Available online at www.sciencedirect.com
Energy Conversion and Management 49 (2008) 1662–1673
www.elsevier.com/locate/enconman
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, Turkey
b
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 2007
Available 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, pressure and temperature have been measured for each pump in different operating conditions and at maximum load. In addition, the electrical power drawn by the electric motor has been measured. The efficiencies of the existing pumps and electric motor have been
calculated 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 electric motor. As a conclusion, improvements should be made each system. The required investment costs for these improvements have been
determined, 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 whose
efficiencies 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.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Pump; Energy savings; Energy efficiency
1. Introduction
In the studies that have been conducted for energy saving, it has been seen that one of the areas of high potential
energy saving is pumping systems [1–4]. According to a
study that the American Hydraulics Institute has made,
20% of the consumed energy has been consumed by pumps
in developed countries [5]. It has been explained that 30%
of this energy can be saved with good design of systems
and choosing suitable pumps. This situation has caused
new searches to be made to find more efficient systems in
production and operation by producers and users of pumps
[6–10]. Furthermore, some legal regulations have started to
be enacted on this topic in some countries [11]. For exam*
Corresponding author. Tel.: +90 262 677 29 53; fax: +90 262 641 23
09.
E-mail address: [email protected] (D. Kaya).
0196-8904/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.enconman.2007.11.010
ple, obligatory labeling of circulation pumps (P < 2.5 kW)
has been in the last stage in the EU. Placing a letter on the
label to show energy efficiency is obligatory for circulation
pumps that have been produced in Germany. Besides, it
has been stated and published at the end of the studies that
have been conducted that the flow rate, pump head and
period number of the pump for which the required efficiency is attained should be showed on the diagrams to
inform clients about the efficiency of the centrifugal pumps
they purchase in the EU [12–14].
That pumps have high efficiency alone is not enough for
a pump system to work in maximum efficiency. Working in
maximum efficiency of a pump system depends not only on
a good pump design but also a good design of the complete
system and its working conditions. Otherwise, it is inevitable that even the most efficient pump in a system that has
been wrongly designed and wrongly assembled is going to
be inefficient [15–20].
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
2. Energy efficiency and the factors that influence the
effectiveness in pumps
1663
Motor Efficiency-Loading Curve
Effective usage of energy in pumps can be considered in
two 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 the
most active and effective system, the needs of the process
should be known. Also, the flow rate-time intervals and
pump head of the system throughout one year should be
well known.
The system should be selected not only to meet the needs
of working in maximum capacity but also, in an economic
point of view, it should also be known what capacity will
be required. After this, the pipe installation can be
designed. If the maximum capacity required is for a short
time period, there is no need to have a pipe with a big
diameter. If the system works with a high capacity for a
long time, this situation should be taken into consideration
in the selection of the pipe diameter [21,22].
When designing a pipe system, the system curve must
definitely be drawn. It is very important to choose a pump
with maximum efficiency and the most convenient running
clearance. Because the first purchasing costs are only in the
range of 3–5% of the life cycle costs, it is the obligation of
the administrators to make more careful selections of the
pump.
2.1.2. The selection of an electric motor in suitable power
It is very important to select an electric motor of suitable
power to work efficiently. In general, motors are chosen in
big capacities to meet extra load demands. Big capacities
cause motors to work inefficiently at low load. Normally,
motors are operated more efficiently at 75% of rated load
and above. Motors operated lower than 50% of rated load,
because they were chosen in big capacity, performing inefficiently, and due to the reactive current increase, power
factors also are decreased. These kinds of motors do not
consume the energy efficiently because they have been chosen in big power, not according to the needs. These motors
should be replaced with new suitable capacities motors,
and when purchasing new motors, energy saving motors
should be preferred.
The motor shows the stated efficiency on the label of the
motor when it is fully loaded. The efficiency value in different loads is different from the value that has been showed
on its label. Fig. 1 shows the variations of motor efficiencies
according to loading. The efficiency at which the motor is
being operated is determined by looking at the efficiency
loading curve. The efficiency value is equal to the maximum value only when the motor is operated at loading values of 75% and bigger of the rated value. The preferred
optimum operating region is between 60% and 90% of
Value of Efficiency [ % ]
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
100
Value of Loading [ % ]
(According to Rated Loading Value)
0-1HP
15-25HP
1,5-5HP
30-60HP
10HP
75-100HP
Fig. 1. The variations of the motor efficiencies according to loading.
the rated load for motors; the ideal value is when the motor
is operated in its full load.
2.1.3. The selection of high efficiency electric motor
The energy that electric motors consumed in plants is
about 65% of the total energy consumption. Therefore, it
is important to choose ‘‘high efficiency” motors in plants.
