Refrigeration systems having prescriptive refrigerant flow control

Abstract

A refrigeration system for a frozen product dispenser is controlled to have a variable cooling capacity that is determined by variable cooling load demands of the dispenser. This is accomplished, in part, by providing the refrigeration system with a variable speed compressor and one or more adjustable expansion valves for metering refrigerant to associated evaporators that are heat exchange coupled to associated freeze barrels of the dispenser, and by controlling the metering setting of the expansion valves and the speed of operation of the compressor in accordance with the cooling load demands of the dispenser. The arrangement provides for efficient operation of the refrigeration system from an energy standpoint and for a reduction in on/off cycling of the system.

1 . A refrigeration system, comprising:
 an evaporator for being heat exchange coupled to a load to be chilled to within a selected temperature range, wherein the load is of a type that places a variable heat load on the refrigeration system;   an adjustable expansion valve for metering refrigerant to said evaporator at selected flow rates;   a variable speed compressor for delivering refrigerant to said expansion valve at selected flow rates determined by the speed of operation of said compressor, the refrigerant being metered by said expansion valve to said evaporator to cool said evaporator to chill the load; and   means for operating said refrigeration system to adjust said expansion valve to meter refrigerant to said evaporator at a flow rate, and to control the speed of operation of said compressor to deliver refrigerant to said expansion valve at a flow rate, determined in accordance with the heat load placed on said refrigeration system by the load.   
   
   
       2 . A refrigeration system as in  claim 1 , wherein in response to a heat load being placed on said refrigeration system by the load, said means for operating adjusts said expansion valve refrigerant metering rate, and controls said compressor operating speed and thereby said compressor refrigerant delivery rate, such that said refrigeration system provides a selected cooling output to said evaporator and thereby to the load within a selected time. 
   
   
       3 . A refrigeration system as in  claim 1 , wherein said means for operating comprises:
 means for sensing the cooling requirement of the load in order to chill the load to within the selected temperature range;   means responsive to said sensing means for determining the mass flow of refrigerant through said expansion valve necessary for said evaporator to at least closely chill the load to within the selected temperature range and for also determining the flow rate of refrigerant through said expansion valve in order for said expansion valve to meter the determined mass flow of refrigerant to said evaporator within a determined cycle time;   means for adjusting said expansion valve to meter the determined mass flow of refrigerant to said evaporator within the determined cycle time; and   means for operating said compressor at a speed to deliver the determined mass flow of refrigerant to said expansion valve within the determined cycle time.   
   
   
       4 . A refrigeration system for a frozen product dispenser, comprising:
 an evaporator for being heat exchange coupled to a freeze barrel of a frozen product dispenser to chill product in the barrel to within a selected temperature range, the barrel being of a type from which frozen product is dispensed and into which relatively warm product is flowed to replace dispensed product, the barrel placing on said refrigeration system a heat load that varies with flow of relatively warm product into the barrel;   an adjustable expansion valve for metering refrigerant to said evaporator at selected flow rates;   a variable speed compressor for delivering refrigerant to said expansion valve at selected flow rates determined by the speed of operation of said compressor, the refrigerant being metered by said expansion valve to said evaporator to cool said evaporator to chill product in the barrel; and   means for operating said refrigeration system to adjust said expansion valve to meter refrigerant to said evaporator at flow rates, and to control the speed of operation of said compressor to deliver refrigerant to said expansion valve at flow rates, determined in accordance with the heat load placed on said refrigeration system by product in the barrel, and thereby in accordance with the cooling requirement of product in the barrel to be supplied by said refrigeration system.   
   
   
       5 . A refrigeration system as in  claim 4 , including means for sensing the cooling requirement of product in the barrel, said sensing means comprising means for monitoring the amount and temperature of relatively warm replacement product flowed into the barrel, and means responsive to said monitoring means for determining the number of Btu's of cooling required to be provided by said refrigeration system to chill product in the barrel to within the selected temperature range. 
   
   
       6 . A refrigeration system as in  claim 4 , including means for sensing the cooling requirement of product in the barrel, and means for determining the volume flow of refrigerant that must be metered to said evaporator for said refrigeration system to provide the sensed cooling requirement of product in the barrel, said means for operating adjusting said expansion valve and controlling the speed of operation of said compressor to meter the determined volume of refrigerant to said evaporator within a selected cycle time. 
   
   
       7 . A refrigeration system as in  claim 4 , including means for sensing the number of Btu's of cooling required to be provided by said refrigeration system to chill product in the barrel to within the selected temperature range, said sensing means comprising a Btu counter, means responsive to each flow of relatively warm product into the barrel for incrementing a count in said Btu counter by the number of Btu's of cooling to be provided by said refrigeration system to chill the product flowed into the barrel to within the selected temperature range, and means for decrementing the count in said Btu counter by the number of cooling Btu's provided by said refrigeration system to product in the barrel, whereby the count in said Btu counter is representative of the number of Btu's of cooling required to be provided by said refrigeration system to chill product in the barrel to within the selected temperature range. 
   
