energy eﬃciency in pumps - kocaeli Üniversitesilaboratuar.kocaeli.edu.tr/hidromekanik/sci/... ·...

Available online at www.sciencedirect.com

www.elsevier.com/locate/enconman

Energy Conversion and Management 49 (2008) 1662–1673

Energy efficiency in pumps

Durmus Kaya a,*, E. Alptekin Yagmur a, K. Suleyman Yigit b, Fatma Canka Kilic c,A. Salih Eren b, Cenk Celik b

a TUBITAK-MRC, P.O. Box 21, 41470 Gebze, Kocaeli, Turkeyb Engineering Faculty, Kocaeli University, Kocaeli, Turkey

c Department of Air Conditioning and Refrigeration, Kocaeli University, Kullar, Kocaeli, Turkey

Received 26 March 2007; accepted 22 November 2007Available online 14 January 2008

Abstract

In this paper, ‘‘energy efficiency” studies, done in a big industrial facility’s pumps, are reported. For this purpose; the flow rate, pres-sure and temperature have been measured for each pump in different operating conditions and at maximum load. In addition, the elec-trical power drawn by the electric motor has been measured. The efficiencies of the existing pumps and electric motor have beencalculated by using the measured data.

Potential energy saving opportunities have been studied by taking into account the results of the calculations for each pump and elec-tric motor. As a conclusion, improvements should be made each system. The required investment costs for these improvements have beendetermined, and simple payback periods have been calculated.

The main energy saving opportunities result from: replacements of the existing low efficiency pumps, maintenance of the pumps whoseefficiencies start to decline at certain range, replacements of high power electric motors with electric motors that have suitable power,usage of high efficiency electric motors and elimination of cavitation problems.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Pump; Energy savings; Energy efficiency

1. Introduction

In the studies that have been conducted for energy sav-ing, it has been seen that one of the areas of high potentialenergy saving is pumping systems [1–4]. According to astudy that the American Hydraulics Institute has made,20% of the consumed energy has been consumed by pumpsin developed countries [5]. It has been explained that 30%of this energy can be saved with good design of systemsand choosing suitable pumps. This situation has causednew searches to be made to find more efficient systems inproduction and operation by producers and users of pumps[6–10]. Furthermore, some legal regulations have started tobe enacted on this topic in some countries [11]. For exam-

0196-8904/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.enconman.2007.11.010

* Corresponding author. Tel.: +90 262 677 29 53; fax: +90 262 641 2309.

E-mail address: [email protected] (D. Kaya).

ple, obligatory labeling of circulation pumps (P < 2.5 kW)has been in the last stage in the EU. Placing a letter on thelabel to show energy efficiency is obligatory for circulationpumps that have been produced in Germany. Besides, ithas been stated and published at the end of the studies thathave been conducted that the flow rate, pump head andperiod number of the pump for which the required effi-ciency is attained should be showed on the diagrams toinform clients about the efficiency of the centrifugal pumpsthey purchase in the EU [12–14].

That pumps have high efficiency alone is not enough fora pump system to work in maximum efficiency. Working inmaximum efficiency of a pump system depends not only ona good pump design but also a good design of the completesystem and its working conditions. Otherwise, it is inevita-ble that even the most efficient pump in a system that hasbeen wrongly designed and wrongly assembled is going tobe inefficient [15–20].

mailto:[email protected]

Motor Efficiency-Loading Curve

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90 100

Value of Loading [ % ](According to Rated Loading Value)

Valu

e of

Effi

cien

cy [

% ]

0-1HP 1,5-5HP 10HP15-25HP 30-60HP 75-100HP

Fig. 1. The variations of the motor efficiencies according to loading.

D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673 1663

2. Energy efficiency and the factors that influence the

effectiveness in pumps

Effective usage of energy in pumps can be considered intwo stages, design and operation.

2.1. The effectiveness in pump design

2.1.1. Selection of pump of suitable capacity and type and

design of pipe installation

When planning the selection of a pump to provide themost active and effective system, the needs of the processshould be known. Also, the flow rate-time intervals andpump head of the system throughout one year should bewell known.

The system should be selected not only to meet the needsof working in maximum capacity but also, in an economicpoint of view, it should also be known what capacity willbe required. After this, the pipe installation can bedesigned. If the maximum capacity required is for a shorttime period, there is no need to have a pipe with a bigdiameter. If the system works with a high capacity for along time, this situation should be taken into considerationin the selection of the pipe diameter [21,22].

When designing a pipe system, the system curve mustdefinitely be drawn. It is very important to choose a pumpwith maximum efficiency and the most convenient runningclearance. Because the first purchasing costs are only in therange of 3–5% of the life cycle costs, it is the obligation ofthe administrators to make more careful selections of thepump.

2.1.2. The selection of an electric motor in suitable power

It is very important to select an electric motor of suitablepower to work efficiently. In general, motors are chosen inbig capacities to meet extra load demands. Big capacitiescause motors to work inefficiently at low load. Normally,motors are operated more efficiently at 75% of rated loadand above. Motors operated lower than 50% of rated load,because they were chosen in big capacity, performing inef-ficiently, and due to the reactive current increase, powerfactors also are decreased. These kinds of motors do notconsume the energy efficiently because they have been cho-sen in big power, not according to the needs. These motorsshould be replaced with new suitable capacities motors,and when purchasing new motors, energy saving motorsshould be preferred.

The motor shows the stated efficiency on the label of themotor when it is fully loaded. The efficiency value in differ-ent loads is different from the value that has been showedon its label. Fig. 1 shows the variations of motor efficienciesaccording to loading. The efficiency at which the motor isbeing operated is determined by looking at the efficiencyloading curve. The efficiency value is equal to the maxi-mum value only when the motor is operated at loading val-ues of 75% and bigger of the rated value. The preferredoptimum operating region is between 60% and 90% of

the rated load for motors; the ideal value is when the motoris operated in its full load.

