Energy Efficient Fluid Flow

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Energy Efficient Fluid Flow

• Kelly Kissock, Ph.D., P.E.
• Department of Mechanical and Aerospace
  Engineering
• University of Dayton, Dayton, Ohio

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Outline of Presentation

• Approach
• Pumping Fundamentals
• Saving Opportunities

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Approaches to Energy Efficiency

• Exergy approach
• Inside-out approach
• Plant as whole system approach

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Exergy Approach

• Exergy
• Potential useful work in energy
• Best measure of quantity and quality of energy
• Exergy destroyed in all real processes
• Important mechanisms of exergy destruction
• Friction and turbulence
• Mixing
• Heat transfer through large temperature
  differences
• Mismatch between exergy supplied and end-use.

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Inside Out Approach
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Pumping System Fundamentals

• Wfluid V DPtotal

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Pumping System Savings Opportunities
Welec V DPtotal / Effpumpx Effdrivex Effmotor

• Reduce volume flow rate
• Reduce required pump head
• DPstatic
• DPvelocity
• DPelevation
• DPheadloss
• Increase pump, drive, motor efficiency

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Pumping System Fundamentals
Wmotor Wfluid / (Effmotor x Effdrive x Effpump)
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Inside-Out Approach Maximizes Savings At
Minimum First Cost

• Outside

Inside
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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

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Pump System Saving Opportunities

• Reduce Required Pump Head
• Employ Energy Efficient Flow Control
• Use Efficient Pumps, Drives, Motors

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Minimize Required Pump Head
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Minimize Pipe Friction

• Use large diameter pipes
• DP headloss C / D5
• Doubling pipe diameter reduces pumping costs by
  97
• Use smooth plastic pipes
• fsteel 0.021 fplastic 0.018
• Pumping savings from plastic pipe
• (0.021 0.018) / 0.018 17
• Less friction reduces pumping costs and cooling
  load

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Total Head Rise Across Pump

• Wf V DPtotal
• DPtotal DPstaticDPvelocityDPelevationDPfricti
  on
• Wf (hp) V (gpm) DPtotal (ft-H20) / 3,960

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Maintain Higher Reservoir Level to
Reduce Pump Suction Head

• Maintain reservoir level at 14 feet
• Estimated savings 3,000 /yr

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Use Low Friction Fittings and Smooth Large Pipes

• DPfriction fittings (kf rfluid / 2) V2
• DPfriction,pipes (f L / 2 D) V2 c / D5

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Employ Energy Efficient Flow Control
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Employ Energy Efficient Flow Control

• Pumping Power k V3
• What to look for
• By-pass
• Throttling
• Parallel pumping
• Solutions
• Trim impellor
• Slow pump speed (pulley or VSD)
• Pump long, pump slow

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Variable Speed Pumping

• W2 W1 (V2/V1)3
• Reducing flow by 50 reduces pumping costs by 87

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3 Pumps in Parallel
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5,000 gpm Bypass
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Three-way Chilled Water Valve on AHU
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Control Flow Trim Pump Impellor

• 20-hp pump with discharge valve set at 60 open.
• More energy-efficient to downsize the pump by
  trimming impellor blades than throttle flow
• Estimated savings
• 800 /yr

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Pump Long, Pump Slow

• Current to refill tank, run two 100-hp pumps in
  parallel for four hours
• Recommended run one pump for 6 hours
• Estimated Savings 500 /yr

System Curve DP k V2 Wfluid V DP k V3
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Use Efficient Pumps, Drives, Motors
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Refurbish/Resize Inefficient Pumps

• Pump not operated at peak efficiency in middle of
  operating range

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Refurbish/Resize Inefficient Pumps

• Pump operating at off-design point M (Eff 47)
• Replace with properly sized pump
• Estimated savings 14,000 /yr

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Use Notched V-Belts on Belt Drives

• Belts with notches flex more easily
• 4 more efficient that standard belts
• Last between 50 and 400 longer.
• Small increased first cost more than compensated
  by increased lifetime.
• Estimated Savings 5,200 /yr

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Use Notched V-Belts
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Motors Energy Cost gtgt Purchase Cost

• Consider
• 20-hp, 93 efficient motor costing 1,161
• Motor 75 loaded, 8,000 hrs/year, 0.06 /kWh
• Energy cost 20 hp x 75 x .75 kW/hp / 93 x
  8,000 hr/yr x 0.06 /kWh 5,806 /yr

Over 20-yr motor life, energy cost is 100x
greater than purchase cost!
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Replace Failed Motors lt (20-50) hp
Comparison between rewinding standard 87.3
efficiency 20-hp motor for 690 or replacing it
with a new 93 efficient motor costing 1,161.
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Summary

• Reduce Pumping Pressure
• Control Flow Wisely
• Use Efficient Motors, Drives, Pumps
• Minimize Compressed Air/Blowers
• Identify and Maximize Efficient Systems

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Energy Efficient Fan Systems
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Use Gradual Elbows
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Install VFDs on Vent Hoods
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VFDs on Vent Hoods
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No VFDs on Dust Collection
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VFD Cooltower Fans