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