**3. The possibilities for the energy efficiency increase in the CAS**

The establishment of measures for efficient production, preparation and distribution and rational consumption of compressed air is important in order to increase the energy efficiency. By applying the procedures for pneumatic system optimisation, rational consumption, compressed air preparation and appropriate equipment selection, with skilled management and software support, and proper maintenance, it is possible to significantly improve the energy efficiency of CAS. Production and distribution of compressed air is one of the most expensive and least-understood processes in a manufacturing facility. The costs of compressed air are often unknown or hidden within other operation costs.

In the majority of plants only a portion of total produced compressed air is used in an efficient manner. The system's operation depends on characteristics of each element but even more on the design of the entire system. Identification of possibilities for increasing energy efficiency in compressed air systems are very important step in overall optimisation procedure (Šešlija et al., 2009). The following technical measures can improve the functioning of the entire process of a compressed air system with the return of investment of less than 3 years:


#### **3.1. Power drive improvement**

154 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

at least € 8.07 million every year.

ending.

speed drives,

compressors,

• Air leakage elimination,

• Reduction of operation pressure,

energy consumption by about 2.8%. On the other hand, the introduction of frequency regulation would result in the saving of 10% (Wissink, 2007). If this is combined with the potential saving that could be achieved by eliminating air leak in CASs, which is in average 30%, and if this mode of saving is applicable in about 80% of companies (Radgen and Blaustein, 2001), the additional reduction would be 24%. This would result in the potential saving of 36.8% of the total energy consumed by CASs. With the current price, which is regulated by the government, of approximately 0.04 €/kWh (EPS, 2009b), Serbia could save

Energy saving measures should be applied in all developing countries, also as in developed countries, because the process for increasing energy efficiency is continuous and never

The establishment of measures for efficient production, preparation and distribution and rational consumption of compressed air is important in order to increase the energy efficiency. By applying the procedures for pneumatic system optimisation, rational consumption, compressed air preparation and appropriate equipment selection, with skilled management and software support, and proper maintenance, it is possible to significantly improve the energy efficiency of CAS. Production and distribution of compressed air is one of the most expensive and least-understood processes in a manufacturing facility. The costs of

In the majority of plants only a portion of total produced compressed air is used in an efficient manner. The system's operation depends on characteristics of each element but even more on the design of the entire system. Identification of possibilities for increasing energy efficiency in compressed air systems are very important step in overall optimisation procedure (Šešlija et al., 2009). The following technical measures can improve the functioning of the entire process

• Power drive improvement: usage of high efficiency drives and integration of variable

• Improvement in compressor technology, particularly in the segment of multistage

• Improvement of compressed air preparation: reduction of pressure and energy lost in processes of cooling, drying and filtering; optimisation of filtering and drying as a

• Optimal choice of compressor type, as a function of specific needs of end users,

• Application of sophisticated control systems, for compressed air production,

• Overall system design, including the systems with multiple pressure levels,

• Regeneration of the dissipated heat and using it in other functions,

function of consumer needs and temperature conditions,

• Reduction of pressure losses due to friction in the pipeline,

**3. The possibilities for the energy efficiency increase in the CAS** 

compressed air are often unknown or hidden within other operation costs.

of a compressed air system with the return of investment of less than 3 years:

Usage of high efficiency drives increases the energy efficiency. Integration of variable speed drives (VSD) into compressors can lead to energy efficiency improvements with respect to characteristics of the load. Application of high efficiency drives renders the largest savings to new systems, because the chances of users installing high efficiency drives into existing compressor systems, without changing the compressor itself, are rather small. Integration of speed controllers (frequency inverters) into compressed air systems is a very cost effective measure, under the conditions of variable demands, and it is estimated that such systems participate in the industry with 25%. In compressor rooms where several compressors are installed, variable speed drives are integrated into only one machine and are usually coupled with more sophisticated control system for the whole compressor station that powers on and off individual compressors with a constant speed and also varies the speed of one compressor in order to adjust the production of compressed air to instantaneous requirements of consumers.

#### **3.2. The optimal selection of compressor type**

The segment of the market covering power range from 10 to 300 kW is now dominated by rotary screw compressors with oil injection – it is estimated that around 75% of compressors sold in EU belong to this category (Radgen and Blaustein, 2001). Besides, there are other compressor types available that have other advantages within certain exploitation characteristics. In order to make an optimal selection of compressor it is necessary to consider the users' demands. The choice of compressor can greatly influence the energy efficiency of the system, with respect to compressor performance, but also regarding multiple interactions with other elements in the system. The advantages of multiple compressor systems are especially emphasized in production systems with the high workload that operates almost continuously.

#### **3.3. Improvements in compressor technology**

A whole array of efforts is directed towards improving the existing compressor lines but also the development of new types, which are usually customized to different segments of industry. Another aspect of research is concerned with improving production methods such as applying narrower tolerances in order to reduce the leakage within the compressor.

