Engineering Manual o.. - HVAC.Amickracing

INDOOR AIR QUALITY FUNDAMENTALSFLOW TRACKING SYSTEM WITH MIXINGBOX STATIC PRESSURE CONTROLFigure 5 is the same as the Flow Tracking System except forthe addition of a method of controlling the amount of outdoorair. The outdoor air is controlled by maintaining a constantnegative static pressure in the mixed air. The pressure sensor isreferenced across the outdoor air damper which is maintainedat a variable minimum position until the economizer calls foradditional outdoor air. During non-economizer periods the EA/RA dampers modulate to maintain static pressure constant atthe filter inlet. This is accomplished by separating the controlof the outdoor air damper from the control of the return andrelief dampers. Note that the OA damper minimum positionand the MA static pressure setpoint must be determined inconjunction with the air balancing contractor. Refer to VAVAHU WITH RETURN FAN AND FLOW TRACKING in theAir Handling System Control Applications section.RETURN FANEARACT VSDFRA FAN RA FANSTATUS SPEEDRAFANRATEMPER-ATURERA FLOWSIGNALSUPPLY FANOASAVSDCTFOATEMPER-ATURERETURNAND RELIEFDAMPEROADAMPERSTATICPRESSUREMATEMPER-ATUREHEATINGVALVECOOLINGVALVESA SA FANFAN SPEEDSA FANSTATUSSATEMPER-ATURESA FLOWSIGNALSAPRESSUREROOMTEMPER-ATUREAFTERHOURSM10487Fig. 5. HVAC Flow Tracking with Differential Pressure Control of OA.166ENGINEERING MANUAL OF AUTOMATIC CONTROL