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A multiple-compressor refrigeration system for use in commercial refrigeration applications includes a plurality of compressors of unequal refrigeration capacity connected in a refrigeration circuit that includes a condenser and a plurality of associated evaporators and expansion devices in remotely

A multiple-compressor refrigeration system for use in commercial refrigeration applications includes a plurality of compressors of unequal refrigeration capacity connected in a refrigeration circuit that includes a condenser and a plurality of associated evaporators and expansion devices in remotely located refrigerated enclosures. A system controller is connected to a pressure responsive transducer that measures the suction pressure of the system and compares the so-measured suction pressure to a desired suction pressure and selects one of a plurality of 2 n available compressor operating states in accordance with the measured difference. The system advantageously increases overall system efficiency by providing increments or decrements of compressor capacity that are more precisely matched to system load changes as compared to prior multiple-compressor systems.

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1. A multiple compressor refrigeration system for refrigerating spaces, comprising: a plurality of compressors, each having an inlet and an outlet, said compressors being operable individually or in various combinations, said system thereby capable of achieving any one of a plurality of discrete

1. A multiple compressor refrigeration system for refrigerating spaces, comprising: a plurality of compressors, each having an inlet and an outlet, said compressors being operable individually or in various combinations, said system thereby capable of achieving any one of a plurality of discrete compressor capacity operating states, at least two of said compressors being connected in parallel and no two compressors being operable in a required fixed predetermined sequence; condenser means connected to said compressors for receiving a compressed working fluid therefrom; expansion and evaporator means connected to said condenser means for receiving condensed working fluid therefrom for expansion and evaporation thereof thereby to effect refrigeration of said spaces, said expansion and evaporation means connected to the inlet of said compressors to provide the expanded working fluid thereto; pressure-responsive means connected to said compressors for providing a signal output representative of the pressure of the working fluid on the inlet side of said compressors, said working fluid pressure representing the load requirements of said system and said pressure-representative signal representing a pressure value within one of a plurality of discrete zones of values each defined by a threshold pressure, said threshold pressures being sequentially and incrementally representative of deviations of system load from a preferred range of pressure values; and controller means connected to said pressure-responsive means for receiving said signal therefrom and connected to said compressors for effecting individual control of said compressors in response to said signal output, said controller means selecting any one of said compressor capacity operating states as a function of said pressure value within said discrete pressure zone and the compressor capacity operating state in effect when said pressure-representative signal is received, said controller means responding to said sensed pressure-representative signal in a step independent of any possible intermediate compressor capacity operating states, said step determined at least in part as a function of the rate of working fluid pressure rise or fall, said controller thus controlling compressor capacity in accordance with system load by determining which one of said compressor capacity operating states optimally meets said system load and providing a signal for turning on or off selected ones of said plurality of compressors, thereby to provide compressor capacity to said system responsive to said load requirements without predeterminably enabling a selected one of said compressors in an ordered and predetermined sequence prior to enabling a required another one of said compressors. 2. A multiple compressor refrigeration system for refrigerating a plurality of discrete spaces, comprising: a plurality of compressors, each having an inlet and an outlet, said compressors being operable individually or in various combinations, said system thereby capable of achieving any one of a plurality of discrete compressor capacity operating states, at least two of said compressors being connected in parallel and no two compressors being operable in a required fixed predetermined sequence, at least one of said compressors having a compressor capacity different from another; condenser means connected to said compressors for receiving a compressed working fluid therefrom; expansion and evaporator means connected to said condenser means for receiving condensed working fluid therefrom for expansion and evaporation thereof to effect refrigeration of said discrete spaces, said expansion and evaporation means connected to the inlet of said compressors to provide the expanded working fluid thereto; pressure-responsive means connected to said compressors for providing a signal output representative of the pressure of the working fluid on the inlet side of said compressors, said signal output being representative of operating evaporator load for said system; and controller means connected to said pressure-responsive means for receiving said signal therefrom and connected to said compressors for effecting individual control of said compressors in response to said signal output, said controller means including means for comparing said measured inlet pressure with predetermined pressure limits for successively higher pressure ranges relative to a preferred pressure range and with predetermined pressure limits for successively lower pressure ranges relative to said predetermined pressure range, said controller independently selecting cumulatively greater