Accurex XDG Installation, Operation And Maintenance Manual
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Contents
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Direct Gas Make-Up Air35Start-Up: Direct Gas-Fired HeatingOptional FeaturesVariable Air Volume (VAV) (continued)minimum airflow, the bypass damper will be mostlyclosed and a majority of the air will pass though theburner profile. In this way, the airflow through the burnerprofile remains relatively constant through the range ofairflow operation.Due to the movement of the bypass damper throughoutthe airflow range of the unit, a change in RPM doesnot result in a directly proportional change in airflow. Inthese units, a 33% fan RPM reduction results in a 50%airflow reduction.Burner Pressure Differential CheckThe bypass damper is designed to open and close tomaintain the correct pressure differential through theburner profile for proper operation. The counterbalancearm and weights are factory adjusted for the correctpressure drop and do not require field adjustment. Inmany cases, the bypass damper is able to compensatefor variations in supply airflow and no adjustments tothe burner profile are necessary.Reference the Start-Up: Direct Gas-Fired Heating,All Units section in this Installation, Operation andMaintenance Manual for more information aboutmeasuring burner pressure differential and adjustingburner baffles. Before making any adjustments to theburner baffles on a variable air volume unit, checkthe burner pressure differential with the supply fanat maximum speed and again with the supply fan atminimum speed. The burner pressure differential willvary slightly throughout the range of airflow. Verifythat the burner pressure differentials at maximum andminimum speed are both in the correct range:• Natural Gas: 0.5 to 0.8 in. wg• Liquid Propane (LP) Gas: 0.7 to 1.0 in. wgIf adjustment is necessary, adjust the fan RPM viaadjustable motor sheaves (if equipped), VFD, or sheavereplacement to achieve proper burner pressure drop.Motor amp draw must not exceed full load amperage(FLA) on motor nameplate. If fan RPM cannot beadjusted, evenly adjust the baffles above and below theburner, keeping the burner centered in the opening untilthe required pressure is obtained. |
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