8
CHAPTER 2
LITERATURE REVIEW
The various research works attempted in the area of energy
conservation and specifically in the area of air compressor and pneumatic
systems have been referred and discussed here. The articles from journals,
magazines, books, specific reports and web sources have been collected,
reviewed and presented in the following sections.
2.1 STUDIES ON AIR COMPRESSORS AND ENERGY
CONSERVATION
As described in the source book for industry (U.S. 2003), though
the production of compressed air is one of the most expensive processes in
manufacturing facilities, compressed air itself is used inappropriately in
several ways such as open blowing, sparging, atomising, cabinet cooling and
vacuum generation. The energy wasted in compressed air systems because of
poor installation and maintenance can account for up to 50% of the energy
consumed by the compressor, and about half of this amount can be saved by
practicing energy conservation measures.
A broad classification of various possibilities for energy
conservation in air compressors and compressed air supply system as given
by several researchers is given in Figure 2.1 and are discussed in detail in the
following sections.
9
Figure 2.1 Energy conservation opportunities in air compressors
Type of compressor
Selection of
size Optimisation
of compressor Selection of
ancillary equipments
Air inlet temperature
Effective inter
cooling Heat recovery Pressure
bandwidth
Selection of apt control method
Intelligence in
control Flexibility in
control
Pressure required
Leakage of
air Improper
usage of air Variation in
consumption
High efficiency motors
Variable
Speed Drives IC engine for
drive
Maintenance Systems
approach Awareness and
training Benchmarking
Compressor Process Parameters Control strategy Usage
parameters Drive systems Management
Energy conservation opportunities in air compressors
10
According to John (1995), the opportunities for cost savings in
compressed air supply system includes but not limited to waste heat recovery,
compressed air leakage reduction, use of outside air for compressor,
compressor control, air pressure control, compressor selection and usage of IC
engine for compressor driving.
The solution for compressed air leaks is to make leak finding and
correcting as a part of the normal maintenance process and repeating leak
survey at least once a year (John Holdsworth 1997). Over-pressurization can
also result from short sighted selection of ancillary equipments. Bill Howe
and Bill Scales (1998) report that the opportunities for improved compressed
air efficiency where air is used internally, but uneconomically are less
understood. Supplying air at required pressure, appropriate use of air,
automated controls are some of the recommendations given by the authors.
Cost effective efficiency opportunities in production and usage of
compressed air are often ignored by the industries due to various reasons and
selection of correct compressor control also plays a major role in the energy
consumption by the air compressors (Robert 1999). Leaks, inappropriate
usage of compressed air, poor selection of compressors and ancillary
equipments, pressure problem and poor attempts to solve these problems are
some other common causes of inefficiency in the compressor system.
According to David (1999), estimates and actual measurements of
compressed air systems show that 10 % to 35% air is lost due to leak or
improper use. Proper maintenance, sound design and appropriate usage of the
compressed air can contribute for energy savings.
Three methods have been proposed for estimation of compressed
air consumption by John (1999), out of which measuring the time for few of
11
the load / unload cycles of the compressor and calculating the consumption
based on that is the one reported as the quickest method which can give useful
information. Providing separate duct to enable cool air intake and using
synthetic lubricating oil for compressors are attempted in few glass
manufacturing industries, with about 5 % energy savings (Gopalakrishnan
et al 2001).
Durmus Kaya et al (2002) attempted energy conservation with
repairing air leaks, installing high efficiency motors, reducing the average air
inlet temperature by using outside air and reducing compressor air pressure.
The pay back periods for the investments made with these measures were
very less. Proper maintenance and appropriate use of compressed air can
contribute to cost effective and energy efficient compressed air system, along
with the control mode (U.S 2003). Different efficiencies are considered for
performance evaluation of compressors (Ueno et al 2003).
Maintenance, monitoring, blocking leakage, minimising air inlet
temperature, minimising allowable pressure dew point at air intake, controls,
properly sized pipes, heat recovery, usage of natural gas engine for driving air
compressor, system improvement and improvement in the motor are the
options described by Christina et al (2003). Asfaw (2005), lists leak and air
supply at higher pressure than required are the major causes besides over
sized compressors, running compressors when not needed, wrong application
of compressed air etc.
Bureau of Energy Efficiency (2005) suggests reducing the air
intake temperature and every 4 degree centigrade rise in inlet air temperature
results in higher energy consumption by 1% to achieve equivalent output.
