Energy saving opportunities-

In industrial applications, motors account for 60% of the energy consumed

A number of different measures can be adopted to save energy (seeFig. K7).

Reduce energy use

These measures try to achieve the same results by consuming less (e.g. installing highly energy-efficient lights which provide the same quality of light but consume less energy) or reduce energy consumption by taking care to use no more energy than is strictly necessary (e.g. another method would be to have fewer lights in a room which is too brightly lit).

Save energy

These measures reduce costs per unit rather than reducing the total amount of energy used. For example, day-time activities could be performed at night to in order to take advantage of cheaper rates. Similarly, work could be scheduled to avoid peak hours and demand response programmes.

Energy reliability

As well as contributing to operational efficiency by avoiding lost production, these measures avoid the energy losses associated with frequent restarts and the extra work generated when batches of products go to waste.

Fig. K7: An overall strategy for energy management

Everyone immediately thinks of equipment for transforming energy (motors, lighting/heating devices) when considering areas where savings can be made. Less obvious, perhaps, are the potential savings offered by the various control devices and programmes associated with this type of equipment.

Motors

Motorised systems are one of the potential areas where energy savings can be made.
Those wishing to improve passive energy efficiency often consider replacing motors as a starting point. There are two reasons for this:

To benefit from the advantages offered by new high-performance motors (see. Fig. K8)

Fig. K8: Definition of energy efficiency classes for LV motors established by the European Commission and the European Committee of Manufacturers of Electrical Machines and Power Electronics (CEMEP)

To rectify oversizing

Motors operating for long periods are obvious candidates for replacement by high-performance motors, particularly if these existing motors are old and require rewinding.
Depending on the power they generate, high-performance motors can improve operational efficiency by up to 10% compared to standard motors. Where motors have undergone rewinding, efficiency is reduced by 3% to 4% compared to the original motor.
By contrast, replacement with high-performance motors will not prove to be cost effective if the existing standard-efficiency motor – particularly if it has not undergone rewinding – experiences low or moderate levels of use (e.g. less than 30,000 hours per year). It is also important to ensure that the new motor’s critical performance characteristics (such as speed) are equivalent to those of the existing motor.

As well as being inefficient, oversized motors are more expensive to buy than correctly sized motors. Motors are at their most effective when operating at between 60% and 100% of their nominal load. Efficiency reduces rapidly at loads below 50%. In the past, designers tended to develop oversized motors in order to provide an adequate safety margin and eliminate the risk of failure, even in conditions which were highly unlikely to occur. Studies show that at least a third of motors are clearly oversized and operate at below 50% of their nominal load. The average load for a motor is around 60%.

Larger motors also tend to have lower power factors, which can lead to charges being levied for reactive power. When deciding whether to replace a motor, it is essential to take these factors, as well as the motor’s remaining life cycle, into consideration. It is also important to remember that the expense of replacing an admittedly oversized motor may not be justified if its load is very small or it is only used infrequently.
All things considered, every parameter needs to be taken into account before making a decision on replacing a motor.
Other approaches are also possible, as far as motors are concerned:

Improving active energy efficiency by simply stopping motors when they no longer need to be running. This method may require improvements to be made in terms of automation, training or monitoring, and operator incentives may have to be offered. If an operator is not accountable for energy consumption, he/she may well forget to stop a motor at times when it is not required.
Monitoring and correcting all the components within the drive chains, starting with those on the larger motors capable of affecting overall efficiency. This may involve, for example, aligning shafts or couplings as required. An angular offset of 0.6 mm in a coupling can result in a power loss of as much as 8%.
Paying special attention to pumps and fans, because:

- 63% of the energy used by motors is for fluid propulsion in components such as pumps and fans.
- Flow control often uses valves, dampers and throttles, all of which cause energy to be lost by blocking ducts whilst motors are
operating at full speed.
- Effective project planning can often recoup investments in less than ten months.

Speed variation

Savings can be made by sizing motors correctly and using speed control and/or a variable speed drive

A number of technologies can be used to vary flow or pressure within a system (see Fig. K9). The technology chosen will depend on how the pump and fan have been designed. For example, the pump used may be a displacement or centrifugal pump, and the fan used may be a centrifugal or axial-flow fan.