2.1.3. The selection of high efficiency electric motor

The energy that electric motors consumed in plants isabout 65% of the total energy consumption. Therefore, itis important to choose ‘‘high efficiency” motors in plants.Like all motors, electric motors also can not transformall the energy they use into mechanical energy. The ratioof the mechanical power output of a motor and its drawnelectric power is named the motor efficiency, and accordingto its size, it can range between 70% and 96% [23]. Also,motors that are operated at partial load are operated atlow efficiencies. These efficiencies can vary from motor tomotor. For example, while the efficiency of a motor is90% when it is fully loaded, 87% when it is half loadedand 80% when it is 1/4 loaded; the efficiency of an anothermotor may be 91% when it is fully loaded and only 75%when it is 1/4 loaded.

The costs of high efficiency motors that have been devel-oped in the last years are more expensive, around 15–25%more than that of standard motors. Usually, because of thelow operating costs, this difference can be regained in ashort time [24–27]. By increasing the cross section of thecopper conductors that are used in the motor winding,the primary I2R loss can be decreased. Iron core loss withthe decrease of flux density, usually, can be limited byincreasing the neck of the stator core. Beside, these lossescan be decreased by decreasing the thickness of the panelsand using good quality alloys. On the other hand, in highefficiency motors, because of the decreased losses, the needof disposing of the revealed heat decreases (Fig. 2).

2.1.4. Selection of a system with variable flow rate

The different methods to get a pump system with vari-able flow rate are: to operate the pump when it is needed(part load operation), to operate the pump continuously

Fig. 3. The effect of periodic maintenance on pump efficiency.

Efficiency Loading Curve

0.80.820.840.860.880.9

0.920.940.960.98

0 10 20 30 40 50 60 70 80 90 100

Value of Motor Loading (%)

Mot

or E

ffici

ency

Standard Motor High Efficient Motor

Fig. 2. The efficiency of standard and high efficient motors.

1664 D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673

but send back some of the fluid to the tank (by pass sys-tem), by feeding the system from a tank to operate thepump at part load operation in respect to the level of thetank, adjust the flow rate by changing a flow rate controlvalve at the outlet of the pump and system curve, to adjustthe pump rotational speed according to the needs of flowrate or pressure by putting a hydraulic or electrical cou-pling between the constant speed electric motor and thepump, to set a parallel operating pump system, to changethe belt and pulley system and pump rotational speedand to use a frequency converter.

From the methods mentioned above, the most usableand widespread one is the systems with frequency convert-ers [28].

2.2. The saving at the facility

The most important performance loss at the operationstage of pumps arises from operating at part load. In thesituation of pumps operated at nominal capacities, thehighest efficiency can be achieved. Besides, on centrifugalpumps, if the flow rate value assumed is 100%, maximumefficiency exists, but if operated at a flow rate value ofapproximately 40%, usually, vibration, increase of radialloads, excessive sound and decrease of efficiency can beexperienced. For this reason, more attention should begiven to operating the pumps close to their nominalcapacities.

Elimination of clogging in valves, pipelines and pumps,assurance of the impermeability of the pipe circuit; regularmaintenance of belts, pulleys, bearings and filters, insula-tion of the heating circuit and prevention of vibration willall assure energy saving and financial economy.

It has been stated that it is necessary to examine theeconomy of variable flow rate systems at the design stageof the pumps. In the same way, it is very important thatexaminations should be made for the existing pumps. Inthe studies that have been made about energy efficiency,it has been calculated that frequency control applicationto existing pumps will assure a very important rate ofsaving.

Pumps, like other machines, are also worn away in time;the flow rate and pump head may decrease. In this case,Fig. 3 compares the efficiency variations for the conditionsof the pump that has been worn away being repaired peri-odically and rejoined in the circuit and when it is notrepaired [5].

Although there is some extra cost, the pump efficiencycan be increased by polishing the pump surface coatingand elimination of the surface roughness. This is very effec-tive, especially in low powered pumps.

Pumps finally complete their economic period at theirworking conditions. If the pumps are in this state, they willbe renewed in the investment plan.

3. The measurement method, measurement devices and

measurement results

In the facility, for the pumps in the scope of the energyefficiency study, the measurements that have been per-formed in the factory comprise two different groups; oneis electrical ant the other is mechanical. The electrical mea-surements are comprised of the measurements that havebeen taken from the electric motors that are used to drivethe pumps. The mechanical measurements are comprisedof the values that have been measured of flow rate, pressureand temperature of the pumps.


3.1. Electrical measurements

In the electrical measurements in pump motors that aredriven by an electric motor, the motor supply voltage, cur-rent drawn from the network, apparent power, activepower, reactive power and motor power factor have beenmeasured. By using the measured data, the electric motorloadings, operation efficiencies and the power value thathas been transmitted to the pump have been calculated,and the results have been evaluated.

3.1.1. The assumptions

During the measurements that have been performed forall the pumps, the assumption has been made that there isno big sudden change about the load variations thatchanges the behavior of system in a wide range, and themeasurements have been performed on the electric motorsby getting the values for short terms.

3.1.2. The form of the measurement

In the measurements, an electric energy analyzer devicemarked as UPM 6100 has been used; the measurementshave been performed in the form ‘‘3 phases, 1 line”. Inthe measurements three voltage sensors and a 200 amperecurrent sensor have been used.

The measurements have been made over the current andvoltage transformer existing in the secondary part of thesupply point in the main panel of the motors that are fedfrom the medium voltage (2300 V) level. In the measure-ments, the three voltage sensors of the energy analyzerare connected to the secondary part of the voltage trans-formers and a 200 ampere current sensor is connected tothe secondary part of the current transformer.