Chris and Kelly (2004) presented a methodology for modelling air
compressor performance and calculating projected energy savings from easily
12
obtainable performance data such as full-load power, no-load power, rated
capacity and average fraction full-load power or average fraction rated
capacity. Using load/unload type of control and fixing the leak are the major
contributors for the reported savings.
The drivepower of selected industrial processes has been
investigated and found that 42% of the electricity goes to drivepower (pumps,
compressors, etc.). An estimate shows that 6.3 % of drive power can be saved
without major changes in the equipment (Gabriel 1993). Normally in
industries, compressed air consumption is not constant throughout a given
time period and it varies depending on the simultaneous usage of the utilities.
One such varying consumption, as reported by an energy audit report
(EnergAir) is shown in Figure 2.2.
Figure 2.2 Variation in energy consumption (EnergAir)
Tim
e
13
2.1.1 Studies on Compressor Control
Compressed air system control is one of the most important
determinants of overall system energy efficiency. The type of control selected
for any system is mainly determined by the type of compressor used and the
air consumption profile. Importance of the correct selection of compressor
control methodology is insisted by John (1995), Bill Howe and Bill Scales
(1998), Robert (1999) and Christina et al (2003). Even simulation tools are
used as powerful methods for designing digital control systems (Wojciech
1996).
For air supply system with multiple compressors, varying demand,
and many types of end uses require a more sophisticated strategy. In any case,
careful consideration should be given to both compressor and system control
selection because they can be the most important factors affecting system
performance and efficiency (Compressed air system controls fact sheet #6
1998).
Robert (1999) reports that out of several compressor control
strategies load/unload type of control is the most efficient modulation control
for small and medium size. Gary (1999) and Joseph (2002) express that air
compressor control should provide efficient volume and pressure regulation
of compressor air delivery. Energy savings of 15 % to 20 % and long term
maintenance savings of 7 % to 10 % is possible for advanced control systems.
Inadequate compressor control causes over pressurisation of the compressors
which is the most common and most significant energy misuse.
The goal of supplying the air at required quality and pressure with
maximum possible efficiency cannot be accomplished by a simple controller
for a multiple compressor system (Joseph 2002). Compressor control system
14
selection affects the performance considerably (U.S. 2003). Start/stop,
load/unload, modulating control, multi step control and variable frequency
drive are some of the methods used in the industries. Compressor modulation
plays an important role in the energy savings of compressors for residential
cooling and inverter based control is less successful in the U.S. due to higher
initial cost (Kurt et al 2004).
2.1.2 Studies on air receiver size
Compressed air receiver serves to stabilize the compressed air
supply and smoothens pressure fluctuations in the network when air is
consumed. The size of the receiver can be decided based on air consumption,
network, type of regulation and permissible pressure difference in the network
(Meixner and Kobler 1978).
The size of the receiver is governed by the rate at which
compressed air is consumed and the capacity of the compressor if the air
consumption is assumed as at constant rate (Werner and Kurt 1975). Other
factors controlling the size of the air receiver are capacity control provided for
the compressor and the maximum cycle rate. But, the storage function and
assumed relatively constant consumption of air are the principal determinants.
Majumdar (2006) lists that the delivery volume of compressor, air
consumption, pipeline network, type and nature of regulation and permissible
pressure difference are the parameters on which the receiver size depends.
NCDENR (2004) reports that choosing a receiver, or storage tank, to fit the
needs of the system demand and prevent system pressure from dropping
below minimum required pressure during times of peak demand is important.
A drop in pressure causes the end tools to function improperly. The common
response to the tool malfunction is to increase the system pressure. The
15
energy used in increasing system pressure could have been saved through the
use of a properly sized receiver.
2.1.3 Studies on the use of variable speed drives
Some literature support the usage of variable frequency drives
(VFD) to compressors. Most of the compressors run below their capacity and
for about 70% of the compressors, the air demand varies from 40 % to 80 %.
Motors fitted to such compressor systems cannot give savings beyond certain
level because, standard production motors cannot run below certain speed
without heating problems (Elie 2002).
Bob (2002) reports that adjustable frequency drives help to improve
the compressed air system efficiency and that can be further improved by the
automated control system. Variable frequency drives fitted to a boiler air
supply fan for providing optimum air at different operating conditions could
save considerable electrical energy within a month in a fan fitted with
13.5 kW motor (Ibrahim and Engin 2004).