It must be taken into consideration that the laws of thermodynamics limit the further improvements of compressor so that only minor improvements can be made in the area of energy efficiency, while the greatest potentials lie in adequate design of the entire system and procedures for system control and maintenance.

## **3.4. Application of sophisticated control systems for compressed air production**

Increasing the Energy Efficiency in Compressed Air Systems 157

• *Increases product quality*. In some production systems, compressed air enters the end product directly or comes into contact with the end product (for example in food and pharmaceutical industries or electronics). In these cases, poor compressed air quality

The equipment for drying and filtering causes the pressure to drop while dryers often consume electrical energy or partially use compressed air for their operation and regeneration. Because of that, the optimisation of compressed air preparation as a function of the user needs is one of the main sources of energy savings. The possible measures are:

• The dynamical setting of the degree of drying in accordance with external temperature conditions. This is applicable only when the purpose of drying is to keep the air temperature above the dew point in order to prevent the condensation. This measure can be inappropriate if drying is required to fulfil the precisely defined needs of a

• To optimise the degree of particle filtering as well as oil and oil vapour filtering, so it can precisely match the needs of the system. Excessive filtering leads to unnecessary

• Increase the filter capacity. The increase of the number of filters in parallel operation decreases the speed of air and thus reduces pressure loss. This investment can be very

In order to optimise the filtering process it is necessary to (Golubović et al., 2007; Mitrović et

• Define the flows, pressures, temperatures, allowed pressure drops, compatibility and

• Define the types and concentrations of contaminants (particles, water, oil, oil vapours, etc.),

Every aspect of the previous algorithm deserves special attention. When the selection of filter elements is in question, they are generally expected to have a high throughput, large filtration surface, high mechanical resilience, high thermal resistance, high contamination capacity, long operation period between the services, low price and low exploitation costs as well as appropriate certification, the possibility to fulfil quotas, standards and legislature requirements in their area of application. Proper dimensioning of filters is a precondition for energy efficient functioning of pneumatic systems (Golubović et al., 2007). Improperly dimensioned filter can cause either disabling the system from fulfilling its task, or partial usage with higher investment costs. Each filter should be dimensioned in accordance with

• Determine the needed filtration stages for each characteristic location,

waste of energy. This problem is explained in detail in chapter 3.6.1.

leads to decrease in the end product quality.

process with respect to compressed air quality.

cost effective for new as well as for existing systems.

al., 2006; Šešlija, 2002a; Šešlija, 2002b; Šešlija et al., 2008):

• Choose the adequate filter elements for each location, • Choose the housings for each characteristic location.

exploitation conditions and final conditions of filtration.

*3.6.1. Optimisation of filtering process* 

• Identify the possible filter locations,

needs for validation in critical places,

Sophisticated control systems are applied in order to adjust the compressor outlet flow to the requirements of the consumers. They save the energy by optimising the transition between non-loaded working state, loaded working state, and non-operating state of compressor. Sequencers optimise the operation of multiple compressor system and can be combined with applications of variable speed drives. Predictive control uses fuzzy logic and other algorithms to predict the future behaviour of consumers, assuming history of system behaviour. Since the price of control technologies is decreasing and industrial familiarity with its usage is simultaneously increasing, their usage is rapidly expanding and their applications on compressors are rising in the occurrence. This kind of control can be purchased along with new machines but can also be applied onto existing systems.

### **3.5. Regeneration of dissipated heat**

Compressors intrinsically generate heat, which might be used for other functions. The recommendations for its usage depend on the presence of those consumers of thermal energy whose characteristics comply with the amounts of generated heat, whose usage is enabled by adequate equipment (heat exchangers, pipelines, regulators etc.). The price of that equipment should be favourable in comparison with alternative solutions. The design of the heat regeneration system must provide appropriate compressor cooling.

The heat dissipated by the compressor is in most cases too low in temperature, or too limited by its quality to adequately respond to the needs of industry regarding their main processes or heating. The climate and seasonal changes also influence the ratio between investments and yields. Typical application is heating the space close to the location of compressor, when needed. Possibilities for using the compressor recycled energy are:


The cost efficiency of heat regeneration depends on available alternative energy sources. It could be very cost effective, only if it is alternative to electrical energy. However, if natural gas is available, or the process residual heat, the cost efficiency of regenerated heat is much smaller. However, the attention should be placed on renewable energy sources, instead of using fossil fuels.

#### **3.6. Improvements in preparation of compressed air**

Well prepared compressed air has the following purposes:

• *Prevents damaging of the production equipment.* The impurities contained in compressed air can cause malfunction of production equipment that uses it. The appropriate quality of compressed air increases the reliability of equipment that uses it.

