Analyzing and Optimizing Pumping Systems · U.S. Department of Energy Office of Industrial Technologies BestPractices Workshop 1 Analyzing and Optimizing Pumping Systems October 12,

1 U.S. Department of Energy Office of Industrial Technologies BestPractices Workshop

Analyzing and Optimizing Pumping Systems

October 12, 2016

Glenn T. Cunningham, PhD, P.E.

Mechanical Engineering Department

Tennessee Tech University

[email protected]


3 U.S. Department of Energy Office of Industrial Technologies BestPractices Workshop 3

• Look for:

– Throttle valve-controlled systems

– Bypass (recirculation) line normally open

– Multiple parallel pump system with same number of

pumps always operating

– Constant pump operation in a batch environment or

frequent cycle batch operation in a continuous process

– Cavitation noise (at pump or elsewhere in the system)

– High system maintenance

– Systems that have undergone change in function

– Pump at higher flow rates than are necessary for shorter

periods of time

Continuing to narrow the field: symptoms in

pumping systems that indicate potential opportunity


Component and system approaches to energy

and reliability improvement contrasted

• Component optimization involves

segregating components and analyzing in

isolation – How efficiently does the pump

provide flow to the system?

• System optimization involves looking at

how the whole group functions together

and how changing one can help another –

How efficient is the overall system at

delivering the needed flow?


Pumping Power Diagram

Shaft Power (bhp) = Motor Input Power * (ηM)

Fluid Energy Increase (whp) = Shaft Power (bhp) * (ηP)

(1 HP = 0.746 kW)

Motor

ηM

Pump

ηP

Input Power

Electrical, kW Fluid Power Increase

(whp)

Flow Out

Flow In

Shaft Power (bhp)

Mechanical Power

Pin

Pout


VFD on Pump Motor

VFD Input Power = whp/(ηD * ηM * ηP)

Motor

ηM

Pump

ηP

Input Power

whp

Flow Out

Flow In

Shaft Power

VFD

ηD


The system operating point is at the intersection

of the pump and system head-capacity curves

Operating

point

Flow rate

Head


Pump performance characteristics


There are four types of performance curves that

are used to characterize pumps

• Head

• Shaft power

• Efficiency

• Net positive suction head required (NPSHR)


Actual Pump Curve


Actual Pump Curve


And finally, efficiency curves for the two pumps

100

80

60

40

20

0

Effic

iency,

%

5000 4000 3000 2000 1000 0

Flow rate, gpm

Pump 2

Pump 1


The system operating point is at the intersection

of the pump and system head-capacity curves

Operating

point

Flow rate

Head


Each system has its own

unique system curve

The system curve describes everything in the system except

the pump and gives the required head to move a given flow

rate through the system.


We’ll use this system as an example: water is

pumped from one tank to another

There are two tank level

indicators, four pressure

gauges, and a flow meter

available for our use.

P3

P4

P2

P1

F

Pressure gauges 2 and

3 are in the same size pipe


System curves are made up of two fundamental

components - the static head and the frictional head

• Static head refers to the change in elevation from the

suction tank to the discharge tank

• Tank over-pressures must be included in calculations

• This is basically the change in potential energy of fluid

as it moves from the suction tank to the discharge tank

• Closed systems do not have static head

• Static heads can be positive, negative or zero




• Static head refers to the change in elevation from the

suction tank to the discharge tank

• Tank over-pressures must be included in calculations

• This is basically the change in potential energy of fluid

as it moves from the suction tank to the discharge tank

• Closed systems do not have static head

• Static heads can be positive, negative or zero


System Curves

System curves display the total head required to move

different amounts of flow through the piping system

System curve equations:

Htotal = Hstatic + k’Q1.9

Closed piping systems have zero static head

Open piping systems generally have some static head








P3

P4

P2

P1

F










P3

P4

P2

P1

F










P3

P4

P2

P1

F






120

80

40

0

Head

, ft

5000 4000 3000 2000 1000 0 Flow rate, gpm

Static/ Fixed

Friction

Total


200

150

100

50

0

Head

, ft

5000 4000 3000 2000 1000 0

Flow rate, gpm

System head curves for all frictional,

all static, and combined static and frictional systems

Static and

friction

Friction

only Static only

NOTE: These are three different systems


Actual Pump Data for VSD Operation

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

110.0

120.0

130.0

140.0

150.0

160.0

0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700 1,800 1,900 2,000 2,100 2,200 2,300 2,400 2,500

Fe

et

of

Hea

d

Flow (gpm)

