Capacity boosting during pulldown

Abstract

The transcritical refrigeration system is provided with a main compressor and booster compressor that is made to operate in parallel with the main compressor only during pulldown conditions. A single, two stage compressor is provided with valving which is controlled so as to provide for the two stages operating in series in normal operation and for operating in parallel during pulldown conditions.

1 . A method of operating a transport refrigeration system of the type having CO 2  as the refrigerant, comprising the steps of:
 during normal operation, compressing the refrigerant in the system by the operation of only a first compression unit; and   only during operation under pulldown conditions, operating a second compressor unit in parallel with said first compression unit to thereby increase the system mass flow and improve the overall capacity thereof.   
     
     
         2 . A method as set forth in  claim 1  wherein said first compression unit is a single stage compressor. 
     
     
         3 . A method as set forth in  claim 1  wherein said second compression unit is a single stage compressor. 
     
     
         4 . A method as set forth in  claim 1  wherein said first and second compression units comprise first and second stages of a two stage compressor, and further wherein valving is provided to selectively cause the two stages to operate either in series or parallel relationship. 
     
     
         5 . A method as set forth in  claim 4  wherein said valving includes a valve between the first and second stage, and a valve connected in parallel across each of said stages. 
     
     
         6 . A method as set forth in  claim 5  wherein, during normal operation, the valve between the two stages is open and other valves are closed, and during pulldown operation, the valve between the two stages are closed, and the other two valves are open. 
     
     
         7 . A transport refrigeration system comprising:
 a vapor compression system including a compression unit, a condenser, an expansion device and an evaporator connected in serial refrigeration flow relationship and adapted to operate with CO 2  as the refrigerant;   said compression unit being a two stage compressor and including valving apparatus capable of being selectively operated such that during normal operation the refrigerant flows through the two stages in series relationship and during periods of operation in which greater capacities are desired the refrigerant flows through the two stages in parallel relationship to thereby boost the capacity of the system.   
     
     
         8 . A transport refrigerant system as set forth in  claim 7  wherein said valving apparatus includes a first valve between the two stages and second and third valves connected in parallel with the respective stages, such that for normal operation said first valve is opened and said second and third valves are closed wherein during periods in which higher capacities are desired said first valve is closed and said second and third valves are opened.