• *Increases product quality*. In some production systems, compressed air enters the end product directly or comes into contact with the end product (for example in food and pharmaceutical industries or electronics). In these cases, poor compressed air quality leads to decrease in the end product quality.

The equipment for drying and filtering causes the pressure to drop while dryers often consume electrical energy or partially use compressed air for their operation and regeneration. Because of that, the optimisation of compressed air preparation as a function of the user needs is one of the main sources of energy savings. The possible measures are:


## *3.6.1. Optimisation of filtering process*

156 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

**3.4. Application of sophisticated control systems for compressed air production** 

purchased along with new machines but can also be applied onto existing systems.

of the heat regeneration system must provide appropriate compressor cooling.

Compressors intrinsically generate heat, which might be used for other functions. The recommendations for its usage depend on the presence of those consumers of thermal energy whose characteristics comply with the amounts of generated heat, whose usage is enabled by adequate equipment (heat exchangers, pipelines, regulators etc.). The price of that equipment should be favourable in comparison with alternative solutions. The design

The heat dissipated by the compressor is in most cases too low in temperature, or too limited by its quality to adequately respond to the needs of industry regarding their main processes or heating. The climate and seasonal changes also influence the ratio between investments and yields. Typical application is heating the space close to the location of

• Compressed air preparation (integral dryers with compressor, standard dryer regeneration),

The cost efficiency of heat regeneration depends on available alternative energy sources. It could be very cost effective, only if it is alternative to electrical energy. However, if natural gas is available, or the process residual heat, the cost efficiency of regenerated heat is much smaller. However, the attention should be placed on renewable energy sources, instead of

• *Prevents damaging of the production equipment.* The impurities contained in compressed air can cause malfunction of production equipment that uses it. The appropriate quality

of compressed air increases the reliability of equipment that uses it.

compressor, when needed. Possibilities for using the compressor recycled energy are:

• Use in buildings (water heating and building heating),

**3.6. Improvements in preparation of compressed air** 

Well prepared compressed air has the following purposes:

**3.5. Regeneration of dissipated heat** 

• In processes (heating, drying),

using fossil fuels.

• Boiler preheating (drinking water, boilers).

Sophisticated control systems are applied in order to adjust the compressor outlet flow to the requirements of the consumers. They save the energy by optimising the transition between non-loaded working state, loaded working state, and non-operating state of compressor. Sequencers optimise the operation of multiple compressor system and can be combined with applications of variable speed drives. Predictive control uses fuzzy logic and other algorithms to predict the future behaviour of consumers, assuming history of system behaviour. Since the price of control technologies is decreasing and industrial familiarity with its usage is simultaneously increasing, their usage is rapidly expanding and their applications on compressors are rising in the occurrence. This kind of control can be

> In order to optimise the filtering process it is necessary to (Golubović et al., 2007; Mitrović et al., 2006; Šešlija, 2002a; Šešlija, 2002b; Šešlija et al., 2008):


Every aspect of the previous algorithm deserves special attention. When the selection of filter elements is in question, they are generally expected to have a high throughput, large filtration surface, high mechanical resilience, high thermal resistance, high contamination capacity, long operation period between the services, low price and low exploitation costs as well as appropriate certification, the possibility to fulfil quotas, standards and legislature requirements in their area of application. Proper dimensioning of filters is a precondition for energy efficient functioning of pneumatic systems (Golubović et al., 2007). Improperly dimensioned filter can cause either disabling the system from fulfilling its task, or partial usage with higher investment costs. Each filter should be dimensioned in accordance with exploitation conditions and final conditions of filtration.

It is possible to present general guidelines for the selection of the right filter. However, it is advisable to comply with the filter manufacturer's requirements. If the filter manufacturer gave no recommendations, it is recommended to follow the general guidelines listed in table 1.

Increasing the Energy Efficiency in Compressed Air Systems 159

**Figure 1.** Wireless filter monitoring system

**3.7. Designing the overall system** 

The goal of a proper system design is to adjust the pressure, quantity and quality of compressed air to the needs of different users at their points of use. Although this can be a very simple task, complications are possible in cases when different end users have different

• One or multiple pressure levels within a system. Typical systems are designed to deliver the air according to the highest pressure and quality required by an end user. This approach can cause unnecessary expenses of energy if air prepared in such a way is required only by a small portion of consumers. The alternative solutions may be: • To build a system that delivers lower pressure and to install a pressure amplifiers

• To provide and install separate compressor for devices that require higher pressure. • Limitation of the pressure variations. Inadequate control systems may produce large pressure oscillations which in turn consume an excessive amount of energy. When certain consumers have stochastic demand, the solution could be found in installation of an additional reservoir close to those consumers in order to reduce pressure variations.