Like all motors, electric motors also can not transform
all the energy they use into mechanical energy. The ratio
of the mechanical power output of a motor and its drawn
electric power is named the motor efficiency, and according
to its size, it can range between 70% and 96% [23]. Also,
motors that are operated at partial load are operated at
low efficiencies. These efficiencies can vary from motor to
motor. For example, while the efficiency of a motor is
90% when it is fully loaded, 87% when it is half loaded
and 80% when it is 1/4 loaded; the efficiency of an another
motor 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 developed in the last years are more expensive, around 15–25%
more than that of standard motors. Usually, because of the
low operating costs, this difference can be regained in a
short time [24–27]. By increasing the cross section of the
copper conductors that are used in the motor winding,
the primary I2R loss can be decreased. Iron core loss with
the decrease of flux density, usually, can be limited by
increasing the neck of the stator core. Beside, these losses
can be decreased by decreasing the thickness of the panels
and using good quality alloys. On the other hand, in high
efficiency motors, because of the decreased losses, the need
of 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 variable flow rate are: to operate the pump when it is needed
(part load operation), to operate the pump continuously
1664
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
Motor Efficiency
Efficiency Loading Curve
0.98
0.96
0.94
0.92
0.9
0.88
0.86
0.84
0.82
0.8
0
10
20
30
40
50
60
70
80
90
100
Value of Motor Loading (%)
Standard Motor
High Efficient Motor
Fig. 2. The efficiency of standard and high efficient motors.
but send back some of the fluid to the tank (by pass system), by feeding the system from a tank to operate the
pump at part load operation in respect to the level of the
tank, adjust the flow rate by changing a flow rate control
valve at the outlet of the pump and system curve, to adjust
the pump rotational speed according to the needs of flow
rate or pressure by putting a hydraulic or electrical coupling between the constant speed electric motor and the
pump, to set a parallel operating pump system, to change
the belt and pulley system and pump rotational speed
and to use a frequency converter.
From the methods mentioned above, the most usable
and widespread one is the systems with frequency converters [28].
2.2. The saving at the facility
The most important performance loss at the operation
stage of pumps arises from operating at part load. In the
situation of pumps operated at nominal capacities, the
highest efficiency can be achieved. Besides, on centrifugal
pumps, if the flow rate value assumed is 100%, maximum
efficiency exists, but if operated at a flow rate value of
approximately 40%, usually, vibration, increase of radial
loads, excessive sound and decrease of efficiency can be
experienced. For this reason, more attention should be
given to operating the pumps close to their nominal
capacities.
Elimination of clogging in valves, pipelines and pumps,
assurance of the impermeability of the pipe circuit; regular
maintenance of belts, pulleys, bearings and filters, insulation of the heating circuit and prevention of vibration will
all assure energy saving and financial economy.
It has been stated that it is necessary to examine the
economy of variable flow rate systems at the design stage
of the pumps. In the same way, it is very important that
examinations should be made for the existing pumps. In
the studies that have been made about energy efficiency,
it has been calculated that frequency control application
to existing pumps will assure a very important rate of
saving.
Fig. 3. The effect of periodic maintenance on pump efficiency.
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 conditions
of the pump that has been worn away being repaired periodically and rejoined in the circuit and when it is not
repaired [5].
Although there is some extra cost, the pump efficiency
can be increased by polishing the pump surface coating
and elimination of the surface roughness. This is very effective, especially in low powered pumps.
Pumps finally complete their economic period at their
working conditions. If the pumps are in this state, they will
be 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 energy
efficiency study, the measurements that have been performed in the factory comprise two different groups; one
is electrical ant the other is mechanical. The electrical measurements are comprised of the measurements that have
been taken from the electric motors that are used to drive
the pumps. The mechanical measurements are comprised
of the values that have been measured of flow rate, pressure
and temperature of the pumps.
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
3.1. Electrical measurements
In the electrical measurements in pump motors that are
driven by an electric motor, the motor supply voltage, current drawn from the network, apparent power, active
power, reactive power and motor power factor have been
measured. By using the measured data, the electric motor
loadings, operation efficiencies and the power value that
has 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 for
all the pumps, the assumption has been made that there is
no big sudden change about the load variations that
changes the behavior of system in a wide range, and the
measurements have been performed on the electric motors
by getting the values for short terms.
1665
3.1.3. Power measurement
In electrical power measurements that have been made
by an energy analyzer, the values are drawn from the network of the pump three phase electric motor; the apparent
power, active power, reactive power, voltage, current and
power factor have been measured.
3.1.4. The measurement points
The measurements have been performed on the pump
motors that are driven by 10 electric motors in the factory.
