Variable capacity multiple compressor refrigeration system

Abstract

A variable capacity multiple compressor refrigeration system having first and second compressors with the first compressor to be always running when the system is operating and the second compressor to be cycled off or to vary the capacity of the system on while the first compressor continues to run. The discharge lines of both compressors are connected together in parallel to the system and a check valve is provided in the discharge line connection between the compressors to prevent discharge pressure from the operating compressor from entering the discharge port of the nonrunning compressor. A by-pass line connects the suction of the system at the inlet of the second compressor to its discharge line between the check valve and its discharge port and a solenoid valve in the by-pass line is arranged to be closed when the second compressor is running and open when it is cycled off. In one form of the invention, both compressors are multiple cylinder hermetic shell compressors and the inlet of the second compressor is connected to the system through the shell of the first compressor. Also, the first compressor is provided with unloading mechanism to unload some of its cylinders for part unloaded operation, so that four steps of different capacity may be obtained by running the first compressor either loaded or partly unloaded while the second compressor is cycled off or on and therefore, with the aforementioned inlet arrangement, effectively high saturated gas discharge temperatures may be obtained without over heating either compressor for any of the capacity steps of operation.

What we claim is: 
     
       1. A variable capacity multiple compressor refrigeration system comprising first and second .Iadd.hermetic shell .Iaddend.refrigerant compressors, each compressor having suction inlet and discharge ports, .Iadd.the first compressor having its suction inlet port .Iaddend.adapted to be connected to the suction line of the system, .Iadd.and the second compressor having its suction inlet port connected to the interior of the shell of the first compressor so that gas received by said second compressor is received only through the shell of said first compressor, .Iaddend.means to connect the discharge ports in parallel to the refrigeration system, means to cycle-off said second compressor while the first compressor continues to run for reduced capacity of the system, a check valve in said means to connect to prevent discharge gas from said first compressor from entering the discharge port of the second cycled-off compressor, a bypass line connected to the suction of the system and to said means to connect at a point between the check valve and the discharge port of the second compressor, a valve in said bypass line, and valve control means to control said valve to be closed when both compressors are running and to be open when said second compressor is cycled-off.Iadd., said first compressor is a multiple cylinder compressor having means to controllably unload some of its cylinders for running part unloaded to reduce the capacity of the system and said first compressor is always running when the system is operating. .Iaddend. .[. 
     
     
       2.  The invention of claim 1 in which said compressors are hermetic shell compressors..]. .[.3. The invention of claim 1 in which said first compressor is a multiple cylinder compressor having means to controllably unload some of its cylinders for running part unloaded to reduce the 
     
     
        capacity of the system..]. .[.4.  The invention of claim 3 in which said 
     
     
        compressors are hermetic shell compressors..]. 5. The invention of claim .[.4.]. .Iadd.1 .Iaddend.in which multiple steps of variable capacity are provided .[.with the inlet of said second compressor being connected to the system through the shell of said first compressor.]., and a multi-step capacity control comprising logic switch cycle control means responsive to refrigeration demand to cycle both compressors on for one capacity step corresponding to maximum capacity, to operate said first compressor unloading means to unload some of its cylinders while both compressors are cycled-on for a second capacity step of reduced capacity, to cycle-off said second compressor while at the same time operating said first compressor unloading means to not unload any of its cylinders and thereby cause only said first compressor to run at full capacity for a third capacity step of reduced capacity, and to cycle-off said second compressor and at the same time operate said first compressor unloading means to unload some of the cylinders of the first compressor while only the first compressor is running for a fourth capacity step of reduced capacity of 
     
     
        the system. 6. The invention of claim .[.4.]. .Iadd.1 .Iaddend.in which multiple steps of variable capacity are provided .[.with the inlet of said second compressor being connected to the system through the shell of said first compressor.]., and a multi-step capacity control comprising logic switch cycle control means responsive to refrigeration demand to cycle both compressors on for one capacity step corresponding to maximum capacity, to operate said first compressor unloading means to unload some of its cylinders while both compressors are cycled-on for a second capacity step of reduced capacity, to cycle-off said second compressor and operate said valve control means to control said valve to be open while at the same time operating said first compressor unloading means to not unload any of its cylinders and thereby cause only said first compressor to run at full capacity for a third capacity step of reduced capacity, and to cycle-off said second compressor and operate said valve control means to control said valve to be open and at the same time operate said first compressor unloading means to unload some of the cylinders of the first compressor while only the one compressor is running for a fourth capacity step of reduced capacity of the system.