Autocascade system with superheat control based on working fluid concentration levels

Abstract

An autocascade heat transfer fluid circuit includes an evaporator, a sub-cooler, a heat exchanger, a compressor, a condenser, a working fluid concentration sensor, a pressure sensor, a temperature sensor, and a unit controller. The unit controller converts properties of respective components of a working fluid flowing through the heat transfer fluid circuit; receive a temperature and pressure of the working fluid; convert the received properties, temperature, and pressure of the working fluid into concentration percentages for the respective components of the working fluid; determine a suction super heat of the working fluid based on the concentration percentages for the respective components of the working fluid; and control an expander to regulate a flow of the working fluid into an evaporator based on the determined suction super heat of the working fluid.

We claim 
     
         1 . A controller method of operating an autocascade heat transfer fluid circuit, comprising:
 receiving properties of respective components of a working fluid flowing through an autocascade heat transfer fluid circuit;   receiving a temperature and pressure of the working fluid;   converting the received properties, temperature, and pressure of the working fluid into concentration percentages for the respective components of the working fluid;   determining a suction super heat of the working fluid based on the concentration percentages for the respective components of the working fluid; and   controlling an expander to regulate a flow of the working fluid into an evaporator.   
     
     
         2 . The controller method of  claim 1 , wherein the properties of the respective components of the working fluid are determined by a fluid property sensor. 
     
     
         3 . The controller method of  claim 1 , wherein the properties of the respective components of the working fluid include speed of sound. 
     
     
         4 . The controller method of  claim 1 , wherein the properties of the respective components of the working fluid include density. 
     
     
         5 . The controller method of  claim 1 , wherein the converting includes mapping the percentages for the respective components of the working fluid against the received temperature and pressure of the working fluid. 
     
     
         6 . The controller method of  claim 1 , wherein the controlling includes:
 opening the expander to increase a volume of working fluid in the evaporator when the determined suction super heat of the working fluid exceeds a threshold value; or   closing the expander to decrease a volume of a working fluid in the evaporator when the determined suction super heat of the working fluid is below the threshold value.   
     
     
         7 . A controller method of operating an autocascade heat transfer fluid circuit, comprising:
 receiving properties of respective components of a working fluid flowing through an autocascade heat transfer fluid circuit;   receiving a temperature and pressure of the working fluid;   converting the received properties, temperature, and pressure of the working fluid into concentration percentages for the respective components of the working fluid;   determining a suction super heat of the working fluid based on the concentration percentages for the respective components of the working fluid; and   controlling an expander to regulate a charge of a liquid component of the working fluid within a phase separator.   
     
     
         8 . The controller method of  claim 7 , wherein the properties of the respective components of the working fluid are determined by a fluid property sensor. 
     
     
         9 . The controller method of  claim 7 , wherein the properties of the respective components of the working fluid include speed of sound. 
     
     
         10 . The controller method of  claim 7 , wherein the properties of the respective components of the working fluid include density. 
     
     
         11 . The controller method of  claim 7 , wherein the converting includes mapping the percentages for the respective components of the working fluid against the received temperature and pressure of the working fluid. 
     
     
         12 . The controller method of  claim 7 , wherein the controlling includes controlling the expander to retain a higher level of a component of the working fluid having a higher concentration of the respective component having a higher temperature and lower pressure relative to other components of the working fluid. 
     
     
         13 . A heat transfer fluid circuit, comprising:
 an evaporator;   a sub-cooler;   a heat exchanger;   a compressor;   a condenser;   a working fluid concentration sensor;   a pressure sensor;   a temperature sensor; and   a unit controller configured to:
 receive properties of respective components of a working fluid flowing through the heat transfer fluid circuit; 
 receive a temperature and pressure of the working fluid; 
 convert the received properties, temperature, and pressure of the working fluid into concentration percentages for the respective components of the working fluid; 
 determine a suction super heat of the working fluid based on the concentration percentages for the respective components of the working fluid; and 
 control an expander to regulate a flow of the working fluid into the evaporator based on the determined suction super heat of the working fluid. 
   
     
     
         14 . The heat transfer fluid circuit of  claim 13 , wherein the properties of the respective components of the working fluid are determined by a fluid property sensor. 
     
     
         15 . The heat transfer fluid circuit of  claim 13 , wherein the properties of the respective components of the working fluid include speed of sound. 
     
     
         16 . The heat transfer fluid circuit of  claim 13 , wherein the properties of the respective components of the working fluid include density. 
     
     
         17 . The heat transfer fluid circuit of  claim 13 , wherein the converting includes mapping the percentages for the respective components of the working fluid against the received temperature and pressure of the working fluid. 
     
     
         18 . The heat transfer fluid circuit of  claim 13 , wherein the controlling includes:
 opening the expander to reduce a volume of the working fluid in the evaporator when the determined suction super heat of the working fluid exceeds a threshold value; or   closing the expander to increase the volume of the working fluid in the evaporator when the determined suction super heat of the working fluid is below the threshold value.