IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 58, NO. 6, JUNE 2011
2117
Ecoanalysis of Variable-Speed Drives for Flow
Regulation in Pumping Systems
Fernando J. T. E. Ferreira, Senior Member, IEEE, João A. C. Fong, and Anibal T. de Almeida, Senior Member, IEEE
Abstract—Electronic variable-speed drives (VSDs) can produce
large energy and environmental savings in variable-load variablespeed applications when compared with other conventional technologies. There are a very large number of applications (e.g.,
fluid motion, materials handling, and materials processing) which
would benefit, both in terms of process improvement and energy
savings, through the use of speed control. Previous studies have
shown that the variable-flow fluid motion applications (pumps,
fans, and compressors) have the largest savings potential. In this
paper, an ecodesign analysis of two different technologies for the
flow regulation in pumping systems—constant-speed pump with
an output throttle valve (motor directly fed from the line) and
variable-speed pump without an output throttle valve (motor fed
by a variable-speed drive)—is presented. A European standard
methodology for the ecodesign analysis of energy-using products
is used in this paper. This paper includes a comparative analysis
of the environmental impacts and life-cycle costs. The identified
large environmental benefits on top of the energy savings provide
a strong argument for an increased use of VSDs. The presented
analysis is of major importance for industrial electronics manufacturers, designers, and users, widening their awareness to the
importance of taking into account the energy and environmental
issues when evaluating different system design options.
Index Terms—Ecodesign analysis, energy efficiency, energy
savings, environmental impact, induction motors (IMs), life-cycle
cost (LCC), variable-speed drives (VSDs).
I. I NTRODUCTION
I
N industrialized countries, electric motors consume, on
average, more than half of the generated electrical energy.
In the European Union, electric motors are, by far, the most
important type of load in the industry, using about 65%–70%
of the consumed electrical energy. In the tertiary sector (nonresidential buildings), although it is not so relevant, electric
motors use about 1/3 of the consumed electrical energy. It is
their wide use that makes electric motors particularly attractive
for the application of efficiency improvements. In spite of the
wide range of electric motors available in the market, threephase squirrel-cage induction motors (IMs) represent, by far,
the vast majority of the market of electric motors [1], [2].
Manuscript received January 20, 2009; revised May 22, 2009, September 3,
2009, and October 19, 2009; accepted June 21, 2010. Date of publication
July 15, 2010; date of current version May 13, 2011.
F. J. T. E. Ferreira is with the Department of Electrical Engineering, Engineering Institute of Coimbra (ISEC), 3030-199 Coimbra, Portugal, and also
with the Institute of Systems and Robotics, University of Coimbra, 3030-290
Coimbra, Portugal (e-mail: fernandoferreira@ieee.org).
J. A. C. Fong and A. T. de Almeida are with the Institute of Systems
and Robotics, University of Coimbra, 3030-290 Coimbra, Portugal (e-mail:
joaofong@isr.uc.pt; adealmeida@isr.uc.pt).
Digital Object Identifier 10.1109/TIE.2010.2057232
There are a very large number of applications driven by IMs
which would benefit, both in terms of the process improvement and energy savings, through the use of speed control/
adjustment. Generally speaking, the variable-flow pumping,
ventilation, and compressor applications, driven by IMs,
present huge savings potential through the use of variablespeed drives1 (VSDs). The same can be said in applications
with motion control in which the variable speed and frequent
start/stop cycles are required. However, it must be stated that
not all motor applications can benefit from the VSDs since, for
constant-speed applications, they not only do not save energy
but also lead to extra losses and capital expenses [3]–[5].
In general, power electronics provide very large potential for
cost-effective energy savings and for the reduction of environmental impacts [6], [7].
Nowadays, for electronic equipment (such as the VSDs)
designers and manufacturers producing either individual electronic units or integrated systems (e.g., variable-speed pumps),
it is important to take into account not only the technical
(mainly related to the equipment or system operation) and
manufacturing cost issues but also the use-phase cost (related
to the consumed energy cost over the system lifetime) and the
environmental benefits and drawbacks (related to the overall
energy consumption and the amount and type of materials used)
when comparing different system design options.