In the motors that are fed from the low voltage (400 V)level, the voltage has been measured by voltage sensors thatare directly connected to the supply point in the main panelof the motor, and the motor current has been measuredover the current transformer by using a 200 ampere sensor.

All measurements have been made in normal operatingtime of the motors while driving the existing pump.

Table 1The electric motors that measurements have been made on and nominal (labe

Electric motors

Number 1 and 2 boiler, electric motor of boiler feeding pump-ANumber 1 and 2 boiler, electric motor of boiler feeding pump-BNumber 3 and 4 boiler, electric motor of C pumpNumber 5 boiler, electric motor of B pumpNumber 6 waste heat boiler, electric motor of number 2 medium pressure pumNumber 7 waste heat boiler, electric motor of number 1 medium pressure pum1. High furnace electrical booster pump motor (second motor)2. High furnace electrical booster pump motor (first motor)Seaside electric motor of number 2 pumpSeaside electric motor of number 4 pump

1 HP* = 0.745 kW (accepted as).

3.1.3. Power measurement

In electrical power measurements that have been madeby an energy analyzer, the values are drawn from the net-work of the pump three phase electric motor; the apparentpower, active power, reactive power, voltage, current andpower factor have been measured.

3.1.4. The measurement points

The measurements have been performed on the pumpmotors that are driven by 10 electric motors in the factory.The names of the measurements points and the nominallabel values of the electric motors on which measurementshave been made are given in Table 1.

3.1.5. Electrical measurement results

The results of the electric motors of the pumps in thearea of the measurements are given in Table 2.

3.2. Mechanical measurements

In the scope of the mechanical measurements, the pumpfluid flow rate and the inlet and outlet temperatures andpressures of the fluid have been measured.

The flow rate that the pumps discharge has been mea-sured by an ultrasonic flow meter, brand of ‘‘PANAMET-RICS”. Two transducers that belong to the flow meter areconnected to the pipe from the outside, in the form parallelto the flow; the first transducer has been operated as a sig-nal generator and the second one as a signal receiver. Thefluid velocity has been determined as the difference betweenthe measured signal arrival time and the sound velocity.The device has also measured the diameter of the pipe,and the amount of the flow rate has been measured online.The system of measurement is given schematically in Fig. 4.

The measurement of the fluid inlet and outlet pressurevalues has been performed by existing pressure gauges thatare verified by another calibrated gauge.

The fluid temperatures have been determined by theexisting pump inlet and outlet line temperatures that havebeen measured by a thermal camera and added about

l) values

Nominal (label) values

Power Voltage(V)

Current(A)

Speed(rpm)

Powerfactor (–)

Efficiency(–)(HP) (kW)*

450 335 2300 100 2950 – –450 335 2300 100 2950 – –790 590 2300 176.1 2973 0.84 –670 500 2400 149 2965 – –

p 150 110 380 202 2975 0.86 –p 150 110 380 202 2975 0.86 –

250 186 2400 59 1450 – –340 250 2400 78 1480 – –600 447 2400 143 735 – –600 447 2400 143 735 – –

Table 2The power measurement of electric motor of pumps

Name Currenttransformerchange rate

Voltagetransformerchange rate

Voltage(V)

Current(A)

Apparentpower(kVA)

Activepower(kW)

Reactivepower(kVAr)

Powerfactor

The number 1 and 2 boiler, electric motor of boiler feedingpump-1

150/5A 2400/120V 2386 78 289.8 140.3 0.91

The number 1 and 2 boiler, electric motor of boiler feedingpump-2

150/5A 2400/120V 2397 75 311 279.9 135.5 0.9

Number 3 and 4 boiler, electric motor of C pump 200/5A 2400/120V 2400 156 647.7 570 307.6 0.88Number 5 boiler, electric motor of B pump 150/5A 2400/120V 2432 120 504.8 459.9 208 0.911Number 6 waste heat boiler, number 2 electric motor of

medium pressure pump300/5A – 403 150 104.6 94.2 45.6 0.9

Number 7 waste thermal boiler, number 1 electric motor ofmedium pressure pump

300/5A – 403 152.4 106.3 95.7 46.3 0.9

The number 1 high furnace electrical booster pump motor-2 75/5A 2400/120V 2398 52.5 217.7 179.7 123 0.825The number 2 high furnace electrical booster pump motor 100/5A 2400/120V 2412 68 283.7 242.6 147 0.855Seaside number 2 pump electric motor – – 2400 120 498.2 423.5 262.4 0.85Seaside number 4 pump electric motor – – 2400 119 494 420 260 0.85

Fig. 4. Schematic projection of the measurement system.


+2 �C as the surface temperature loss value. It has beenseen that these measurement values are in harmony withthe values measured by the thermometers on the system.

The result of the mechanical measurements is given inSection 4.

4. The calculation of the efficiencies

4.1. The calculation of loading and operating efficiency of the

motors

With the active power drawn by the electric motor fromthe network ss Pnetwork and the efficiency value as gm, the

electric motor pump

Pnetwork

Pmech The Efficiency oThe Efficiency of the Electric Motor

Fig. 5. Schematic projection of the el

mechanical power value the motor shaft transfers to thepump is calculate as Pmec

P mec ¼ P network � gm: ð1ÞIt is showed schematically in Fig. 5.

The Pe power values of the electrically driven pumpmotors, which have been drawn from the network, havebeen measured in the factory. The efficiency values of thesemotors and the efficiency loading curves that show the var-iation of motor efficiency with loading do not exist. There-fore, the operation load and efficiency of the motors havebeen found by calculating. In these calculations, area mea-surements and motor nameplate values have been used.

The electric motors loading value has been calculatedaccording to the current measurement technique. In the cal-culation of motor efficiency when being operated at thisloading value, the calculated loading value, the power themotor has drawn from the network and the nominal(nameplate) power have been used.