   
       8 . A refrigeration system as in  claim 7 , wherein said operating means operates said refrigeration system to have a cooling capacity that varies in accordance with the magnitude of the count in said Btu counter. 
   
   
       9 . A refrigeration system as in  claim 4 , including means for sensing the heat load placed on said refrigeration system by product in the barrel, said sensing means comprising a Btu counter, and means responsive to a flow of relatively warm product into the barrel to increment a count in the counter by the number of Btu's of cooling required to be provided by said refrigeration system to chill the product flowed into the barrel to a temperature within the selected temperature range, and means for decrementing the count in the counter by the number of Btu's of cooling provided by said refrigeration system to product in the barrel, said operating means controlling said refrigeration system to have a cooling capacity such that, following a flow of product into the barrel and in the absence of a further flow of product into the barrel, the count in said Btu counter will be decremented to zero over a selected period of time. 
   
   
       10 . A refrigeration system as in  claim 4 , including means for sensing the temperature and viscosity of product in the barrel, and means for terminating operation of said refrigeration system to chill product in the barrel upon the sensed temperature and viscosity being within selected temperature and viscosity ranges. 
   
   
       11 . A refrigeration system as in  claim 4 , wherein said means for operating is responsive to the heat load placed on the refrigeration system by product in the barrel to adjust said expansion valve to meter to said evaporator a selected amount of liquid refrigerant within a determined cycle time in order to provide a selected amount of cooling for product in the barrel within the cycle time, and to control the speed of operation of said compressor so as to deliver refrigerant to said expansion valve at a rate that is not significantly greater than the metering rate of said expansion valve. 
   
   
       12 . A refrigeration system as in  claim 4 , including means for sensing the cooling requirement of product in the barrel to be provided by said refrigeration system, said means for operating said refrigeration system being responsive to said means for sensing to operate said refrigeration system at a capacity selected to chill product in the barrel to a temperature within the selected temperature range within a determined cycle time, and said operating means increasing the cooling capacity of said refrigeration system in response to a sensed increase in the cooling requirement of product in the barrel while said refrigeration system is chilling product in the barrel. 
   
   
       13 . A refrigeration system as in  claim 4 , wherein the frozen product dispenser has a product pre-chiller through which replacement product flows before flowing into the barrel, said refrigeration system further including a second evaporator for being heat transfer coupled to the product pre-chiller, and a second expansion valve for metering refrigerant to said second evaporator, said variable speed compressor also delivering refrigerant to said second expansion valve for being metered to said second evaporator to chill the pre-chiller to chill product flowed through the pre-chiller, said means for operating being responsive to a flow of product through the pre-chiller to the barrel to operate said compressor to deliver refrigerant to said second expansion valve and to operate said second expansion valve to meter refrigerant to said second evaporator to chill said second evaporator and thereby to chill the pre-chiller and product flowed through the pre-chiller. 
   
   
       14 . A method of operating a refrigeration system having an evaporator heat exchange coupled to a load that places a variable heat load on the refrigeration system and is to be chilled to within a selected temperature range, an expansion valve that is adjustable to meter refrigerant to the evaporator at selected flow rates, and a compressor that is operable at various speeds to deliver refrigerant to the expansion at selected flow rates, said method comprising the steps of:
 sensing the heat load being placed on the refrigeration system by the load;   adjusting, in response to said sensing step, the expansion valve to meter refrigerant to the evaporator at flow rates in accordance with the sensed heat load being placed on the refrigeration system by the load; and   controlling, in response to said sensing step, the speed of operation of the compressor to deliver refrigerant to the expansion valve at flow rates in accordance with the heat load being placed on the refrigeration system by the load.   
   
   
       15 . A method as in  claim 14 , wherein said adjusting and operating steps adjust the expansion valve refrigerant metering rate and control the compressor operating speed in accordance with the sensed heat load and such that the refrigeration system provides a selected amount of cooling to the load within a selected time. 
   
   
       16 . A method as in  claim 14 , including the of determining the mass flow of refrigerant to the evaporator that is required to chill the load to a temperature within the selected temperature range, and determining the flow rate of refrigerant through the expansion valve in order for the expansion valve to meter the determined mass flow of refrigerant to the evaporator within a selected time, said adjusting step adjusting the expansion valve to meter the determined mass flow of refrigerant to the evaporator within the selected time and said operating step operating the compressor at a speed to deliver the determined mass flow of refrigerant to the expansion valve within the selected time. 
   
   
       17 . A method of operating a refrigeration system for a frozen product dispenser, having a freeze barrel from which frozen product is dispensed and into which relatively warm product is flowed to replace dispensed product, the barrel placing on the refrigeration system a heat load that varies with flow of relatively warm replacement product into the barrel, and wherein the refrigeration system has an evaporator heat exchange coupled to the barrel, an expansion valve that is adjustable to meter refrigerant to the evaporator at selected flow rates, and a variable speed compressor for delivering refrigerant to the expansion valve at flow rates in accordance with its speed of operation, said method comprising the steps of:
 sensing the heat load being placed on the refrigeration system by the freeze barrel;   adjusting, in response to said sensing step, the expansion valve to meter refrigerant to the evaporator at a flow rate in accordance with the sensed heat load being placed on the refrigeration system by the barrel; and   controlling, in response to said sensing step, the speed of operation of the compressor to deliver refrigerant to the expansion valve at a flow rate in accordance with the sensed heat load being placed on the refrigeration system by the barrel to chill product in the barrel to a temperature within a selected temperature range.   
   
