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*
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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
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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
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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.
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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 – – – –
– – – – – – – – – –
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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.
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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
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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.
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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
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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
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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. References _ So¨zbir N, Saracß HI, _ Brawn DM. Experimental [1] Yig˘it KS, C ¸ allıI, investigation of optimum centrifugal pumps speeds. In: Second international conference on pumps and fans, vol. II, Beijing, China, October 1995. _ Gu¨ven R, So¨zbir N, Yig˘it KS. New method for simulation [2] Saracß HI, of centrifugal pump plants. In: International conference engineering problems, 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: 5th world conference on experimental heat transfer, fluid mechanics, and thermodynamics, Thessaloniki, 24–28 September 2001. _ O ¨ ztu¨rk R, Toklu E, Yig˘it KS. An experimental study on front [4] C ¸ alli I, declined open impeller vane in circulation pumps. In: 10th Turkish national conference on thermal sciences and technologies, vol. 1. p. 739-48. Ankara, Tu¨rkey, 6-8 September 1995. ¨ . Energy efficiency in pumps. In: 6th national installations [5] Erto¨z AO engineering 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, mixed flow 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.
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