The motor loading value has been calculated in% asshowed below:

Loading ð%Þ ¼ Inetwork

Inominal

� �� V network

V nominal

� �� 100 ð2Þ

where Inominal is the nominal current of the motor (A),Inetwork the current that has been drawn by the motor fromthe network (A), Vnominal the nominal voltage of the motor

The Power that has been taken from the Pump

f the Pump

ectric motor system of the pump.

Table 3Electric motors loading, efficiency and the power values that have been transferred to the pump

Measured electric motors Measured electricmotors power (kW)

Loadingvaluea (%)

Operatingefficiencyb (%)

The power that is transferredto the pump Pmec (kW)

Number 1 and 2 boiler, electric motor of boiler feeding pump-A 278.50 80.92 97 271.07Number 1 and 2 boiler, electric motor of boiler feeding pump-B 251.62 72.85 97 244.06Number 3 and 4 boiler, electric motor of C pump 565.49 95.28 99 562.16Number 5 boiler, electric motor of B pump 459.95 81.61 89 408.05Number 6 waste heat boiler, number 2 electric motor of medium

pressure pump94.17 78.79 92 86.67

Number 7 waste thermal boiler, number 1 electric motor of mediumpressure pump

95.68 80.46 92 88.50

1. High furnace electrical booster pump motor 179.68 8891 92 165.372. High furnace electrical booster pump motor 242.60 87.62 90 219.04Seaside number 2 pump electric motor 423.50 83.92 89 375.10Seaside number 4 pump electric motor 419.97 83.22 89 371.98

a In the calculation of the loading electric motor value, current measurement is taken as a fundamental.b In the calculation of operating efficiency, motor loading value has also taken into consideration.


(V) and Vnetwork the voltage that has been measured at theterminals of the motor (V).

Motor efficiency has been calculated by the ratio of use-ful exit power of the motor to the power that has beendrawn from the network Pnetwork.

gm ð%Þ ¼Loading � P nominal ðkWÞ

P network ðkWÞ ð3Þ

Motors loading and operating efficiency values are given inTable 3. The mechanical power value that is connected tothe motor shaft and transferred to the pump has been cal-culated with Eq. (1).

As can be seen in Table 3, all of the engine’s loading val-ues are 60–90% of their nominal load in our calculations.The motors working efficiencies are higher than 80%. Also,it is a suitable value for the electric motor.

In our investigations, for the number 6 and 7 waste ther-mal boiler’s medium pressure pump’s electric motors(110 kW). We calculate the motors loading values as 78%and 80% and the Pmec power values as 86.6 kW and88.5 kW, respectively. These values are lower than the ori-ginal motors label values. If the pumps driven by thesemotors efficiencies have low calculated values, we will pro-pose new lower power ones.

4.2. The calculations of the pump efficiency

The pump efficiency for normal operation conditions ineach pump station has been calculated by using the pumpflow rate, inlet and outlet pressures and the electrical powerthat has been provided to the pump. The results of theefficiency for the pumps are given in Table 4.

5. Potential saving options and recommendations

In the studies that have been conducted in the facilitypump systems, the potential saving options have beendetermined as follows: replacements of the existing lowefficiency pumps, maintenance of the pumps whose efficien-

cies have started to decline at a certain range, replacementsof the electric motors that have been chosen at high powerwith electric motors that have suitable power, usage of highefficiency electric motors and elimination of cavitationsproblems.

5.1. The replacements of the existing low efficient pumps

It has been determined that the pump efficiencies arebetween 46% and 56% from the measurements that havebeen performed at operation conditions on number 1 and2 boiler feeding pumps, number 1 and 2 high furnace boos-ter pumps and seaside pumps. New pump offers have beenreceived from the producer firms for these mentionedpumps that have the same pressure and capacities. Toassure the flow rate and pressure values at measurementsconditions, the electric motor power and pump efficiencyvalue have been determined by using the offered pump effi-ciency, power, pressure and flow rate diagrams. For theexisting low efficiency pumps that are being replaced bynew ones, the calculated efficient values before and afterthe replacements, the saving potentials, the required invest-ment amounts and the payback periods are given in Table5.

As given above, number 1 and 2 boiler pumps, 1st highfurnace number 2 pump and 2nd high furnace number 1pump are operated 4320 h per year and seaside number 4pump is operated 4748 h per year. Instead of this, the samecalculations have been performed for the replacements inthis plant at the condition of one each pump and its newpump being operated continuously (one is a spare) aregiven in Table 6.

As it can be seen above, when the replacement of theexisting pumps has been realized, the efficiencies areimproved 12–14%.

As it can be seen in Table 6, when we changed pumpnumber 1 and ran it always, without changing pump num-ber 2, the payback period of the investment is 14 months.Reversal of this change method yields a payback period

Tab

le4

Th

eca

lcu

lati

on

resu

lts

of

the

effici

ency

for

pu

mp

s

Usa

gep

urp

ose

s1

and

2b

oil

erfe

edin

gp

um

ps

Nu

mb

er3

and

4b

oil

erp

um

ps

Nu

mb

er5

bo

iler

Bp

um

p

Nu

mb

er6

bo

iler

pu

mp

nu

mb

er2

Nu

mb

er7

bo

iler

pu

mp

nu

mb

er1

1H

igh

furn

ace

bo

ost

erp

um

ps

Nu

mb

er2

hig

hfu

rnac

eb

oo

ster

pu

mp

s

Sea

sid

esa

lted

wat

ern

um

ber

2an

d4

pu

mp

s

Sea

sid

esa

lted

wat

ern

um

ber

2an

d4

pu

mp

s

Nam

eo

fth

ep

um

ps

Nu

mb

er1

Nu

mb

er2

Pu

mp

CP

um

pB

Nu

mb

er2

Nu

mb

er1

Nu

mb

er2

Nu

mb

er1

Nu

mb

er2

Nu

mb

er4

Flo

wra

te(Q

,to

ne/

h)

6364

160

144

8284

900

950

6000

6200

Flu

idin

let

pre

ssu

re(P

1,

Bar

)1.