In the particular case of variable-flow pumping systems with
centrifugal pumps driven by IMs, two widely used technologies
can be compared (presented in Fig. 1):
1) throttle-based flow regulation (constant pump speed) using a line-fed IM and a throttle valve at the pump output;
2) speed-based flow regulation (variable pump speed) using
a VSD-fed IM and no throttle valve at the pump output.
In Fig. 2, an approximate comparison of the performance
of those two different systems is shown. The throttling system
induces large losses for a part-load operation (output flow is
lower than nominal), and therefore, its efficiency performance
is much poorer [3]–[5], [8].
It should be noted that, when varying the motor speed to
regulate the flow, the output pressure head also varies (approximately with the speed squared). The speed-based flow regulation can be applied in most pumping systems without a static
pressure head (e.g., closed-loop systems). However, in pumping
systems with a significant static pressure head (e.g., water
lifting), the speed-based flow regulation use has to be carefully
1 Since the three-phase rectifier plus voltage-source inverter topology is used
in the vast majority of the VSDs for medium–low power, in this paper, the
acronym VSD refers only to that particular technology.
0278-0046/$26.00 © 2010 IEEE
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Fig. 3.
Integrated units (VSD–IM) from two different motor manufacturers.
Fig. 4.
Analysis methodology for ecodesign of energy-using products [9].
Fig. 1. Two different variable-flow pumping systems. (a) Constant-speed
throttle-based flow regulation system driven by a line-fed IM. (b) Speed-based
flow regulation system driven by a VSD-fed IM.
Fig. 2. Input power for different flow regulation methods of a centrifugal
pump: conventional throttle-based flow regulation using a throttle valve at the
pump output versus speed-based flow regulation using a VSD-fed motor [4].
assessed in order to avoid inefficient pump operation when the
speed is reduced [3]–[5], [8].
In the low power range (up to 45 kW), there are commercially
available VSD–IM integrated units, which can be purchased as
a single package/component, simplifying the installation and
reducing the costs. In Fig. 3, two examples of such VSD–IM integrated units, from different manufacturers, are shown. These
integrated products are potentially less expensive and overcome
many of the barriers associated with the application of the
VSDs, e.g., motor properly matched to the VSD, reduced
overvoltage at the motor terminals due to the short length of the
connection, and minimization of the radiated radio frequency
interference [3]–[5].
Typically, the life cycle of the products can be divided
into four phases: production (including material extraction),
distribution, use, and end of life. In general, the use-phase cost
of most constant- or variable-speed industrial IMs, including
the consumed energy and maintenance costs, dominates by far
their overall life-cycle cost2 (LCC). A study to identify and
recommend ways of improving the life-cycle environmental
performance of the electric motors and VSDs at their design
phase was carried out for the European Commission, as reported in [1].
An ecodesign analysis methodology, named as the
Methodology Study for Ecodesign of Energy-Using Products
(MEEUP), for the assessment of the environmental impact and
ecodesign of energy-using products was used, as outlined in
Fig. 4 [1], [9], [10].
In the referred study, a comparison of different singlespeed motor efficiency classes (as defined in International
Electrotechnical Commission 60034-30 Standard) was carried
out, whose main results are reported in [1] and [10]. The
results of that study show that if high-efficiency motors replace
the current IE1-class standard efficiency motors, a significant
reduction in the environmental impact3 will be achieved. A very
significant reduction of the LCC for the low-power motors,
with savings reaching more moderate levels as the motor power
increases, will be also achieved.
2 The LCC is the total discounted cost of owning, operating, maintaining,
and disposing of a product.
3 The environmental impact is evaluated through a set of the most significant
indicators (e.g., global warming potential (GWP) emissions and waste to
landfill) during the life-cycle of the product into easily comparable amounts.