The names of the measurements points and the nominal
label values of the electric motors on which measurements
have been made are given in Table 1.
3.1.5. Electrical measurement results
The results of the electric motors of the pumps in the
area of the measurements are given in Table 2.
3.2. Mechanical measurements
3.1.2. The form of the measurement
In the measurements, an electric energy analyzer device
marked as UPM 6100 has been used; the measurements
have been performed in the form ‘‘3 phases, 1 line”. In
the measurements three voltage sensors and a 200 ampere
current sensor have been used.
The measurements have been made over the current and
voltage transformer existing in the secondary part of the
supply point in the main panel of the motors that are fed
from the medium voltage (2300 V) level. In the measurements, the three voltage sensors of the energy analyzer
are connected to the secondary part of the voltage transformers and a 200 ampere current sensor is connected to
the 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 that
are directly connected to the supply point in the main panel
of the motor, and the motor current has been measured
over the current transformer by using a 200 ampere sensor.
All measurements have been made in normal operating
time of the motors while driving the existing pump.
In the scope of the mechanical measurements, the pump
fluid flow rate and the inlet and outlet temperatures and
pressures of the fluid have been measured.
The flow rate that the pumps discharge has been measured by an ultrasonic flow meter, brand of ‘‘PANAMETRICS”. Two transducers that belong to the flow meter are
connected to the pipe from the outside, in the form parallel
to the flow; the first transducer has been operated as a signal generator and the second one as a signal receiver. The
fluid velocity has been determined as the difference between
the 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 pressure
values has been performed by existing pressure gauges that
are verified by another calibrated gauge.
The fluid temperatures have been determined by the
existing pump inlet and outlet line temperatures that have
been measured by a thermal camera and added about
Table 1
The electric motors that measurements have been made on and nominal (label) values
Electric motors
Nominal (label) values
Power
Number 1 and 2 boiler, electric motor of boiler feeding pump-A
Number 1 and 2 boiler, electric motor of boiler feeding pump-B
Number 3 and 4 boiler, electric motor of C pump
Number 5 boiler, electric motor of B pump
Number 6 waste heat boiler, electric motor of number 2 medium pressure pump
Number 7 waste heat boiler, electric motor of number 1 medium pressure pump
1. High furnace electrical booster pump motor (second motor)
2. High furnace electrical booster pump motor (first motor)
Seaside electric motor of number 2 pump
Seaside electric motor of number 4 pump
1 HP* = 0.745 kW (accepted as).
(HP)
(kW)*
450
450
790
670
150
150
250
340
600
600
335
335
590
500
110
110
186
250
447
447
Voltage
(V)
Current
(A)
Speed
(rpm)
Power
factor (–)
Efficiency
(–)
2300
2300
2300
2400
380
380
2400
2400
2400
2400
100
100
176.1
149
202
202
59
78
143
143
2950
2950
2973
2965
2975
2975
1450
1480
735
735
–
–
0.84
–
0.86
0.86
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1666
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
Table 2
The power measurement of electric motor of pumps
Name
Current
transformer
change rate
Voltage
transformer
change rate
Voltage
(V)
Current
(A)
The number 1 and 2 boiler, electric motor of boiler feeding
pump-1
The number 1 and 2 boiler, electric motor of boiler feeding
pump-2
Number 3 and 4 boiler, electric motor of C pump
Number 5 boiler, electric motor of B pump
Number 6 waste heat boiler, number 2 electric motor of
medium pressure pump
Number 7 waste thermal boiler, number 1 electric motor of
medium pressure pump
The number 1 high furnace electrical booster pump motor-2
The number 2 high furnace electrical booster pump motor
Seaside number 2 pump electric motor
Seaside number 4 pump electric motor
150/5A
2400/120V
2386
78
150/5A
2400/120V
2397
75
200/5A
150/5A
300/5A
2400/120V
2400/120V
–
2400
2432
403
300/5A
–
75/5A
100/5A
–
–
2400/120V
2400/120V
–
–
Apparent
power
(kVA)
Active
power
(kW)
Reactive
power
(kVAr)
Power
factor
289.8
140.3
0.91
311
279.9
135.5
0.9
156
120
150
647.7
504.8
104.6
570
459.9
94.2
307.6
208
45.6
0.88
0.911
0.9
403
152.4
106.3
95.7
46.3
2398
2412
2400
2400
52.5
68
120
119
217.7
283.7
498.2
494
179.7
242.6
423.5
420
123
147
262.4
260
0.9
0.825
0.855
0.85
0.85
mechanical power value the motor shaft transfers to the
pump is calculate as Pmec
P mec ¼ P network gm :
ð1Þ
4.1. The calculation of loading and operating efficiency of the
motors
It is showed schematically in Fig. 5.