Reimund (2005) found that the use of variable speed drives (VSD)
compressor gives good energy savings but a VSD compressor is not a
standard compressor with frequency converter. The design of the compressor
has to consider the specific demands on the total system. If there is a
combination of VSD compressors and fixed speed compressors, a
sophisticated regulation is required.
At the same time, several literature report that usage of VFD is a
trustable solution for energy conservation only for certain conditions. Vern
(2000) observed that application of VFD for turbo machinery does not
16
produce energy savings always and sometimes fail in achieving the results
particularly in the retrofitted systems due to various reasons.
Mark (2002) observed the power consumed by compressor at
different load conditions with different types of drives or controllers and are
presented in Table 2.1. From the Table 2.1, it can also be noted that the
variable frequency drive is more efficient only if the average consumption is
within certain range and otherwise various other methods are efficient. For
lower percentage of loads, online / offline is more efficient.
Table 2.1 Power requirement at various load conditions (Mark 2002)
% Load
% of power Var. SR
Drive
Var. Freq. Drive
OL/OL*w/ Storage
MOD ACS GEOM
0 20 50 20 60 20 20 10 20 50 28 64 28 28 20 20 50 36 68 36 36 30 30 50 44 72 44 44 40 40 50 52 76 52 64 50 50 50 60 80 60 67 60 60 60 70 84 84 72 70 70 70 78 88 88 78 80 80 80 85 92 92 85 90 90 90 93 97 97 93
100 100 100 100 100 100 100 Avg.0-100
60-100 0-60
52.7 80
34.3
63.6 80
51.4
61 85 44
76 92 66
64 92 46
62 86 47
Where, Var. SR Drive refers to Variable Switched Reluctance Drive, Var. Freq. Drive refers to Variable Frequency Drive, Ol/OL refers to Online/Offline, MOD refers to Modulation control, ACS refers to Auto Control Select, GEOM refers to Geometry control.
17
Michael (2003) reports that VSD compressors are more costly
compared to standard compressors when operate at 100 % capacity as extra
energy is wasted in the addition of VSD itself. It is also reported that
retrofitting standard compressors with VSD is not efficient always and at
certain flow rate, the fixed speed compressor is more efficient than the
variable speed compressors as shown in Figure 2.3.
Figure 2.3 Flow rate and specific power (Michael 2003)
Usage of variable frequency drives is rare for industrial air
compressors because of high initial cost (U.S. 2003).
2.1.4 Managerial approach required
Jay Stein (1996) identified a list of fourteen common mistakes
committed during the implementation of energy efficiency projects.
Inadequate definition of the baseline for energy savings, limited or
inappropriate solutions, neglect of interaction between the building systems,
18
failure to verify the results and inadequate operation and maintenance of
efficiency measures are some of the common mistakes.
Khemiri-Enit and Annabi (1996) report that one of the technical
instruments of energy saving is the energy audit study, that is useful to
determine the actual consumption, reveal the anomalies and suggest
corrective measures. Nair and Sugathakumar (1996) used a linear
programming approach for the installation of energy saving devices with an
aim of optimising the subsidy given with given target of energy savings.
Energy conservation efforts can result in huge amounts of savings if equated
to carbon dioxide emissions and the expenses to provide necessary trainings
on energy conservation can be met easily (John 1998).
Hans-Dieter and Eberhard (1998) expressed that for reaching the
goal of reduction in energy conditioned emissions, an emphasis on rational
use of energy is required in small and medium sized enterprises as the
potentials exist there. These potentials are often not realized due to existing
obstacles in enterprises, which however can be overcome with suitable tools.
Apart from important financial obstacles, missing characteristic energy ratios
to enable a comparison with the benchmarking as well as missing information
in the enterprises about energy saving measures represent the largest obstacles
for an energy management in operation avoiding energy losses.
Felipe and Nicolás (1998) express energy conservation programs
should be based on the practical knowledge of energy experts, who can
diagnose every case and prescribe the relevant recommendations. The
decisions can be made taking into account a combination of scientific theories
and analytic techniques, experimental methods and individual experience and
judgment as well as common sense.