FERREIRA et al.: ECOANALYSIS OF VARIABLE-SPEED DRIVES FOR FLOW REGULATION IN PUMPING SYSTEMS
II. E CODESIGN S TUDY OF VSD–IM I NTEGRATED U NITS
To apply the MEEUP methodology/tool in the analysis
of two different centrifugal pump flow regulation methods/
technologies, namely, the VSD–IM integrated units (i.e.,
variable-speed IM) and the fixed-speed IM plus throttle valve4
at the pump output, several preliminary assumptions were
defined, which are presented in the following sections. The last
mentioned technology is considered the base-case technology
(BCT), and the other is the best available technologies (BATs)
since it is the most efficient. In both cases, it is assumed to be
standard efficiency class IMs, because the aim of this paper is to
compare throttle valves with integrated VSDs and not the motor
efficiency classes. The focus is on the LCC and the environmental impact assessment.
A. Some Relevant Assumptions
The product “electric motor” is defined as a device that
converts electric energy into mechanical energy. The VSD–IM
integrated units are assumed as “variable-speed motors”; therefore, they are considered equivalent to electric motors. According to the MEEUP methodology, the primary and secondary
performance parameters were defined on the basis of the functional aspects of the product considered. In this paper, since the
overall pumping system (including motor and pump) is being
considered, the assumed primary functional parameters are the
pump-output hydraulic power (the provided hydraulic power at
the pump output) and the respective output flow. The assumed
main secondary functional parameter is the pumping-system
nominal efficiency, corresponding to the full-load (or full-flow)
efficiency.
An IM is normally repaired at least two times during its
lifetime, but this can happen up to four times [1], [10]. Typically, the repair process includes rewinding and bearing the replacement. A value of 2.5 repairs is assumed for IMs operating
8000 h/year. For the sake of simplicity, it is assumed that
the number of repairs decreases linearly with the decrease of
the operating time. For the VSDs and valves, no repairs were
assumed due to the lack of reliable data.
In all LCC calculations, a discount rate (interest minus
inflation) of 2% is assumed [1], [10].
Concerning the material recycling at the end of life, it is
assumed that 5% is not recovered (landfill), 1% of the plastics
are reused (closed-loop recycling), 9% of the plastics are recycled, 90% of the plastics are thermal recycled (nonhazardous
incineration optimized for energy recovery), and 95% of the
metals are recycled.
Since the study on motors covered the power range of 0.75
to 200 kW (1 to 275 hp), three motor output powers were
considered in the analysis, namely 1.1, 11, and 110 kW. For
the sake of simplicity, it is considered that the motor efficiency
remains constant, regardless of the motor frequency, voltage,
and load. However, it is well known that the motor peak efficiency achieved at frequencies lower than the nominal is lower
than that at the nominal frequency. Nevertheless, since modern
VSDs can search for the peak efficiency values at any speed and
load, the variation of the motor efficiency is attenuated, even for
the small IMs [5], [11]–[13]. The IM and/or VSD–IM system
efficiency maximization capability at any particular motor load
point (by means of a proper magnetizing flux regulation) is
an important advantage of the VSDs, which can compensate
the IM additional losses caused by the VSD output pulsewidth
modulation voltages) [4], [5], [14]–[16]. Typically, at the rated
frequency and voltage, the IM peak efficiency occurs between
65% and 85% load.
The efficiency of commercial VSDs depends on its rated
power, load, and brand [5], [17], [18]. For the sake of simplicity,
an average efficiency of 95% is assumed for the VSDs over the
considered operating speed range (50%–100%), corresponding
to the BAT in the market (high-efficiency VSDs).
Lifetimes of 12, 15, and 20 years for the 1.1-, 11-, and
110-kW motors are considered, respectively.
In terms of motor price distribution, the average list price of
the standard efficiency class IMs ranges from 160 C (EURO5 )
for a 0.75-kW motor to 15 000 C for a 200-kW motor [1], [10].
In general, the market is very competitive with large discounts
offered to original equipment manufacturers. At higher power
ratings, there are lesser pressures as the degree of competition is
not considered fierce. For this paper, an average 40% discount
below the list price is assumed, and the prices for the VSD–IM
integrated units are assumed as three times the price of the
motor individually [these values are shown in Tables VI–XI].
