Compressor cycling control for variable flow systems

Abstract

Systems and methods for preventing excessive restarting of compressors in variable primary flow systems operating at low loads, with system embodiments including temperature sensors both upstream and downstream from a heat exchanger, using the sensor downstream from the heat exchanger to determine when to stop a compressor and the sensor upstream from the heat exchanger to determine when to start the compressor. Methods may include a delay period between restarting operations of the compressor, or use a soft loading period in which the compressor is operated at a low level to reduce the frequency of starts and stops.

1 . A variable flow system comprising:
 a pump,   a chiller including a compressor and a heat exchanger,   at least one sensor measuring one or more operational parameters of the variable flow system,   one or more cooling coils, and   a processor, connected to the at least one sensor and the compressor, the processor:
 determines, based on at least one of the one or more operational parameters, whether a stopping threshold satisfied; 
 commands the compressor to stop when the stopping threshold is satisfied; 
 determines, based on at least one of the one or more operational parameters, whether a starting threshold is satisfied; 
 determines a starting condition for the compressor; 
 operates the compressor, based on the starting condition and the satisfaction of the starting threshold. 
   
     
     
         2 . The variable flow system of  claim 1 , wherein the one or more operational parameters comprises at least one of:
 a temperature measurement from a temperature sensor located upstream of the heat exchanger with respect to a fluid flow through the heat exchanger;   a temperature measurement from a temperature sensor downstream of the heat exchanger with respect to the fluid flow through the heat exchanger;   a temperature measurement from a temperature sensor downstream of a bypass and upstream of the one or more cooling coils with respect to a fluid flow through the variable flow system; and   a temperature measurement from a temperature sensor upstream of a bypass pipe by downstream of the one or more cooling coils with respect to the fluid flow through the variable flow system.   
     
     
         3 . The variable flow system of  claim 1 , wherein the processor sets a delay period preventing starting of the compressor for a period of time following the starting of the compressor. 
     
     
         4 . The variable flow system of  claim 3 , wherein the delay period is a dynamic value based on a number of compressor starts within a predetermined time period. 
     
     
         5 . The variable flow system of  claim 1 , wherein the starting condition for the compressor comprises a soft loading period. 
     
     
         6 . The variable flow system of  claim 5 , wherein the soft loading period is determined based on the number of starting operations of the compressor in a selected time period. 
     
     
         7 . The variable flow system of  claim 5 , wherein the soft loading period is determined based on variable flow system design conditions and a temperature measurement. 
     
     
         8 . The variable flow system of  claim 1 , wherein the starting condition for the compressor is a soft loading rate of loading. 
     
     
         9 . The variable flow system of  claim 8 , wherein the soft loading rate of loading is determined based on the number of starting operations of the compressor in a selected time period. 
     
     
         10 . The variable flow system of  claim 8 , wherein the soft loading rate of loading is determined based on variable flow system design conditions and a temperature measurement. 
     
     
         11 . A method for controlling a compressor in a variable flow system, comprising:
 measuring one or more operational parameters of the variable flow system;   comparing the at least one of the one or more operational parameters to a starting threshold;   determining, based on a starting condition, a compressor start procedure;   operating the compressor according to the determined compressor start procedure.   
     
     
         12 . The method of  claim 11 , wherein the one or more operational parameters comprise a first temperature measured by a temperature sensor that is located upstream from a heat exchanger connected to the compressor with respect to the direction of fluid flow in the variable flow system. 
     
     
         13 . The method of  claim 11 , further comprising:
 comparing at least one of the one or more operational parameters to a stopping threshold; and   stopping the compressor based on the comparison of the at least one of the one or more operational parameters and the stopping threshold.   
     
     
         14 . The method of  claim 13 , wherein the one or more operational parameters comprise a temperature measured by a temperature sensor that is located downstream from a heat exchanger connected to the compressor with respect to the direction of fluid flow in the variable flow system. 
     
     
         15 . The method of  claim 11 , wherein the starting condition comprises a delay period between starting operations for the compressor and the determined start procedure comprises a time at which to start the compressor. 
     
     
         16 . The method of  claim 11 , wherein the starting condition comprises a soft loading period for the compressor and the determined start procedure comprises a compressor capacity and a period of time to operate the compressor at the compressor capacity. 
     
     
         17 . The method of  claim 11 , further comprising determining a starting condition based on a number of compressor starting operations within a predetermined period of time. 
     
     
         18 . The method of  claim 11 , further comprising determining a starting condition based on variable flow system design conditions and a temperature measurement. 
     
     
         19 . A control system for a compressor, comprising:
 at least one sensor measuring one or more operational parameters,   a memory, storing a starting threshold temperature and a stopping threshold temperature;   a processor, connected to the at least one sensor and the compressor, the processor:
 determines, based on at least one of the one or more operational parameters, whether a stopping threshold satisfied; 
 commands the compressor to stop when the stopping threshold is satisfied; 
 determines, based on at least one of the one or more operational parameters, whether a starting threshold is satisfied; 
 determines a starting condition for the compressor; and 
 operates the compressor, based on the starting condition and the satisfaction of the starting threshold. 
   
     
     
         20 . The control system of  claim 19 , wherein the one or more operational parameters comprise at least one of:
 a temperature measurement from a temperature sensor that is located downstream of a heat exchanger with respect to a fluid flow through the heat exchanger;   a temperature measurement from a temperature sensor downstream of the heat exchanger with respect to the fluid flow through the heat exchanger;   a temperature measurement from a temperature sensor downstream of a bypass and upstream of the one or more cooling coils with respect to a fluid flow through the variable flow system; and   a temperature measurement from a temperature sensor upstream of a bypass pipe by downstream of the one or more cooling coils with respect to the fluid flow through the variable flow system.