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Energy Efficient Fluid Flow

Energy Efficient Fluid Flow. Pumping System Fundamentals. V = volume flow rate D P total = pressure gain to overcome inlet/outlet affects and friction D P static (pressure difference between inlet and outlet) D P velocity (velocity difference between inlet and outlet)

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Energy Efficient Fluid Flow

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  1. Energy Efficient Fluid Flow

  2. Pumping System Fundamentals • V = volume flow rate • DPtotal= pressure gain to overcome inlet/outlet affects and friction DPstatic (pressure difference between inlet and outlet) DPvelocity(velocitydifference betweeninlet and outlet) DPelevation(elevation difference between inlet and outlet) DPfriction • Eff = efficiencies of pump, drive, motor Welec= V DPtotal / [EffpumpxEffdrivexEffmotor]

  3. Pumping System Savings Opportunities • Reduce volume flow rate • Reduce required pump head DPstatic DPvelocity DPelevation DPfriction • Increase pump, drive, motor efficiency Welec = V DPtotal / [Effpumpx Effdrivex Effmotor ]

  4. Fluid Flow System Saving Opportunities • Reduce Required Pump/Fan DP • Employ Energy Efficient Flow Control • Improve Efficiency of Pumps/Fans

  5. Reduce Pump/Fan DP

  6. Minimize Elevation GainIncrease Initial Reservoir Level • Welev = V DPelevation difference between inlet and outlet • Reducing elevation difference reduces work to overcome elevation by 20%

  7. Minimize FrictionUse Large Diameter Pipes/Ducts • Wfriction = V DPfriction • DPfriction=k / D5 • Wfriction= V k / D5 • Work to overcome friction varies inversely with 5th power of pipe diameter • Doubling pipe diameter reduces work to overcome friction by 97%

  8. Minimize FrictionUse Smooth Pipes/Ducts • Wfriction= V DPfriction • DPfriction~ friction factor f • fsteel = 0.021 fplastic = 0.018 • Smoother pipes reduce work to overcome friction by: (0.021 – 0.018) / 0.018 = 17%

  9. Minimize FrictionUse Gradual Elbows Long radius elbows reduce work to overcome friction by 90%

  10. Employ Energy Efficient Flow Control

  11. Flow Control • Systems designed for peak flow • Systems operate at less than peak flow • Use energy efficient method to control (reduce) flow

  12. Inefficient Flow Control • By-pass loop • (No savings) • By-pass damper • (No savings) • Outlet valve/damper • (Small savings) • Inlet vanes • (Moderate savings)

  13. Efficient Flow Control • Trim impellor for constant-volume pumps • Slow fan for constant-volume fans • VFD for • variable-volume pumps or fans

  14. Energy Efficiency of Flow Control

  15. Pump/Fan and System Curves W = V DP = area of rectangle Pump/Fan Curve DP System Curve V

  16. Bypass Flow: Zero Energy Savings • When bypassing, V through pump is constant • Thus, pump work is constant and no savings Pump/Fan Curve DP System Curve V V2 = V1

  17. Throttle Flow: Small Energy Savings Throttled System Curve • With throttling and inlet vanes, V decreases but P increases • Thus, net decrease in W (area under curves) is small DP Design System Curve V2 = V1 / 2 V1 V

  18. Reduce Pump/Fan Flow: Big Energy Savings • W = V DP = V (k V2) = k V3 • When flow reduced by pump/fan rather than system, W varies with cube of flow • Reducing flow by 50% reduces work to overcome friction by 88% Pump/Fan Curve DP System Curve V1 V2 = V1 / 2 V

  19. Three Ways to Reduce Pump/Fan Flow • Trim impellor for constant-flow pumping applications • Slow fan for constant-flow fan applications • Install VFD for • variable-flow pumps or fans

  20. Constant Flow Pumping:Cooling Towers With Throttling Valves

  21. Constant Flow Pumping:Process Pumps with Throttling Valves

  22. Constant Flow Pumping: Open Throttling Valve and Trim Pump Impellor A: Flow throttled by partially closed valve B: Max flow with valve open C: Valve open and impellor trimmed

  23. Constant Flow Fans:Slow Fan by Changing Pulley Diameter

  24. Constant Flow Fans:Slow Fan by Changing Pulley Diameter A: Flow throttled by partially closed damper B: Max flow with damper open C: Damper open and fan speed (RPM) reduced

  25. Variable Flow Pumping:Process Cooling Loop • W2 = W1 (V2/V1)3 • Reducing flow by 50% reduces pumping costs by 87%

  26. Variable Flow Pumping: HVAC Chilled Water Loops

  27. Variable Flow Pumping:Open Throttling Valve and Install VFD

  28. Full-Open Pumping:Install 2-Way Valves and VFDs

  29. Big Cooling Towers

  30. Big Cooling Loop Pumps

  31. Worlds Largest Bypass Pipe

  32. Savings From Installing VFDs A B C A: Flow throttled by partially closed valve B: Max flow with valve open C: Valve open and pump slowed by VFD Wsav for throttle to VFD = A – C Wsav for bypass to VFD = B – C Wsav for bypass to VFD W2 = W1(V2/V1)2.5 Wsav = W1 – W2

  33. 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

  34. Optimize Efficiency of Pumps/Fans

  35. Correct Fan Inlet/Exit Conditions No Yes

  36. Resize Over-sized Pumps • Pump operating at off-design point M • Eff = 47% • Replace with properly sized pump • Eff = 80% • Savings: $14,000 /yr

  37. Fluid Flow Summary • Reduce Required Pump/Fan Head • Reduce excess elevation head • Use larger diameter pipes • Use smoother pipes/ducts • Use long-radius elbows and low-friction fittings • Employ Energy Efficient Flow Control • Constant flow pumping: trim impellor blade • Constant flow fans: Slow fan • Variable flow pumps and fans: Install VFDs • Pump slow, pump long • Improve Efficiency Pumps/Fans • Correct fan inlet/exit conditions • Resize miss-sized pumps/fans

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