control using electronic evaporator pressure regulators and a floating suction pressure set point.
SUMMARY OF THE INVENTION
• In accordance with the teachings of the present invention, a method and apparatus for refrigeration system control utilizing electronic evaporator pressure regulators and a floating suction pressure set point is disclosed. To achieve the above objects of the present invention, the present method and apparatus employs electronic stepper regulators (ESR) instead of mechanical evaporator pressure regulators. The method and apparatus may also utilize temperature display modules at each case that can be configured to collect case temperature, product temperature and other temperatures. The display modules are daisy-chained together to form a communication network with a master controller that controls the electric stepper regulators and the suction pressure set point. The communication network utilized can either be a RS-485 or other protocol, such as LonWorks from Echelon.
• In this regard, the data is transferred to the master controller where the data is logged, analyzed and control decisions for the ESR valve position and suction pressure set points are made. The master controller collects the case temperature for all the cases in a given circuit, takes average/min/max (based on user configuration) and applies PI/PID/Fuzzy Logic algorithms to decide the ESR valve position for each circuit. Alternatively, the master controller may collect liquid sub-cooling or relative humidity information to control the ESR valve position for each circuit. The master controller also controls the suction pressure set point for the rack which is adaptively changed, such that the set point is adjusted in such a way that at least one ESR valve is always kept substantially 100% open.
• In one preferred embodiment, an apparatus for refrigeration system control includes a plurality of circuits with each of the circuits having at least one refrigeration case. An electronic evaporator pressure regulator is in communication with each circuit with each electronic evaporator pressure regulator operable to control the temperature of each circuit. A sensor is in communication with each circuit and is operable to measure a parameter from each circuit. A plurality of compressors is also provided with each compressor forming a part of a compressor rack. A controller controls each evaporator pressure regulator and a suction pressure of the compressor rack based upon the measured parameters from each of the circuits.
• In another preferred embodiment, a method for refrigeration system control is set forth. This method includes measuring a first parameter from a first circuit where the first circuit includes at least one refrigeration case, measuring a second parameter from a second circuit where the second circuit includes at least one refrigeration case, determining a first valve position for a first electronic evaporator pressure regulator associated with the first circuit based upon the first parameter, determining a second valve position for a second electronic evaporator pressure regulator associated with the second circuit based upon the second parameter, electronically controlling the first and the second evaporator pressure regulators to control the temperature in the first circuit and the second circuit.
• In another preferred embodiment, a method for refrigeration system control is set forth. This method includes a lead circuit having a lowest temperature set point from a plurality of circuits where each circuit has at least one refrigeration case, initializing a suction pressure set point for a compressor rack having at least one compressor based upon the identified lead circuit, determining a change in suction pressure set point based upon measured parameters from the lead circuit and updating the suction pressure based upon the change in suction pressure set point.
• In yet another preferred embodiment, a method for refrigeration system control is also set forth. This method includes setting a maximum allowable product temperature for a circuit having at least one refrigeration case, determining a product simulated temperature for the circuit, calculating the difference between the product simulated temperature and the maximum allowable product temperature, and adjusting the temperature set point of the circuit based upon the calculated difference.
• Use of the present invention provides a method and apparatus for refrigeration system control. As a result, the aforementioned disadvantages associated with the currently available refrigeration control systems have been substantially reduced or eliminated.
• Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:FIG. 1 is a block diagram of a refrigeration system employing a method and apparatus for refrigeration system control according to the teachings of the preferred embodiment in the present invention;
• FIG. 2 is a wiring diagram illustrating use of a display module according to the teachings of the preferred embodiment in the present invention;
• FIG. 3 is a flow chart illustrating circuit pressure control using an electronic pressure regulator;
• FIG. 4 is a flow chart illustrating circuit temperature control using an electronic pressure regulator;
• FIG. 5 is an adaptive flow chart to float the rack suction pressure set point according to the teachings of the preferred embodiment of the present invention;
• FIG. 6 is an illustration of the fuzzy logic utilized inmethods1 and2 ofFIG. 5;
• FIG. 7 is an illustration of the fuzzy logic utilized inmethod3 ofFIG. 5; and
• FIG. 8 is a flow chart illustrating floating circuit or case temperature control based upon a product simulator temperature probe;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
