Autocascade system with superheat control based on working fluid concentration levels

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.

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.