Refrigeration – Automatic control – Diverse – cascade or compound refrigeration-producing system
Reexamination Certificate
2000-07-07
2001-12-04
Tapolcai, William E. (Department: 3744)
Refrigeration
Automatic control
Diverse, cascade or compound refrigeration-producing system
C062S335000
Reexamination Certificate
active
06324856
ABSTRACT:
TECHNICAL FIELD
This invention relates to the field of refrigeration systems, and more particularly, to cascade compression refrigeration systems.
BACKGROUND
Refrigeration systems are sometimes used to provide ultra-cold conditions for various applications. Refrigeration system parameters are generally designed for efficient operation under normal operating conditions, where the refrigeration system removes only ambient heat gain from the temperature controlled space to maintain temperature. Such systems do not adequately meet the greater cooling demands encountered on initial cool down of the controlled space, or during periods of increased access. In a typical compressive, two-stage cascade ultra-low temperature refrigeration system cooling capacity is determined primarily by the flow rate of the refrigerant through the expansion or flow control devices when the system compressors are operating.
SUMMARY OF THE INVENTION
The present invention provides for increased refrigerant flow in response to system temperatures warmer than an operator selected temperature. In the preferred embodiment, refrigerant flow is controlled in the higher temperature first stage of a compressive, cascade ultra-low temperature refrigeration system in response to higher-than-desired second stage evaporator outlet temperature. A temperature sensor at the evaporator output sends a signal to a controller. The controller operates a valve to increase refrigerant flow in the first stage, increasing system capacity. The valve allows some refrigerant to bypass the normal or primary flow control device, flowing through a second flow control device. The increased flow in the first stage results in increased pressure in the first stage side of the heat exchanger. The heat exchanger transfers heat from the second stage side to the first stage side in a cascade refrigeration system. The increased first stage pressure results in increased refrigerant flow in the second stage. The increased flow provides more efficient system operation when large cooling demands are present. When evaporator outlet temperature returns to the desired range, the controller operates the valve to restore the normal refrigerant flowpath, reducing refrigerant flow in the first stage to the normal condition.
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Pepper Hamilton LLP
SPX Corporation
Tapolcai William E.
LandOfFree
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