Digital scroll condensing unit controller

#The present invention relates generally to a controller for a condensing unit for a refrigeration system or for other cooling systems. More particularly, the present invention relates to a condensing unit employing a variable capacity compressor which is controlled by pulse width modulation using a variable duty cycle signal derived from one or more system sensors. The condensing unit controller is capable of controlling a single evaporator or multiple evaporators of similar or mixed temperatures.

#The present invention is being described associated with a refrigeration system. It is to be understood that the condensing unit of the present invention could be utilized for any other cooling system if desired.

#Conventionally, refrigeration systems for refrigeration cases have employed air-cooled or water-cooled condensers fed by a rack of compressors. The compressors are coupled in parallel so that they may be switched on and off in stages to adjust the system cooling capacity to the demands of the load. Typically, the compressors and condensers are located outside of the building on the roof or in a machine room adjacent the area where the refrigeration cases are located.

#In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

#FIG. 1 is a system block diagram of a prior art refrigeration system configuration;

#FIG. 2 is a system block diagram of a condensing unit or cooling system in accordance with the present invention;

#Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a conventional refrigeration system that is identified generally by reference numeral 10. Refrigeration system 10 includes a plurality of compressors 12 and a condenser 14 located remote from a plurality of refrigeration cases 16. In this illustration, compressors 12 are configured in a parallel bank located in a machine room or on a roof 18 of a building. Compressors 12 supply condenser 14 that may be air cooled or water cooled. Condenser 14 supplies liquid refrigerant to a receiver 20. Receiver 20, in turn, supplies refrigerant to the individual refrigeration cases 16, which are connected in parallel, as illustrated. In most implementations, a liquid line solenoid valve 22 is used to regulate the flow of refrigerant to the associated evaporator 24. The refrigerant is supplied to evaporator 24 through a suitable expansion device such as expansion valve 26. Expansion valve 26 provides a restricted orifice that causes the liquid refrigerant to atomize into liquid droplets that are introduced into the inlet side of evaporator 24. Evaporator 24, located within refrigerant case 16, extracts heat from case 16 and its contents by vaporization of the liquid droplets into a gas. Compressors 12 extract this gas by suction and compress the gas. The high-temperature compressed gas is then cooled by condenser 14 back into the liquid state and returned to receiver 20, whereupon the cycle continues.

#To match cooling capacity to the load, compressors 12 may be switched on and off individually or in groups as required. In a typical retail outlet installation, there may be several independent systems, each configured as shown in FIG. 1, to handle different operating temperature ranges. Note that a liquid line 28 and a suction line 30 may each need to be quite lengthy (e.g., up to 150 feet) to span the distance from refrigeration cases 16 to a machine room or roof 18.

#FIG. 2 shows a condensing unit or cooling system 40 configured in accordance with the principles of the present invention. Cooling system 40 includes a refrigeration case 42, a compressor 44, a condenser 46, a first expansion valve 48, an economizer 50, a second expansion valve 52 and an evaporator 54. While cooling system 40 is being illustrated in conjunction with refrigeration case 42, it is within the scope of the present invention to use cooling system 40 in conjunction with other cooling devices if desired.