BAE - SWSI & DWDI Airfoil Fans - Twin City Fan & Blower

AccessoriesNested Inlet VanesExternal Inlet VanesVolume Control DevicesOutlet dampers, variable inlet vanes, and variable frequencydrives are three popular devices used to controlvolume for fan systems.Variable Inlet VanesVariable inlet vanes cause the entering air to spin inthe direction of wheel rotation, resulting in reduction involume, static pressure and brake horsepower and thusproviding an infinite number of fan curves approximatelyparallel to the original fan curve. Variable inlet vanescost about 50% to 80% more than outlet dampers butoffer significant savings in energy. Because of their simplicity,inlet vanes can be more reliable when comparedto variable frequency drives.STATIC PRESSURE10864200Performance Curvesat Different Vane Settings2550251007550751002001601208040BRAKE HORSEPOWERThere are two types of variable inlet vanes: nested(internal type) and bolted on (external type).Nested inlet vanes are built into the fan inlet cone andoffer the advantage of saving space and lower cost asopposed to the external type. They are available on allfan sizes 165 and larger. Twin City Fan & Blower offerscantilevered vanes to size 890 Class II fans to minimizeinsertion losses and noise associated with center hubdesign.External inlet vanes are bolted to the inlet of the fanand are available from size 122 to size 890. Use ofexternal vanes should be considered for hostile environmentssince operating linkages are shielded from theairstream. Both types of inlet vanes are available to600°F construction.0 2 4 6 8 10CFM IN 10000'sSYSTEM System CURVE CurveSP @ SP VANE @ Vane SETTING SettingBHP BHP @ VANE @ Vane SETTING SettingOutlet DampersThe closing of the damper adds to the resistance thatthe fan is working against. This moves the operatingpoint to the left of the initial rating point. The savings inhorsepower depends on the relative position on the fancurve and is usually much less than offered by othermethods. Outlet dampers are typically the least expensiveoption and should be considered when infrequentoperation at lesser capacity is desired or when handlinghot, humid or particulate laden air.Parallel BladeOutlet DamperOpposed BladeOutlet DamperThere are two types of outlet dampers: parallel bladeand opposed blade.Parallel blade dampers are recommended for systemswhere air volume is modulated between full-open toabout 75% of open.Opposed blade dampers cost about 10% more andare recommended for systems where volume is modulatedover the entire range. Opposed blades reduceair volume in a closer relationship to the control armmovement.8 Twin City Fan Catalog 370