19
Paresh (1998) proposes a ‘systems approach’ to design a new
system and for debottlenecking of existing system, to improve the operation
and to reduce the lifecycle cost of a compressed air system. Grimaldi et al
(2000) reports that achievement of a more rational use of energy can be
achieved with a well-focused energy analysis, based on experimental data to
point out possible relevant energy savings in large and complex industrial
plants.
Concept of total productive energy management (TPEM) is
introduced by Mohammad (2000). This approach requires the involvement of
all members of the facility in the energy conservation efforts. Commitment of
top management, incentives and continuous trainings are required for the
successful implementation of TPEM. In a survey conducted in European
Union, in many cases users were not aware of the compressed air costs and in
some cases, the managers were not sufficiently aware about the availability of
cost effective energy saving measures (Peter and Edgar 2001), even though
cost data is available.
George (2001) reports benchmarking can be used with focus on
energy efficiency improving measures. Some questions need to be answered
before benchmarking and several methods available for benchmarking. Key
issues need to be considered carefully to obtain meaningful metrics and useful
results.
Douglas and Laura (2001) have identified eight key elements
which are important for best energy management practice. The commitment
by the top management, clearly defined goal for energy reduction,
communication of the goals throughout the organization, assignment of
responsibility, formation and tracking of energy metrics, identifying potential
projects, adaptation of the projects considering risks and rewarding for
20
achieving the goals are the elements. The authors also identified that no
company engages all of these practices to the best degree.
Pinch analysis technique can be used to estimate the target energy
requirement for any process and can be used as a tool for energy efficiency
improvement (Jimmi 2002). Industrial energy outsourcing (IEO) offers one of
the most exciting opportunities for achieving the win-win combination of a
reduction in both energy consumption and energy cost while offering a
profitable business opportunity for an energy service provider (Michael and
Simon 2003).
Money is being wasted on inefficient compressed air systems
throughout the world and most of the companies are unaware about the waste
in their current air system (Michael 2003). James (2004) insist on valuing the
energy savings in money value is as important as taking conservation efforts,
because, it creates more interest in the minds of the upper management
towards energy conservation than the conventional energy units. Energy
savings to the extend of 9,00,000 kWh and 23,45,000 kWh are reported in
two industrial cases (Barbara 2004) by the implementation of system level
approach to the air compressors.
Asfaw (2005) expresses that the energy conservation measures for
air compressors are less expensive and have quickest pay back period. At the
same time, the small and medium sized industries have no in-house expertise
for energy management which require an intensive training.
Compressed air system economics depends on several factors.
According to Compressed air systems fact sheet #9 (1998), too many
decisions regarding compressed air systems are made on initial cost basis, or
with an "if it is not broken, don't fix it" attitude. But to achieve optimum
21
compressed air system economics, users should select the compressor based
on life-cycle economics. Also, proper sizing of the components, turning off
unneeded compressors, using appropriate control and storage strategies, and
operating and maintaining the equipment are important for peak performance.
Gopalakrishnan et al (2005) insists that the energy assessment
process, which explores the opportunities for energy conservation, is a
complicated process for a large sized industry containing the more interacting
energy consuming systems. A structured systems approach and plant - wide
energy assessment is needed in such a case. There are number of essential
actions to be taken to optimise compressed air systems which need to be done
systematically (Scot 2005).
2.1.5 Studies on delivery pressure and pressure bandwidth
John (1995) expresses that in general the operating pressure
bandwidth is maintained at much higher level due to various reasons that exist
inside the plant.
The ratio of power reduction if the operating pressure is reduced is
given by Durmus Kaya et al (2002) as
FRi = ((Pdp + Pi)/Pi)(k-1)/(k x N) – 1.0/((Pdc + Pi)/Pi)(k-1)/(k x N) – 1.0 (2.1)
where Pdp is the discharge pressure at proposed operating pressure conditions,
Pdc is the discharge pressure at current pressure conditions Pi is the inlet
pressure, k is the ratio of specific heat for air (k= 1.4), N is the number of
stages. All ‘P’ are in any constant units; ‘k’ and ‘N’ are dimensionless.
22
Increasing the pressure increases the unregulated usages such as
leakages, open blowing and production application without pressure
regulation or with wide open regulation. This artificial demand increases the
energy consumption (Compressed air system fact sheet # 4 1998).
Dan Howett (2003) advocates that utility costs of the compressor
may be lowered by producing and storing air at higher pressure level and
reducing it to end user level. It depends on the efficacy – the standard cubic
feet of air produced per brake horse power - of the compressor system. But
this approach is countermanded by Richard (2004).