compressor capacity states for each successive pressure-range increase and independently selecting cumulatively lower compressor states for each successive pressure-range decrease, said controller means responding to the difference between said measured inlet pressure and said preferred pressure-range in a step determined at least in part as a function of the operating state in effect when said pressure-representative signal is received and the rate of working fluid pressure rise or fall, said step independent of any possible intermediate compressor capacity operating states, said controller thus controlling compressor capacity in accordance with system load by determining which one of said compressor capacity operating states optimally meets said system load and providing a signal for turning on or off selected ones of said plurality of compressors, thereby to provide compressor capacity to said system responsive to said load requirements without predeterminably enabling a selected one of said compressors in an ordered and predetermined sequence prior to enabling a required another one of said compressors. 3. A multiple compressor refrigeration system for refrigerating spaces, comprising: a plurality of compressors, each having an inlet and an outlet, said compressors being operable individually or in various combinations, said system thereby capable of achieving any one of a plurality of discrete compressor capacity operating states, at least two of said compressors being connected in parallel and no two compressors being operable in a required fixed predetermined sequence; condenser means connected to said compressors for receiving a compressed working fluid therefrom; expansion and evaporator means connected to said condenser means for receiving condensed working fluid therefrom for expansion and evaporation thereof thereby to effect refrigeration of said spaces, said expansion and evaporation means connected to the inlet of said compressors to provide the expanded working fluid thereto; pressure-responsive means connected to said compressors for providing a signal output representative of the pressure of the working fluid on the inlet side of said compressors, said working fluid pressure representing the load requirements of said system and said pressure-representative signal representing a pressure value within one of a plurality of discrete zones of values each defined by a threshold pressure, said threshold pressures being sequentially and incrementally representative of deviations of system load from a preferred range of pressure values; and controller means connected to said pressure-responsive means for receiving said signal therefrom and connected to said compressors for effecting individual control of said compressors in response to said signal output, said controller means selecting any one of said compressor capacity operating states as a function of said pressure valve within said discrete pressure zone and the compressor capacity operating state in effect when said pressure-representative signal is received, said controller means responding to said sensed pressure-representative signal in a step independent of any possible intermediate compressor capacity operating states, said step determined at least in part as a function of the rate of working fluid pressure rise or fall, said controller thus controlling compressor capacity in accordance with system load by determining which one of said compressor capacity operating states optimally meets said system load by providing a signal for turning on or off selected ones of said plurality of compressors, thereby to provide compressor capacity to said system responsive to said load requirements without predeterminably enabling a selected one of said compressors in an ordered and predetermined sequence prior to enabling a required another one of said compressors; and temperature responsive means thermally coupled to said evaporation means and said controller for sensing the temperature of at least one evaporator in said system and providing a temperature signal representative thereof, said controller responding to said temperature signal to inhibit otherwise determined increases in compressor capacity when said temperature of said sensed evaporator is below a predetermined value. 4. The multiple compressor refrigeration system claimed in claims 1, 2 or 3 wherein: each of said compressors has a compressor capacity different from the others. 5. A method of operating a multiple compressor refrigeration system for refrigerating a space or a plurality of spaces of the type having a plurality of individually-operable compressors for compressing a working fluid, at least two of said compressors being connected in parallel and no two compressors being operable in a required fixed predetermined sequence, at least one of said compressors having a different compressor capacity from the others; a working fluid condenser connected to the outlet of said compressors for receiving compressed working fluid therefrom; working fluid expansion and evaporator means to cause expansion and evaporation of said compressed working fluid to effect refrigeration of said space or spaces thereby, said expansion and evaporator means connected to the inlet of said compressors to provide the expanded working fluid thereto from said expansion and evaporator means, pressure-responsive means connected to the inlet of said compressors for providing a measured-pressure signal, and controller means connected to said compressors for effecting operation thereof and connected to said pressure-responsive means for receiving said measured-pressure signal therefrom, said method comprising the steps of: (a) measuring the working fluid pressure on the inlet side of said compressors as an indication of the evaporator load of the system; (b) comparing said so-measured pressure with a preferred range of pressure values; (c) selecting at least one of all of the available compressor operating states as a function of said comparison between said so-measured pressure and said preferred pressure range, the operating state in effect when said measured-pressure signal is received, and the rate of pressure rise or fall; (d) implementing said selected compressor operating state by enabling selected ones of said plurality of compressors and disabling selected ones of said plurality of compressors; (e) repeating steps (a) and (b) on a continuous basis to determine if said pressure is within said preferred pressure range; and (f) repeating steps (c) and (d) if it is determined that said pressure is not within said preferred pressure range. 