Pressure loses in compressed air distribution network mostly depend on several factors: topology (ring or network, etc.), geometry (pipeline diameter, curvature radius), materials used, etc. The proper designing and realisation of distribution network can optimise the friction loses. Regardless of the importance of a network, a majority of the existing

• During the period of factory construction, the compressed air distribution network is often designed and installed by the companies that perform all other fluid related installation works. These companies are often poorly qualified for designing and

• Under-dimensioned pipelines are occurring very often. Even the systems that were initially well designed, become the "energy devourers" if the compressed air consumption is constantly increased and exceeds the level for which the system was initially designed.

compressed air systems has poor distribution networks due to various reasons:

or varying consumption needs. Arising problems in system design are:

for those consumers which require higher pressure.

**3.8. Reduction of pressure loses due to pipeline friction** 

installation of compressed air distribution network.


**Table 1.** General guidelines for the selection of the filter type concerning energy efficiency

The maintenance of all components of the pneumatic system is a precondition for its energy efficient functioning. The malfunctioning of one component in a pneumatic system can generate new pollutants that emerge from component wear and tear (valves, distributor pistons, sealing etc.). In such system filters are subjected to additional load, which is not accounted for in filtration design and their life cycle would be shortened.

If filtering elements are not changed within a predetermined period an increased pressure drop may occur, which directly influences the increase of energy consumption. The basis of proper maintenance of filtering components is to track their operation. For this purpose, it is necessary to increase or optimise the frequency of filter replacements. The maintenance procedures should involve regular filter inspections and, when needed, their replacements. It is advisable to install the filters containing a visible indicator of a condition of filtering element, and numerous systems have been developed for automatic registering and alarming that indicates that the pressure drop has exceeded the allowed value. An especially interesting possibility is the application of wireless technology where a filter is equipped with wireless communication, which receives the pressure drop data from the differential pressure sensors which measures filter contamination and transmits a warning in case excessive contamination has occurred. Equipment maintenance personnel need not, in this case, to check for every individual filter but to carry a wireless receiver which receives the information about contaminated filter.

Wireless filter monitoring system (WFMS) for compressed air filters based on a very low power consumption microcontroller was developed on the Faculty of Technical Sciences in Novi Sad. This system is intended for decreasing of the energy loss due to pressure drop caused by filter clogging. The proposed system consists of two separate units (sensor and base), which constantly monitor the filters, see Fig. 1. WFMS is very easy to install in the existing manufacturing systems. It is simple, low cost, flexible, portable and efficient for production, installation in the existing plant, and use (Ignjatović et al., 2012).

**Figure 1.** Wireless filter monitoring system

**Filter type Removal Max.** Δ**P at operating** 

Regular filters Particles 0,14 - 0,5 No

Coalescent Particles and fluids 0,17 - 0,7 Regular pre-filter

**Table 1.** General guidelines for the selection of the filter type concerning energy efficiency

accounted for in filtration design and their life cycle would be shortened.

receives the information about contaminated filter.

Absorption Fumes and odours 0,0017 - 0,13 Regular and coalescent

Microbiological Biological load 3,0 - 5,3 Regular, coalescent and

The maintenance of all components of the pneumatic system is a precondition for its energy efficient functioning. The malfunctioning of one component in a pneumatic system can generate new pollutants that emerge from component wear and tear (valves, distributor pistons, sealing etc.). In such system filters are subjected to additional load, which is not

If filtering elements are not changed within a predetermined period an increased pressure drop may occur, which directly influences the increase of energy consumption. The basis of proper maintenance of filtering components is to track their operation. For this purpose, it is necessary to increase or optimise the frequency of filter replacements. The maintenance procedures should involve regular filter inspections and, when needed, their replacements. It is advisable to install the filters containing a visible indicator of a condition of filtering element, and numerous systems have been developed for automatic registering and alarming that indicates that the pressure drop has exceeded the allowed value. An especially interesting possibility is the application of wireless technology where a filter is equipped with wireless communication, which receives the pressure drop data from the differential pressure sensors which measures filter contamination and transmits a warning in case excessive contamination has occurred. Equipment maintenance personnel need not, in this case, to check for every individual filter but to carry a wireless receiver which

Wireless filter monitoring system (WFMS) for compressed air filters based on a very low power consumption microcontroller was developed on the Faculty of Technical Sciences in Novi Sad. This system is intended for decreasing of the energy loss due to pressure drop caused by filter clogging. The proposed system consists of two separate units (sensor and base), which constantly monitor the filters, see Fig. 1. WFMS is very easy to install in the existing manufacturing systems. It is simple, low cost, flexible, portable and efficient for

production, installation in the existing plant, and use (Ignjatović et al., 2012).

It is possible to present general guidelines for the selection of the right filter. However, it is advisable to comply with the filter manufacturer's requirements. If the filter manufacturer gave no recommendations, it is recommended to follow the general guidelines listed in table 1.