In most cases, the prices of the throttle valves also benefit
from a 40% discount, where the discounted prices are around
90 C and 1440 C for the sizes 32, 100, and 350 (inner input/output diameter), which are typically used in pumps driven
by 1.1-, 11-, and 110-kW four-pole IMs, as can be seen in
Tables VII, IX, and XI.
The average electricity price of 0.0754 C for a European
industrial consumer was used [1].
B. Bill of Materials
The integrated VSD–IM units are available for low- and
medium-power levels. Therefore, the respective bill of materials (BoM) were estimated based on the small units and on
the material fractions for the separated VSDs and IMs provided
by manufacturers for the larger units. Regarding the BCT, the
BoMs in kilograms per kilowatt (materials average values) for
the IM alone are shown in Table I. In Table II, the BoMs in
kilograms for the throttle valves’ materials considered in the
BCT are shown. In Table III and Fig. 5, the BoMs for the BAT
(VSD–IM integrated units) are shown in kilogram per kilowatt
and percentage, respectively.
It should be noted that the BoMs for the motors were established on the basis of the average values provided by the
European Motors and Drives Manufacturers Association
(CEMEP6 ), and since most small motors sold have an aluminum frame, that material portion is higher than that for
the larger motors. The larger motors typically have cast-iron
EURO ( C ) = 1.385 USD ($), March 3, 2011.
Européen de Constructeurs de Machines Electriques et
d’Electronique de Puissance.
51
4 In
this paper, ball valves [19] are considered because of their low friction
when totally open.
2119
6 CEMEP—Comité
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TABLE I
AVERAGE B O M S FOR S TANDARD IE1-C LASS IM S
TABLE II
B O M S FOR BALL VALVES
TABLE III
E STIMATED B O M S FOR I NTEGRATED VSD–IM U NITS
Fig. 5. Percentage of materials mass per kilowatt for each rated power
considered. (a) Single IMs. (b) VSD–IM integrated units.
frames. The BoMs for the ball valves were provided by a large
European manufacturer [19].
C. Load Profile
Regarding the pumping system load, the typical profile
shown in Fig. 6 is used, which is defined on the basis of
the results of the EuP Pump6 study [20], resulting in a timeweighted average of 75% flow. Four scenarios are considered
for six different operating times: 500, 1000, 2000, 4000, 6000,
and 8000 h/year. The base scenario of 4000 h/year is used for
the present ecoanalysis. A typical 60% load factor is considered
for all motors, based on previous findings [2].
7 EuP—Energy-using
Products.
Fig. 6.
Considered pumping system load profile [20].
FERREIRA et al.: ECOANALYSIS OF VARIABLE-SPEED DRIVES FOR FLOW REGULATION IN PUMPING SYSTEMS
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TABLE IV
U SE -P HASE E NVIRONMENTAL I MPACT ( IN P ERCENT ) OF VSD–IM
I NTEGRATED U NITS , C ONSIDERING O NLY L OSSES AND 4000 h/year
Fig. 7. Total energy [gross energy requirement (GER)] reduction, as a function of the operating time, when a VSD is used for flow regulation instead of a
throttle valve, wherein the latter is the reference.
TABLE V
U SE -P HASE E NVIRONMENTAL I MPACT VARIATION (VSD VERSUS
T HROTTLE VALVE ), C ONSIDERING O NLY L OSSES AND 4000 h/year
III. E NVIRONMENTAL I MPACTS
On the basis of the presented results, in a pumping system,
when using a VSD (i.e., the BAT) instead of a throttle valve
(i.e., the BCT), the majority of the environmental impacts are
in the use phase. In Table IV, the use-phase environmental
impact (in percent of the entire lifetime environmental impact)
associated with the BAT is shown, considering a 4000-h/year
scenario and the electrical energy consumed in the motor and in
the VSD (i.e., their losses). In Table V, the use-phase environmental impact variation associated with the replacement of the
BCT by the BAT is shown, considering only the losses and a
4000-h/year scenario. The reduction in the environmental impact when the throttle valves are replaced by the VSDs is significant, which is more than 14% in all the evaluated indicators
but reaching near 40% in some of them. For example, about
37% reduction is expected in the greenhouse-gas emissions.