41.

41.

51.

82

20.

70.

70

0F

luid

ou

tlet

pre

ssu

re(P

2,

Bar

)74

7367

6515

154.

14.

21.

21.

2P

ress

ure

diff

eren

ce(P

2�

P1,

Bar

)62

.671

.665

.563

.213

133.

43.

51.

21.

2T

he

po

wer

that

has

bee

ngi

ven

toth

efl

uid

(Pf=

Q* (P

2�

P1)/

36,

kW

)12

7.05

127.

2929

1.11

252.

829

.61

30.3

385

92.3

620

020

6.67

Th

ep

ow

erth

ath

asb

een

tran

sfer

red

toth

ep

um

p(P

e,E

lect

rica

lp

ow

er,

kW

)27

126

1.8

545.

440

886

.67

88.5

165.

3721

9.04

375.

137

1.98

Gen

eral

effici

ency

(Pf/

Pe

or

Pf/

Pt,

%)

46.8

848

.62

53.3

861

.96

34.1

734

.27

51.4

42.1

753

.32

55.5

6


of the investment as 16.1 months. This result indicates thatchanging pump number 1 is more effective than changingthe second. Also, after 14 months, the enterprise will savemoney.

5.2. The improvement of the existing pumps efficiencies

5.2.1. Number 5 boiler feeding B pump

At number 5 boiler feeding B pump, the efficiency mea-surement has been determined as between 60% and 62% atthe operation conditions. The new pump offers have beentaken from the producer firms for this mentioned pumpthat has the same pressure and flow rate capacities. Toassure the flow rate and pressure values at the measure-ments conditions, the electric motor power and pump effi-ciency value have been determined by using the new pumpefficiency, power, pressure and flow rate diagrams. The cal-culations that have been made for the existing and theoffered pump are showed in Table 7.

As it can be seen above, the existing pump has beenoperated approximately 9% less efficiently compared withthe new pump. The efficiency rate can be increased about5% by maintenances like renovating the existing pump,blade coating, maintenance of bearing etc. In this condi-tion, the calculations have been performed for the annualmoney saving, the cost of investment and payback periodof the investment cost, and the results are given in Table 8.

5.3. The replacement of the high powered electric motors

with suitable powered ones

5.3.1. Number 6 and 7 waste heat boilers medium pressure

pumps

It has been determined that the pump efficiencies arebetween 34% and 35% in the measurements that have beenperformed in the operating condition in numbers 6 and 7waste heat boilers medium pressure pumps. As a result ofthe calculations, for operation of the pumps in the condi-tion of maximum flow rate and pressure, the fluid powerhas been calculated as 52 kW. If these pumps efficienciesare chosen as 57%, the required power of the motor willbe 90 kW. Consequently, replacement of the existing110 kW electric motor with 90 kW ones carries an assuredsaving of a certain amount. New pump offers have beentaken from the producer firms that have the same pressureand capacities. To assure the flow rate and pressure valuesat the measurements conditions, the electric motor powerand pump efficiency value have been determined by usingthe new pump efficiency, power, pressure and flow rate dia-grams. The calculations that have been made for the exist-ing and new pumps are showed in Table 9.

As it can be seen above, for the condition of replacementof the existing electric motors, to obtain the same fluidpower, approximately 18 kW less power will be used. Forthis condition, the annual monetary saving, the cost ofinvestment and payback period of the investment cost arecalculated and given in Table 10.

Table 5The efficiency values that have been obtained from existing and as a result of the saving, saving potentials, required investment cost and payback periods ofthe investment cost in the condition that replacing of low efficient pumps with new pumps for the same conditions

Name of the station Name ofthe pump

Existing pumpefficiency (%)

Offered pumpefficiency (%)

Energy savingper hour (kW)

Annual moneysaving (USD)

Cost ofinvestment(USD)

Paybackperiod(month)

Number 1 and 2 boiler Number 1 46.88 60.98 71.00 21,470.40 50,000.00 27.9Number 2 48.62 62.76 61.80 18,688.32 50,000.00 32.1

Number 1 and 2 high furnace Number 1. H.F. 2 51.40 71.72 43.37 13,115.25 50,000.00 45.7Number 2. H.F. 1 42.17 71.49 83.04 50,221.66 60,000.00 14.3

Seaside Number 2 53.32 71.11 125.14 73,074.17 200,000.00 32.8Number 4 55.56 71.11 104.97 34,888.80 200,000.00 68.8

Table 6The efficiency values that have been obtained from existing and the as a result of the saving, saving potentials, required investment cost and paybackperiods of the investment cost in the condition that replacing of only one pump that is operated continuously for the same conditions

Name of the station Name ofthe pump

Existing pumpefficiency (%)

Offered pumpefficiency (%)





Number 1 and 2 boiler Number 1 46.88 60.98 71.00 42,940.8 50,000.00 14.0Number 2 48.62 62.76 61.80 37,376.6 50,000.00 16.1

Number 1 and 2 high furnace Number 1. H.F. 2 51.40 71.72 43.37 26,230.5 50,000.00 22.9Number 2. H.F. 1 42.17 71.49 83.04 50,221.6 60,000.00 14.3

Seaside Number 4 55.56 71.11 104.97 61,297.9 200,000.00 39.2

Note: 1 kWh = 7 cent (USD).