**pressure of 7 bar Special demands** 

pre-filters

absorption pre-filters

#### **3.7. Designing the overall system**

The goal of a proper system design is to adjust the pressure, quantity and quality of compressed air to the needs of different users at their points of use. Although this can be a very simple task, complications are possible in cases when different end users have different or varying consumption needs. Arising problems in system design are:

	- To build a system that delivers lower pressure and to install a pressure amplifiers for those consumers which require higher pressure.
	- To provide and install separate compressor for devices that require higher pressure.

## **3.8. Reduction of pressure loses due to pipeline friction**

Pressure loses in compressed air distribution network mostly depend on several factors: topology (ring or network, etc.), geometry (pipeline diameter, curvature radius), materials used, etc. The proper designing and realisation of distribution network can optimise the friction loses. Regardless of the importance of a network, a majority of the existing compressed air systems has poor distribution networks due to various reasons:


• The lack of valves for interrupting the compressed air supply to the parts of the system being no longer in use or for machines that are not operated in second or third shift.

Increasing the Energy Efficiency in Compressed Air Systems 161

Removing leakage sources is based on detecting and repairing locations of leakage and removing the root causes that generated leakage within the system. Proper maintenance is of essential importance when fighting leakages and a good program for leakage detection can prevent unexpected failures from happening and reduce downtimes and loses. In many cases leakage is easily detected because large leakages are audible. Small and very small leakages are hard to detect and are hardly audible. In those cases, the elements of the system should be checked by some of the methods for leakage detection. The methods for detection

The most significant of all these methods is an ultrasonic method that utilizes a special detector that is shown on Figure 2. Figure 3 shows the examples of operating the ultrasonic

of compressed air leakage are:

• Ultrasonic detection and

leakage detector.

• Leakage detection via sense of hearing, • Leakage detection via bubble release,

• Infrared leakage detection (Dudić et al., 2012).

**Figure 2.** The ultrasonic detector kit for Ultraprobe 100

**Figure 3.** Examples of utilisation of ultrasonic detector

Since it is difficult and expensive to improve the existing network, proper designing and installation, which encompasses predictions for future system expansions, represent a significant factor for building of a good system.

#### **3.9. Reduction of air leakage**

Reduction of air leakage is probably the most important measure for obtaining energy savings that are applicable to most of the systems. The awareness regarding importance of introducing regular leakage detection programs is on a very low level, partially because these spots are difficult to visualize and partially because they do not cause direct damage. Leakages can lead to requirements for additional increase of compressor capacity and to increased compressor operating time. If pressure within a system drops below minimum level, the devices utilizing compressed air can be less efficient and equipment life cycle can be shortened, and in some cases breakdown of production lines may occur. In typically well maintained plants, leakages range between 2 and 10% of total capacity, but can amount up to 40% in the plants that are not maintained properly. It is considered that leakage can be tolerated while being less than 10% of total production. An active approach that involves permanent leakage detection and appropriate maintenance work can reduce the leakage to this level. The causes of air leakages are: employees' negligence, poor system design and poor system maintenance.

Table 2 can serve as a guideline in evaluating the scope of loses that arise due to leakage. In this example, it is assumed that the price of electrical energy is 0.1 €/kWh (costs of industrial electrical energy in EU average to 0.09 – 0.12 €/kWh) and that system is operated at 8,000 hours/year, while the price of compressed air preparation is 0.02 €/m³.



Proper design and installation of network can eliminate leakage spots to a great extent, for example, with application of contemporary devices for condensate removal without air loss or by specifying high quality fast decomposing junctions. Awareness must be kept towards the fact that leakage continuously increases after the reparation has been made. The leakage is increasing with the same rate, regardless of whether the reparations are executed or not.

Removing leakage sources is based on detecting and repairing locations of leakage and removing the root causes that generated leakage within the system. Proper maintenance is of essential importance when fighting leakages and a good program for leakage detection can prevent unexpected failures from happening and reduce downtimes and loses. In many cases leakage is easily detected because large leakages are audible. Small and very small leakages are hard to detect and are hardly audible. In those cases, the elements of the system should be checked by some of the methods for leakage detection. The methods for detection of compressed air leakage are:


160 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

are: employees' negligence, poor system design and poor system maintenance.

hours/year, while the price of compressed air preparation is 0.02 €/m³.

**diameter Air loss with 600 kPa (6 bar) Production** 

**Table 2.** Costs of compressed air leakages (Lau, 2006)

significant factor for building of a good system.

