Control for commercial refrigeration system

Capacity control system for a commercial refrigeration system having at least one refrigerator case, said refrigeration system including a compressor system for compressing refrigerant, said compressor system including a variable speed compressor and multiple fixed speed compressors of different capacities whereby the capacity of said system can be controlled by varying the speed of the variable speed compressor and by starting and stopping one or more of the fixed speed compressors, said control system including load sensing means for detecting a variable indicative of the refrigeration load on the system, means for comparing said variable with a target value and generating a difference signal varying in accordance with the difference between the variable and the target value, and calculating means for forming an array of the capacities of the varying combinations of the fixed speed compressors and for generating a compressor control signal as a function of the difference signal representing the capacity of the system required by the system load, said calculating means further including means for selecting a system fixed speed compressor capacity from said array and controlling the speed of said variable speed compressor to provide an approximate total system compressor capacity represented by the compressor control signal, said calculating means calculating a range of desired speeds of said variable speed compressor, said system fixed speed compressor capacity being selected to maintain the speed of said variable speed compressor within said range.

Capacity control system for a commercial refrigeration system having at least one refrigerator case, said refrigeration system including a compressor system for compressing refrigerant, said compressor system including a variable speed compressor and multiple fixed speed compressors of different capacities whereby the capacity of said system can be controlled by varying the speed of the variable speed compressor and by starting and stopping one or more of the fixed speed compressors, said control system including load sensing means for detecting a variable indicative of the refrigeration load on the system, means for comparing said variable with a target value and generating a difference signal varying in accordance with the difference between the variable and the target value, and calculating means for forming an array of the capacities of the varying combinations of the fixed speed compressors and for generating a compressor control signal as a function of the difference signal representing the capacity of the system required by the system load, said calculating means further including means for selecting a system fixed speed compressor capacity from said array and controlling the speed of said variable speed compressor to provide an approximate total system compressor capacity represented by the compressor control signal, said calculating means calculating a range of desired speeds of said variable speed compressor, said calculating means including means for calculating the upper and lower boundaries for the compressor capacity of the fixed speed compressors to be selected from said array, selecting means for selecting a combination of compressors from said array within said range, and means for setting the speed of said variable speed compressor.

Method of controlling capacity of a commercial refrigeration system having at least one refrigerator case, said refrigeration system including a compressor system for compressing refrigerant, said compressor system including a variable speed compressor and multiple fixed speed compressors of different capacities, comprising the steps of controlling the capacity of said system by varying the speed of the variable speed compressor and by starting and stopping one or more of the fixed speed compressors by detecting a variable indicative of the refrigeration load on the system, comparing said variable with a target value and generating a difference signal varying in accordance with the difference between the variable and the target value, forming an array of the capacities of the varying combinations of the fixed speed compressors, generating a compressor control signal as a function of the difference signal representing the capacity of the system required by the system load, selecting a system fixed speed compressor capacity from said array, controlling the speed of said variable speed compressor to provide an approximate total system compressor capacity represented by the compressor control signal, calculating a range of desired speeds of said variable speed compressor and selecting said system fixed speed compressor capacity to maintain the speed of said variable speed compressor within said range.

Method of controlling capacity of a commercial refrigeration system having at least one refrigerator case, said refrigeration system including a compressor system for compressing refrigerant, said compressor system including a variable speed compressor and multiple fixed speed compressors of different capacities, comprising the steps of controlling the capacity of said system by varying the speed of the variable speed compressor and by starting and stopping one or more of the fixed speed compressors by detecting a variable indicative of the refrigeration load on the system, comparing said variable with a target value and generating a difference signal varying in accordance with the difference between the variable and the target value, forming an array of the capacities of the varying combinations of the fixed speed compressors, generating a compressor control signal as a function of the difference signal representing the capacity of the system required by the system load, selecting a system fixed speed compressor capacity from said array, controlling the speed of said variable speed compressor to provide an approximate total system compressor capacity represented by the compressor control signal, calculating the upper and lower boundaries for the compressor capacity of the fixed speed compressors to be selected from said array, selecting a combination of compressors from said array within said range, and setting the speed of said variable speed compressor.