Table 7The pressure, flow rate, efficiency and electric motor power values of existing and new pumps

Name of the pump Transferred power to the pump (kW) Power of the Fluid (kW) Pump efficiency (%)

B Pump Existing pump 408.00 252.80 61.96New pump 440.00 312.80 71.09

Table 8The annual money saving, the cost of investment and payback period of the investment cost in the condition that revision of the existing pump

Name ofthe pump

Existing electricmotor power (kW)

Electric motor powerafter the revision (kW)


Annual operatingperiod (h)


Cost ofinvestment (USD)

Payback period(month)

Pump B 408.00 387.60 20.40 7200 10,281.60 200,000.0 23.3


5.4. High efficiency electric motor usage and energy saving

The energy saving amount has been calculated for thecondition of replacing the electric motor driven pumpmotors with high efficiency motors. How much energy canbe saved has been examined for the condition of only replac-ing the driven motor with the high efficiency motor consider-ing the pump and existing operating conditions are the same.

Economic life spans have been established in the factoryconsidering replacement because of their failure or as aresult of big revisions at the facility. When purchasing anew compressor, HVAC and pump systems, ‘‘high effi-ciency electric motors” are preferred instead of the existingstandard electric motors to assure obtaining more efficientenergy usage and, therefore, energy saving.

The energy that will be saved upon replacement of astandard motor with a high efficiency motor can be calcu-lated with the help of this formula:

Energy saving ¼MN�Nominal power�OP� LC

�UF� ð1=gstandard � =ghigh efficiencyÞ ð4Þ

where MN is motor number in the same power, OP is oper-ating period, LC is loading coefficient, UF isusage factor(for motors that run continuously in the circuit UF = 1),gstandard is standard type motor efficiency and ghigh efficient

is high efficiency type motor efficiency.The comparison of the efficiencies of standard and high

efficiency motors are given in Table 11. As it can be seenfrom this table, for nameplate power bigger than 224 kW

Table 9The calculation of the existing and new electric motors

Name of the pump Transferred power to the pump (kW) Power of the fluid (kW) Pump efficiency (%)

Number 6 boilernumber 2

Existing electric motor 86.67 29.61 34.17New electric motor 68.00 29.61 43.54

Number 7 boilernumber 1

Existing electric motor 88.50 30.33 34.27New electric motor 70.00 30.33 43.33

Table 10The annual money saving, the cost of investment and payback period of the investment cost in the condition that replacing of the existing electric motor

Name of the pump Existing electricmotor power(kW)

New electricmotor power(kW)

Energy savingper hour(kW)

Annualoperatingperiod (h)

Annual moneysaving(USD)



Number 6 boiler number 2 86.67 68.00 18.67 4320 5645.85 3800.00 8.1Number 7 boiler number 1 88.50 70.00 18.50 4320 5594.40 3800.00 8.2


(300 HP), the high efficiency motor efficiencies are notknown.

Note: these average values that belong to eight firms arevalidated in the condition when the motor is at full load.With the establishment of high efficiency motors, themonthly demand power saving for the motors, ‘‘DS”,and the monthly kWh energy usage saving, ‘‘US”, can becalculated as demonstrated below:

DS¼Nominal power�MN�LC�ð1=gstandard� 1=ghigh efficientÞð5Þ

US¼DS�OP�UF ð6Þ

Table 11The comparison of the motor efficiencies

Rated motor power (hp) Rated motor power (kW) Mean efficien

1 0.746 0.8251.5 1.119 0.8402 1.492 0.8402.5 1.865 0.8123 2.238 0.8754 2.984 0.8275 3.73 0.8757.5 5.595 0.895

10 7.46 0.89515 11.19 0.91018 13.428 0.87820 14.92 0.91025 18.65 0.92430 22.38 0.92440 29.84 0.93050 37.3 0.93060 44.76 0.93675 55.95 0.941

100 74.6 0.945125 93.25 0.945150 111.9 0.950200 149.2 0.950250 186.5 0.954300 223.8 0.954

As an example, in a facility having the unit price of its elec-tricity as 0.075 $/kWh, operating at full load continuously7000 h/year, for the condition of replacing 36 motors ofnominal power 45 kW with high efficiency motors, the de-mand energy saving (DS) is

DS ¼ ð45 kW� 36� 1Þ � ½ð1:0=0:936Þ � ð1:0=0:954Þ�DS ¼ 32:656 kW=month

Usage saving (US):

US ¼ ð32; 656 kW=monthÞ � ð7000 h=yearÞUS ¼ 228; 592 kWh=year

cy of standard type motors Mean efficiency of high efficient motors

0.8650.8940.8880.8700.8950.8890.9020.9170.9170.9300.9240.9360.9410.9410.9450.9500.9540.9540.9580.9540.9580.9580.9620.962


The money equal of the saving resources annual usage

(AUS):

AUS¼US�ðthe price of the average electricity unit usageÞAUS¼ 228;592 kWh=year�0:075 $=kWh

AUS¼ 17144:4$=year

The nameplate power of the electric driven pump motors(kW), annual operating periods (OP), loading coefficient(LC) and usage factor (UF) are given in Table 12. Whenthe nameplate powers of the motors that belong to thepumps are examined, there are only three pump motorsthat have powers smaller than 224 kW. Because the highefficiency motors efficiency values are not known for pow-ers bigger than this, the calculations can only be made forthese three electric motors if their powers are smaller than224 kW.

For the condition of replacing these motors with highefficiency motors, the monthly demand saving (DS), usagesaving (US) and the money equal of the saving resourceannual usage (AUS) are given in Table 13. As it is givenin the table, the monthly demand saving (DS) is 2.47 kWand the annual energy usage saving (total energy saving)is 10,662 kWh. When eplacement of the three motors hasbeen examined by accepting the unit price of energy as0.07 $/kWh, with high efficiency motors, the money equal

Table 12The operating periods of the electric motors

Name of the motor Numberthe moto(MN)

Number 1 and 2 boiler feeding electric motor of number 1 pump 1Number 1 and 2 boiler feeding electric motor of number 2 pump 11. High furnace number 2 electrical booster pump motor 12. High furnace number 1 electrical booster pump motor 1Number 3 and 4 boiler feeding, electric motor of C pump 1Number 5 boiler, electric motor of B pump 1Seaside electric motor of number 2 pump 1Seaside electric motor of number 4 pump 1Number 6 waste heat boiler, electric motor of number 2 medium

pressure pump1

Number 6 waste heat boiler, electric motor of number 4 highpressure pump

1

Number 7 waste heat boiler, electric motor of number 1 mediumpressure pump

1

a UF = 1 (for the reason of all motors in the circuit continually).

