Energy Efficient Fluid Flow

Fluid Flow System Fundamentals

motor = 90%

Wfluid

58

Qloss =10 Qloss = 8 Qloss = 25

Wdrive 90 Wpump

83

Wmotor 100

drive = 92%

pump = 70%

Wmotor = Wfluid / (Effmotor x Effdrive x Effpump)

Look For “Inside” Opportunities to Max Savings

• Efficiency losses in distribution and primary energy conversion systems multiply “inside” savings

• Example:– Welec= Wfluid / [Effpumpx Effdrivex Effmotor ]

– Welec= 1 kWh / [.70 x .92 x .90 ] = 1.7 kWh

Fluid Flow System Fundamentals

Wfluid = V Ptotal

P

V

Pump Curve System Curve

Wfluid = V P

Fluid Flow System Fundamentals

Wfluid = V Ptotal = V (k V2) = k V3

Wfriction = V Pfriction = k / D5

P

V

Pump Curve System Curve

Wfluid = V P

Pumping System Savings Opportunities

• Reduce volume flow rate• Reduce required pump head

Pstatic

Pvelocity Pelevation Pheadloss

• Increase pump, drive, motor efficiency

Welec = V Ptotal / [Effpumpx Effdrivex Effmotor ]

Fluid Flow System Saving Opportunities

• Reduce Required Pump/Fan P• Employ Energy Efficient Flow Control • Improve Efficiency of Pumps/Fans

Reduce Pump/Fan P

Increase Reservoir Level toReduce Elevation Head

13 ft

15.5 ft

z = 2.5 ft

13 ft13 ft

15.5 ft

z = 2.5 ft

Minimize Pipe Friction:Use Bigger Pipes/Ducts

Use large diameter pipes: P headloss ~ k / D5

Doubling pipe diameter reduces friction by 97%

Minimize Pipe FrictionUse Smooth Pipes/Ducts

Use smooth plastic pipes: fsteel = 0.021 fplastic = 0.018 Pumping savings from plastic pipe

(0.021 – 0.018) / 0.018 = 17%

Use Gradual Elbows

Use Gradual Elbows

Employ Energy Efficient Flow Control

Inefficient Flow Control

By-pass loop(No savings)

By-pass damper (No savings)

Outlet valve/damper(Small savings)

Inlet vanes(Moderate savings)

Fan w/ Inlet Vanes

Efficient Flow Control

Trim impellor for constant-volume

pumps

Slow fan for constant-volume

fans

VFD for variable-volume pumps or fans

Close Bypass Valve

dP

VFD

Inefficient and Efficient Flow Control

0%

20%

40%

60%

80%

100%

0% 20% 40% 60% 80% 100%

Volume Flow Rate (%)

Po

wer

(%

)

Outlet Damper Variable Inlet Vane Variable Frequency Drive

Cooling Towers

Cooling Loop Pumps

Worlds Largest Bypass Pipe

For Constant Speed Pump Applications: Trim Pump Impellor

• Look for discharge valve at < 100% open • More energy-efficient to downsize the pump by

trimming impellor blades than throttle flow

Trim Impellor and Open Throttling Valve

For Constant Speed Fan Applications: Slow Fan Speed by Changing Pulley Diameter

• Look for discharge damper at < 100% open • More energy-efficient to slow fan than throttle flow

For Variable Flow Applications:Install VFD

• W2 = W1 (V2/V1)3

• Reducing flow by 50% reduces pumping costs by 87%

warm water

cool water

cooling tower

city water make-up

7.5 hp pump

25 hp pump

reservoir

process water return

bypass / pressure

relief valve

cooling water to process loads

dP

VSD

Variable Speed Pumping on HVAC Chilled Water Loops

Replace 3-way Valve with 2-way valve on AHU

VFDs on Vent Hoods

Need Controls for VFDs on Dust Collection

Use VFDs on Cooling Tower Fans

Pump Long, Pump Slow

• Identify intermittent pumping applications• More energy to pump at high flow rate for short period

than low flow rate longer• Example:

– Current: Two pumps in parallel for four hours– Recommended: One pump for six hours– Estimated Savings: $500 /yr

Reason: Wfluid = V DP = k V3

Optimize Efficiency of Pumps/Fans

Correct Fan Inlet/Exit Conditions No Yes

Refurbish Inefficient Pumps

Pump not operated at peak efficiency in middle of operating range

Resize Miss-sized Pumps

• Pump operating at off-design point M

• Eff = 47%• Replace with properly

sized pump• Estimated savings:

$14,000 /yr

Fluid Flow Summary• Reduce Required Pump/Fan Head

– Reduce excess elevation head– Smoother pipes/ducts– Larger diameters– Gradual elbows

• Employ Energy Efficient Flow Control – Constant speed pumping: trim impellor blade– Constant speed fans: Slow fan– Variable flow: Install VFDs– Pump slow, pump long

• Improve Efficiency Pumps/Fans– Correct fan inlet/exit conditions– Refurbish inefficient pumps– Resize miss-sized pumps/fans