2.1.6 Studies on energy conservation in compressors and pneumatic
systems
Several attempts have been made already, to optimise compressor
and its accessories as well as pneumatic systems so as to reduce the energy
consumption. Fujiwara and Osada (1995) used computer simulation for
analysing the performance of the screw compressors. Computer based tools
are also developed for identifying energy saving opportunities in industries,
compressed air system is one of its application areas (Gopalakrishnan et al
1997). Pascal et al (2001) propose a global model for the thermodynamic
analysis of reciprocating air compressor based on five main and four
secondary dimensionless parameters used to predict the performance of a
reciprocating air compressor under various operating conditions.
Exergy analysis as a tool was used for the design, optimization,
and performance evaluation of energy systems (Recep et al 2002). Kagawa et
al also used exergy approach for the energy assessment of pneumatic cylinder
actuation system and reported that the approach is effective on clarifying the
energy distribution in pneumatic cylinders. Attempts had been made to
23
optimise screw compressors during the design stage itself (Stosic et al 2003).
Jiang et al (2003) used an integrated CAD/CAM method for design and
manufacturing of scroll compressors.
Yukio et al (2000) attempted with meter in circuit for energy
saving in pneumatic systems to reduce the air consumption. The reduction of
the air consumption is possible in proportion to the size, irrespective of the
load condition changes. Grzegorz and Johann (2004) suggested the use of
multiple on-off valves to minimise the compressed air consumption in the
actuators used in mobile robots.
2.2 FUZZY LOGIC SYSTEM AND APPLICATIONS
Effective optimisation of the compressed air supply system requires
an intelligent system due to several variations and uncertainties associated
with it. Fuzzy based approach is one such system and the related referred
articles are discussed here. In fuzzy logic models, information is processed in
terms of fuzzy sets, made precise through the definition of an associated
membership function. The specific inference is then processed by the fuzzy
set combined with fuzzy rules. The fuzzy logic model combines one or more
input signals, which are defined by the fuzzy sets, with a collection of fuzzy
rules to produce an output that can be compared with actual values in the real
world (Mamdani and Assilina 1975 and Sugeno 1999).
The advantage of fuzzy logic is that the use of fuzzy logic enables
the heuristic rule based technique commonly applied to discrete variables to
be extended for use in the continuously variable situation, without
significantly increasing the size of the rule base. The fuzzy controller
expresses in natural language the human expertise on the control of the non-
linear system by means of a set of linguistic expressions and fuzzy controller
24
performance is in real time, under a wide range of working conditions
(Lia et al).
Fuzzy logic modelling is a powerful tool for exploring complex
problems (Chen et al 2000). The fuzzy methods give good performance in
controlling non- linear system (Boada et al 2006). Shepherd and Batty (2003)
used fuzzy control strategy to provide energy efficient environmental
conditions, which is a multi variant control problem. Aprea et al (2004) used
fuzzy based algorithm to continuously vary the compressor speed with a help
of an inverter to save the energy in the compressors of refrigeration plant and
energy saving of nearly 13% is reported.
Fuzzy based control system is used for several applications:
integrating the front wheel braking and steering control to improve the vehicle
handling capacity at various driving conditions and manoeuvres (Boada et al
2006), vehicle trajectory controlling (Cho and Yi 2004), chatter suppression
in end milling process (Liang et al 2004), controlling unmanned lawn mover
(Lia et al), X-ray inspection of soldering defects (Wei and Tapio 2002),
evaluate and monitor the gap condition of wire electrical discharge machining
(Yan and Liao 1998).
Fuzzy logic model with genetic algorithm is used to overcome the
uncertainties in the fish stock – recruitment process (Chen et al 2000). Fuzzy
control system is used for ventilation control of naturally ventilated buildings
(Ljiljana and Mahroo 2004), evaluation of welding efficiency and quality of
laser welding (Casalino and Memola 2004), quality assurance in resistance
spot welding, (Lee et al 2001), tool wear monitoring (Srinivasa Rao and
Srikant 2004), for controlling the liquid level in a tank (Heider and
Chukwuma 2000) and many more.
