Energy saving opportunities - Lighting
From Electrical Installation Guide
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).
Fig. K22: 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. 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.