Energy Efficient Fluid Flow

Pumping System Fundamentals Welec = V DPtotal / [Effpumpx Effdrivex Effmotor ] V = volume flow rate DPtotal = pressure gain to overcome inlet/outlet affects and friction DPstatic (pressure difference between inlet and outlet) DPvelocity (velocity difference between inlet and outlet) DPelevation (elevation difference between inlet and outlet) DPfriction Eff = efficiencies of pump, drive, motor

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

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

Reduce Pump/Fan DP

Minimize Elevation Gain Increase Initial Reservoir Level Welev = V DPelevation difference between inlet and outlet Reducing elevation difference reduces work to overcome elevation by 20%

Minimize Friction Use 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%

Minimize Friction Use 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%

Minimize Friction Use Gradual Elbows Long radius elbows reduce work to overcome friction by 90%

Employ Energy Efficient Flow Control

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

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

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

Energy Efficiency of Flow Control 14

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

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

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

Reduce Pump/Fan Flow: Big Energy Savings Pump/Fan Curve DP System Curve V2 = V1 / 2 V1 V 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%

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 19

Constant Flow Pumping: Cooling Towers With Throttling Valves

Constant Flow Pumping: Process Pumps with Throttling Valves

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

Constant Flow Fans: Slow Fan by Changing Pulley Diameter

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

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

Variable Flow Pumping: HVAC Chilled Water Loops

Variable Flow Pumping: Open Throttling Valve and Install VFD

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

Big Cooling Towers

Big Cooling Loop Pumps

Worlds Largest Bypass Pipe

Savings From Installing VFDs 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

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

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

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