Variable air volume economizer minimum position reset

Abstract

A rooftop air conditioner having a variable speed fan and an economizer also includes a control feature for adjusting the minimum damper position in response to the speed of the fan during predetermined conditions in order to maintain a desired volume of fresh air from the economizer.

1 . A system for controlling air quality in a building having an air temperature conditioning unit with a variable speed flow inducing apparatus, and an economizer comprising:
 a damper for controlling the volume of outside air flow through the economizer, said damper having a variable minimum damper position; and   a control for varying the minimum damper position in response to the speed of said flow inducing apparatus during predetermined operating conditions.   
     
     
         2 . A system as set forth in  claim 1  wherein said flow inducing apparatus is a variable speed fan. 
     
     
         3 . A system as set forth in  claim 2  wherein said fan receives its power from an inverter. 
     
     
         4 . A system as set forth in  claim 2  wherein the characteristics of the fan are such that, for a given damper position, the amount of outside air delivered will be substantially proportional to the speed of the fan. 
     
     
         5 . A system as set forth in  claim 2  wherein the characteristics of the fan are such that the volume of the air delivered by the fan will be substantially proportional to the speed of the fan. 
     
     
         6 . A system as set forth in  claim 1  wherein said control also includes software which determines the relationship between the percent of outside air and the damper position for the economizer. 
     
     
         7 . A method for improving air quality in a building having a climate control system that includes in serial flow relationship, an economizer with a minimum damper position, a variable speed flow inducing apparatus and a supply air duct, comprising the steps of:
 as the demand for air in the supply air duct is reduced, reducing the speed of the flow inducing apparatus and, when that speed is within a predetermined range, adjusting the minimum damper position in response to the speed of the flow inducing apparatus.   
     
     
         8 . A method as set forth in  claim 7  and including the step of determining the relationship between the percent of outside air and the damper position for the economizer. 
     
     
         9 . A method as set forth in  claim 7  wherein said minimum damper position is adjusted non-linearly with respect to the speed of the flow inducing apparatus. 
     
     
         10 . A method as set forth in  claim 7  wherein said flow inducing apparatus is a variable speed fan. 
     
     
         11 . A method as set forth in  claim 10  and including the step of providing variable power to said flow inducing device.