Fig. K9: Theoretical energy savings based on reducing fan speed by half

Every time a fan or a pump is installed with a view to achieving specific flow or pressure levels, sizing is based on maximum demand. As a result, oversizing is the norm, and the device concerned will not operate efficiently at other speeds. In general, systematic oversizing, combined with the ineffective control methods described above, allows scope for significant energy savings to be made by using control methods aimed at reducing the pump or fan’s supply current during periods of reduced demand.
Systems with fans and pumps are governed by certain correlations:

Flow is proportional to shaft speed, e.g. reducing speed by half reduces flow by the same amount (see Fig. K10).

Fig. K10: Relationship between energy and flow for different methods of fan control (damper, inlet vanes and variable speed)

Pressure or head is proportional to the square of the shaft speed; halving the shaft speed reduces pressure by a quarter.
Energy is proportional to the cube of the shaft speed.

Halving the shaft speed reduces energy consumption by an eighth and, by implication, halving the flow reduces energy consumption by an eighth.
In light of this, energy consumption can be reduced in cases where the fan or the pump does not have to generate 100% of the flow or pressure. The savings involved are significant, even where the flow is only reduced by a small amount
(see Fig. K11). Unfortunately, the efficiency losses incurred by the various components mean that these theoretical values cannot be achieved in practice.

Technology	Disadvantage
Control of stopping and starting	This method is only effective when intermittent flow is acceptable.
Control valve: a valve is used to control flow by increasing frictional resistance at the pump’s outlet.	Energy is wasted, as the flow produced by the pump is subsequently reduced by the action of the valve. In addition, pumps have an optimal operating level and increasing resistance by this method may force the pump to operate at a less efficient level (with additional energy loss) where it may be less reliable.
Bypass device: with this method, the pump turns continuously at full speed and excess fluid at the pump’s outlet is channelled upstream, causing flow to be reduced without the risk of outlet pressure increasing.	The system is very inefficient, as the energy used to pump excess fluid is completely wasted.
Multiple pumps or fans: these configurations support ad hoc increases by activating extra pumps or fans, making control difficult.	There is usually a loss in efficiency, as the actual need is often somewhere between the different speeds available.
Damper: a similar technology to the control valve in systems with a pump, this reduces flow by partly obstructing the fan’s outlet.	Energy is wasted, as the flow generated by the fan is subsequently reduced by the action of the damper.
Overflow valve: a similar technology to the bypass valve in systems with a pump. The fan rotates at full speed continuously and the excess gas flow is evacuated.	The system is very inefficient, as the energy used to propel the air or gas is completely wasted.
Fan with adjustable blades: the flow can be changed by adjusting the blades.	Energy is wasted, as the flow generated by the fan is subsequently reduced by the action of the blades.
Inlet guide blades: fins are used to obstruct or facilitate gas flow inside a fan, thereby determining its efficiency.	The fan does not generate excess flow, but does not operate at maximum efficiency either.

Fig. K11: Examples of technologies which may benefit from using a variable speed drive

Using a variable speed drive (see Fig. K12), as opposed to the technologies
discussed earlier, constitutes an active energy efficiency method and provides the type of variable efficiency required for optimal pump or fan operation.

Fig. K12: Altivar drives with different power ratings

Certain scenarios favour simple solutions:

When changing the dimensions of the pulleys enables fans or pumps to turn at their optimal speed. This solution does not afford the flexibility associated with variable speed drives, but it involves little work and could well be covered by the maintenance budget without the need for any additional investment.
When the fan or pump can operate at full speed continuously without the control features referred to above being installed, or with these control features installed but unused (e.g. with dampers and valves fully opened). Under this arrangement, the device will operate at or near optimum efficiency.

In reality, the potential savings will depend on the model of the fan or pump used, its intrinsic efficiency, the size of the motor, annual operating hours and the cost of electricity locally. These savings can be calculated using special software or can be estimated with some accuracy by installing temporary meters and analysing the data obtained.

Control

Speed regulation: Correctly adjusting energy consumption in line with needs

The previous section showed how pumps and fans can benefit from the use of variable speed drives. Still further advantages can be enjoyed by using these in conjunction with control devices tailored to meet individual requirements.