• Referring toFIG. 1, a detailed block diagram of arefrigeration system10 according to the teachings of the preferred embodiment in the present invention is shown. Therefrigeration system10 includes a plurality ofcompressors12 piped together with acommon suction manifold14 and adischarge header16 all positioned within acompressor rack18. Thecompressor rack18 compresses refrigerant vapor which is delivered to acondenser20 where the refrigerant vapor is liquefied at high pressure. This high pressure liquid refrigerant is delivered to a plurality ofrefrigeration cases22 by way of piping24. Eachrefrigeration case22 is arranged inseparate circuits26 consisting of a plurality ofrefrigeration cases22 which operate within a same temperature range.FIG. 1 illustrates four (4)circuits26 labeled circuit A, circuit B, circuit C and circuit D. Eachcircuit26 is shown consisting of four (4)refrigeration cases22. However, those skilled in the art will recognize that any number ofcircuits26, as well as any number ofrefrigeration cases22 may be employed within acircuit26. As indicated, eachcircuit26 will generally operate within a certain temperature range. For example, circuit A may be for frozen food, circuit B may be for dairy, circuit C may be for meat, etc.
• Since the temperature requirement is different for eachcircuit26, eachcircuit26 includes apressure regulator28 which is preferably an electronic stepper regulator (ESR) orvalve28 which acts to control the evaporator pressure and hence, the temperature of the refrigerated space in therefrigeration cases22. Eachrefrigeration case22 also includes its own evaporator and its own expansion valve which may be either a mechanical or an electronic valve for controlling the superheat of the refrigerant. In this regard, refrigerant is delivered by piping24 to the evaporator in eachrefrigeration case22. The refrigerant passes through an expansion valve where a pressure drop occurs to change the high pressure liquid refrigerant to a lower pressure combination of a liquid and a vapor. As the hot air from therefrigeration case22 moves across the evaporator coil, the low pressure liquid turns into gas. This low pressure gas is delivered to thepressure regulator28 associated with thatparticular circuit26. At thepressure regulator28, the pressure is dropped as the gas returns to thecompressor rack18. At thecompressor rack18, the low pressure gas is again compressed to a high pressure and delivered to thecondenser20 which again, creates a high pressure liquid to start the refrigeration cycle over.
• To control the various functions of therefrigeration system10, amain refrigeration controller30 is used and configured or programmed to control the operation of each pressure regulator (ESR)28, as well as the suction pressure set point for theentire compressor rack18, further discussed herein. Therefrigeration controller30 is preferably an Einstein Area Controller offered by CPC, Inc. of Atlanta, Georgia, or any other type of programmable controller which may be programmed, as discussed herein. Therefrigeration controller30 controls the bank ofcompressors12 in thecompressor rack18, via an input/output module32. The input/output module32 has relay switches to turn thecompressors12 on an off to provide the desired suction pressure. A separate case controller, such as a CC-100 case controller, also offered by CPC, Inc. of Atlanta, Ga. may be used to control the superheat of the refrigerant to eachrefrigeration case22, via an electronic expansion valve in eachrefrigeration case22 by way of a communication network orbus34. Alternatively, a mechanical expansion valve may be used in place of the separate case controller. Should separate case controllers be utilized, themain refrigeration controller30 may be used to configure each separate case controller, also via thecommunication bus34. Thecommunication bus34 may either be a RS485 communication bus or a LonWorks Echelon bus which enables themain refrigeration controller30 and the separate case controllers to receive information from eachcase22.
• In order to monitor the pressure in eachcircuit26, apressure transducer36 may be provided at each circuit26 (see circuit A) and positioned at the output of the bank ofrefrigeration cases22 or just prior to thepressure regulator28. Eachpressure transducer36 delivers an analog signal to an analog input board38 which measures the analog signal and delivers this information to themain refrigeration controller30, via thecommunication bus34. The analog input board38 may be a conventional analog input board utilized in the refrigeration control environment. Apressure transducer40 is also utilized to measure the suction pressure for thecompressor rack18 which is also delivered to the analog input board38. Thepressure transducer40 enables adaptive control of the suction pressure for thecompressor rack18, further discussed herein. In order to vary the openings in eachpressure regulator28, an electronic stepper regulator (ESR)board42 is utilized which is capable of driving up to eight (8)electronic stepper regulators28. TheESR board42 is preferably an ESR8 board offered by CPC, Inc. of Atlanta, Ga., which consists of eight (8) drivers capable of driving thestepper valves28, via control from themain refrigeration controller30.