**3.9. Reduction of air leakage** 

**Orifice** 

• The lack of valves for interrupting the compressed air supply to the parts of the system being no longer in use or for machines that are not operated in second or third shift. Since it is difficult and expensive to improve the existing network, proper designing and installation, which encompasses predictions for future system expansions, represent a

Reduction of air leakage is probably the most important measure for obtaining energy savings that are applicable to most of the systems. The awareness regarding importance of introducing regular leakage detection programs is on a very low level, partially because these spots are difficult to visualize and partially because they do not cause direct damage. Leakages can lead to requirements for additional increase of compressor capacity and to increased compressor operating time. If pressure within a system drops below minimum level, the devices utilizing compressed air can be less efficient and equipment life cycle can be shortened, and in some cases breakdown of production lines may occur. In typically well maintained plants, leakages range between 2 and 10% of total capacity, but can amount up to 40% in the plants that are not maintained properly. It is considered that leakage can be tolerated while being less than 10% of total production. An active approach that involves permanent leakage detection and appropriate maintenance work can reduce the leakage to this level. The causes of air leakages

Table 2 can serve as a guideline in evaluating the scope of loses that arise due to leakage. In this example, it is assumed that the price of electrical energy is 0.1 €/kWh (costs of industrial electrical energy in EU average to 0.09 – 0.12 €/kWh) and that system is operated at 8,000

**€/year Actual size l/min m³/h kW (approx.)** 

1 80 4.8 0.4 320 768 3 670 40 4 3,200 6,432 5 1,857 111 10 8,000 17,827

10 7,850 471 43 34,400 75,360

Proper design and installation of network can eliminate leakage spots to a great extent, for example, with application of contemporary devices for condensate removal without air loss or by specifying high quality fast decomposing junctions. Awareness must be kept towards the fact that leakage continuously increases after the reparation has been made. The leakage is increasing with the same rate, regardless of whether the reparations are executed or not.

**costs €/year**  **Costs of production, preparation and distribution** 

• Infrared leakage detection (Dudić et al., 2012).

The most significant of all these methods is an ultrasonic method that utilizes a special detector that is shown on Figure 2. Figure 3 shows the examples of operating the ultrasonic leakage detector.


**Figure 2.** The ultrasonic detector kit for Ultraprobe 100

**Figure 3.** Examples of utilisation of ultrasonic detector

### **3.10. Reduction of operating pressure**

Higher pressures increase leakage, and thereby the expenses. Usually, an increase of operating pressure is used to compensate for lack of capacity. The actual effect is quite opposite to the desired one. The higher pressure, higher is leakage, while the irregular consumers consume more air, and thus more energy. Each 1 bar of the pressure increase is followed by an increase in electrical energy consumption required to compress the air in a range between 5*%* and 8% (Šešlija et al., 2011).

Increasing the Energy Efficiency in Compressed Air Systems 163

Blowers (customized compressors that produce compressed air in large quantities)

Vacuum pump or application of Venturi method with appropriate, energy efficient

Blower, electrical actuator or pneumatic

Blowers, cups or application of reduced pressure air (installing the pressure regulators

on guns or constructing low-pressure

Electrical tools are more energy efficient although they have lowered torque control possibilities, shorter life time and are not

turned off when cutting object is absent

**Unsuitable application of compressed air Alternative solution**  Control cabinet cooling Ventilating, air conditioning

removal Brushes, blowers, vacuum system

control

cylinder

network)

Air knifes High pressure blowers that are automatically

Fig. 6 shows that nozzles are positioned too high so that higher flow of compressed air is needed to accomplish the task, which means that for product of different heights the nozzle carrier frame height should be adjusted. Finally, it is necessary to set the active control over nozzles that will allow the air to flow based on sensor that signals the presence of a bakery product, in contrary to situation from Fig. 6 where it can be seen that the air is flowing and that no bakery product is present beneath. Other unsuitable uses of compressed air involve unregulated consumers, supplying abandoned equipment or equipment that will not be

*Unregulated consumers -* This covers all places of usage in which compressed air can be directly released by opening a valve, all places where leakages are present, etc. For example, in applications with pneumatic tools, if the pressure regulator is not installed, the tool will use the full network pressure and this pressure might be significantly higher than the level required for its operation (for example, 8 bars instead of 5.5 bar). Furthermore, this kind of pressure increase leads to greater equipment wear, which leads to greater maintenance costs

inherently safe

Cooling, aspiration, agitation, mixing,

Vacuum production by Venturi pipe

Removal of parts from the moving

production line by nozzles

Blower guns

Pneumatic tools

Cleaning of parts and processing residuals

Powdered materials transport (pneumatic

Vibrating the walls of powdered and

used for a prolonged period of time, etc.

and reduction of the equipment life cycle.

transport) Electrical blowers

granulated materials Electrical vibrators

**Table 3.** Unsuitable applications of compressed air and the alternative solutions

packaging blow-out

If the consumers are allowed to independently determine the amount of their need for compressed air, this system will never operate in an efficient manner, because everybody will be misled by the fact that they can obtain the pressure of any desired amount in any desired quantity. Higher air flow and higher pressure impose higher costs. The characteristic situation in which it is possible to solve this problem is one in which there is one or a small number of consumers in a requirement for higher pressure. In this case, it is suggested to install a secondary, smaller, high pressure unit or an appropriate amplifier (pneumatic booster), instead of operating the compressed air system of the whole factory on the higher level of pressure.

