Compressor Capacity Modulation System For Multiple Compressors

Abstract

A system includes a plurality of compressors, an evaporator, an expansion device, and a system controller. The compressors may be linked in parallel. The system controller may: determine a saturated evaporator temperature, a saturated condensing temperature, and a target capacity demand; determine an estimated system capacity and an estimated power consumption for each compressor operating configuration; compare the estimated system capacity with the target capacity demand and an error tolerance value; select an optimum operating mode based on the comparisons and based on the estimated power consumption; and command activation and deactivation of the plurality of compressors to achieve the selected optimum operating mode. The optimum operating mode may be selected after the normal system logic achieves a steady state and may be selected from a group having the estimated system capacity within the error tolerance of the target capacity demand and a lowest associated power consumption value.

What is claimed is: 
     
         1 . A system comprising:
 a plurality of compressors linked in parallel by a common discharge line and a common suction line;   an evaporator;   a condenser; and   a system controller that determines a saturated evaporator temperature of the evaporator, a saturated condensing temperature of the condenser, a target capacity demand for the plurality of compressors, and an estimated system capacity and an estimated power consumption for each operating configuration of the plurality of compressors based on the saturated evaporator temperature and the saturated condensing temperature;   wherein the system controller compares the estimated system capacity for each operating configuration with the target capacity demand and an error tolerance value and selects an optimum operating mode of the plurality of compressors based on the comparisons and the estimated power consumption for each operating configuration, the optimum operating mode being selected from a group of operating configurations having the estimated system capacity within the error tolerance of the target capacity demand and the optimum operating mode having a lowest associated power consumption value in the group; and   wherein the system controller commands activation and deactivation of the plurality of compressors to achieve the selected optimum operating mode.   
     
     
         2 . The system of  claim 1 , wherein the plurality of compressors includes at least one fixed capacity compressor and at least one two-stage compressor. 
     
     
         3 . The system of  claim 2 , wherein the at least one two-stage compressor includes a compressor having a delayed suction system. 
     
     
         4 . The system of  claim 2 , wherein the at least one two-stage compressor includes a compressor having a variable speed motor. 
     
     
         5 . The system of  claim 2 , wherein the at least one two-stage compressor includes a compressor having a scroll separation system. 
     
     
         6 . The system of  claim 1 , wherein the plurality of compressors includes a variable volume ratio compressor. 
     
     
         7 . The system of  claim 1 , wherein the estimated system capacity is calculated based on characteristics of each of the plurality of compressors. 
     
     
         8 . The system of  claim 1 , wherein the operating configuration for the plurality of compressors includes a location of each of the plurality of compressors and a coefficient performance curve for each of the plurality of compressors. 
     
     
         9 . The system of  claim 1 , wherein the system controller determines the estimated power consumption for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration. 
     
     
         10 . The system of  claim 1 , wherein the system controller determines the estimated system capacity for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration. 
     
     
         11 . The system of  claim 1 , wherein the system controller determines whether the plurality of compressors have stabilized before selecting the optimum operating mode, the determination of whether the plurality of compressors have stabilized being based on an output of at least one of a current sensor, a common suction line temperature sensor, a common discharge line temperature sensor, a common suction line pressure sensor, and a common discharge line pressure sensor. 
     
     
         12 . The system of  claim 1 , wherein the plurality of compressors includes two fixed capacity compressors having different capacities and one two-stage compressor, and has eleven associated operating configurations. 
     
     
         13 . The system of  claim 1 , wherein the plurality of compressors includes two fixed capacity compressors and one two-stage compressor with different capacities, and has seven associated operating configurations. 
     
     
         14 . A system comprising:
 a first circuit having a first plurality of compressors linked in parallel by a first common discharge line and a first common suction line;   a second circuit having a second plurality of compressors linked in parallel by a second common discharge line and a second common suction line; and   a system controller that determines an estimated system capacity and an estimated power consumption for each operating configuration of the plurality of compressors in the first circuit and the plurality of compressors in the second circuit based on a saturated evaporator temperature and a saturated condensing temperature;   wherein the system controller selects an optimum operating mode of the plurality of compressors in the first circuit and the plurality of compressors in the second circuit based on a comparison of the estimated system capacity for each operating configuration with a target capacity demand and an error tolerance value and based on the estimated power consumption for each operating configuration, the optimum operating mode being selected from a group of operating configurations having the estimated system capacity within the error tolerance of the target capacity demand and the optimum operating mode having a lowest associated power consumption value in the group; and   wherein the system controller commands activation and deactivation of the plurality of compressors in the first circuit and the plurality of compressors in the second circuit to achieve the selected optimum operating mode.   
     
     
         15 . A method for operating a system comprising:
 determining a saturated evaporator temperature of the evaporator, a saturated condensing temperature of the condenser, and a target capacity demand for a plurality of compressors;   determining an estimated system capacity and an estimated power consumption for each operating configuration of the plurality of compressors based on the saturated evaporator temperature and the saturated condensing temperature;   comparing the estimated system capacity for each operating configuration with the target capacity demand and an error tolerance value;   selecting an optimum operating mode of the plurality of compressors based on the comparisons and based on the estimated power consumption for each operating configuration, the optimum operating mode being selected from a group of operating configurations having the estimated system capacity within the error tolerance of the target capacity demand and the optimum operating mode having a lowest associated power consumption value in the group; and   commanding activation and deactivation of the plurality of compressors to achieve the selected optimum operating mode.   
     
     
         16 . The method of  claim 15 , wherein the plurality of compressors includes at least one of a fixed capacity compressor, a two-stage compressor, and a variable volume ratio compressor, wherein if the plurality of compressors includes the two-stage compressor, the two-stage compressor includes at least one of a compressor having a delayed suction system, a compressor having a variable speed motor, and a compressor having a scroll separation system. 
     
     
         17 . The method of  claim 15 , further comprising calculating the estimated system capacity based on the operating configuration for the plurality of compressors. 
     
     
         18 . The method of  claim 17 , wherein the operating configuration for the plurality of compressors includes a location of each of the plurality of compressors and a ten coefficient performance curve for each of the plurality of compressors. 
     
     
         19 . The method of  claim 15 , further comprising determining the estimated power consumption for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration. 
     
     
         20 . The method of  claim 15 , further comprising determining the estimated system capacity for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration. 
     
     
         21 . The method of  claim 15 , further comprising determining whether the plurality of compressors have stabilized before selecting the optimum operating mode, the determination of whether the plurality of compressors have stabilized being based on an output of at least one of a current sensor, a common suction line temperature sensor, a common discharge line temperature sensor, a common suction line pressure sensor, and a common discharge line pressure sensor.