• As opposed to using apressure transducer36 to control apressure regulator28, ambient temperature inside thecases22 may be also be used to control the opening of eachpressure regulator28. In this regard, circuit B is shown having temperature sensors44 associated with eachindividual refrigeration case22. Eachrefrigeration case22 in the circuit B may have a separate temperature sensor44 to take average/min/max temperatures used to control thepressure regulator28 or a single temperature sensor44 may be utilized in onerefrigeration case22 within circuit B, since all of the refrigeration cases in acircuit26 operate at substantially the same temperature range. These temperature inputs are also provided to the analog input board38 which returns the information to themain refrigeration controller30, via thecommunication bus34.
• As opposed to using an individual temperature sensor44 to determine the temperature for arefrigeration case22, atemperature display module46 may alternatively be used, as shown in circuit A. Thetemperature display module46 is preferably a TD3 Case Temperature Display, also offered by CPC, Inc. of Atlanta, Ga. The connection of thetemperature display46 is shown in more detail inFIG. 2. In this regard, thedisplay module46 will be mounted in eachrefrigeration case22. Eachmodule46 is designed to measure up to three (3) temperature signals. These signals include the case discharge air temperature, viadischarge temperature sensor48, the simulated product temperature, via the productsimulator temperature probe50 and a defrost termination temperature, via adefrost termination sensor52. These sensors may also be interchanged with other sensors, such as return air sensor, evaporator temperature or clean switch sensor. Thedisplay module46 also includes anLED display54 that can be configured to display any of the temperatures and/or case status (defrost/refrigeration/alarm).
• The productsimulator temperature probe50 is preferably the Product Probe, also offered by CPC, Inc. of Atlanta, Ga. Theproduct probe50 is a 16 oz. container filled with four percent (4%) salt water or with a material that has a thermal property similar to food products. The temperature sensing element is embedded in the center of the whole assembly so that theproduct probe50 acts thermally like real food products, such as chicken, meat, etc. Thedisplay module46 will measure the case discharge air temperature, via thedischarge temperature sensor48 and the product simulated temperature, via the productprobe temperature sensor50 and then transmit this data to themain refrigeration controller30, via thecommunication bus34. This information is logged and used for subsequent system control utilizing the novel methods discussed herein.
• Alarm limits for eachsensor48,50 and52 may also be set at themain refrigeration controller30, as well as defrosting parameters. The alarm and defrost information can be transmitted from themain refrigeration controller30 to thedisplay module46 for displaying the status on theLED display54.FIG. 2 also shows an alternative configuration for temperature sensing with thedisplay module46. In this regard, thedisplay module46 is optionally shown connected to anindividual case controller56, such as the CC-100 Case Controller, offered by CPC, Inc. of Atlanta, Ga. Thecase controller56 receives temperature information from thedisplay module46 to control the electronic expansion valve in the evaporator of therefrigeration case22, thereby regulating the flow of refrigerant into the evaporator coil and the resultant superheat. Thiscase controller56 may also control the alarm and defrost operations, as well as send this information back to thedisplay module46 and/or therefrigeration controller30.
• Briefly, the suction pressure at thecompressor rack18 is dependent in the temperature requirement for eachcircuit26. For example, assume circuit A operates at 10° F., circuit B operates at 15° F., circuit C operates at 20° F. and circuit D operates at 25° F. The suction pressure at thecompressor rack18, which is sensed, via thepressure transducer40, requires a suction pressure set point based on the lowest temperature requirement for all the circuits26 (i.e., circuit A) or thelead circuit26. Therefore, the suction pressure at thecompressor rack18 is set to achieve a 10° F. operating temperature for circuit A. This requires thepressure regulator28 to be substantially opened 100% in circuit A. Thus, if the suction pressure is set for achieving 10° F. at circuit A and nopressure regulator valves28 were used for eachcircuit26, eachcircuit26 would operate at the same temperature. However, since eachcircuit26 is operating at a different temperature, the electronic stepper regulators orvalves28 are closed a certain percentage for eachcircuit26 to control the corresponding temperature for thatparticular circuit26. To raise the temperature to 15° F. for circuit B, thestepper regulator valve28 in circuit B is closed slightly, thevalve28 in circuit C is closed further, and thevalve28 in circuit D is closed even further providing for the various required temperatures.
• Each electronic pressure regulator (ESR)28 may be controlled in one of three (3) ways. Specifically, eachpressure regulator28 may be controlled based upon pressure readings from thepressure transducer36, based upon temperature readings, via the temperature sensor44, or based upon multiple temperature readings taken through thedisplay module46.
• Referring toFIG. 3, apressure control logic60 is shown which controls the electronic pressure regulators (ESR)28. In this regard, theelectronic pressure regulators28 are controlled by measuring the pressure of aparticular circuit26 by way of thepressure transducer36. As shown inFIG. 1, circuit A includes apressure transducer36 which is coupled to the analog input board38. The analog input board38 measures the evaporator pressure and transmits the data to therefrigeration controller30 using thecommunication network34. The pressure control logic oralgorithm60 is programmed into therefrigeration controller30.