The Pe power values of the electrically driven pump
motors, which have been drawn from the network, have
been measured in the factory. The efficiency values of these
motors and the efficiency loading curves that show the variation of motor efficiency with loading do not exist. Therefore, the operation load and efficiency of the motors have
been found by calculating. In these calculations, area measurements and motor nameplate values have been used.
The electric motors loading value has been calculated
according to the current measurement technique. In the calculation of motor efficiency when being operated at this
loading value, the calculated loading value, the power the
motor has drawn from the network and the nominal
(nameplate) power have been used.
The motor loading value has been calculated in% as
showed below:
I network
V network
Loading ð%Þ ¼
100
ð2Þ
I nominal
V nominal
With the active power drawn by the electric motor from
the network ss Pnetwork and the efficiency value as gm, the
where Inominal is the nominal current of the motor (A),
Inetwork the current that has been drawn by the motor from
the network (A), Vnominal the nominal voltage of the motor
Fig. 4. Schematic projection of the measurement system.
+2 °C as the surface temperature loss value. It has been
seen that these measurement values are in harmony with
the values measured by the thermometers on the system.
The result of the mechanical measurements is given in
Section 4.
4. The calculation of the efficiencies
Pnetwork
electric
motor
pump
The Efficiency of the Electric Motor
Pmech
The Power that has been taken from the Pump
The Efficiency of the Pump
Fig. 5. Schematic projection of the electric motor system of the pump.
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
1667
Table 3
Electric motors loading, efficiency and the power values that have been transferred to the pump
Measured electric motors
Measured electric
motors power (kW)
Loading
valuea (%)
Operating
efficiencyb (%)
The power that is transferred
to the pump Pmec (kW)
Number 1 and 2 boiler, electric motor of boiler feeding pump-A
Number 1 and 2 boiler, electric motor of boiler feeding pump-B
Number 3 and 4 boiler, electric motor of C pump
Number 5 boiler, electric motor of B pump
Number 6 waste heat boiler, number 2 electric motor of medium
pressure pump
Number 7 waste thermal boiler, number 1 electric motor of medium
pressure pump
1. High furnace electrical booster pump motor
2. High furnace electrical booster pump motor
Seaside number 2 pump electric motor
Seaside number 4 pump electric motor
278.50
251.62
565.49
459.95
94.17
80.92
72.85
95.28
81.61
78.79
97
97
99
89
92
271.07
244.06
562.16
408.05
86.67
95.68
80.46
92
88.50
179.68
242.60
423.50
419.97
8891
87.62
83.92
83.22
92
90
89
89
165.37
219.04
375.10
371.98
a
b
In the calculation of the loading electric motor value, current measurement is taken as a fundamental.
In the calculation of operating efficiency, motor loading value has also taken into consideration.
(V) and Vnetwork the voltage that has been measured at the
terminals of the motor (V).
Motor efficiency has been calculated by the ratio of useful exit power of the motor to the power that has been
drawn from the network Pnetwork.
gm ð%Þ ¼
Loading P nominal ðkWÞ
P network ðkWÞ
ð3Þ
Motors loading and operating efficiency values are given in
Table 3. The mechanical power value that is connected to
the motor shaft and transferred to the pump has been calculated with Eq. (1).
As can be seen in Table 3, all of the engine’s loading values 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 thermal 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 and
88.5 kW, respectively. These values are lower than the original motors label values. If the pumps driven by these
motors efficiencies have low calculated values, we will propose new lower power ones.
4.2. The calculations of the pump efficiency
The pump efficiency for normal operation conditions in
each pump station has been calculated by using the pump
flow rate, inlet and outlet pressures and the electrical power
that has been provided to the pump. The results of the
efficiency for the pumps are given in Table 4.
5. Potential saving options and recommendations
In the studies that have been conducted in the facility
pump systems, the potential saving options have been
determined as follows: replacements of the existing low
efficiency pumps, maintenance of the pumps whose efficien-
cies have started to decline at a certain range, replacements
of the electric motors that have been chosen at high power
with electric motors that have suitable power, usage of high
efficiency electric motors and elimination of cavitations
problems.
5.1. The replacements of the existing low efficient pumps
It has been determined that the pump efficiencies are
between 46% and 56% from the measurements that have
been performed at operation conditions on number 1 and
2 boiler feeding pumps, number 1 and 2 high furnace booster pumps and seaside pumps. New pump offers have been
received from the producer firms for these mentioned
pumps that have the same pressure and capacities. To
assure the flow rate and pressure values at measurements
conditions, the electric motor power and pump efficiency
value have been determined by using the offered pump efficiency, power, pressure and flow rate diagrams. For the
existing low efficiency pumps that are being replaced by
new ones, the calculated efficient values before and after
the replacements, the saving potentials, the required investment amounts and the payback periods are given in Table
5.