Control based on fixed pressure and variable flow: this type of control is often used for water distribution systems (drinking water, irrigation). It is also used to circulate fluids in cooling applications.
Control for heating systems: in heating and cooling circuits, flow should vary with temperature.
Control based on fixed flow and variable pressure: mainly associated with pumping applications (pressure differences caused by different levels) such as cleaning, watering, cooling and freezing installations. These require a certain amount of water, even where suction and discharge conditions vary.

The immediate advantages are:

Improved control and greater accuracy in terms of pressure and flow values
Significant reduction of transient effects within the electrical network and of mechanical restrictions affecting systems
Reduced noise and vibrations, as drives support fine speed adjustments, thereby preventing equipment from operating at the resonance frequency for ducts and pipes
Smooth starting and stopping

These in turn bring about further advantages:

Greater reliability and extended service lives for systems
Simpler tubing and pipe systems (by dispensing with dampers, control valves and bypass pipes)
Reduced maintenance

The ultimate goal is to reduce energy consumption and its associated costs.

Lighting

Lighting can account for over 35% of energy consumption in buildings, depending on the types of activities carried out in them. Lighting control is one of the easiest ways to make substantial energy savings for very little investment and is one of the most common energy saving measures.
Lighting systems for commercial buildings are governed by standards, regulations and building codes. Lighting not only needs to be functional, but must also meet occupational health and safety requirements and be fit for purpose.
In many cases office lighting is excessive and there is considerable scope for making passive energy savings. These can be achieved by replacing inefficient luminaires, by replacing obsolete lights with high-performance/low-consumption alternatives and by installing electronic ballasts. These kinds of approach are especially appropriate in areas where lighting is required constantly or for long periods and savings cannot be achieved by simply switching lights off. The time taken to recoup investments varies from case to case, but many projects require a period of around two years.

Lights and electronic ballasts

More efficient lights may be a possibility, depending on the needs, type and age of the lighting system. For example, new fluorescent lights are now available, although ballasts also need to be replaced when lights are changed.
New types of ballast are also available, offering significant energy savings compared to the earlier electromagnetic ballasts. For example, T8 lights with electronic ballasts use between 32% and 40% less electricity than T12 lights fitted with electromagnetic ballasts.
Having said this, electronic ballasts do have a number of disadvantages compared with magnetic ballasts. Their operating frequency (between 20,000 and 60,000 Hz) can introduce harmonic noise or distortion into the electrical network and presents the risk of overheating or reducing the service life of transformers, motors and neutral lines. There is even a danger of overvoltage trips being deactivated and electronic components sustaining damage. However, these problems are mainly restricted to facilities with heavy lighting loads and a large number of electronic ballasts. Most current types of electronic ballast feature passive filtering in order to keep harmonic distortion to less than 20 percent of fundamental current, or even 5% for more sensitive facilities (hospitals, sensitive manufacturing environments, and so on).
Other types of lighting may be more appropriate, depending on the conditions involved. An assessment of lighting needs will focus on evaluating the activities performed and the required levels of illumination and colour rendering. Many existing lighting systems were designed to provide more light than required. Designing a new system to closely fit lighting needs makes it easier to calculate and ultimately achieve savings.
Apart from the issue of savings, and without forgetting the importance of complying with the relevant standards and regulations, there are other advantages associated with retrofitting lighting systems. These include lower maintenance costs, the chance to make adjustments based on needs (office areas, “walk-through” areas etc.), greater visual comfort (by eradicating the frequency beat and flickering typically associated with migraine and eye strain) and improved colour rendering.

Reflectors

A less common passive energy efficiency measure, but one which is worth considering in tandem with the use of lights fitted with ballasts, is to replace the reflectors diverting light to areas where it is needed. Advances in materials and design have resulted in better quality reflectors which can be fitted to existing lights. These reflectors intensify useful light, so that fewer lights may be required in some cases. Energy can be saved without having to compromise on lighting quality.
New, high-performance reflectors offer a spectral efficiency of over 90%
(see Fig. K13). This means:

Two lights can be replaced by a single light, with potential savings of 50% or more in terms of the energy costs associated with lighting.
Existing luminaires can be retrofitted by installing mirror-type reflectors without having to adjust the distance between them. This has the advantage of simplifying the retrofitting process and reducing the work involved, with minimal changes made to the existing ceiling design.

