Method and apparatus for controlling ventilation rates and indoor air quality in an HVAC system

An apparatus for determining the flow rate of outside air introduced into an HVAC system for circulating in a structure supply air, the apparatus comprising:

• a supply air duct coupled to said structure to introduce the supply air comprising said outside air and a portion of return air into said structure;
• a return air duct coupled to said structure to remove said return air from said structure;
• at least one outside air sensor operatively coupled to said supply air duct and said return air duct for measuring a component of the outside air and producing an outside air signal indicative of said component, for measuring a component of said return air and producing a return air signal indicative of said component, and for measuring said component of supply air and producing a supply air signal indicative of said component;
• means for effecting circulation of said supply air in said structure;
• means coupled to said supply means for determining a ventilation air flow rate;
• and
• control means for determining said flow rate of outside air from the product of said ventilation air flow rate and the ratio of the difference between said return air sensor means output and said supply air sensor means output to the difference between said return air sensor means output and said outside air sensor means output.

A method for determining the flow rate of outside air introduced into a structure wherein supply air comprising outside air and return air is circulated in the structure, the method comprising the steps of:

• removing return air from said structure;
• recirculating at least a portion of said return air;
• measuring a concentration of a component in said return air and producing a return air component concentration;
• measuring a concentration of said component in said outside air and producing an outside air component concentration;
• measuring a concentration of said component in said supply air and producing a supply air component concentration;
• determining said flow rate of outside air from the ratio of the difference between said return air component concentration and said supply air component concentration to the difference between said return air component concentration and said outside air component concentration.

A method for use in an apparatus for controlling the amount of outside air introduced into a system for circulating ventilation air in a structure, said apparatus comprising intake control means, recirculation control means, outside air sensor means, return air sensor means and supply air sensor means, said method for calibrating said supply air sensor means and said return air sensor means and comprising the steps of:

• opening said intake control means;
• closing said recirculation control means;
• calibrating said supply air sensor means to said outside air sensor means;
• closing said intake control means;
• opening said recirculation control means;
• and
• calibrating said return air sensor means to said supply air sensor means.