25
2.3 TARGET COSTING
Target costing is not a costing system as such, rather it is an activity
which is aimed at reducing the lifecycle costs while ensuring quality,
reliability and customer requirements (Yutaka 1993). For over a decade,
target costing has been recognised as an important tool for lowering costs and
increasing competitiveness. Target costing is a process whereby an
organization determines the ‘‘estimated selling price’’ for its product or
service, less the ‘‘desired profit,’’ with the remainder equalling the ‘‘target
cost.’’ The target cost amount must cover all of the firm’s expenses for
producing/procuring the product or service (Lisa 2002). In target cost
management system, interactive control and simultaneous engineering
approach are required (Takeyuki 1995).
Gopalakrishnan et al (2004) expressed that target costing is a
structured approach to determine the cost at which a proposed product,
meeting the quality and functionality requirements, must be produced in order
to generate the desired profits. Companies in automotive, electronic and
process industries have reaped the benefits of target costing, still it need to
find applications in other segments of the industry.
Target costing concept is used for several applications other than
identifying the manufacturing cost of a product. The relationship among the
loss function, process capability indices and control charts to establish goal
control limits is determined by extending the target costing concept (Hsin-
Hung Wu 2004), target costing has been used as a means to improve the
management of supply chains (Archie and Wilbur 2000), for quality
management and for depicting the relationship among Taguchi loss function,
process capability indices, and traditional control charts to setup goal control
limits (Hsin-Hung Wu 2003).
26
Jürgen and Richard (1998) integrated design costs and Quality
Function Deployment (QFD) to optimise product development resources. Ugo
and Paulo (2007) suggested a methodology for the product development
process in an automotive company, aiming at the correct systematic approach
of Value Engineering (VE) and target-costing in cost management.
2.4 REENGINEERING
Reengineering is the fundamental rethinking and radical redesign of
business processes to achieve dramatic improvements in critical,
contemporary measures of performance such as cost, quality, service and
speed (Michael and James 1993).
Process reengineering can be considered to be a combination of
industrial engineering techniques, operations research methods, management
theory and information systems analysis that utilise the power of information
technology to radically change processes of organizations to achieve dramatic
performance improvements in order to compete in the markets within which
they operate (Love and Gunasekaran 1997).
Business process reengineering has been touted as necessary for
dramatic improvement in the competitiveness of the organization and it needs
a rigorous and systematic assessment of the factors needed for the
organization. It requires a cross functional effort and makes radical change in
one or more processes of the organization (Tor 1999).
Peter and Amrik (1999) insist that to be a truly world class
organization, the company needs to work as a team and all the functional
areas of the business need to be properly integrated with each understanding
the importance of the cross functional process. Lyu (1996) integrated two
27
different approaches – kaizen and automation are integrated to reengineer a
manufacturing process and it resulted in 50% improvement in the labour
productivity.
Fromme (1996) expressed that restructuring of production can lead
to a 30% reduction in energy demand. In total, energy savings of 47% of
current demand can be achieved. These savings can be achieved by local
means. Many of these measures are achieved at no cost or with low cost. A
general lack of awareness stemming from traditional thinking and structures,
compounded by a lack of financing possibilities constitute some of the most
important obstacles.
According to many investigators, reengineering should focus on
processes and not to be limited to thinking about organizations only
(Subramanian et al 1999). Reengineering is also applied for several areas such
as heat treatment (Zainul 2005), production planning (Erne and Victor 1997),
materials management system (Mohanty and Deshmuk 2001), service
operations (Ram and Jayanth 1998), cultural change in laboratory's design
process (Kane and Robert 1995) and many more.
2.5 SUMMARY, MOTIVATION AND SCOPE OF THIS
RESEARCH WORK
The important points discussed in the area of energy conservation
in compressed air supply system and the area of tools used in literature are
given in the Table 2.2.
28
Table 2.2 Summary of literature review
Sl. No
Points discussed, [Researcher, year]
Recommendations Remarks
1 Delivery Pressure [John (1995), Bill Howe and Bill Scales (1998), Durmus Kaya et al (2002), Dan Howett (2003), Richard (2004), Asfaw (2005)].
Reduction of delivery pressure can reduce the energy consumption.
General methodology to identify the lowest possible delivery pressure and minimum operating pressure bandwidth is hardly available.
2 Air receivers [Werner and Kurt (1975), Meixner and Kobler (1978), NCDENR (2004), Majumdar (2006)]
Air receivers are used to smoothen the fluctuations and its size depends on consumption, compressor output and control strategy.
Focus on the effect of air receiver on energy consumption is found to be rare.