Fig. K13: Illustration of the general operating principle for high-performance reflectors

Lighting control

The passive energy saving measures described above leave further scope for making savings. The aim of lighting control programmes is to give users the required levels of convenience and flexibility, whilst supporting active energy savings and cost reduction by switching lights off as soon as they are no longer needed. There are a number of technologies available with various degrees of sophistication, although the time taken to recoup investments is generally short at six to twelve months. A multitude of different devices are currently available too (see Fig. K14).

Fig. K14: A selection of lighting control devices: timers, light sensors, movement sensors

Timers to turn off lights after a certain period has passed. These are best used in areas where the typical time spent or period of activity is clearly defined (such as corridors).
Occupancy/movement sensors to turn off lights when no movement has been detected for a certain period. These are particularly well suited to areas where the time spent or period of activity cannot be accurately predicted (storerooms, stairwells, etc.).
Photoelectric cells/daylight harvesting sensors to control lights near windows. When sufficient daylight is available, lights are turned off or switched to night-light mode.
Programmable clocks to switch lights on and off at predetermined times (shop fronts, office lights at nights and weekends)
Dimmable lights to provide a low level of illumination (night light) at off-peak periods (e.g. a car park requiring full illumination until midnight, but where lower levels will suffice between midnight and dawn)
Voltage regulators, ballasts or special electronic devices to optimise energy consumption for lights (fluorescent tubes, high-pressure sodium lights, etc.)
Wireless remote control devices for simple and economical retrofitting of existing applications

These various technologies may be combined and can also be used to create a specific effect or atmosphere. For example, programmable lighting panels in meeting areas (for board meetings, presentations, conferences, etc.) have a number of different light settings which can be changed at the flick of a switch.

Centralised lighting management

Some of the lighting control systems currently available, such as those based on the KNX protocol, have the additional advantage of supporting integration into building management systems (see Fig. K15).

Fig. K15: An example of links established using Schneider Electric’s KNX system

If this type of system is to produce results, the design and implementation stage must begin with an audit of energy consumption and a study of the lighting system with a view to devising the best lighting solution and identifying potential reductions in terms of both costs and energy consumption. As far as this kind of technology is concerned, Schneider Electric also has solutions for offices as well as exterior lighting, car parking facilities, parks and landscaped gardens.

Power factor correction and harmonic filtering

If the energy distribution company imposes penalties for reactive power consumption, improving power factor correction is a typically passive energy saving measure. It takes immediate effect after implementation and does not require any changes to procedures or staff behaviour. The investment involved can be recouped in less than a year.

See Chapter L for further details.

Many types of equipment (variable speed drives, electronic ballasts, etc.) and computers generate harmonics within their line supply. The effects produced can sometimes be significant (transient overvoltages causing protection relays to trip, or heat and vibration potentially reducing the efficiency and service life of such equipment as capacitor banks used for power factor correction). Harmonic filtering is another typical passive energy saving measure to consider.

See Chapter M for further details.

Load management

As part of their drive towards synchronizing the consumption and production of electrical energy over the long term, energy distribution companies tailor their rates to encourage consumers to reduce their requirements during peak periods.
A number of different strategies are possible, depending on consumption levels and operating requirements: restricting demand (see Fig. K16), avoiding peak periods, load scheduling or even generating additional energy on site.

Fig. K16: An example of a load-management strategy

Demand restriction

Energy distribution companies can use this solution in supply contracts containing optional or emergency (involving compulsory limits) restrictive clauses whose application is determined by the consumer (based on special rates). This management policy is typically used during the hottest or coldest months of the year when companies and private customers have very high requirements for ventilation, air conditioning and heating, and when electricity consumption exceeds normal demand considerably. Reducing consumption in this way can prove problematic in residential and service sector environments, as they may considerably inconvenience building occupants. Customers from industry may show more of an interest in this type of scheme and could benefit from contracts reducing unit costs by up to 30% if they have a high number of non-essential loads.

Peak demand avoidance

This method involves moving consumption peaks in line with the different rates available. The idea is to reduce bills, even if overall consumption remains the same

Load scheduling

This management strategy is an option for companies able to benefit from lower rates by scheduling consumption for all their processes where time of day is neither important nor critical.

Additional energy generation on site

The use of generating sets to supply energy improves operational flexibility by providing the energy needed to continue normal operations during periods of peak or restricted demand. An automated control system can be configured to manage this energy production in line with needs and the rates applicable at any given time. When energy supplied from outside becomes more expensive than energy generated internally, the control system automatically switches between the two.