As given above, number 1 and 2 boiler pumps, 1st high
furnace number 2 pump and 2nd high furnace number 1
pump are operated 4320 h per year and seaside number 4
pump is operated 4748 h per year. Instead of this, the same
calculations have been performed for the replacements in
this plant at the condition of one each pump and its new
pump being operated continuously (one is a spare) are
given in Table 6.
As it can be seen above, when the replacement of the
existing pumps has been realized, the efficiencies are
improved 12–14%.
As it can be seen in Table 6, when we changed pump
number 1 and ran it always, without changing pump number 2, the payback period of the investment is 14 months.
Reversal of this change method yields a payback period
55.56
371.98
6200
0
1.2
1.2
206.67
53.32
42.17
34.27
48.62
46.88
53.38
61.96
34.17
51.4
375.1
219.04
88.5
261.8
271
545.4
408
86.67
165.37
6000
0
1.2
1.2
200
950
0.7
4.2
3.5
92.36
84
2
15
13
30.33
64
1.4
73
71.6
127.29
63
1.4
74
62.6
127.05
Flow rate (Q, tone/h)
Fluid inlet pressure (P1, Bar)
Fluid outlet pressure (P2, Bar)
Pressure difference (P2 P1, Bar)
The power that has been given to the fluid
(Pf = Q*(P2 P1)/36, kW)
The power that has been transferred to the pump
(Pe, Electrical power, kW)
General efficiency (Pf/Pe or Pf/Pt, %)
160
1.5
67
65.5
291.11
144
1.8
65
63.2
252.8
82
2
15
13
29.61
900
0.7
4.1
3.4
85
Number 2
Number 1
Number 1
Number 1
Name of the pumps
Number 2
Pump C
Pump B
Number 2
Number 2
Seaside salted
water number
2 and 4 pumps
Number 2
high furnace
booster pumps
1 High furnace
booster
pumps
Number 7
boiler pump
number 1
Number 6
boiler pump
number 2
Number
5 boiler
B pump
1 and 2 boiler
feeding pumps
Number 3
and 4 boiler
pumps
of the investment as 16.1 months. This result indicates that
changing pump number 1 is more effective than changing
the second. Also, after 14 months, the enterprise will save
money.
5.2. The improvement of the existing pumps efficiencies
Usage purposes
Table 4
The calculation results of the efficiency for pumps
Number 4
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
Seaside salted
water number
2 and 4 pumps
1668
5.2.1. Number 5 boiler feeding B pump
At number 5 boiler feeding B pump, the efficiency measurement has been determined as between 60% and 62% at
the operation conditions. The new pump offers have been
taken from the producer firms for this mentioned pump
that has the same pressure and flow rate capacities. To
assure the flow rate and pressure values at the measurements conditions, the electric motor power and pump efficiency value have been determined by using the new pump
efficiency, power, pressure and flow rate diagrams. The calculations that have been made for the existing and the
offered pump are showed in Table 7.
As it can be seen above, the existing pump has been
operated approximately 9% less efficiently compared with
the new pump. The efficiency rate can be increased about
5% by maintenances like renovating the existing pump,
blade coating, maintenance of bearing etc. In this condition, the calculations have been performed for the annual
money saving, the cost of investment and payback period
of 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 are
between 34% and 35% in the measurements that have been
performed in the operating condition in numbers 6 and 7
waste heat boilers medium pressure pumps. As a result of
the calculations, for operation of the pumps in the condition of maximum flow rate and pressure, the fluid power
has been calculated as 52 kW. If these pumps efficiencies
are chosen as 57%, the required power of the motor will
be 90 kW. Consequently, replacement of the existing
110 kW electric motor with 90 kW ones carries an assured
saving of a certain amount. New pump offers have been
taken from the producer firms that have the same pressure
and capacities. To assure the flow rate and pressure values
at the measurements conditions, the electric motor power
and pump efficiency value have been determined by using
the new pump efficiency, power, pressure and flow rate diagrams. The calculations that have been made for the existing and new pumps are showed in Table 9.
As it can be seen above, for the condition of replacement
of the existing electric motors, to obtain the same fluid
power, approximately 18 kW less power will be used. For
this condition, the annual monetary saving, the cost of
investment and payback period of the investment cost are
calculated and given in Table 10.