• Thepressure control logic60 includes a set point algorithm62. The set point algorithm62 is used to adaptively change the desired circuit pressure set point value (SP_ct) for theparticular circuit26 being analyzed based on the level of liquid sub-cooling after thecondenser20 or based on relative humidity (RH) inside the store. The sub-cooling value is the amount of cooling in the liquid refrigerant out of thecondenser20 that is more than the boiling point of the liquid refrigerant. For example, assuming the liquid is water which boils at 212° F. and the temperature out of the condenser is 55° F., the difference between 212° F. and 55° F. is the sub-cooling value (i.e., sub-cooling equals difference between boiling point and liquid temperature). In use, a user will simply select a desired circuit pressure set point value (SP_-ct) based on the desired temperature within theparticular circuit26 and the type of refrigerant used from known temperature look-up tables or charts. The set point algorithm62 will adaptively vary this set point based on the level of liquid sub-cooling after thecondenser20 or based on the relative humidity (RH) inside the store. In this regard, if the circuit pressure set point (SP_ct) for acircuit26 is chosen to be30 psig for summer conditions at 80% RH, and 10° F. liquid refrigerant sub-cooling, then for 20% RH or 50° F. sub-cooling, the circuit pressure set point (SP_ct) will be adaptively changed to 33 psig. For other relative humidity (RH%) percentages or other liquid sub-cooling, the values can simply be interpolated from above to determine the corresponding circuit pressure set point (SP_ct). The resulting adaptive circuit pressure set point (SP_ct) is then forwarded to a valve opening control64.
• The valve opening control64 includes anerror detector66 and a PI/PID/Fuzzy Logic algorithm68. Theerror detector66 receives the circuit evaporator pressure (P_ct) which is measured by way of thepressure transducer36 located at the output of thecircuit26. Theerror detector26 also receives the adaptive circuit pressure set point (SP_ct) from the set point algorithm62 to determine the difference or error (E_ct) between the circuit evaporator pressure (P_ct) and the desired circuit pressure set point (SP_ct). This error (E_ct) is applied to the PI/PID/Fuzzy Logic algorithm68. The PI/PID/Fuzzy Logic algorithm68 may be any conventional refrigeration control algorithm that can receive an error value and determine a percent (%) valve opening (VO_ct) value for the electronicevaporator pressure regulator28. It should be noted that in the winter, there is a lower load which therefore requires a higher circuit pressure set point (SP_ct), while in the summer there is a higher load requiring a lower circuit pressure set point (SP_ct). The valve opening (VO_ct) is then used by therefrigeration controller30 to control the electronic pressure regulator (ESR)28 for theparticular circuit26 being analyzed via theESR board42 and thecommunication bus34.
• Referring toFIG. 4, atemperature control logic70 is shown which may be used in place of thepressure control logic60 to control the electronic pressure regulator (ESR)28 for theparticular circuit26 being analyzed. In this regard, eachelectronic pressure regulator28 is controlled by measuring the case temperature with respect to theparticular circuit26. As shown inFIG. 1, circuit B includes case temperature sensors44 which are coupled to the analog input board38. The analog input board38 measures the case temperature and transmits the data to therefrigeration controller30 using thecommunication network34. The temperature control logic oralgorithm70 is programmed into therefrigeration controller30.
• Thetemperature control logic70 may either receive case temperatures (T₁, T₂, T₃, . . . T_n) from eachcase22 in theparticular circuit26 or a single temperature from onecase22 in thecircuit26. Should multiple temperatures be monitored, these temperatures (T₁, T₂, T₃, . . . T_n) are manipulated by an average/min/max temperature block72. Block72 can either be configured to take the average of each of the temperatures (T₁, T₂, T₃, . . . T_n) received from each of thecases22. Alternatively, the average/min/max temperature block72 may be configured to monitor the minimum and maximum temperatures from thecases22 to select a mean value to be utilized or some other appropriate value. Selection of which option to use will generally be determined based upon the type of hardware utilized in therefrigeration control system10. From block72, the temperature (T_ct) is applied to an error detector74. The error detector74 compares the desired circuit temperature set point (SP_ct) which is set by the user in therefrigeration controller30 to the actual measured temperature (T_ct) to provide an error value (E_ct). Here again, this error value (E_ct) is applied to a PI/PID/Fuzzy Logic algorithm76, which is a conventional refrigeration control algorithm, to determine a particular percent (%) valve opening (VO_ct) for the particular electronic pressure regulator (ESR)28 being controlled via theESR board42.
• While thetemperature control logic70 is efficient to implement, it has inherent logistic disadvantages. For example, each case temperature sensor44 requires connecting from eachdisplay case22 to a motor room where the analog input board38 is generally located. This creates a lot of wiring and installation costs. Therefore, an alternative to this configuration is to utilize thedisplay module46, as shown in circuit A ofFIG. 1. In this regard, a temperature sensor within eachcase22 passes the temperature information to thedisplay module46 which is daisy-chained to thecommunication network34. This way, the dischargeair temperature sensor48 or theproduct probe50 may be used to determine the case temperature (T₁, T₂, T₃, . . . T_n). This information can then be transferred directly from thedisplay module46 to therefrigeration controller30 without the need for the analog input board38, thereby substantially reducing wiring and installation costs.