Communication and information systems

Information systems

Whether it relates to measurements, operating statuses or rate bases, raw data can only be useful when converted into usable information and distributed on a need-to-know basis to all those involved in energy efficiency with a view to improving the expertise of all participants in the energy management process. Data must also be explained, as people can only develop the management and intervention skills integral to any effective energy saving policy if they fully understand the issues involved. Data distribution must produce actions, and these actions will have to continue if energy efficiency is to be sustained (see Fig. K19).
However, this cycle of operations requires an effective communication network to be in place.

Fig. K17: Operating cycle for data essential to energy efficiency

The information system can then be used on a daily basis by the operators at the various locations where electricity is consumed (for industrial processes, lighting, air conditioning, and so on) to achieve the energy efficiency objectives specified by company management. It can also ensure these same locations make a positive contribution to company operations (in terms of product volumes, conditions for supermarket shoppers, temperatures in cold rooms, etc.).

Monitoring systems

For quick audits which can be performed on an ongoing basis.

Encouraging familiarity with data and distributing it can help keep everything up to date, but electrical networks develop rapidly and are permanently raising questions about their ability to cope with such new developments.
With this in mind, a system for monitoring the transfer and consumption of energy is able to provide all the information needed to carry out a full audit of the site. As well as electricity, this audit would cover water, air, gas and steam.
Measurements, comparative analyses and standardised energy consumption data can be used to determine the efficiency of processes and industrial installations.

For rapid, informed decision making

Suitable action plans can be implemented. These include control and automation systems for lighting and buildings, variable speed drives, process automation, etc.
Recording information on effective equipment use makes it possible to determine accurately the available capacity on the network or a transformer and to establish how and when maintenance work should be performed (ensuring measures are taken neither too soon nor too late).

Communication networks

Information and monitoring systems are synonymous with both intranet and Internet communication networks, with exchanges taking place within computer architectures designed on a user-specific basis.

Intranet

For the most part, data exchange in the industrial sector uses Web technologies permanently installed on the company’s communications network, typically an intranet network for the sole use of the operator.
As far as industrial data exchange between systems connected via a physical transmission link, such as RS485 and modem (GSM, radio, etc.), is concerned, the Modbus protocol is very widely used with metering and protection devices for electrical networks. Initially created by Schneider Electric, this is now a standard protocol.
In practice, electrical data is recorded on industrial Web servers installed in enclosures. The popular TCP/IP standard protocol is used for transmitting this data in order to reduce the ongoing maintenance costs associated with any computer network. This same principle is used by Schneider Electric to communicate data associated with promoting energy efficiency. No additional software is needed – a PC with an Internet browser is all that is required. The fact that enclosures are autonomous removes the need for an additional computer system. As such, all energy efficiency data is recorded and can be communicated in the usual manner via intranet networks, GSM, fixed telephony, etc

Internet

Remote monitoring and control improve data availability and accessibility, whilst offering greater flexibility in terms of servicing. Figure K18 shows a diagram of this type of installation. Connection to a server and a standard Web browser makes it much easier to use data and export it to Microsoft Excel™ spreadsheets for the purpose of tracing power curves in real time.

Fig. K18: Example of an intranet information network protected by a server (EGX400 – Schneider Electric) and monitored from the Internet network

Architectures

Historically and for many years, monitoring and control systems were centralised and based on SCADA automation systems (Supervisory Control And Data Acquisition).
These days, a distinction is made between three architecture levels (see Fig. 19 ).
- Level 1 architecture
Thanks to the new capabilities associated with Web technology, recent times have witnessed the development of a new concept for intelligent equipment. This equipment can be used at a basic level within the range of monitoring systems, offering access to information on electricity throughout the site. Internet access can also be arranged for all services outside the site.