6. The method claimed in claim 5 wherein: each of said compressors has a different compressor capacity from the other. 7. The method claimed in claim 5 wherein: said multiple compressor refrigeration system further comprises temperature-responsive means thermally coupled to said evaporator means and said method further comprises the step, after said selecting step and before said implementing step, of measuring said evaporator temperature and enabling said controller for operation when said so-measured temperature is greater than a preselected limit. 8. A controller for controlling a plurality of refrigeration compressors, at least two of which are connected in parallel, in a refrigeration system in which no two compressors are operable in a required fixed predetermined sequence and at least one of said compressors is of unequal refrigeration capacity relative to the others, said compressors being operable individually or in various combinations, said system thereby capable of achieving any one of a plurality of discrete compressor capacity operating states, said refrigeration system including pressure-responsive means for measuring the system suction pressure representative of system load, said suction pressure having a value within one of a plurality of discrete zones of values each defined by a threshold pressure, said threshold pressures being sequentially and incrementally representative of deviations of system load from a predetermined preferred range of pressure values, said controller including means for comparing said so-called suction pressure with said preferred range of pressure values, said controller responding to the difference between said sensed suction pressure and said preferred range by selecting any one of said compressor capacity operating states in a step determined at least in part as a function of the operating state in effect when said suction pressure is sensed and the rate of suction pressure rise or fall, said step independent of any possible intermediate compressor capacity operating states, said controller thus controlling compressor capacity in accordance with system load by determining which one of said compressor capacity operating states optimally meets said system load and providing a signal for turning on or off selected ones of said plurality of compressors, thereby to provide compressor capacity to said system responsive to said load requirements without predeterminably enabling a selected one of said compressors in an ordered and predetermined sequence prior to enabling a required another one of said compressors. 9. The controller of claim 8 further including temperature sensing means for sensing temperatures of at least one of said refrigerated spaces and providing a temperature signal representative thereof, said controller responding to said temperature signal to inhibit otherwise determined increases in compressor capacity when said refrigerated space temperature is below a predetermined level. 10. The multiple compressor refrigeration system of claims 1 or 2 further including temperature sensing means for sensing temperature of at least one of said refrigerated spaces and providing a temperature signal representative thereof, said contoller responding to said temperature signal to inhibit otherwise determined increases in compressor capacity when said refrigerated space temperature is below a predetermined level. 11. A multiple compressor refrigeration system for refrigerating spaces, comprising: a plurality of compressors, each having an inlet and an outlet, said compressors being operable individually or in various combinations, said system thereby capable of achieving any one of a plurality of discrete compressor capacity operating states, at least two of said compressors being connected in parallel and no two compressors being operable in a required fixed predetermined sequence; condenser means connected to said compressors for receiving a compressed working fluid therefrom; expansion and evaporator means connected to said condenser means for receiving condensed working fluid therefrom for expansion and evaporation thereof thereby to effect refrigeration of said spaces, said expansion and evaporation means connected to the inlet of said compressors to provide the expanded working fluid thereto; pressure-responsive means connected to said compressors for providing a signal output representative of the pressure of the working fluid on the inlet side of said compressors, said working fluid pressure representing the load requirements of said system and said pressure-representative signal representing a pressure value within one of a plurality of discrete zones of values each defined by a threshold pressure, said threshold pressures being sequentially and incrementally representative of deviations of system load from a preferred range of pressure values; and microprocessor based controller means connected to said pressure-responsive means for receiving said signal therefrom and connected to said compressors for effecting individual control of said compressors in response to said signal output, said controller means selecting any one of said compressor capacity operating states as a function of said pressure value within said discrete pressure zone and the compressor capacity operating state in effect when said pressure-representative signal is received, said controller means responding to said sensed pressure-representative signal in a step independent of any possible intermediate compressor capacity operating states, said step determined at least in part as a function of the rate of working fluid pressure rise or fall, said controller thus controlling compressor capacity in accordance with system load by determining which one of said compressor capacity operating states optimally meets said system load and providing a signal for turning on or off selected ones of said plurality of compressors, thereby to provide compressor capacity to said system responsive to said load requirements without predeterminably enabling a selected one of said compressors in an ordered and predetermined sequence prior to enabling a required another one of said compressors. 