• An adaptive suctionpressure control logic80 to control the rack suction pressure set point (P_SP) is shown inFIG. 5. In contrast, the suction pressure set point for a conventional rack is generally manually configured and fixed to a minimum of all the set points used for circuit pressure control. In other words, assume circuit A operates at 0° F., circuit B operates at 5° F., circuit C operates at 10° F. and circuit D operates at 20° F. A user would generally determine the required suction pressure set point based upon pressure/temperature tables and the lowest temperature circuit26 (i.e., circuit A). In this example, for circuit A operating at 0° F., this would generally require a suction of 30 psig with R404A refrigerant. Therefore, pressure at thesuction header14 would be fixed slightly lower than30 psig to support each of the circuits A-D. However, according to the teachings of the present invention, the suction pressure set point (P_SP) is not only chosen automatically but also it adaptively changed or floated during the regular control.FIG. 5 illustrates the adaptive suctionpressure control logic80 to control the rack suction pressure set point according to the teachings of the present invention. This suction pressure setpoint control logic80 is also generally programmed into therefrigeration controller30 which adaptively changes the suction pressure, via turning thevarious compressors12 on and off in thecompressor rack18. The primary purpose of this adaptive suctionpressure control logic80 is to change the suction pressure set point in such a way that at least one electronic pressure regulator (ESR)28 is substantially 100% open.
• The suction pressure setpoint control logic80 begins atstart block82. Fromstart block82, theadaptive control logic80 proceeds tolocator block84 which locates or identifies thelead circuit26 based upon the lowest temperature set point circuit that is not in defrost. In other words, should circuit A be operating at −10° F., circuit B should be operating at 0° F., circuit C would be operating at 5° F. and circuit D would be operating at 10° F., circuit A would be identified as thelead circuit26 inblock84. Fromblock84, thecontrol logic80 proceeds todecision block86. Atdecision block86, a determination is made whether or not thelead circuit26 has changed from theprevious lead circuit26. In this regard, upon initial start-up of thecontrol logic80, thelead circuit26 selected inblock84 which is not in defrost will be anew lead circuit26, therefore following the yes branch ofdecision block86 toinitialization block88.
• Atinitialization block88, the suction pressure set point P_SP for thelead circuit26 is determined which is the saturation pressure of the lead circuit set point. For example, the initialized suction pressure set point (P_SP) is based upon the minimum set point from each of the circuits A-D (SP_ct1, SP_ct2, . . . SP_ctN) or thelead circuit26. Accordingly, if theelectronic pressure regulators28 are controlled based upon pressure, as set forth inFIG. 3, the known required circuit pressure set point (SP_ct) is selected from the lead circuit (i.e., circuit A) for this initialized suction pressure set point (P_SP). If theelectronic pressure regulators28 are controlled based on temperature, as set forth inFIG. 4, then pressure-temperature look-up tables or charts are used by thecontrol logic80 to convert the minimum circuit temperature set point (SP_ct) of thelead circuit26 to the initialized suction pressure set point (P_SP). For example, for circuit A operating at −10°, thecontrol logic80 would determine the initialized suction pressure set point (P₁₃SP) based upon pressure-temperature look-up tables or charts for the refrigerant used in the system. Since the suction pressure set point (P_SP) is taken from the lead circuit A, this is essentially a minimum of all the coolant saturation pressures of each of the circuits A-D.
• Once the minimum suction pressure set point (P_SP) is initialized ininitialization block88, the adaptive control oralgorithm80 proceeds tosampling block90. Atsampling block90, theadaptive control logic80 samples the error value (E_ct) (difference between actual circuit pressure and corresponding circuit pressure set point if pressure based control is performed (seeFIG. 3), if temperature based control then E_ct is the difference between actual circuit temperature and corresponding circuit temperature set point (seeFIG. 4)) and the valve opening percent (VO_ct) in the lead circuit every 10 seconds for 10 minutes. When the lead circuit A is in defrost, sampling is then performed on the next lead circuit (i.e., next higher temperature set point circuit) further discussed herein. This set of sixty samples of data from the lead circuit A is then used to calculate the percentage of error values (E_ct) and valve openings (VO_ct) that satisfy certain conditions incalculation block92.
• Incalculation block92, the percentage of error values (E_ct) that are less than 0 (E0); the percent of error values (E_ct) which are greater than 0 and less than 1 (E1) and the valve openings (VO_ct) that are greater than ninety percent are determined incalculation block92, represented by VO as set forth inblock92. For example, assuming the sample block90 samples the following error data:

  	1	2	3	4	5	6

  1	+0.5	[−1.0]	+0.1	+1.8	[−1.0]	[−1.0]
  2	+1.0	[−1.5]	[−1.5]	+2.0	[−2.0]	0.1
  3	+2.0	[−3.0]	+0.5	+6.0	[−2.5]	0.2
  4	+3.0	[−7.0]	[−0.3]	+3.0	[−2.2]	0.5
  5	+1.5	[−4.0]	+0.4	+1.5	[−2.8]	0.9
  6	+0.7	[−2.0]	+0.7	+0.9	[−2.3]	1.2
  7	+0.2	[−3.0]	+0.8	+0.8	[−5.5]	1.3
  8	0.0	[−1.5]	+1.1	+0.1	[−6.0]	1.6
  9	[−0.3]	[−0.5]	+1.7	[−0.3]	[−4.0]	1.8
  10	[−0.8]	[−0.1]	+1.3	[−0.8]	[−2.0]	2.0

  
  where each column represents a measurement taken every ten seconds with six columns representing a total data set of 60 data points. There are 17 error values (E_ct) that are between 0 and 1 identified above by underlines, providing an E1 of 17/60×100%=28.3%. There are also 27 error values (E_ct) that are less than 0, identified above by brackets, providing an E0 of 27/60×100%=45%. Likewise, valve opening percentages are determined substantially in the same way based upon valve opening (VO_ct) measurements.
• Fromcalculation block92, thecontrol logic80 proceeds to eithermethod1branch94,method2branch96, ormethod3branch98 with each of these methods providing a substantially similar final control result.Methods1 and2 utilize E0 and E1 data only, whilemethod3 utilizes El and VO data only.Methods1 and3 may be utilized withelectronic pressure regulators28, whilemethod2 may be used with mechanical pressure regulators. A selection of which method to utilize is therefore generally determined based upon the type of hardware utilized in therefrigeration system10.
• Frommethod1branch94, thecontrol logic80 proceeds to setblock100 which sets the electronicstepper regulator valve28 for the lead circuit A at 100% open during refrigeration. Once the electronicstepper regulator valve28 for circuit A is set at 100% open, thecontrol logic80 proceeds to fuzzy logic block102. Fuzzy logic block102, further discussed in detail, utilizes membership functions for E0 and E1 to determine a change in the suction pressure set point (dP). Once this change in suction pressure set point (dP) is determined based on the fuzzy logic block102, thecontrol logic80 proceeds to updateblock104. Atupdate block104, a new suction pressure set point P_SP is determined based upon the change in pressure set point (dP) where new P_SP=old P_SP+dP.
• From theupdate block104, thecontrol logic80 returns tolocator block84 which locates or again identifies thelead circuit26. In this regard, should the current lead circuit A be put into defrost, the next lead circuit from the remainingcircuits26 in the system (circuit B-circuit D) is identified atlocator block84. Here again,decision block86 will identify that thelead circuit26 has changed such thatinitialization block88 will determine a new suction pressure set point (P_SP) based upon thenew lead circuit26 selected. Should circuit A not be in defrost and the temperatures for eachcircuit26 have not been adjusted, the control logic will proceed to sampleblock90 fromdecision block86 to continue sampling data. In this way, should the lead circuit A be placed in defrost, the next leadingcircuit26 will control the rack suction pressure and since thislead circuit26 will have a temperature that is not as cold as the initial lead temperature, power is conserved based upon this power conserving loop formed byblocks84,86 and88.
• Referring tomethod2branch96, this method also proceeds to afuzzy logic block106 which determines the change in suction pressure set point (dP) based on E0 and E1, substantially similar to fuzzy logic block102. Fromblock106, thecontrol logic80 proceeds to update block108 which updates the suction pressure set point (P_SP) based on the change in suction pressure set point (dP). Fromupdate block108, thecontrol logic80 returns tolocator block84.
• Referring to themethod3branch98, this method utilizesfuzzy logic block110 which determines a change in suction pressure set point (dP) based upon E1 and VO, further discussed herein. Fromfuzzy logic block110, thecontrol logic80 proceeds to update block112 which again updates the suction pressure set point P_SP=old P_SP+dP. From theupdate block112, thecontrol logic80 returns again tolocator block84. It should be noted that whilemethod1branch94 forces the lead circuit A to 100% open viablock100,method branches2 and3 will eventually direct the electronicstepper regulator valve28 of lead circuit A to substantially 100% open, based upon the controls shown inFIGS. 3 and 4.
• Turning toFIG. 6, the fuzzy logic utilized inmethod1branch94 andmethod2branch96 for fuzzy logic blocks102 and106 is further set forth in detail. In this regard, the membership function for E0 is shown ingraph6A, while the membership function for E1 is shown ingraph6B. Membership function E0 includes an E0_Lo function, an E0_Avg and an E0_Hi function. Likewise, the membership function for E1 also includes an E1_Lo function and E1_Avg function and an E1_Hi function, shown ingraph6B. To determine the change in suction pressure set point (dP), a sample calculation is provided inFIG. 6 for E0=40% and E1=30%.