In Figs. 7–10, the variation of the main environmental impact
indicators is shown as a function of the number of operating
Fig. 8. Electricity part (in primary megajoule) of the total energy (GER)
reduction, as a function of the operating time, when a VSD is used for flow
regulation instead of a throttle valve, wherein the latter is the reference.
time, demonstrating that only below 2000 h/year does the
environmental impact reduction starts to decrease sharply when
the throttle valves are replaced by the VSDs. The percentage reduction ΔQ(%) of each presented quantity is given by (1), where
QIM+VSD is the quantity associated with the IM+VSD system
and QIM+valve is the quantity associated with the IM+valve
system
QIM+VSD
· 100%.
(1)
ΔQ(%) = 1 −
QIM+valve
In Figs. 11–14, the variations of all the environmental impact
indicators for the 1.1-kW case are shown. In all the cases, for an
operating time longer than 2000 h/year, the environmental impact reduction is significant for all integral horsepower ranges
(≥ 1 hp), demonstrating the benefits associated with the VSDs
in variable-load variable-speed motors.
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Fig. 9. Waste nonhazardous/landfill reduction, as a function of the operating
time, when a VSD is used for flow regulation instead of a throttle valve, wherein
the latter is the reference.
Fig. 11. Total energy (GER) reduction, as a function of the operating time,
when a VSD is used for flow regulation instead of a throttle valve in the
1.1-kW system, wherein the latter is the reference.
Fig. 10. Greenhouse-gas (in GWP 100) reduction, as a function of the
operating time, when a VSD is used for flow regulation instead of a throttle
valve, wherein the latter is sthe reference.
Fig. 12. Water (process) nonhazardous/landfill waste and hazardous/
incinerated waste reduction, as a function of the operating time, when a VSD
is used for flow regulation instead of a throttle valve in the 1.1-kW system,
wherein the latter is the reference.
IV. LCC
(3)
Fig. 15 shows the percentage segregation of the LCC (excluding the repair and maintenance costs) of the IM+VSD and
the IM+valve systems, evidencing the much higher relevance
of the consumed energy cost in relation to the overall system
initial price.
The percentage LCC reduction ΔLCC(%) is given by (4),
where LCCIM+VSD is the LCC associated with the IM+VSD
system and the LCCIM+valve is the LCC associated with the
IM+valve system
LCCIM+VSD
ΔLCC(%) = 1 −
· 100%.
(4)
LCCIM+valve
Tables VI–XI present the LCC for the three analyzed
VSD–IM units, considering a different lifetime in each case.
In Fig. 16, the percentage LCC reduction when a VSD
is used for the flow regulation instead of a throttle valve is
shown. It is clear that there are economic and environmental
In an approximate form, the LCC is given by (2), where
P P is the initial system purchase price, OE is the operating
expense, including the consumed electrical energy and the
repair and maintenance costs, and P W F is the present worth
factor. The P W F is defined by (3), where n is the product
lifetime (in years) and r is the discount rate (interest rate minus
inflation rate)
LCC = P P + P V F · OE
1
1
.
1−
PWF =
r
(1 + r)n
(2)
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TABLE VII
LCC FOR 1.1-kW IM P LUS VALVE (12-Y EAR L IFETIME)
TABLE VIII
LCC FOR I NTEGRATED 11-kW VSD–IM U NIT (15-Y EAR L IFETIME)
TABLE IX
LCC FOR 11-kW IM P LUS VALVE (15-Y EAR L IFETIME)
Fig. 13. Greenhouse gases (in GWP100), acidification, volatile organic compounds, persistent organic pollutants, heavy metals, polycyclic aromatic hydrocarbons (PAHs), and particulate matter reduction, as a function of the operating
time, when a VSD is used for flow regulation instead of a throttle valve in the
1.1-kW system, wherein the latter is the reference.