12. A multiple compressor refrigeration system for refrigerating a plurality of discrete spaces, comprising: a plurality of compressors, each having an inlet and an outlet, said compressors being operable individually or in various combinations, said system thereby capable of achieving any one of a plurality of discrete compressor capacity operating states, at least two of said compressors being connected in parallel and no two compressors being operable in a required fixed predetermined sequence, at least one of said compressors having a compressor capacity different from another; condenser means connected to said compressors for receiving a compressed working fluid therefrom; expansion and evaporator means connected to said condenser means for receiving condensed working fluid therefrom for expansion and evaporation thereof to effect refrigeration of said discrete spaces, said expansion and evaporation means connected to the inlet of said compressors to provide the expanded working fluid thereto; pressure-responsive means connected to said compressors for providing a signal ouput representative of the pressure of the working fluid on the inlet side of said compressors, said signal output being representative of operating evaporator load for said system; and microprocessor based controller means connected to said pressure-responsive means for receiving said signal therefrom and connected to said compressors for effecting individual control of said compressors in response to said signal output, said controller means including means for comparing said measured inlet pressure with predetermined pressure limits for successively higher pressure ranges relative to a preferred pressure range and with predetermined pressure limits for successively lower pressure ranges relative to said preferred pressure range, said controller independently selecting cumulatively greater compressor capacity states for each successive pressure-range increase and independently selecting cumulatively lower compressor states for each successive pressure-range decrease, said controller means responding to the difference between said measured inlet pressure and said preferred pressure-range in a step determined at least in part as a function of the operating state in effect when said pressure-representative signal is received and the rate of working fluid pressure rise or fall, said step independent of any possible intermediate compressor capacity operating states, said controller thus controlling compressor capacity in accordance with system load by determining which one of said compressor capacity operating states optimally meets said system load and providing a signal for turning on or off selected ones of said plurality of compressors, thereby to provide compressor capacity to said system responsive to said load requirements without predeterminably enabling a selected one of said compressors in an ordered and predetermined sequence prior to enabling a required another one of said compressors. 13. A multiple compressor refrigeration system for refrigerating spaces, comprising: a plurality of compressors, each having an inlet and an outlet, said compressors being operable individually or in various combinations, said system thereby capable of achieving any one of a plurality of discrete compressor capacity operating states, at least two of said compressors being connected in parallel and no two compressors being operable in a required fixed predetermined sequence; condenser means connected to said compressors for receiving a compressed working fluid therefrom; expansion and evaporator means connected to said condenser means for receiving condensed working fluid therefrom for expansion and evaporation thereof thereby to effect refrigeration of said spaces, said expansion and evaporation means connected to the inlet of said compressors to provide the expanded working fluid thereto; pressure-responsive means connected to said compressors for providing a signal output representative of the pressure of the working fluid on the inlet side of said compressors, said working fluid pressure representing the load requirements of said system and said pressure-representative signal representing a pressure value within one of a plurality of discrete zones of values each defined by a threshold pressure, said threshold pressures being sequentially and incrementally representative of deviations of system load from a preferred range of pressure values; and microprocessor based controller means connected to said pressure-responsive means for receiving said signal therefrom and connected to said compressors for effecting individual control of said compressors in response to said signal output, said controller means selecting any one of said compressor capacity operating states as a function of said pressure valve within said discrete pressure zone and the compressor capacity operating state in effect when said pressure-representative signal is received, said controller means responding to said sensed pressure-representative signal in a step independent of any possible intermediate compressor capacity operating states, said step determined at least in part as a function of the rate of working fluid pressure rise or fall, said controller thus controlling compressor capacity in accordance with system load by determining which one of said compressor capacity operating states optimally meets said system load by providing a signal for turning on or off selected ones of said plurality of compressors, thereby to provide compressor capacity to said system responsive to said load requirements without predeterminably enabling a selected one of said compressors in an ordered and predetermined sequence prior to enabling a required another one of said compressors; and temperature responsive means thermally coupled to said evaporation means and said controller for sensing the temperature of at least one evaporator in said system and providing a temperature signal representative thereof, said controller responding to said temperature signal to inhibit otherwise determined increases in compressor capacity when said temperature of said sensed evaporator is below a predetermined value. 