## **3.11. Unsuitable applications of compressed air**

Compressed air is extensively misused for applications in which it is not energy efficient, for which better solutions exist or, its implementation is incorrect in the places where its usage is justified. Compressed air is the most expensive form of energy in a plant but its good characteristics, such as simplicity in application, safety of operation and availability in the whole plant area, often lead people to apply it even where more cost effective solutions exist. The users should therefore, always primarily consider the cost effective energy sources before applying the energy of compressed air. Table 3 gives examples of unsuitable usage of compressed air and alternative solutions that should be applied instead.

Figure 4 shows an example of unsuitable application of compressed air. Nozzles are positioned above the line for bakery products in order to clean the product from the powder present and in order to cool it.

The nozzles themselves present an energetically unfavourable solution and an effort should be made to replace it with another solution. In this case, a fan could be used. Furthermore, if usage of nozzles is insisted upon, it's more energy efficient version should be used.

**Figure 4.** Cleaning of bakery products with compressed air (Norgren, 2011)


**Table 3.** Unsuitable applications of compressed air and the alternative solutions

162 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

Higher pressures increase leakage, and thereby the expenses. Usually, an increase of operating pressure is used to compensate for lack of capacity. The actual effect is quite opposite to the desired one. The higher pressure, higher is leakage, while the irregular consumers consume more air, and thus more energy. Each 1 bar of the pressure increase is followed by an increase in electrical energy consumption required to compress the air in a

If the consumers are allowed to independently determine the amount of their need for compressed air, this system will never operate in an efficient manner, because everybody will be misled by the fact that they can obtain the pressure of any desired amount in any desired quantity. Higher air flow and higher pressure impose higher costs. The characteristic situation in which it is possible to solve this problem is one in which there is one or a small number of consumers in a requirement for higher pressure. In this case, it is suggested to install a secondary, smaller, high pressure unit or an appropriate amplifier (pneumatic booster), instead of operating the compressed air system of the whole factory on the higher level of pressure.

Compressed air is extensively misused for applications in which it is not energy efficient, for which better solutions exist or, its implementation is incorrect in the places where its usage is justified. Compressed air is the most expensive form of energy in a plant but its good characteristics, such as simplicity in application, safety of operation and availability in the whole plant area, often lead people to apply it even where more cost effective solutions exist. The users should therefore, always primarily consider the cost effective energy sources before applying the energy of compressed air. Table 3 gives examples of unsuitable usage of

Figure 4 shows an example of unsuitable application of compressed air. Nozzles are positioned above the line for bakery products in order to clean the product from the powder

The nozzles themselves present an energetically unfavourable solution and an effort should be made to replace it with another solution. In this case, a fan could be used. Furthermore, if

usage of nozzles is insisted upon, it's more energy efficient version should be used.

**3.10. Reduction of operating pressure** 

range between 5*%* and 8% (Šešlija et al., 2011).

**3.11. Unsuitable applications of compressed air** 

present and in order to cool it.

compressed air and alternative solutions that should be applied instead.

**Figure 4.** Cleaning of bakery products with compressed air (Norgren, 2011)

Fig. 6 shows that nozzles are positioned too high so that higher flow of compressed air is needed to accomplish the task, which means that for product of different heights the nozzle carrier frame height should be adjusted. Finally, it is necessary to set the active control over nozzles that will allow the air to flow based on sensor that signals the presence of a bakery product, in contrary to situation from Fig. 6 where it can be seen that the air is flowing and that no bakery product is present beneath. Other unsuitable uses of compressed air involve unregulated consumers, supplying abandoned equipment or equipment that will not be used for a prolonged period of time, etc.

*Unregulated consumers -* This covers all places of usage in which compressed air can be directly released by opening a valve, all places where leakages are present, etc. For example, in applications with pneumatic tools, if the pressure regulator is not installed, the tool will use the full network pressure and this pressure might be significantly higher than the level required for its operation (for example, 8 bars instead of 5.5 bar). Furthermore, this kind of pressure increase leads to greater equipment wear, which leads to greater maintenance costs and reduction of the equipment life cycle.

*Abandoned equipment -* From time to time, reconstructions occur in factories that often lead to abandonment of some parts of compressed air equipment leaving the air supply pipeline intact. The airflow going through the pipeline to the abandoned piece of equipment should be interrupted, as close as possible to the air supply source, because it will inevitably generate some leakage and create unnecessary loses.