Table 13Energy efficiency with high efficient motor usage

Name of the motor DS

Number 6 waste heat boiler, medium pressure number 2 pump electricMotor

0.7

Number 6 waste heat boiler, number 4 high pressure pump electric motor 0.9Number 7 waste heat boiler, medium pressure number 1 pump electric

motor0.7

Total 2.4

of the total saving amount that will be obtained in everyyear is 746 $/year.

The payback period of the price difference that will bepaid when purchasing high efficiency motors instead ofstandard motors can be found from the price differenceof the high efficiency motor from the standard motor.The price difference has been taken as approximately600 $ for the motor of 110 kW.

Payback period

¼ ðThe cost of investmentÞ=ðAnnual money savingÞPayback period ¼ ð1800$Þ=ð746$=yearÞ � 12 month=year

Payback period ¼ 28:9month ð7Þ

After the payback period, 10,662 kWh/year energy savingor 746 $/year money saving will be obtained in every year.

5.5. Cavitation

Cavitation is the phenomenon where small and largelyempty cavities are generated in a fluid that expand to alarge size and then rapidly collapse, producing a sharpsound. Cavitation occurs in pumps, propellers, impellersetc. A liquid, when it is subjected to a low pressure belowa threshold, ruptures and forms vaporous cavities. Thisphenomenon is termed cavitation. When the local ambient

ofr

Labelpower(kW)

Nameplate powerthat the motordraws (kW)

Operatingperiod(OP)

Loadingcoefficient(LC)

Usagefactor(UF)a

335 289.8 4320 80.92 1335 279.9 4320 78.17 1186 179.7 4320 88.91 1250 242.6 4320 87.62 1590 570.0 7200 92.44 1500 459.9 7200 81.61 1447 423.5 8342 83.92 1447 420.0 8342 83.22 1110 94.2 4320 78.79 1

110 105.0 4320 96.00 1

110 95.7 4320 80.46 1

(kW/month) US (kWh) AUS ($/year) Cost of investment ($)

62 3291 230.38 600

28 4010 280.70 60078 3361 235.26 600

68 10,662 746 1800

Table 14The pumps cavitations calculations that have been measured at the facility

Name of the pump Pa (Pa) Pb (Pa) Q (tone/h) n (rpm) Dy (m) he (m) Pe (bar) Pinlet(P1)(bar)

Cavitationresults

Number 1 and 2 boiler feeding pumps 101,325 143,270 113 2950 5.30 �10.57 1.04 1.40 Not existNumber 3 and 4 boiler feeding A pump 101,325 174,954 211 2970 5.40 �13.91 1.36 1.50 Not existNumber 3 and 4 boiler feeding C–D pumps 101,325 174,954 211 2982 5.27 �13.78 1.35 1.50 Not existNumber 5 boiler feeding pump 101,325 174,954 203 2954 5.07 �13.58 1.33 1.80 Not existNumber 6 and 7 boiler feeding pumps 101,325 198,540 144 2976 6.30 �17.21 1.69 2.00 Not existNumber 1 high furnace booster pumps 101,325 3171 1000 1480 9.04 �0.03 0.00 0.70 Not existNumber 2 high furnace booster pumps 101,325 3171 1100 1450 9.37 �0.36 0.04 0.70 Not existBrine station pumps 101,325 3171 6300 735 12.12 �3.12 0.31 0.30 Exist


pressure at a point in the liquid falls below the liquid’svapor pressure at the local ambient temperature, the liquidcan undergo a phase change, creating largely empty voidstermed cavitation bubbles. When the cavitation bubblescollapse, they focus the liquid energy on very small vol-umes. Thereby, they create spots of high temperature andemit shock waves, which are the source of the noise. Thenoise created by cavitation is a particular problem inpumps. The collapse of cavities involves very high energies,and can cause major damage. Cavitation can damagealmost any substance. The pitting caused by the collapseof cavities produces great wear on the components andcan dramatically shorten a propeller or pump’s lifetime.

As a result, cavitation is, in many cases, an undesirableoccurrence. In pumps and propellers, cavitation causes agreat deal of noise, damage to components, vibrationsand a loss of efficiency [20].

According to the operating conditions of the pumps andfluid temperatures that have been measured at the facility,cavitation calculations and their related results are given inTable 14.

he max ¼P m

q � g �P sat

q � g � NPSH � hloss ð8Þ

P s ¼ q � g � he max ð9Þ

The formulae, which are given above, have been used forcalculation of cavitation. In these formulae; Pm is the med-ium pressure of the pump established in the region (N/m2),Psat is the saturation pressure of the pump that is related tothe inlet water temperature (N/m2), Ps is the pressure suc-

Fig. 6. The pump picture which has been d

tion NPSH (net positive suction head) (m), hloss is the pres-sure losses in the suction pipes and local components (m)and hemax is the maximum head of the suction line (m).

The Ps value should be smaller than the Pinlet (P1) valuefor the pump operation without cavitation. Otherwise, thepump will operate with cavitation.

When the table results of the pumps that have beenoperating at the seaside brine plant are examined, it canbe clearly seen that Ps = 0.31 bar, which is over the (P1)inlet pressure value. Therefore, the cavitation possibilityis more than likely for these pumps. Even if it is operatingat the limit, especially with the increase of the sea watertemperature in summer, the cavitation problem willincrease more. For the examination that has been con-ducted at the facility, a picture of a water pump that hasbeen dismantled at the seaside is given in Fig. 6.

