VAV airflow control for preventing processor overflow and underflow

A method for initializing a control system for a variable air flow apparatus having an airflow sensor for providing an airflow sensor signal to an airflow controller, a stored relationship representative of a plot of airflow sensor signal values versus airflow values having a first portion of relatively low airflow signal values and relatively low air flows and a second portion of relatively high air flow signal values and relatively high air flows, a damper for varying airflow, and an actuator for positioning said damper, comprising the steps of:

• energizing said airflow controller;
• determining a minimum allowed airflow value based on a property of said first portion;
• determining a maximum allowed airflow value based on a property of said second portion;
• and
• subsequently periodically positioning said damper to provide an airflow value within a range defined by said minimum allowed airflow value and said maximum allowed airflow value in response to a signal from said airflow controller.

A method for initializing a control system for a variable air flow apparatus so as to reduce subsequent calculations, said apparatus having an air flow sensor for providing an air flow sensor signal to an air flow controller, a stored relationship representative of a plot of air flow sensor signal values versus airflow values having a first portion of relatively low air flow signal values and relatively low air flows and having a second portion of relatively high air flow signal values and relatively high air flows, a damper for varying air flow and an actuator for positioning said damper comprising the steps of:

• energizing said air flow controller;
• determining a first slope of a portion of said plot within said first portion;
• determining a first intersection of said first slope with an absolute minimum voltage value or an absolute minimum airflow value;
• determining a minimum allowed airflow value based on said first intersection with an absolute minimum voltage value or an absolute minimum airflow value;
• determining a second slope of a portion of said plot within said second portion;
• determining a first intersection of said second slope with an absolute maximum voltage value or an absolute maximum airflow value;
• determining a maximum allowed airflow based on said first intersection of said second slope with an absolute maximum voltage value or an absolute maximum airflow value;
• and
• subsequently periodically positioning said damper to provide an air flow value within a range defined by said minimum allowed air flow value and said maximum allowed air flow value in response to a signal from said air flow controller.

A control initialization system for a variable airflow apparatus, said apparatus having an airflow sensor providing a signal to an airflow controller, a stored relationship representative of a plot of air flow sensor signal values versus airflow values having a first portion of relatively low air flow signal values and relatively low air flows and having a second portion of relatively high air flow signal values and relatively high air flows, a damper for varying said airflow, and an actuator for positioning said damper comprising:

• means for energizing said controller;
• means for calculating a minimum allowed airflow value based on a characteristic of said first portion and an absolute minimum voltage value or an absolute minimum airflow and for calculating a maximum allowed airflow value based on a characteristic of said second portion and an absolute maximum voltage value or an absolute maximum airflow value;
• means for storing said minimum allowed airflow value and said maximum allowed airflow value;
• and
• means for subsequently positioning said damper to provide an airflow value within a range defined by said minimum allowed airflow value and said maximum allowed airflow value in response to said airflow sensor signal.