Objectives Discuss Exam Finish with Diffuser Selection Learn
Objectives • Discuss Exam • Finish with Diffuser Selection • Learn about Fan and Pumps
Find Characteristic Length (L)
Indicator of Air Distribution Quality • ADPI = air distribution performance index • Fraction of locations that meet criteria: • -3 °F < EDT < 2 °F or -1. 5 °C < EDT < 1 °C • Where, EDT = effective draft temperature • Function of V and Δt (Eqn 18. 1) • EDT=(tlocal-taverage)-M(Vlocal-Vaverage) , M=7 °C/(m/s) ADPI considers ONLY thermal comfort (not IAQ)
Ideal and Reasonable Throws
Diffuser testing
ADPI
Select Register • Pick throw, volumetric flow from register catalog • Check noise, pressure drop http: //www. titus-hvac. com/ecatalog/subcategory. aspx? refid=186 http: //www. nailor. com/ http: //www. price-hvac. com/
Fans • Driving force to move air in buildings • Raise pressure and produce flow • Two main types: • Centrifugal • Axial
Relevant Fan Parameters • • Total pressure rise Static pressure rise Power requirement Efficiency • Note ηtot does not account for motor efficiency
Balance Point
Fan Performance
Centrifugal fans
Axial Fans
Fan Laws • “Approximate relationships” • Given two aerodynamically similar fans, can extrapolate performance data • Be very careful
Controlling Air Flow
Dampers
Effect on Fan Curve
VAV Operation
Dampers
Dampers
Pumps • Driving force to move air water in buildings • Raise pressure and produce flow • One main type • Centrifugal
Pump curves • NPSHR = Net Positive Suction Head Required
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