Pumping System Fundamentals V volume flow rate D P total pressure gain to overcome inletoutlet affects and friction D P static pressure difference between inlet and outlet D ID: 272765
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Slide1
Energy Efficient Fluid FlowSlide2
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 (velocity difference between inlet and outlet)DPelevation (elevation difference between inlet and outlet)DPfrictionEff = efficiencies of pump, drive, motor
W
elec
= V
D
P
total
/ [
Eff
pump
x
Eff
drive
x
Eff
motor
] Slide3
Pumping System Savings Opportunities
Reduce volume flow rate
Reduce required pump head
DPstatic DPvelocity DPelevation DPfrictionIncrease pump, drive, motor efficiencyWelec = V DPtotal
/ [Eff
pump
x Eff
drive
x Eff
motor
] Slide4
Fluid Flow System Saving Opportunities
Reduce Required Pump/Fan
D
PEmploy Energy Efficient Flow Control Improve Efficiency of Pumps/FansSlide5
Reduce Pump/Fan D
PSlide6
Minimize Elevation Gain
Increase Initial Reservoir Level
W
elev = V DPelevation difference between inlet and outletReducing elevation difference reduces work to overcome elevation by 20%Slide7
Minimize Friction
Use Large Diameter Pipes/Ducts
W
friction
= V
D
P
friction
D
P
friction
=
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%Slide8
Minimize Friction
Use Smooth Pipes/Ducts
W
friction
= V
D
P
friction
D
P
friction
~ friction factor f
fsteel = 0.021 fplastic = 0.018 Smoother pipes reduce work to overcome friction by: (0.021 – 0.018) / 0.018 = 17%Slide9
Minimize Friction
Use Gradual Elbows
Long
radius elbows reduce work to overcome friction by 90%Slide10
Employ Energy Efficient Flow ControlSlide11
Flow Control
Systems designed for peak flow
Systems operate at less than peak flow
Use energy efficient method to control (reduce) flowSlide12
Inefficient Flow Control
By-pass loop
(No savings)
By-pass damper (No savings)Outlet valve/damper(Small savings)Inlet vanes(Moderate savings)Slide13
Efficient Flow Control
Trim impellor for constant-volume pumps
Slow fan for constant-volume fans
VFD for variable-volume pumps or fansSlide14
Energy Efficiency of Flow ControlSlide15
Pump/Fan and System Curves
D
P
V
Pump/Fan Curve
System Curve
W = V
D
P = area of rectangleSlide16
Bypass Flow: Zero Energy Savings
D
P
V
Pump/Fan Curve
System Curve
V
2
= V
1
When bypassing, V through pump is constant
Thus, pump work is constant and no savingsSlide17
Throttle Flow: Small Energy Savings
With throttling and inlet vanes,
V decreases but P increases
Thus, net decrease in W (area under curves) is small
D
P
V
Throttled System Curve
Design System Curve
V
1
V
2
= V
1
/ 2Slide18
Reduce Pump/Fan Flow: Big Energy Savings
W = V
D
P = V (k V2) = k V3When flow reduced by pump/fan rather than system, W varies with cube of flowReducing flow by 50% reduces work to overcome friction by 88%
D
P
V
Pump/Fan Curve
System Curve
V
2
= V
1
/ 2
V
1Slide19
Three Ways to Reduce Pump/Fan Flow
Trim impellor for
constant-flow pumping applications
Slow fan for constant-flow fan applicationsInstall VFD for variable-flow pumps or fansSlide20
Constant Flow Pumping:Cooling Towers With
Throttling
ValvesSlide21
Constant Flow Pumping:Process Pumps with Throttling ValvesSlide22
Constant Flow Pumping:
Open Throttling Valve and Trim
Pump Impellor
A: Flow throttled by partially closed valveB: Max flow with valve openC: Valve open and impellor trimmedSlide23
Constant Flow Fans:
Slow
Fan by Changing Pulley DiameterSlide24
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) reducedSlide25
Variable Flow
Pumping:
Process Cooling Loop
W
2
= W
1
(V
2
/V
1
)
3
Reducing flow by 50% reduces pumping costs by 87%Slide26
Variable Flow Pumping: HVAC Chilled Water LoopsSlide27
Variable Flow Pumping:Open Throttling Valve and Install VFD Slide28
Full-Open Pumping:Install 2-Way Valves and VFDs Slide29
Big Cooling TowersSlide30
Big Cooling Loop PumpsSlide31
Worlds Largest Bypass PipeSlide32
Savings From Installing VFDs
A: Flow throttled by partially closed valve
B: Max flow with valve open
C: Valve open and pump slowed by VFD
A
B
C
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 – W2Slide33
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 hoursRecommended: One pump for six hoursEstimated Savings: $500 /yr
Reason: W
fluid
= V DP = k V
3Slide34
Optimize Efficiency of Pumps/FansSlide35
Correct Fan Inlet/Exit Conditions
No YesSlide36
Resize Over-sized
Pumps
Pump operating at off-design point M
Eff = 47%Replace with properly sized pumpEff = 80%Savings: $14,000 /yrSlide37
Fluid Flow Summary
Reduce Required Pump/Fan Head
Reduce excess elevation head
Use larger diameter pipesUse smoother pipes/ductsUse long-radius elbows and low-friction fittingsEmploy Energy Efficient Flow Control Constant flow pumping: trim impellor bladeConstant flow fans: Slow fanVariable flow pumps and fans: Install VFDsPump slow, pump long
Improve Efficiency Pumps/Fans
Correct fan inlet/exit conditions
Resize
miss-sized pumps/fans