Prevention of refrigerant solidification

Abstract

A refrigerant system may utilize CO 2 as a refrigerant. Should the sensed operating conditions indicate that the refrigerant might be approaching a condition at which the refrigerant could solidify, corrective actions are taken to prevent refrigerant transformation to a solid thermodynamic state. In one embodiment, hot gas from a compressor discharge is bypassed to a location upstream of the evaporator. In another embodiment, the high-side pressure of a refrigerant system is adjusted. In yet another embodiment, an additional charge of refrigerant is delivered on demand into the refrigerant system. In still another embodiment, a defrost cycle is initiated on demand. These embodiments prevent the refrigerant from approaching the conditions at which it may solidify.

1 . A refrigerant system comprising:
 a compressor for compressing a refrigerant and delivering it downstream to a heat rejection heat exchanger, refrigerant from said heat rejection heat exchanger passing through an expansion device and then through an evaporator, refrigerant from the evaporator returning to said compressor; and   a control for said system taking a corrective action, if said refrigerant system is approaching a condition at which said refrigerant may solidify.   
   
   
       2 . The refrigerant system as set forth in  claim 1 , wherein said control takes the corrective action to prevent system shutdown. 
   
   
       3 . The refrigerant system as set forth in  claim 1 , wherein said refrigerant system is charged with CO2 refrigerant. 
   
   
       4 . The refrigerant system as set forth in  claim 1 , wherein said control takes the corrective action utilizing a sensor for sensing a condition at which said refrigerant could solidify. 
   
   
       5 . The refrigerant system as set forth in  claim 1 , wherein said refrigerant can solidify in said evaporator. 
   
   
       6 . The refrigerant system as set forth in  claim 1 , wherein said condition is a pressure of the refrigerant. 
   
   
       7 . The refrigerant system as set forth in  claim 6 , wherein said pressure is taken at a location associated with said evaporator. 
   
   
       8 . The refrigerant system as set forth in  claim 1 , wherein said condition is a temperature of the refrigerant. 
   
   
       9 . The refrigerant system as set forth in  claim 8 , wherein said temperature is taken at a location associated with said evaporator. 
   
   
       10 . The refrigerant system as set forth in  claim 1 , wherein a hot gas bypass line is positioned to take at least a portion of refrigerant compressed by said compressor and deliver this portion of refrigerant directly to said evaporator, and said control operating a valve on said hot gas bypass line to expand this portion of refrigerant to a lower pressure, if said refrigerant system is approaching a condition at which said refrigerant may solidify. 
   
   
       11 . The refrigerant system as set forth in  claim 10 , wherein said portion of refrigerant is delivered to a location upstream of the evaporator. 
   
   
       12 . The refrigerant system as set forth in  claim 1 , wherein said control changes a high-side pressure of the refrigerant system, if said refrigerant system is approaching a condition at which said refrigerant may solidify. 
   
   
       13 . The refrigerant system as set forth in  claim 12 , wherein said high-side pressure is changed by controlling a valve opening. 
   
   
       14 . The refrigerant system as set forth in  claim 1 , wherein said refrigerant system further includes a receiver for storing an additional charge of refrigerant, and a valve on a line communicating said receiver into the refrigerant system, said control opening said valve to deliver additional refrigerant into the refrigerant system, if said refrigerant system is approaching a condition at which said refrigerant may solidify. 
   
   
       15 . The refrigerant system as set forth in  claim 1 , wherein a defrost cycle is associated with said evaporator, and said control actuating said defrost cycle, if said refrigerant system is approaching a condition at which said refrigerant may solidify. 
   
   
       16 . The refrigerant system as set forth in  claim 15 , wherein a defrost coil is associated with said evaporator to provide said defrost cycle, and wherein said defrost coil being actuated by the control. 
   
   
       17 . A method of operating a refrigerant system comprising the steps of:
 providing a compressor for compressing a refrigerant and delivering it downstream to a heat rejection heat exchanger, refrigerant from said heat rejection heat exchanger passing through an expansion device and then through an evaporator, refrigerant from the evaporator returning to said compressor; and   a control for said system taking a corrective action, if said refrigerant system is approaching a condition at which said refrigerant may solidify.   
   
   
       18 . The method as set forth in  claim 17 , wherein said control takes the corrective action to prevent system shutdown. 
   
   
       19 . The method as set forth in  claim 17 , wherein said refrigerant system is charged with CO2 refrigerant. 
   
   
       20 . The method as set forth in  claim 17 , wherein said control takes the corrective action utilizing a sensor for sensing a condition at which said refrigerant could solidify. 
   
   
       21 .- 32 . (canceled)