3 Compressor control [John (1995), Wojciech (1996) Bill Howe and Bill Scales (1998), Robert (1999), Gary (1999), Joseph (2002) Chiristina et al (2003)]
Compressor control system affects the performance considerably; maximum possible efficiency cannot be accomplished by a simple controller.
Methods to control the compressors for varying load and uncertain variations in load are found to be rare.
4 Drive systems, VFD [Vern (2000), Elie (2002), Mark (2002), Durmus Kaya et al (2002), Michael (2003), Ibrahim and Engin (2004), Reimund (2005)]
Selection of drive is important. Each drive system is advantageous only under certain conditions.
VFD is advantageous for narrow range of loads.
29
Table 2.1 (Continued)
Sl. No
Points discussed, [Researcher, year]
Recommendations Remarks
5 Managerial approach for energy conservation [Jay Stein (1996), Khemri-Enit and Annabi (1996), John (1998), Hans-Dieter and Eberhard (1998), Felipe and Nicolás (1998), Paresh (1998), Grimaldi et al (2000), George (2001), Peter and Edgar (2001) Asfaw (2005), Gopalakrishnan et al (2005)]
Management approach is required in implementation of energy saving programmes. Benchmarking of energy consumption is needed. Some managers not aware of the energy conservation potentials in compressed air systems.
A comprehensive methodology for implementation of energy conservation efforts in industries hardly exists.
6 Fuzzy logic system [Mamdani and Assilina (1975), Sugeno (1999), Chen et al (2000), Chen et al (2000), Wei and Tapio (2002), Cho and Yi (2004), Liang et al (2004), Srinivasa Rao and Srikant (2004), Ljiljana and Mahroo (2004), Boada et al (2006)]
Fuzzy logic system is suitable for problems with uncertainty. Effectively used in several applications.
Usage of fuzzy logic system for energy conservation in air compressor systems is found to be rare.
7 Target costing (TC) [Yutaka (1993), Takeyuki (1995), Jiigren and Richard (1998),Lisa (2002), Gopalakrishnan et al (2004), Hsin-Hung Wu (2003; 2004), Ugo and Paulo (2007)]
TC is a useful tool to achieve effective cost control. Used for various applications other than cost control of new products.
Application of TC approach for energy conservation in compressed air system is to be attempted
8 Reengineering [Michael and James (1993), Lyu (1996), Love and Gunasekaran (1997), Tor (1999), Peter and Amrik (1999), Mohanty and Deshmuk (2001), Zainul Huda (2005)]
Fundamental rethinking and redesign of existing system. It is applied to several requirements.
Application of RE for energy conservation in compressed air supply system is yet to be applied.
30
From the referred articles the following can be summarised and
based on that the area of this research work is identified.
i) Energy saving is important and good amount of energy can be
saved in air compressors.
ii) Several measures have been suggested by the researchers for
energy conservation in air compressors.
iii) Reduction of operating pressure of air compressors
recommended by the most of the researchers to reduce the
energy consumption. But the methodology to identify the
lowest possible or optimum pressure for a specific industry is
not available in the open literature.
iv) Still in most of the industries, air compressors are run with
high pressure due to various reasons mainly non availability of
methods to estimate the optimum pressure.
v) Variable speed drives fitted to compressor are effective for
certain range of consumption only.
vi) Compressor control also plays a role in energy consumed by
the compressor. Most of the compressed air systems use
load/unload type of regulation for the control of the
compressor.
vii) As the complexity of compressed air system increases, the
solution becomes more complicated.
viii) Energy conservation attempts require a systematic approach
with intelligent tools if the system is complicated.
ix) Energy conservation activities require a change in the
management approach of energy conservation efforts.
31
Keeping the above in consideration, the scope of this research
work has the following objectives:
i) To suggest a suitable method to identify the optimum
operating pressure for air compressors so that it can be
employed by the industries readily to conserve energy
consumed by air compressors. It is done considering different
working conditions, different combinations and variations in
the parameters.
ii) To suitably modify the existing compressor controller so that
it dynamically adjusts the pressure based on the pattern of the
consumption of air.
iii) To study the possibility of optimising pressure bandwidth
using fuzzy based method at various levels of consumption.
iv) To use a target costing and reengineering based approach for
energy conservation in compressors.
Above objectives are attempted individually and the results are
presented in the following chapters.