• Instep1, which is the fuzzification step, for E0=40%, we have both an E0_Lo of 0.25 and an E0_Avg of 0.75, as shown ingraph6A. For E1=30%, we have E1_Lo=0.5 and E1_Avg=0.5, as shown ingraph6B. Once thefuzzification step1 is performed, the calculation proceeds to step2 which is a min/max step based upon the truth table6C. In this regard, each combination of the fuzzification step is reviewed in light of the truth table6C. These combinations include E0_Lo with E1_Lo; E0_Lo with E1_Avg; E0_Avg with E1_Lo; and E0_Avg with E1_Avg. Referring to the Truth Table6C, E0_Lo and E1_Lo provides for NBC which is a Negative Big Change. E0_Lo and E1_Avg provides NSC which is a Negative Small Change. E0_Avg and E1_Lo provides for PSC or Positive Small Change. E0_Avg and E1_Avg provides for PSC or Positive Small Change. In the minimization step, a minimum of each of these combinations is determined, as shown inStep2. The maximum is also determined which provides a PSC=0.5; and NSC=0.25 and an NBC=0.25.
• Fromstep2, the sample calculation proceeds to step3 which is the defuzzification step. Instep3, the net pressure set point change is calculated by using the following formula:$\frac{+2\left(\mathrm{PBC}\right)+1\left(\mathrm{PSC}\right)+0\left(\mathrm{NC}\right)-1\left(\mathrm{NSC}\right)-2\left(\mathrm{NBC}\right)}{\mathrm{PBC}+\mathrm{PSC}+\mathrm{NC}+\mathrm{NSC}+\mathrm{NBC}}$
  By inserting the appropriate values for the variables, we obtain a net pressure set point change of −0.25, as shown instep3 of the defuzzification step which equals dP. This value is then subtracted from the suction pressure set point in the corresponding update blocks104 or108.
• Correspondingly formethod3branch98, the membership function for VO and the membership function for E1 are shown inFIG. 7. Here again, the same three calculations from step1 (fuzzification); step2 (min/max) and step3 (defuzzification) are performed to determine the net pressure set point change dP, based upon the membership function for VO shown ingraph7A, the membership function for E1 shown ingraph7B, and the Truth Table7C.
• Referring now toFIG. 8, a floating circuit temperature control logic116 is illustrated. The floating circuit temperature control logic116 is based upon taking temperature measurements from theproduct probe50 shown inFIG. 2 which simulates the product temperature for the particular product in theparticular circuit26 being monitored. The floating circuit temperature control logic116 begins atstart block118. From start block118, the control logic proceeds todifferential block120. Indifferential block120, the average product simulation temperature for the past one hour or other appropriate time period is subtracted from a maximum allowable product temperature to determine a difference (diff). In this regard, measurements from theproduct probe50 are preferably taken, for example, every ten seconds with a running average taken over a certain time period, such as one hour. The maximum allowable product temperature is generally controlled by the type of product being stored in theparticular refrigeration case22. For example, for meat products, a limit of 41° F. is generally the maximum allowable temperature for maintaining meat in arefrigeration case22. To provide a further buffer, the maximum allowable product temperature can be set 5° F. lower than this maximum (i.e., 36° for meat).
• Fromdifferential block120, the control logic116 proceeds to either determination block122, determination block124 ordetermination block126. In determination block122, if the difference between the average product simulator temperature and the maximum allowable product temperature fromdifferential block120 is greater than 5° F., a decrease of the temperature set point for theparticular circuit26 by 5° F. is performed atchange block128. From here, the control logic returns to startblock118. This branch identifies that the average product temperature is too warm, and therefore, needs to be cooled down. Atdetermination block124, if the difference is greater than −5° F. and less than 5° F., this indicates that the average product temperature is sufficiently near the maximum allowable product temperature and no change of the temperature set point is performed inblock130. Should the difference be less than −5° F. as determined indetermination block126, an increase in the temperature set point of the circuit by 5° F. is performed inblock132.
• By floating the circuit temperature for theentire circuit26 or theparticular case22 based upon the simulated product temperature, therefrigeration case22 may be run in a more efficient manner since the control criteria is determined based upon the product temperature and not the case temperature which is a more accurate indication of desired temperatures. It should further be noted that while a differential of 5° F. has been identified in the control logic116, those skilled in the art would recognize that a higher or a lower temperature differential, may be utilized to provide even further fine tuning and all that is required is a high and low temperature differential limit to float the circuit temperature. It should further be noted that by using the floating circuit temperature control logic116 in combination with the floating suctionpressure control logic80 further energy efficiencies can be realized.
• The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Claims (9)

