Transport refrigeration unit

Abstract

A refrigerant unit associated with a product transport container is provided with a dual-path, parallel flow expansion circuit. The expansion circuit includes a primary expansion device disposed in a primary refrigerant flow path and an auxiliary expansion device disposed in a secondary refrigerant flow path. During operation of the refrigeration unit in a stable temperature maintenance mode, refrigerant flow is supplied to the evaporator coil through the primary refrigerant flow path only. During operation of the refrigeration unit in a temperature pull-down mode, to increase the refrigerant mass flow through the evaporator coil, refrigeration flow is supplied to the evaporator coil through the primary refrigerant flow path and the secondary refrigerant flow path of the expansion circuit.

1 . A refrigeration unit comprising:
 a refrigerant flow circuit including a refrigerant compressor, a condenser coil, and an evaporator coil connected by refrigerant lines in refrigerant flow communication; and   a dual-path, parallel flow expansion circuit having a primary expansion device disposed in a primary refrigerant flow path and an auxiliary expansion device disposed in a secondary refrigerant flow path, said expansion circuit inserted in said refrigerant circuit downstream with respect to refrigerant flow of said condenser coil and upstream with respect to said evaporator coil.   
   
   
       2 . A refrigeration unit as recited in  claim 1  wherein said primary expansion device comprises a thermostatic expansion valve. 
   
   
       3 . A refrigeration unit as recited in  claim 2  wherein said auxiliary expansion device comprises a fixed orifice. 
   
   
       4 . A refrigeration unit as recited in  claim 2  wherein said auxiliary expansion device comprises a thermostatic expansion valve. 
   
   
       5 . A refrigeration unit as recited in  claim 2  wherein said auxiliary expansion device comprises a capillary tube. 
   
   
       6 . A refrigeration unit as recited in  claim 1  wherein said auxiliary expansion device comprises a fixed orifice. 
   
   
       7 . A refrigeration unit as recited in  claim 1  wherein said auxiliary expansion device comprises a thermostatic expansion valve. 
   
   
       8 . A refrigeration unit as recited in  claim 1  wherein said auxiliary expansion device comprises a capillary tube. 
   
   
       9 . A refrigeration unit as recited in  claim 1  wherein said secondary refrigerant flow path comprises a bypass line having an inlet in refrigerant flow communication with said refrigerant flow circuit at a point upstream with respect to refrigerant flow of said primary expansion device and an outlet in refrigerant flow communication with said refrigerant flow circuit at a point downstream with respect to refrigerant flow of said primary expansion device. 
   
   
       10 . A refrigeration unit as recited in  claim 9  further comprising a bypass valve disposed in said bypass line, said bypass valve operative to selectively open and close said bypass line to refrigerant flow there through. 
   
   
       11 . A refrigerant unit as recited in  claim 10  wherein said auxiliary expansion device is disposed in said bypass line upstream with respect to refrigerant flow of said bypass valve. 
   
   
       12 . A refrigerant unit as recited in  claim 10  wherein said auxiliary expansion device is disposed in said bypass line downstream with respect to refrigerant flow of said bypass valve. 
   
   
       13 . A refrigerant unit as recited in  claim 1  wherein said refrigerant flow circuit further includes an economizer circuit. 
   
   
       14 . A refrigerant unit as recited in  claim 13  wherein said compressor comprises a scroll compressor. 
   
   
       15 . A method of operating a refrigeration unit for providing a temperature controlled environment within a container having a product disposed therein to be maintained at a product storage temperature, the refrigeration unit having a refrigerant flow circuit including a refrigerant compressor, a condenser coil, and an evaporator coil connected by refrigerant lines in refrigerant flow communication, said method comprising the steps of:
 providing a dual-path, parallel flow expansion circuit having a primary expansion device disposed in a primary refrigerant flow path and an auxiliary expansion device disposed in a secondary refrigerant flow path;   passing refrigerant flow to the evaporator coil through the primary refrigerant flow path only when the refrigeration unit is operating in a stable temperature maintenance mode; and   passing refrigerant flow to the evaporator coil through both the primary refrigerant flow path and the secondary refrigerant flow path when the refrigeration unit is operating in a temperature pull-down mode.   
   
   
       16 . A method of operating a refrigeration unit as recited in  claim 15  wherein the step of passing refrigerant flow to the evaporator coil through the primary refrigerant flow path only when the refrigeration unit is operating in a stable temperature maintenance mode includes the step of passing the refrigerant flow through a thermostatic expansion valve disposed in the primary refrigerant flow path. 
   
   
       17 . A method of operating a refrigeration unit as recited in  claim 16  wherein the step of passing refrigerant flow to the evaporator coil through both the primary refrigerant flow path and the secondary refrigerant flow path when the refrigeration unit is operating in a temperature pull-down mode includes the step of passing refrigerant flow to the evaporator coil includes passing the refrigerant flow through a thermostatic expansion valve disposed in the primary refrigerant flow path and through a fixed orifice disposed in the secondary refrigerant flow path. 
   
   
       18 . A method of operating a refrigeration unit as recited in  claim 16  wherein the step of passing refrigerant flow to the evaporator coil through both the primary refrigerant flow path and the secondary refrigerant flow path when the refrigeration unit is operating in a temperature pull-down mode includes the step of passing refrigerant flow to the evaporator coil includes passing the refrigerant flow through a thermostatic expansion valve disposed in the primary refrigerant flow path and through a thermostatic expansion device disposed in the secondary refrigerant flow path. 
   
   
       19 . A method of operating a refrigeration unit as recited in  claim 16  wherein the step of passing refrigerant flow to the evaporator coil through both the primary refrigerant flow path and the secondary refrigerant flow path when the refrigeration unit is operating in a temperature pull-down mode includes the step of passing refrigerant flow to the evaporator coil includes passing the refrigerant flow through a thermostatic expansion valve disposed in the primary refrigerant flow path and through a capillary tube disposed in the secondary refrigerant flow path.