Increasing the Energy Efficiency in Compressed Air Systems 165

In these way savings of 4.32 l/min, or 0.072 l/s of compressed air are accomplished. If vacuum cups operate for 30 s every minute, 8 h/day, 250 days/year, 259,200 l of compressed air savings could be achieved for a year. This represents the savings for engagement of one group of vacuum cups for manipulating one workpiece on one workplace. The production processes often use a larger number of vacuum cups. Therefore, the amount of compressed

In traditional design of pneumatic control system there were no concerns about energy efficiency. Several approaches are developed for energy efficient control of pneumatic systems. Here we will stress only two: Optimising servo-pneumatic systems using PWM

If servo control is required by means of pneumatic actuator, it is necessary to use proportional valve in order to control pressure in cylinder chambers. Regardless of the type, the proportional valve is the most expensive component of pneumatic servo system (Liu

Instead of proportional valves and servo valves, on/off electromagnetic valves (2/2 or 3/2 way) are being investigated in order to develop cheap pneumatic servo systems. On/off electromagnetic valves take either entirely open or entirely closed position according to electric command. A pneumatic actuator with on/off electromagnetic valves can be

The control of pneumatic actuator by means of PWM enables servo control by on/off electromagnetic valves at significantly lower cost than the cost of the control done by proportional valves. If response rate and positioning accuracy are taken into account, the results obtained by PWM control are approximately the same as the results obtained by

In the case of proportional valve based systems, the fluid flow is continuously varied. In the case of PWM-controlled systems, the valve is entirely open or entirely closed while the control is done by time of keeping the valves in final positions. Thus, the valve delivers discrete quantity of fluid mass whose size depends on control signal. If the frequency of valve opening and closing is much higher than boundary frequency of the system, the system responds to mean value of discrete flow which is the case of continuous flow, too. With

controlled by Pulse Width Modulation (PWM) (Barth et al., 2003; Shen et all., 2004).

air that could be saved is significantly higher (Ignjatović et al., 2011).

**Figure 6.** Vacuum level at operating pressure of 6 bar (left) and 5.4 bar (right)

**3.13. Optimising the control system at the point of use** 

*3.13.1. Optimising servo-pneumatic systems using PWM* 

and Recycling of used compressed air.

and Bobrow, 1988; Lai et al., 1990).

proportional control.

## **3.12. Optimisation of devices that consume compressed air**

Many devices that consume compressed air can be used in a more energy efficient manner. The optimisation of devices that consume compressed air is one aspect of systemic approach (Šešlija, 2003) to designing a compressed air system. The optimisation can be achieved by: replacing the existing components with more energy efficient ones; installing the additional elements, and better use of existing components.

For example, in the case of applying a vacuum generator, the savings in the compressed air are realised by using more energy efficient components, which have an integrated vacuum switch with an air saving function - example is Air saving circuit (Festo, 2011). The vacuum range is set on the vacuum switch. The switch generates a pulsating signal which actuates the solenoid valves for vacuum when the vacuum pressure has fallen below the selected upper limit value (due to leakage etc.). At all other times, the vacuum is maintained with the non-return valve, even when the vacuum generator is not switched on. Fig. 5 presents the operational diagram for vacuum pump and vacuum generator with implemented Air saving function. Since the price of vacuum produced in this way is too high and vacuum suction elements represent significant consumers of compressed air, this option contributes to the increase of energy efficiency of the system. The savings are proportional to participation of time Δt, shown in Fig. 5, within a total time of holding the working object. This solution is especially suitable for application in which time of holding an object significantly participates in the total cycle of material handling.

Using contemporary engineering tools for supporting the design of vacuum applications, it can be analysed the change of system parameters or parameters of devices that are installed in the system. For example, by using the FESTO vacuum engineering module, for manipulation of an object with a cylindrical shape whose dimensions are: diameter of 150 mm, height of 40 mm and weight of 200 g, a total of 6 vacuum cups are needed. The change of operation pressure enables the usage of highest vacuum level. Air consumption, in the case of 6 bar pressure (see Fig. 6 left) is 27.60 l/min, while with the pressure of 5.4 bar (see Fig. 6 right) is 23.28 l/min.

**Figure 5.** Operation of vacuum pump and vacuum generator with implemented Air saving function

In these way savings of 4.32 l/min, or 0.072 l/s of compressed air are accomplished. If vacuum cups operate for 30 s every minute, 8 h/day, 250 days/year, 259,200 l of compressed air savings could be achieved for a year. This represents the savings for engagement of one group of vacuum cups for manipulating one workpiece on one workplace. The production processes often use a larger number of vacuum cups. Therefore, the amount of compressed air that could be saved is significantly higher (Ignjatović et al., 2011).


**Figure 6.** Vacuum level at operating pressure of 6 bar (left) and 5.4 bar (right)