Variable Speed Pumping

90% Speed

80% Speed

70% Speed

System with Valve Throttled

System with Valve Open

Operating Point Throttling Control

Operating Point VSD Control


PSAT Introduction


Example Water Treatment Plant

• County water treatment facility • 200 HP pump

• 2 100 HP pumps

• Typically run the 200 HP and one 100 HP

• Peak demand is just under 1.6 MGD

• Demand is less than 1.5 MGD 99.5% of

the time

• Would like to operate the plant 12

hours/day or less

• Electric rate has a significant demand

charge


Example Water Treatment Plant

System Curves


City Water

System


Parallel and series pumping “laws”, like the

pump affinity laws apply to the pump curves only

• Parallel pumps - sum the flow rates at a

given head

• Series pumps - sum the heads at a given

flow rate


Parallel pumps can help adapt to changing

system requirements and provide redundancy

200

150

100

50

0

Head

, ft

15000 12000 9000 6000 3000 0

Flow rate, gpm

Note: this is for

identical pumps


Unlike pumps can also be used in parallel,

but with caution

160

140

120

100

80

60

Head

, ft

8000 6000 4000 2000 0 Flow rate, gpm


Identical pumps in series; add head at a given

flow rate to estimate overall performance

500

400

300

200

100

0

Hea

d,

ft

5000 4000 3000 2000 1000 0

Flow rate, gpm


Parallel Pumping Example





With 2-pumps,

each produces

2,600 gpm, 5,200

gpm total; With 5-

pumps, the last

pump produces

1,100 gpm, from

8,900 to 10,000

gpm


Parallel Pumps: Header Pressure


Variable speed drive

performance characteristics


Change in speed for the all frictional system results

in maintenance of constant pump efficiency

200

150

100

50

0

Head

, ft

5000 4000 3000 2000 1000 0

Flow rate, gpm

30 40 50

70 60

75

75

80.5 (BEP)


What happens if we reduce

pump speed in the three

system types mentioned

earlier?


In a system with ONLY static head, the effect is

even more dramatic

5000 4000 3000 2000 1000 0

Flow rate, gpm

30 40 50

70 60

75 80.5 (BEP)

200

150

100

50

0

Head

, ft

75



even more dramatic

5000 4000 3000 2000 1000 0

Flow rate, gpm

30 40 50

70 60

75 80.5 (BEP)

200

150

100

50

0

Head

, ft

75



even more dramatic

5000 4000 3000 2000 1000 0

Flow rate, gpm

30 40 50

70 60

75 80.5 (BEP)

200

150

100

50

0

Head

, ft

75



even more dramatic

5000 4000 3000 2000 1000 0

Flow rate, gpm

30 40 50

70 60

75 80.5 (BEP)

200

150

100

50

0

Head

, ft

75



even more dramatic

5000 4000 3000 2000 1000 0

Flow rate, gpm

30 40 50

70 60

75 80.5 (BEP)

200

150

100

50

0

Head

, ft

75



even more dramatic

5000 4000 3000 2000 1000 0

Flow rate, gpm

30 40 50

70 60

75 80.5 (BEP)

200

150

100

50

0

Head

, ft

75


How about parallel pump

operation with different

system types?


The effect of turning on a parallel pump also

depends on the nature of the system

200

150

100

50

0

Head

, ft

10000 8000 6000 4000 2000 0 Flow rate, gpm

7000 gpm

4835 gpm 4060 gpm

3500 gpm


The effect of turning on a parallel pump also

depends on the nature of the system

200

150

100

50

0

Head

, ft

10000 8000 6000 4000 2000 0 Flow rate, gpm

7000 gpm

4835 gpm 4060 gpm

3500 gpm


An introduction to the Pumping System

Assessment Tool (PSAT)

• Goal: to assist pump users in identifying

pumping systems that are the most likely

candidates for energy and cost savings

• Requires field measurements or estimates of

flow rate, pressure, and motor power or current

• Uses pump and motor performance data from

Hydraulic Institute standard ANSI/HI-1.3 and

MotorMaster+ to estimate existing, achievable

performance


Assessing the magnitude of the opportunity

• Pumping System Assessment Tool

– Focus on systems flagged by the size and

symptom filters (size alone is, however,

sufficient)

– Quantifies energy and cost savings

opportunity

– Does not identify the solution




Input data Results




Input data Results




Input data Results




Input data Results




Input data Results




Input data Results




Input data Results




Input data Results




Input data Results




Input data Results




Input data Results




Input data Results


Pump affinity laws and

parallel or series pump operation


Pump affinity laws can be used to predict pump

curves for different speeds and impeller diameters

Q1 N1

Q2 N2 ( ) ( ) =

H1 N1

H2 N2 ( ) ( ) =

1

2

P1 N1

P2 N2 ( ) ( ) =

3

Q1 D1

Q2 D2 ( ) ( ) =

H1 D1

H2 D2 ( ) ( ) =

1

2

P1 D1

P2 D2 ( ) ( ) =

3

Speed Diameter

Q = flow rate H = head P = power N = speed D = diameter




Q1 N1

Q2 N2 ( ) ( ) =

H1 N1

H2 N2 ( ) ( ) =

1

2

P1 N1

P2 N2 ( ) ( ) =

3

Q1 D1

Q2 D2 ( ) ( ) =

H1 D1

H2 D2 ( ) ( ) =

1

2

P1 D1

P2 D2 ( ) ( ) =

3

Speed Diameter

Q = flow rate H = head P = power N = speed D = diameter













Documents

Analyzing and Optimizing Pumping Systems · U.S. Department of Energy Office of Industrial Technologies BestPractices Workshop 1 Analyzing and Optimizing Pumping Systems October 12,