- Level 2 architecture
This system has been specifically designed for electricians and adapted to meet the demands of electrical networks.
This architecture is based on a centralised monitoring system designed to satisfy all the monitoring requirements for the electrical network. As might be expected, installation and maintenance work requires less expertise than for Level 3, since all the electrical distribution devices are already contained in a specialised library. In addition, acquisition costs can be kept to a minimum, as there are few requirements in terms of system integration.
Level 2 and Level 3 can be used side by side at certain sites.
- Level 3 architecture
Investment in this type of system is usually restricted to top-of-the-range facilities consuming large amounts of energy or using equipment which is highly sensitive to variations in energy quality and has high demands in terms of electricity availability. To ensure these high demands for availability are met, the system often requires responsibility to be taken for installation components as soon as the first fault occurs. This should be done in a transparent manner (any impact should be clear). In view of the substantial front-end costs, the expertise required to implement the system correctly and the update costs generated as the network develops, potential investors may be deterred and they may require highly detailed prior analyses to be conducted.

Fig. K19: Layout of a monitoring system

Designing information and monitoring systems

In reality, systems for monitoring and energy control are physically very similar and overlap with the electrical distribution architecture whose layout they often replicate.The arrangements shown in Figure K20 to Figure K24 represent possible examples and reflect the requirements typically associated with the distribution involved (in terms of feeder numbers, the amount and quality of energy required, digital networks, management mode, etc.). They help to visualise and explain all the various services which can be used to promote energy efficiency.

Fig. K20: Monitoring architecture for a small site which only supports sub-metering

Fig. K21: Monitoring and control architecture for a company with several small sites

Fig. K22:Architecture for large multiple-site arrangements

Fig. K23: Monitoring and control architecture for a large, sensitive industrial site

Fig. K24:Architecture for a large service-industry site

In addition, these diagrams make it clear that the choice of components is determined by the choice of architecture (for example, the sensors must be right for the digital bus). The reverse also applies, however, since the initial choice of architecture may be affected by a technological/economic assessment of component installation and the results sought. In fact, the cost (in terms of purchase and installation) of these components, which sometimes have the same name but different characteristics, may vary widely and produce very variable results:

A measuring device can measure one or more parameters with or without using calculations (energy, power, cos ϕ).
Replacing a standard circuit breaker with a circuit breaker containing an electronic control unit can provide a great deal of information on a digital bus (effective and instantaneous measurements of currents, phase-to-neutral and phase-to-phase voltages, imbalances of phase currents and phase-to-phase voltages, frequency, total or phase-specific active and reactive power, etc.).

When designing these systems, therefore, it is very important to define objectives for energy efficiency and be familiar with all the technological solutions, including their respective advantages, disadvantages and any restrictions affecting their application (see Fig. K27).
To cover all the various scenarios, it may be necessary to search through various hardware catalogues or simply consult a manufacturer offering a wide range of electrical distribution equipment and information systems. Certain manufacturers, including Schneider Electric, offer advisory and research services to assist those looking to select and implement all these various pieces of equipment.

	Energy savings	Cost optimisation	Availability and reliability
Variable speed drives	[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]	[math]\displaystyle{ \bullet }[/math]	[math]\displaystyle{ \bullet }[/math]
High-performance motors and transformers	[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]
Supply for MV motors	[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]
Power factor correction	[math]\displaystyle{ \bullet }[/math]	[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]
Harmonics management	[math]\displaystyle{ \bullet }[/math]	[math]\displaystyle{ \bullet\ \bullet }[/math]	[math]\displaystyle{ \bullet }[/math]
Circuit configuration			[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]
Auxiliary generators		[math]\displaystyle{ \bullet\ \bullet }[/math]	[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]
Outage-free supply devices (see page N11)			[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]
Smooth starting	[math]\displaystyle{ \bullet }[/math]	[math]\displaystyle{ \bullet }[/math]	[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]
iMCC		[math]\displaystyle{ \bullet\ \bullet }[/math]	[math]\displaystyle{ \bullet\ \bullet }[/math]
Architecture based on intelligent equipment Level 1	[math]\displaystyle{ \bullet\ \bullet }[/math]	[math]\displaystyle{ \bullet }[/math]
Specialised, centralised architecture for electricians Level 2	[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]	[math]\displaystyle{ \bullet\ \bullet }[/math]	[math]\displaystyle{ \bullet }[/math]
General/conventional, centralised architecture Level 3	[math]\displaystyle{ \bullet }[/math]	[math]\displaystyle{ \bullet\ \bullet }[/math]	[math]\displaystyle{ \bullet\ \bullet\ \bullet }[/math]

Fig. K27: Solutions chart