TABLE X
LCC FOR S EPARATED 110-kW IM P LUS VSD (20-Y EAR L IFETIME)
TABLE XI
LCC FOR 110-kW IM P LUS VALVE (20-Y EAR L IFETIME)
Fig. 14. Heavy metals and eutrophication reduction, as a function of the
operating time, when a VSD is used for flow regulation instead of a throttle
valve in the 1.1-kW system, wherein the latter is the reference.
TABLE VI
LCC FOR I NTEGRATED 1.1-kW VSD–IM U NIT (12-Y EAR L IFETIME)
benefits associated with the replacement of the throttle valves
by the VSDs.
V. C ONCLUSION
In this paper, the improvement potential in terms of the
environmental impact and LCC for two different flow regulation technologies in pumping systems has been analyzed, and
the main outcomes of this paper have been reported. It has been
concluded that, in variable-flow IM-driven pumping systems
operating more than 2000 h/year, the use of the VSDs instead of
the throttle valves to regulate the flow can produce a substantial
reduction in both the environmental impact and the LCC. The
estimated reduction in the greenhouse-gas emissions can reach
over 35%, with a low dependency on the motor rated power,
and the LCC reduction can reach over 25%, with a significant
dependency on the motor rated power. Therefore, aside from the
well-known direct process benefits to users (e.g., better process
control and less wear and tear in the mechanical components),
the VSD–IM units are an important technology to reduce the
environmental impacts of many motor applications, particularly
in pumping, ventilation, and compressor systems, over their
useful lifetime.
The identified large environmental benefits on top of the
energy savings provide a strong argument for an increased use of
the VSDs in a wide variety of applications. The environmental
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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 58, NO. 6, JUNE 2011
Fig. 15. Percentage segregation of the LCC (excluding the repair and maintenance costs) of IM+VSD and IM+valve systems, as a function of the operating
time. (a) 1.1-kW system. (b) 11-kW system. (c) 110-kW system.
Fig. 16. LCC reduction as a function of the operating time when a VSD is
used for flow regulation instead of a throttle, wherein the latter is the reference.
benefits come virtually free since, in many cases, the VSDs are
cost effective due to the achieved energy savings.
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Fernando J. T. E. Ferreira (SM’09) received the
Ph.D. degree in electrical engineering from the University of Coimbra (UC), Coimbra, Portugal.
He is currently a Professor with the Department
of Electrical Engineering, Engineering Institute of
Coimbra (ISEC), Coimbra, Portugal. Since 1998, he
has also been a Researcher with the Institute of Systems and Robotics, UC, where he is working in the
area of motors and drives. He has participated in several European projects dealing with energy-efficient
motor technologies.
Dr. Ferreira was a recipient of the Best Paper Award at the 2001 IEEE Industry Applications Society Industrial and Commercial Power Systems Technical
Conference.
FERREIRA et al.: ECOANALYSIS OF VARIABLE-SPEED DRIVES FOR FLOW REGULATION IN PUMPING SYSTEMS
João A. C. Fong received the Licentiate degree
in mechanical engineering from the University of
Coimbra (UC), Coimbra, Portugal, in 2005.
He is currently a Researcher with the Institute of
Systems and Robotics, UC, where he is participating
in projects on energy-efficiency-related areas.
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Anibal T. de Almeida (SM’03) received the Ph.D.
degree in electrical engineering from Imperial College, University of London, London, U.K.
He is currently a Professor with the Department of
Electrical Engineering and Computers, University of
Coimbra (UC), Coimbra, Portugal. He is also a Consultant with the European Commission Framework
Programmes and the U.S. Department of Energy. He
is the coauthor of six books on energy efficiency
and more than 200 papers published in international
journals and conference records and presented at
meetings. He has coordinated eight European projects dealing with energyefficient motor technologies. He was also a Consultant on several international
projects to promote energy efficiency in developing countries.
Dr. de Almeida was a recipient of the Best Paper Award at the 2001
IEEE Industry Applications Society Industrial and Commercial Power Systems
Technical Conference.