US 4,180,986 AGranted

Refrigeration system on/off cycle

AssigneeDunham-Bush, Inc.

InventorDavid N. Shaw

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Abstract

A positive displacement compressor, such as a helical screw rotary compressor without capacity control element, is coupled in a refrigeration loop main line between the evaporator and an oil separator and upstream of the condensor. To unload the screw compressor at low evaporator load, any refrigerant discharging from the compressor is bypassed by a line connecting the suction and discharge sides of the screw compressor, and main line connection from the evaporator to the screw compressor is shut off such that the driven, unloaded screw compressor pulls oil from the separator through a restrictor and oil injection port and some refrigerant vapor which passes to the evaporator side through the screw compressor bypass line. As the evaporator pressure increases, the evaporator is connected through a restrictor within the main line to the screw compressor suction. As the evaporator load increases, normal operation returns, with the bypass line being closed and oil fed from the oil separator to the screw compressor injection port bypassing the restrictor for that oil line.

Claims6

Dependent claims

An on/off cycle refrigeration system comprising:

(a) an evaporator;
(b) a condensor;
(c) an oil-flooded positive displacement compressor having low suction and high discharge sides;
(d) a first line carrying refrigerant and oil and connecting said evaporator, said compressor and said condenser in a closed-series loop, in that order;
(e) an oil separator within said loop and positioned between said compressor and said condensor;
(f) a second line connected between the oil separator and the compressor for supplying separated oil to the compressor for lubrication, the improvement comprising:
(a) means responsive to low load conditions of said evaporator for connecting the low side of the evaporator to the discharge side of the compressor and for cutting off the low side of the evaporator to the suction side of said compressor;
and
(b) means for restricting the flow of oil from said oil separator through said second line to said compressor such that the low side of the screw compressor is pulled down into the vacuum range, and the high side of the screw compressor is bled off to the low pressure existing in the system evaporator, with the compressor operating at essentially zero load under low power consumption and with limited lubricating oil being fed to the compressor.

6 more elements

Dependencies are inferred from the claim text.