   
       18 . A method as in  claim 17 , wherein said sensing step comprises the steps of monitoring the amount and temperature of relatively warm replacement product flowed into the barrel and, in response to said monitoring step, determining the number of Btu's of cooling required to be provided by the refrigeration system to chill product in the barrel to within the selected temperature range. 
   
   
       19 . A method as in  claim 17 , including the step, responsive to said sensing step, of determining the volume flow of liquid refrigerant to be metered to the evaporator to chill product in the barrel to within the selected temperature range, said adjusting and controlling steps adjusting the metering rate of the expansion valve and controlling the speed of operation of the compressor to meter the determined volume of liquid refrigerant to the evaporator within a selected time. 
   
   
       20 . A method as in  claim 17 , wherein said sensing step comprises the steps of incrementing into a Btu counter, in response to a flow of relatively warm product into the barrel, a count representative of the number of Btu's of cooling required to be provided by the refrigeration system to chill the product flowed into the barrel to within the selected temperature range, and decrementing from the Btu counter, in response to cooling of the product in the barrel by the refrigeration system, a count representative of the number of Btu's of cooling provided by the refrigeration system to product in the barrel, whereby the count in the Btu counter is representative of the number of Btu's of cooling required to be provided by the refrigeration system to chill product in the barrel to within the selected temperature range, said sensing step sensing the count in the Btu counter. 
   
   
       21 . A method as in  claim 20 , wherein said adjusting and controlling steps adjust the metering rate of the expansion valve and control the operating speed of the compressor so that the refrigeration system has a cooling capacity that varies directly in accordance with the magnitude of the count in the Btu counter. 
   
   
       22 . A method as in  claim 20 , wherein said adjusting and controlling steps are performed such that, in the absence of a flow of product into the barrel, the count in the Btu counter will be decremented to zero within a selected period of time. 
   
   
       23 . A method as in  claim 17 , including the steps of monitoring the temperature and viscosity of product in the barrel, and terminating operation of the refrigeration system to chill product in the barrel upon the monitored temperature and viscosity of the product being within selected temperature and viscosity ranges. 
   
   
       24 . A method as in  claim 17 , wherein said adjusting and controlling steps are responsive to said sensing step to adjust the expansion valve metering rate to meter to the evaporator a selected amount of liquid refrigerant within a determined cycle time in order to provide a selected amount of cooling for product in the barrel within the cycle time, and to control the speed of operation of the compressor to deliver refrigerant to the expansion valve at a rate that is not significantly greater than the metering rate of the expansion valve. 
   
   
       25 . A method as in  claim 17 , wherein said adjusting and controlling steps are responsive to said sensing step to adjust the metering rate of the expansion valve and operate the compressor at a speed to provide a cooling capacity of the refrigeration system that chills product in the barrel to a temperature within the selected temperature range within in a determined cycle time, and including the step, performed while the refrigeration system is providing a first cooling capacity, of controlling said adjusting and controlling steps to increase the cooling capacity of the refrigeration system to a second and greater cooling capacity in response to a sensed increase in the heat load placed on the refrigeration system by the barrel. 
   
   
       26 . A method as in  claim 17 , wherein the frozen product dispenser has a product pre-chiller through which the relatively warm product flows before flowing into the barrel, the refrigeration system further including a second evaporator heat transfer coupled to the pre-chiller and a second expansion valve for metering refrigerant to the second evaporator, the variable speed compressor also delivering refrigerant to the second expansion valve for being metered to the second evaporator to chill the pre-chiller to chill product flowed through the pre-chiller to the barrel, said adjusting and controlling steps being responsive to a flow of product through the pre-chiller to operate the compressor to deliver refrigerant to the second expansion valve and to adjust the second expansion valve to meter refrigerant to the second evaporator to chill the second evaporator and thereby to chill the pre-chiller and product flowing through the pre-chiller. 
   
   
       27 . A method as in  claim 17 , wherein said sensing step comprises the steps of detecting the volume and temperature of relatively warm product flowed into the barrel, determining the number Btu's required to be provided by the refrigeration system to chill the product flowed into the barrel to a temperature within the selected temperature range, selecting a cycle time for the refrigeration system to provide the determined number of Btu's, and ascertaining the mass flow of refrigerant required to be metered by the expansion valve to the evaporator to provide the determined number of Btu's, said adjusting step adjusting the metering rate of the expansion valve to meter to the evaporator the ascertaining mass flow of refrigerant within the selected cycle time. 
   
   
       28 . A method as in  claim 17 , wherein said adjusting and controlling steps are performed such that the refrigerant metering rate of the expansion valve closely matches the refrigerant delivery rate of the compressor.