1. In a refrigeration system having a plurality of refrigeration circuits, a control system operable to modulate a suction pressure of each of said refrigeration circuits by controlling an evaporator pressure regulator respectively associated with said each of said refrigeration circuits independently of evaporator refrigerant superheat to meet cooling demand, and a sensor assembly providing refrigeration case temperature and evaporator pressure regulator valve position data to said control system to determine cooling demand.

2. The system ofclaim 1, further operable to adaptively control a suction pressure of said refrigeration system until said evaporator pressure regulator is approximately fully open.

3. The system ofclaim 1, wherein said refrigeration case temperature is an average of multiple temperature measurements.

4. A method comprising:

measuring a refrigeration system operating parameter;

determining a demand for cooling;

controlling electronic variable valves independently of expansion valves to meet the demand for cooling;

positioning at least one of said electronic variable valves at approximately fully open;

positioning another of said electronic variable valves at less than approximately fully open.

5. The method ofclaim 4, further comprising controlling a compressor.

6. The method ofclaim 4, wherein said refrigeration system operating parameter is temperature.

7. The method ofclaim 4, wherein said refrigeration system operating parameter is an average of multiple temperature measurements.

8. The method ofclaim 4, wherein said refrigeration system operating parameter is pressure.

9. The method ofclaim 4, wherein said refrigeration system operating parameter is an evaporator pressure regulator valve position.

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