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
1669
Table 5
The efficiency values that have been obtained from existing and as a result of the saving, saving potentials, required investment cost and payback periods of
the investment cost in the condition that replacing of low efficient pumps with new pumps for the same conditions
Name of the station
Name of
the pump
Existing pump
efficiency (%)
Offered pump
efficiency (%)
Energy saving
per hour (kW)
Annual money
saving (USD)
Cost of
investment
(USD)
Payback
period
(month)
Number 1 and 2 boiler
Number 1
Number 2
46.88
48.62
60.98
62.76
71.00
61.80
21,470.40
18,688.32
50,000.00
50,000.00
27.9
32.1
Number 1 and 2 high furnace
Number 1. H.F. 2
Number 2. H.F. 1
51.40
42.17
71.72
71.49
43.37
83.04
13,115.25
50,221.66
50,000.00
60,000.00
45.7
14.3
Seaside
Number 2
Number 4
53.32
55.56
71.11
71.11
125.14
104.97
73,074.17
34,888.80
200,000.00
200,000.00
32.8
68.8
Table 6
The efficiency values that have been obtained from existing and the as a result of the saving, saving potentials, required investment cost and payback
periods 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 of
the pump
Existing pump
efficiency (%)
Offered pump
efficiency (%)
Energy saving
per hour (kW)
Annual money
saving (USD)
Cost of
investment
(USD)
Payback
period
(month)
Number 1 and 2 boiler
Number 1
Number 2
46.88
48.62
60.98
62.76
71.00
61.80
42,940.8
37,376.6
50,000.00
50,000.00
14.0
16.1
Number 1 and 2 high furnace
Number 1. H.F. 2
Number 2. H.F. 1
51.40
42.17
71.72
71.49
43.37
83.04
26,230.5
50,221.6
50,000.00
60,000.00
22.9
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 7
The pressure, flow rate, efficiency and electric motor power values of existing and new pumps
Name of the pump
B Pump
Existing pump
New pump
Transferred power to the pump (kW)
Power of the Fluid (kW)
Pump efficiency (%)
408.00
440.00
252.80
312.80
61.96
71.09
Table 8
The annual money saving, the cost of investment and payback period of the investment cost in the condition that revision of the existing pump
Name of
the pump
Existing electric
motor power (kW)
Electric motor power
after the revision (kW)
Energy saving
per hour (kW)
Annual operating
period (h)
Annual money
saving (USD)
Cost of
investment (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 the
condition of replacing the electric motor driven pump
motors with high efficiency motors. How much energy can
be saved has been examined for the condition of only replacing the driven motor with the high efficiency motor considering the pump and existing operating conditions are the same.
Economic life spans have been established in the factory
considering replacement because of their failure or as a
result of big revisions at the facility. When purchasing a
new compressor, HVAC and pump systems, ‘‘high efficiency electric motors” are preferred instead of the existing
standard electric motors to assure obtaining more efficient
energy usage and, therefore, energy saving.
The energy that will be saved upon replacement of a
standard motor with a high efficiency motor can be calculated with the help of this formula:
Energy saving ¼ MN Nominal power OP LC
UF ð1=gstandard =ghigh efficiency Þ
ð4Þ
where MN is motor number in the same power, OP is operating 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 seen
from this table, for nameplate power bigger than 224 kW
1670
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
Table 9
The 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 boiler
number 2
Existing electric motor
New electric motor
86.67
68.00
29.61
29.61
34.17
43.54
Number 7 boiler
number 1
Existing electric motor
New electric motor
88.50
70.00
30.33
30.33
34.27
43.33
Table 10
The 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 electric
motor power
(kW)
New electric
motor power
(kW)
Energy saving
per hour
(kW)
Annual
operating
period (h)
Annual money
saving
(USD)
Cost of
investment
(USD)
Payback
period
(month)
Number 6 boiler number 2
Number 7 boiler number 1
86.67
88.50
68.00
70.00
18.67
18.50
4320
4320
5645.85
5594.40
3800.00
3800.00
8.1
8.2
(300 HP), the high efficiency motor efficiencies are not
known.
Note: these average values that belong to eight firms are
validated in the condition when the motor is at full load.
