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 = 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
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%
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
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
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
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
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