14. The multiple compressor refrigeration system claimed in claims 11, 12 or 13 wherein: each of said compressors has a compressor capacity different from the others. 15. A method of operating a multiple compressor refrigeration system for refrigerating a space or a plurality of spaces of the type having a plurality of individually-operable compressors for compressing a working fluid, at least two of said compressors being connected in parallel and no two compressors being operable in a required fixed predetermined sequence, at least one of said compressors having a different compressor capacity from the others; a working fluid condenser connected to the outlet of said compressors for receiving compressed working fluid therefrom; working fluid expansion and evaporator means to cause expansion and evaporation of said compressed working fluid to effect refrigeration of said space or spaces thereby, said expansion and evaporator means connected to the inlet of said compressors to provide the expanded working fluid thereto from said expansion and evaporator means, pressure-responsive means connected to the inlet of said compressors for providing a measured-pressure signal, and microprocessor based controller means connected to said compressors for effecting operation thereof and connected to said pressure-responsive means for receiving said measured-pressure signal therefrom, said method comprising the steps of: (a) measuring the working fluid pressure on the inlet side of said compressors as an indication of the evaporator load of the system; (b) comparing said so-measured pressure with a preferred range of pressure values; (c) selecting at least one of all of the available compressor operating states as a function of said comparison between said so-measured pressure and said preferred pressure range, the operating state in effect when said measured-pressure signal is received, and the rate of pressure rise or fall; (d) implementing said selected compressor operating state by enabling selected ones of said plurality of compressors and disabling selected ones of said plurality of compressors; (e) repeating steps (a) and (b) on a continuous basis to determine if said pressure is within said preferred pressure range; and (f) repeating steps (c) and (d) if it is determined that said pressure is not within said preferred pressure range. 16. The method claimed in claim 15 wherein: each of said compressors has a different compressor capacity from the other. 17. The method claimed in claim 15 wherein: said multiple compressor refrigeration system further comprises temperature-responsive means thermally coupled to said evaporator means and said method further comprises the step, after said selecting step and before said implementing step, of measuring said evaporator temperature and enabling said controller for operation when said so-measured temperature is greater than a preselected limit. 18. A microprocessor based controller for controlling a plurality of refrigeration compressors, at least two of which are connected in parallel, in a refrigeration system in which no two compressors are operable in a required fixed predetermined sequence and at least one of said compressors is of unequal refrigeration capacity relative to the others, said compressors being operable individually or in various combinations, said system thereby capable of achieving any one of a plurality of discrete compressor capacity operating states, said refrigeration system including pressure-responsive means for measuring the system suction pressure representative of system load, said suction pressure having a value within one of a plurality of discrete zones of values each defined by a threshold pressure, said threshold pressures being sequentially and incrementally representative of deviations of system load from a predetermined preferred range of pressure values, said controller including means for comparing said so-called suction pressure with said preferred range of pressure values, said controller responding to the difference between said sensed suction pressure and said preferred range by selecting any one of said compressor capacity operating states in a step determined at least in part as a function of the operating state in effect when said suction pressure is sensed and the rate of suction pressure rise or fall, said step independent of any possible intermediate compressor capacity operating states, said controller thus controlling compressor capacity in accordance with system load by determining which one of said compressor capacity operating states optimally meets said system load and providing a signal for turning on or off selected ones of said plurality of compressors, thereby to provide compressor capacity to said system responsive to said load requirements without predeterminably enabling a selected one of said compressors in an ordered and predetermined sequence prior to enabling a required another one of said compressors. 19. The microprocessor based controller of claim 18 further including temperature sensing means for sensing temperatures of at least one of said refrigerated spaces and providing a temperature signal representative thereof, said controller responding to said temperature signal to inhibit otherwise determined increases in compressor capacity when said refrigerated space temperature is below a predetermined level. 20. The multiple compressor refrigeration system of claims 11 or 12 further including temperature sensing means for sensing temperature of at least one of said refrigerated spaces and providing a temperature signal representative thereof, said contoller responding to said temperature signal to inhibit otherwise determined increases in compressor capacity when said refrigerated space temperature is below a predetermined level.