With the establishment of high efficiency motors, the
monthly demand power saving for the motors, ‘‘DS”,
and the monthly kWh energy usage saving, ‘‘US”, can be
calculated as demonstrated below:
As an example, in a facility having the unit price of its electricity as 0.075 $/kWh, operating at full load continuously
7000 h/year, for the condition of replacing 36 motors of
nominal power 45 kW with high efficiency motors, the demand energy saving (DS) is
DS ¼ Nominal power MN LC ð1=gstandard 1=ghigh efficient Þ
Usage saving (US):
ð5Þ
US ¼ DS OP UF
ð6Þ
DS ¼ ð45 kW 36 1Þ ½ð1:0=0:936Þ ð1:0=0:954Þ
DS ¼ 32:656 kW=month
US ¼ ð32; 656 kW=monthÞ ð7000 h=yearÞ
US ¼ 228; 592 kWh=year
Table 11
The comparison of the motor efficiencies
Rated motor power (hp)
Rated motor power (kW)
Mean efficiency of standard type motors
Mean efficiency of high efficient motors
1
1.5
2
2.5
3
4
5
7.5
10
15
18
20
25
30
40
50
60
75
100
125
150
200
250
300
0.746
1.119
1.492
1.865
2.238
2.984
3.73
5.595
7.46
11.19
13.428
14.92
18.65
22.38
29.84
37.3
44.76
55.95
74.6
93.25
111.9
149.2
186.5
223.8
0.825
0.840
0.840
0.812
0.875
0.827
0.875
0.895
0.895
0.910
0.878
0.910
0.924
0.924
0.930
0.930
0.936
0.941
0.945
0.945
0.950
0.950
0.954
0.954
0.865
0.894
0.888
0.870
0.895
0.889
0.902
0.917
0.917
0.930
0.924
0.936
0.941
0.941
0.945
0.950
0.954
0.954
0.958
0.954
0.958
0.958
0.962
0.962
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
The money equal of the saving resources annual usage
(AUS):
AUS ¼ US ðthe price of the average electricity unit usageÞ
AUS ¼ 228; 592 kWh=year 0:075 $=kWh
AUS ¼ 17144:4$=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. When
the nameplate powers of the motors that belong to the
pumps are examined, there are only three pump motors
that have powers smaller than 224 kW. Because the high
efficiency motors efficiency values are not known for powers bigger than this, the calculations can only be made for
these three electric motors if their powers are smaller than
224 kW.
For the condition of replacing these motors with high
efficiency motors, the monthly demand saving (DS), usage
saving (US) and the money equal of the saving resource
annual usage (AUS) are given in Table 13. As it is given
in the table, the monthly demand saving (DS) is 2.47 kW
and the annual energy usage saving (total energy saving)
is 10,662 kWh. When eplacement of the three motors has
been examined by accepting the unit price of energy as
0.07 $/kWh, with high efficiency motors, the money equal
1671
of the total saving amount that will be obtained in every
year is 746 $/year.
The payback period of the price difference that will be
paid when purchasing high efficiency motors instead of
standard motors can be found from the price difference
of the high efficiency motor from the standard motor.
The price difference has been taken as approximately
600 $ for the motor of 110 kW.
Payback period
¼ ðThe cost of investmentÞ=ðAnnual money savingÞ
Payback period ¼ ð1800$Þ=ð746$=yearÞ 12 month=year
Payback period ¼ 28:9month
ð7Þ
After the payback period, 10,662 kWh/year energy saving
or 746 $/year money saving will be obtained in every year.
5.5. Cavitation
Cavitation is the phenomenon where small and largely
empty cavities are generated in a fluid that expand to a
large size and then rapidly collapse, producing a sharp
sound. Cavitation occurs in pumps, propellers, impellers
etc. A liquid, when it is subjected to a low pressure below
a threshold, ruptures and forms vaporous cavities. This
phenomenon is termed cavitation. When the local ambient
Table 12
The operating periods of the electric motors
Name of the motor
Number of
the motor
(MN)
Label
power
(kW)
Nameplate power
that the motor
draws (kW)
Operating
period
(OP)
Loading
coefficient
(LC)
Usage
factor
(UF)a
Number 1 and 2 boiler feeding electric motor of number 1 pump
Number 1 and 2 boiler feeding electric motor of number 2 pump
1. High furnace number 2 electrical booster pump motor
2. High furnace number 1 electrical booster pump motor
Number 3 and 4 boiler feeding, electric motor of C pump
Number 5 boiler, electric motor of B pump
Seaside electric motor of number 2 pump
Seaside electric motor of number 4 pump
Number 6 waste heat boiler, electric motor of number 2 medium
pressure pump
Number 6 waste heat boiler, electric motor of number 4 high
pressure pump
Number 7 waste heat boiler, electric motor of number 1 medium
pressure pump
1
1
1
1
1
1
1
1
1
335
335
186
250
590
500
447
447
110
289.8
279.9
179.7
242.6
570.0
459.9
423.5
420.0
94.2
4320
4320
4320
4320
7200
7200
8342
8342
4320
80.92
78.17
88.91
87.62
92.44
81.61
83.92
83.22
78.79
1
1
1
1
1
1
1
1
1
1
110
105.0
4320
96.00
1
1
110
95.7
4320
80.46
1
a
UF = 1 (for the reason of all motors in the circuit continually).
