Energy saving opportunities
A number of different measures can be adopted to save energy (see Fig. K15).
- 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
- They not only contribute to operational effectiveness by avoiding production downtime, but also avoid the energy losses associated with frequent restarts and the additional work associated with batches of spoiled products.
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.
Energy saving opportunities - Motors
Motors represent 80% of electrical energy consumption in the industry segment
Motorised systems are one of the potential areas where energy savings can be made.
Many solutions exist to improve the energy efficiency of these motorized systems, as described below. You can also refer to the white paper "Energy efficiency of machines: the choice of motorization"
Choice/replacement of the motor
Those wishing to improve passive energy efficiency often consider replacing motors as a starting point, especially if the existing motors are old and require rewinding.
This trend is reinforced by the determination of major countries to stop low-efficiency motor sales in the near future. Based on the IEC60034-30 Standard’s definition of three efficiency classes (IE1, IE2,IE3), many countries have defined a plan to gradually force IE1 and IE2 motor sales to meet IE3 requirements.
In the EU, for example, motors of less than 375 kW have to be IE3-compliant by January 2015 (EC 640/2009).
There are two reasons for replacing an old motor:
- To benefit from the advantages offered by new high-performance motors (see Fig. K16)
Depending on their rated power, high-performance motors can improve operational efficiency by up to 10% compared to standard motors. By comparison, motors which have undergone rewinding see their efficiency reduced by 3% to 4% compared to the original motor.
- To avoid oversizing
- In the past, designers tended to install 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 one-third of motors are clearly oversized and operate at below 50% of their nominal load.
- Oversized motors are more expensive.
- Oversized motors are sometimes less efficient than correctly sized motors: motors are at their most effective working point when operating between 30% and 100% of rated load and are built to sustain short periods at 120% of their rated load.
- Efficiency declines rapidly when loads are below 30%.
- The power factor drops drastically when the motor does not work at full load, which can lead to charges being levied for reactive power.
Knowing that energy costs account for over 97% of the lifecycle costs of a motor, investing in a more expensive but more efficient motor can quickly be very profitable.
However, before deciding whether to replace a motor, it is essential:
- to take the motor’s remaining life cycle into consideration.
- to remember that the expense of replacing a motor even if it is clearly oversized, may not be justified if its load is very small or if it is only used infrequently (e.g. less than 800 hours per year see Fig. K17).
- to ensure that the new motor’s critical performance characteristics (such as speed)are equivalent to those of the existing motor.
Operation of the motor
Savings can be made by:
- Replacing an oversized old motor with an appropriate high-efficiency motor
- Operating the motor cleverly
- Choosing an appropriate motor starter/controller
Other approaches are also possible to improve the energy efficiency of motors:
- 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 in drive chains, starting with those on the larger motors, which may affect the 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%.
Control of the motor
The method for starting/controlling a motor should always be based on a system-level analysis, considering several factors such as variable speed requirements, overall efficiency and cost, mechanical constraints, reliability, etc.
To ensure the best overall energy efficiency, the motor’s control system must be chosen carefully, depending on the motor’s application:
- For a constant speed application, motor starters provide cheap, low-energyconsumption solutions. Three kinds of starters can be used, depending on the system’s constraints:
- Direct on line starter (contactor)
- Star Delta starter: to limit the inrush current, provided that the load allows a starting torque of 1/3 of nominal torque
- Soft starter: when Star Delta starter is not suitable to perform a limited inrush current function and if soft braking is needed.
Example of constant speed applications: ventilation, water storage pumps, waste water treatment stirring units, conveyors, etc.
- When the application requires varying the speed, a Variable Speed Drive (VSD) provides a very efficient active solution as it adapts the speed of the motor to limit energy consumption.
- It competes favourably with conventional mechanical solutions (valves, dampers and throttles, etc.), used especially in pumps and fans, where their operating principle causes energy to be lost by blocking ducts while motors are operating at full speed.
