Feed forward control of expansion valve

A method of controlling an expansion valve in a refrigeration system, the method comprising the steps of:

• controlling the modulation of the expansion valve based upon a first feedback control criteria;
• and also
• controlling the modulation of the expansion valve based upon a second feed forward control criteria;
• wherein the feedback modulation of the expansion valve is based on conventional PID control and wherein the feed forward modulation of the expansion valve is based on feed forward control strategies;
• and
• wherein the system includes an evaporator providing chilled water, the chilled water having an entering water temperature and a leaving water temperature, and wherein the second criteria is a function of the difference between the entering water temperature and a setpoint.

A method of controlling an expansion valve comprising the steps of:

• constantly controlling an expansion valve based upon a first measured criteria;
• determining a disturbance in a second measured criteria in the system being controlled by the expansion valve;
• providing a feed forward control signal to the expansion valve based upon the second criteria;
• and
• controlling the expansion valve based upon the second criteria;
• wherein the feedforward control signal is modified in response to secondary variations in system disturbance such as changes in saturated evaporator temperature, saturated evaporator pressure, saturated condenser temperature or saturated condenser pressure.

A method of controlling an expansion valve comprising the steps of:

• constantly controlling an expansion valve based upon a first measured criteria;
• determining a disturbance in a second measured criteria in the system being controlled by the expansion valve;
• providing a feed forward control signal to the expansion valve based upon the second criteria;
• and
• controlling the expansion valve based upon the second criteria;
• and
• wherein the first criteria is either measured superheat or a measured liquid level and whether the second criteria is a measure of the temperature of a fluid being cooled by an evaporator, or a measure of the cooling capacity of the system.

A method of controlling an expansion valve in a refrigeration or HVAC system comprising the steps of:

• providing closed loop control of an expansion valve based upon a first criteria;
• and
• providing open loop control of the expansion valve based upon at least a second criteria differing from said first criteria;
• wherein the first criteria is either measured superheat or a measured liquid level and wherein the second criteria is a measure of the temperature of a fluid being cooled by an evaporator, or a measure of the cooling capacity of the system.

A method of controlling the flow of refrigerant in a refrigeration system, the system including an expansion device and a compression device, the method comprising the steps of:

• measuring the capacity of the compression device;
• modulating the expansion device in response to the measured compressor capacity;
• determining a measure of superheat in the system;
• and
• modulating the expansion valve based upon measured superheat until a change in measured compressor capacity exceeds predefined parameters;
• wherein the measured compressor capacity is determined by making a measurement;
• wherein the refrigeration system includes an evaporator for cooling water, and an entering water temperature sensor for measuring the temperature of water entering the evaporator to be cooled, and
• wherein the measurement is indicative of the entering water temperature.

A method of controlling the capacity of a chiller system, the chiller system including a circularly linked compressor, condenser, expansion device, and an evaporator where the evaporator receives entering water having an entering water temperature and provides leaving water having a leaving water temperature and where the compressor compresses refrigerant having a measured superheat, the method comprising the steps of:

• measuring a water temperature and the refrigerant superheat;
• determining a water temperature error as a function of the difference between the water temperature and a setpoint;
• providing a first mode of capacity control wherein the expansion valve is modulated in response to the measured superheat;
• and
• providing a second mode of capacity control where the expansion valve is modulated in response to the water temperature error.

A method of repositioning an expansion valve in a chiller system in response to changes in system capacity, the chiller system having an evaporator for conditioning entering water and providing leaving water, the method comprising the steps of:

• monitoring the entering water temperature of the evaporator;
• monitoring the leaving water temperature of the evaporator;
• determining a water temperature difference between the entering water temperature and the leaving water temperature;
• determining a temperature differential setpoint;
• comparing the water temperature difference to the differential temperature setpoint to establish an error;
• and
• repositioning the expansion valve to minimize the error.

A water chiller system comprising an evaporator for chilling a fluid;

• a compressor, receiving heated refrigerant from the evaporator, for changing the condensation temperature of the refrigerant by compression;
• a condenser, receiving compressed refrigerant from the compressor, for condensing the compressed refrigerant;
• an expansion device, receiving condensed refrigerant from a condenser, for controllably returning the condensed refrigerant to the evaporator;
• a controller, operatively connected to the expansion device, for controlling the operation of the expansion device;
• and
• feed forward control, coupled to the controller, for anticipating changes in the load of the evaporator whereby the feed forward control includes a first sensor sensing a first value and controlling the operation of the expansion valve in response to the sensed first value, the first sensor being operably connected to the controller and measuring the temperature of the first fluid as it enters the evaporator, and wherein the entering fluid temperature is said first value.