Table 13
Energy efficiency with high efficient motor usage
Name of the motor
DS (kW/month)
Number 6 waste heat boiler, medium pressure number 2 pump electric
Motor
Number 6 waste heat boiler, number 4 high pressure pump electric motor
Number 7 waste heat boiler, medium pressure number 1 pump electric
motor
0.762
3291
230.38
600
0.928
0.778
4010
3361
280.70
235.26
600
600
2.468
10,662
Total
US (kWh)
AUS ($/year)
746
Cost of investment ($)
1800
1672
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
Table 14
The 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)
Cavitation
results
Number 1 and 2 boiler feeding pumps
Number 3 and 4 boiler feeding A pump
Number 3 and 4 boiler feeding C–D pumps
Number 5 boiler feeding pump
Number 6 and 7 boiler feeding pumps
Number 1 high furnace booster pumps
Number 2 high furnace booster pumps
Brine station pumps
101,325
101,325
101,325
101,325
101,325
101,325
101,325
101,325
143,270
174,954
174,954
174,954
198,540
3171
3171
3171
113
211
211
203
144
1000
1100
6300
2950
2970
2982
2954
2976
1480
1450
735
5.30
5.40
5.27
5.07
6.30
9.04
9.37
12.12
10.57
13.91
13.78
13.58
17.21
0.03
0.36
3.12
1.04
1.36
1.35
1.33
1.69
0.00
0.04
0.31
1.40
1.50
1.50
1.80
2.00
0.70
0.70
0.30
Not exist
Not exist
Not exist
Not exist
Not exist
Not exist
Not exist
Exist
pressure at a point in the liquid falls below the liquid’s
vapor pressure at the local ambient temperature, the liquid
can undergo a phase change, creating largely empty voids
termed cavitation bubbles. When the cavitation bubbles
collapse, they focus the liquid energy on very small volumes. Thereby, they create spots of high temperature and
emit shock waves, which are the source of the noise. The
noise created by cavitation is a particular problem in
pumps. The collapse of cavities involves very high energies,
and can cause major damage. Cavitation can damage
almost any substance. The pitting caused by the collapse
of cavities produces great wear on the components and
can dramatically shorten a propeller or pump’s lifetime.
As a result, cavitation is, in many cases, an undesirable
occurrence. In pumps and propellers, cavitation causes a
great deal of noise, damage to components, vibrations
and a loss of efficiency [20].
According to the operating conditions of the pumps and
fluid temperatures that have been measured at the facility,
cavitation calculations and their related results are given in
Table 14.
Pm
P sat
NPSH hloss
qg qg
P s ¼ q g he max
he max ¼
ð8Þ
tion NPSH (net positive suction head) (m), hloss is the pressure 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) value
for the pump operation without cavitation. Otherwise, the
pump will operate with cavitation.
When the table results of the pumps that have been
operating at the seaside brine plant are examined, it can
be clearly seen that Ps = 0.31 bar, which is over the (P1)
inlet pressure value. Therefore, the cavitation possibility
is more than likely for these pumps. Even if it is operating
at the limit, especially with the increase of the sea water
temperature in summer, the cavitation problem will
increase more. For the examination that has been conducted at the facility, a picture of a water pump that has
been dismantled at the seaside is given in Fig. 6.
The pump has been operated at the cavitation limit as it
can be understood by this picture. Because of this reason,
the impeller and casing of the pump have been worn out
by cavitation.
As it can be seen by the calculations for the pumps from
the seaside brine pump plant, for their operation without
any cavitation, the pump impeller should be operated at
least 3.5 m under sea level.
ð9Þ
6. Results
The formulae, which are given above, have been used for
calculation of cavitation. In these formulae; Pm is the medium pressure of the pump established in the region (N/m2),
Psat is the saturation pressure of the pump that is related to
the inlet water temperature (N/m2), Ps is the pressure suc-
This is a study of the energy efficiency of pumps that has
been performed in a big industrial manufacturing facility.
By using measured data; the existing pump and electric
motor efficiencies have been calculated.
Fig. 6. The pump picture which has been dismantled from the seaside brine plant.
D. Kaya et al. / Energy Conversion and Management 49 (2008) 1662–1673
As a result of this study, the main saving opportunities
are: replacements of existing low efficiency pumps, maintenance of pumps whose efficiencies have started to decline at
certain ranges, replacements of electric motors that have
been chosen at high power with electric motors that have
suitable power, usage of high efficiency electric motors
and elimination of cavitation problems. For each saving
opportunity that is mentioned above, their investment
costs and payback periods are given.
We hope that these results will be helpful for manufacturers and engineers and to motivate them for investment.
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