The pump has been operated at the cavitation limit as itcan be understood by this picture. Because of this reason,the impeller and casing of the pump have been worn outby cavitation.

As it can be seen by the calculations for the pumps fromthe seaside brine pump plant, for their operation withoutany cavitation, the pump impeller should be operated atleast 3.5 m under sea level.

6. Results

This is a study of the energy efficiency of pumps that hasbeen performed in a big industrial manufacturing facility.By using measured data; the existing pump and electricmotor efficiencies have been calculated.

ismantled from the seaside brine plant.


As a result of this study, the main saving opportunitiesare: replacements of existing low efficiency pumps, mainte-nance of pumps whose efficiencies have started to decline atcertain ranges, replacements of electric motors that havebeen chosen at high power with electric motors that havesuitable power, usage of high efficiency electric motorsand elimination of cavitation problems. For each savingopportunity that is mentioned above, their investmentcosts and payback periods are given.

We hope that these results will be helpful for manufac-turers and engineers and to motivate them for investment.

References

[1] Yigit KS, Callı_I, Sozbir N, Sarac� H_I, Brawn DM. Experimentalinvestigation of optimum centrifugal pumps speeds. In: Secondinternational conference on pumps and fans, vol. II, Beijing, China,October 1995.

[2] Sarac� H_I, Guven R, Sozbir N, Yigit KS. New method for simulationof centrifugal pump plants. In: International conference engineeringproblems, AMSE, Malta Island, December 1993.

[3] Yigit KS, Arık M, Bar-Cohen A, New CHF enhancement techniques:passive impeller micropump and gravity driven fluid flow. In: 5thworld conference on experimental heat transfer, fluid mechanics, andthermodynamics, Thessaloniki, 24–28 September 2001.

[4] Calli _I, Ozturk R, Toklu E, Yigit KS. An experimental study on frontdeclined open impeller vane in circulation pumps. In: 10th Turkishnational conference on thermal sciences and technologies, vol. 1. p.739-48. Ankara, Turkey, 6-8 September 1995.

[5] Ertoz AO. Energy efficiency in pumps. In: 6th national installationsengineering and congress, Istanbul; 2003.

[6] The pump terms guide. Published by POMSAD, Turkey, no. 2; 1997.[7] ISO 3555. Fundamentals of acceptance experiments for radial, mixed

flow and axial pumps, class B. Published by POMSAD, Turkey, no. 3;1998.

[8] ISO 2548. Fundamentals of acceptance experiments for radial, mixedflow and axial pumps, class C. Published by POMSAD. Turkey, no.4; 1998.

[9] ISO 9905. Technical properties of radial (centrifugal) pump, class I.Published by POMSAD. Turkey, no. 7; 2000.

[10] ISO 9908 Technical Properties of Radial (Centrifugal) Pump, ClassIII, Published by POMSAD Turkey No: 8; 2000.

[11] Cuha D. The presentation of energy economy in centrifugal pumpsand centrifugal pump systems. Hotel Dedeman Istanbul, Turkey, 9thJune 2005.

[12] NPSH for rotodynamic pumps. Published by POMSAD, Turkey, no.9; 2001.

[13] The operation of rotodynamic pumps with different values than theiroriginal design. Published by POMSAD, Turkey, no. 11; 2001.

[14] Accessible efficiency for centrifugal pumps. Published by POMSAD,no. 10; 2001.

[15] Lifelong cost in pumps: lifelong cost for plants that using pumps.Published by POMSAD, no. 12; 2001.

[16] Kovats A, Desmur G. Pumps, ventilators and radial and axialcompressors. Verlag G. Braun; 1968.

[17] Lakshminarayana B. Methods of predicting the tip clearance effects inaxial-flow turbomachinery. J Basic Eng 1970:467–82.

[18] Lakshminarayana B. End wall and profile losses in a flow-low-speedaxial flow compressor rotor. J Eng Gas Turbines Power 1986;108:131–7.

[19] Cherkassky VM. Pumps fans compressors. Mir Publishers; 1980.[20] Kovats DA. Design and performance of centrifugal and axial flow

pumps and compressors. New York: A Pergamon Press Book, TheMacmillan Company; 1964.

[21] Kaya D. An experimental study on regaining the tangential velocityenergy of axial flow pump. Energ Convers Manage 2003;44:1817–29.

[22] Kaya D, Sarac� HI, Olgun H, Tırıs M. A study of axial flow pumpimpellers-effects of pump design parameters on its performance. In:Proc the twelfth international symposium on transport phenomena,Istanbul; 2000. p. 701–5.

[23] MotorMaster Data base, WA: Washington State Energy Office; 1993.[24] Cengel YA, Cerci Y. Opportunities to save energy in industry, 12. In:

Turkish national conference on thermal sciences and technologieswith international participation, conference proceeding, Sakarya/Turkey; 2000, vol. 2. p. 392-9.

[25] Kaya D, Phelan P, Chau D, Sarac H_I. Energy conservation incompressed-air systems. Int J Energy Res 2002;26:837–49.

[26] Kaya D, Gungor C. The potential of energy economy in industry – I.Eng Mech 2002;514:20–30.

[27] Kaya D, Gungor C. The potential of energy economy in industry – II.Eng Mech 2002;515:36–44.

[28] Kaya D, Canka Kılıc� F. Energy conservation opportunity in VSDsystem – a case study. In: World energy engineering congressproceedings, 21-24 September 2004, Austin, Texsas, USA.

energy eﬃciency in pumps - kocaeli Üniversitesilaboratuar.kocaeli.edu.tr/hidromekanik/sci/... ·...

Documents