Capacity modulation of refrigerant vapor compression system

Abstract

A carbon dioxide refrigerant vapor compression system and a method of operating that system are provided. The refrigerant vapor compression system includes a compression device, a refrigerant heat rejection heat exchanger and a refrigerant heat absorption heat exchanger disposed in a primary refrigerant circuit, and a compression device unload circuit in parallel refrigerant flow relationship with the primary refrigerant circuit. At full load, the primary refrigerant circuit is open, but the unload circuit is closed. To modulate capacity, a controller alternates operation between a first cycle for a first period of time wherein the primary circuit is open and the unload circuit is closed and a second cycle for a second period of time wherein the primary circuit is closed and the unload circuit is open.

1 . A refrigerant vapor compression system comprising:
 a refrigerant compression device having a refrigerant discharge outlet and a refrigerant suction inlet, a refrigerant heat rejection heat exchanger for passing refrigerant received from said compression device at a high pressure in heat exchange relationship with a cooling medium, and a refrigerant heat absorption heat exchanger for passing refrigerant at a low pressure refrigerant in heat exchange relationship with a heating medium disposed in serial refrigerant flow communication in a primary refrigerant circuit;   an expansion device disposed in the primary refrigerant circuit downstream of said refrigerant heat rejection heat exchanger and upstream of said refrigerant heating heat exchanger;   a first flow control device disposed in the primary refrigerant circuit downstream with respect to refrigerant flow of the discharge outlet of said compression device and upstream with respect to refrigerant flow of the refrigerant heat rejection heat exchanger;   an unload circuit operatively associated with said compression device including an unload refrigerant line having an inlet in refrigerant flow communication with the primary refrigerant circuit at a first location downstream with respect to refrigerant flow of the discharge outlet of said compression device and upstream with respect to refrigerant flow of said first flow control device and at a second location downstream with respect to refrigerant flow of said refrigerant heat absorption heat exchanger and upstream with respect to refrigerant flow of the suction inlet to said compression device, and a unload circuit flow control device disposed in said unload refrigerant line; and   a controller operatively associated with said first flow control device and said unload circuit flow control device, said controller operative to switch said refrigerant vapor compression system between a first operating mode wherein said compression device operates in a loaded cycle and a second operating mode wherein said compression device operates in an unloaded cycle.   
     
     
         2 . A refrigerant vapor compression system as recited in  claim 1  wherein the controller positions said unload circuit flow control device in a closed position and positions said first flow control device in an open position to operate said refrigerant vapor compression system in the first operating mode. 
     
     
         3 . A refrigerant vapor compression system as recited in  claim 2  wherein the controller modulates said expansion device in the first operating mode. 
     
     
         4 . A refrigerant vapor compression system as recited in  claim 1  wherein the controller positions said unload circuit flow control device in an open position and positions said first flow control device in a closed position to operate said refrigerant vapor compression system in the second operating mode. 
     
     
         5 . A refrigerant vapor compression system as recited in  claim 4  wherein the controller positions said expansion device in a closed position in the second operating mode. 
     
     
         6 . A refrigerant vapor compression system as recited in  claim 1  further comprising:
 a second flow control device disposed in the primary refrigerant circuit downstream with respect to refrigerant flow of the refrigerant heat absorption heat exchanger and upstream with respect to refrigerant flow of the suction inlet of said compression device.   
     
     
         7 . A refrigerant vapor compression system as recited in  claim 6  wherein the controller positions said unload circuit flow control device in a closed position and positions each of said first flow control device and said second flow control device in a open position to operate said refrigerant vapor compression system in the first operating mode. 
     
     
         8 . A refrigerant vapor compression system as recited in  claim 7  wherein the controller modulates said expansion device in the first operating mode. 
     
     
         9 . A refrigerant vapor compression system as recited in  claim 6  wherein the controller positions said unload circuit flow control device in a open position and positions each of said first flow control device and said second flow control device in a closed position to operate said refrigerant vapor compression system in the second operating mode. 
     
     
         10 . A method for modulating the capacity of a refrigerant vapor compression system including a refrigerant compression device, a refrigerant heat rejection heat exchanger, an expansion device, and a refrigerant heat absorption heat exchanger disposed in series flow arrangement in a primary refrigerant circuit, said method comprising the steps of:
 operating said compression device in a loaded cycle for a first period of time;   operating said compression device in an unloaded cycle for a second period of time; and   repeatedly alternating operation of said compression device between operation in the loaded cycle and the unloaded cycle.   
     
     
         11 . A method for modulating the capacity of a refrigerant vapor compression system as recited in  claim 10  comprising the step of providing a compression device unloader circuit in parallel refrigerant flow relationship with the primary refrigerant circuit, the unloader circuit connecting a refrigerant discharge outlet of said compression device in direct refrigerant flow communication with a refrigerant suction inlet of said compression device.