Energy saving opportunities - Lighting
From Electrical Installation Guide
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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.
