Objectives Finish duct design Discuss HW 4 Learn
Objectives • Finish duct design • Discuss HW 4 • Learn about pumps
Frictional Losses
Non-circular Ducts
Dynamic (local) losses • Losses associated with • • Changes in velocity Obstructions Bends Fittings and transitions
Loss Coefficients ΔPt = Co ΔPv, o
Duct Design Example • Determine total pressure drop from in this duct system F l 1=150 ft l 3=100 ft l 2=50 ft A VA = 1000 CFM pdiffuser. A = 10 Pa VA = 1000 CFM B VA = 2000 CFM pdiffuser. B = 15 Pa
Solution Equal friction method: section L[ft] V [CFM] D[in] Dp/100 ft [“wg] V [fpm] Dptot[“wg] Local Dp Coef. Sum Co Dp_loc[“wg] Tot_Dp[“wg] L 1 L 2 L 3 150 50 100 3000 1000 2000 18” 12” 16” 0. 22 0. 18 1700 1300 1400 0. 33 0. 10 0. 18 Co=0. 5 Co=0. 28 Co=13, Co=0. 09 0. 5 0. 28 0. 22 0. 09 0. 03 0. 42 0. 13 0. 21
Two design methods Equal friction method (Example 18. 9): Static regain method (Example 18. 10):
Fan Performance
Controlling Air Flow
VAV Operation
How to use multiple pumps
Dampers
Summary of Air Distribution Systems • Select diffuser based on ADPI • Given a layout of duct system • Calculate total pressure drop • Deal with non-circular ducts and fitting losses • Select the fan based on fan and duct curve
HW 4 Design: • • • Air handling unit (AHU) with components (cooling coil and fan) Duct system Diffusers Chiller Pump Power requirement
Pumps and Plumbing • Very similar to fans and ducts • Same principles based on fluid dynamics • With some specifics
Hydronic Terms • Head loss • Open-loop vs. closed loop
Head Loss
Fittings
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
Use Multiple Pumps
Plumbing Arrangements
Example 19. 7 • Similar to equal friction method • Calculate head loss for common pieces of system • Size pipes to have equal head loss between points 2 and 3
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