- VSDs also offer improved control as well as reduced noise, transient effects and vibration. Further advantages can be obtained by using these VSDs in conjunction with control devices tailored to meet individual requirements.
- As VSDs are costly devices which generate additional energy losses and can be a source of electrical disturbances, their usage should be limited to applications that intrinsically require variable speed or fine control functions.
- Example of variable speed applications: hoisting, positioning in machine tools, closed-loop control, centrifugal pumping or ventilation (without throttle) or booster pumps, etc.
- To handle loads that change depending on application requirements, starters, VSDs, or a combination of both with an appropriate control strategy (see cascading pumps example Fig. K20) should be considered, in order to provide the most efficient and profitable overall solution.
- Example of applications: HVAC for buildings, goods transport, water supply systems, etc.
- The method for starting/controlling a motor should always be based on a system level analysis, considering several factors such as variable speed requirements, overall efficiency and cost, mechanical constraints, reliability, etc.
Energy saving opportunities - 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 a relatively small 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 or LED technology
More efficient lights may be a possibility, depending on the needs, type and age of the lighting system. For example, new fluorescent lights are available, although ballasts also need to be replaced when lights are changed.
New electronic 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.
However, electronic ballasts do have a number of points of attention compared with magnetic ballasts:
- Their operating frequency (between 20 and 60 kHz) can introduce high frequency conducted and radiated disturbances, which can interfere with power line communication devices for example. Adequate filters must be incorporated.
- The supply current of standard devices is highly distorted, so that typical disturbances linked to harmonics are present, such as neutral current overload. Low harmonic emission devices are now available, which keep harmonic distortion to less than 20 percent of fundamental current, or even 5% for more sensitive facilities (hospitals, sensitive manufacturing environments ...).
The LED technology, introduced only a few years ago, offers significant prospects for progress, especially for smart control. LED are considered as the sustainable alternative solution to achieve energy savings objectives in the lighting sector.
This is the first lighting technology suitable for all fields (residential, service sector buildings, infrastructure ...) providing great energy efficiency and smart management capability.
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.
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. K21). 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.
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. K22).
- 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. K23).
They offer greater flexibility of management and centralised monitoring, and provide more scope for energy savings by enabling lighting controls to be integrated into other systems (e.g. air conditioning). Certain systems enable energy savings of 30%, although efficiency levels will depend on the application involved and this must be chosen with some care.
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.
Energy saving opportunities - 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 Power Factor Correction 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 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 Power harmonics management for further details.
Energy saving opportunities - 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. K24), avoiding peak periods, load scheduling or even generating additional energy on site.
This is also known as "demand response".
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
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.
Energy saving opportunities - Communication and information systems
No Energy Efficiency is possible without communication.
But 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. K25).
However, this cycle of operations requires an effective communication network to be in place.
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.).
- 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).
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.
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.
Concerning data exchange between components connected via a physical transmission link, the Modbus protocol is very widely used. Connection is possible with metering and protection devices in electrical networks. Initially created by Schneider Electric, it is very popular also in the building sector and considered as a standard protocol.
For carrying large amount of data between electrical distribution systems, the latest technology which is now introduced is Ethernet. It is strongly promoted for simplicity and performance. It is the most adapted media for either local display or distant servers.
In practice, electrical data is recorded on industrial Web servers installed in panel boards. 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 principle is well adapted to communicate data associated with promoting energy efficiency. No additional software is needed – a PC with an Internet browser is all that is required. As such, all energy efficiency data is recorded and can be communicated in the usual manner via intranet networks, GSM/GPRS, wifi, etc…
For simplicity and consistency, measurement devices and communication interfaces are advantageously embedded in the distribution panel boards. See Smart Panels.
Remote monitoring and control improve data availability and accessibility, whilst offering greater flexibility in terms of servicing. Fig. K26 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.
Now, Ethernet technology allows easy connection of panel boards to the Internet, with compatibility with the rapidly developing Smart Grid facilities.
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. K27).
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 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.
Level 2 and Level 3 can be used side by side at certain sites.