Electric Lighting Strategies PDF

10. ENERGY EFFECTIVE LIGHTING STRATEGIES 1 0.0 INTRODUCTION The real or total cost of lighting installation includes the capital cost, installation, maintenance and running energy consumption. Analysis of these costs over a number of years shows that the major contributing factor is th...

10. ENERGY EFFECTIVE LIGHTING STRATEGIES 1 0.0 INTRODUCTION The real or total cost of lighting installation includes the capital cost, installation, maintenance and running energy consumption. Analysis of these costs over a number of years shows that the major contributing factor is the energy cost associated with the running of the lights. Proper energy management in both the initial design and the running of the lighting system alters the pattern of cost structure of the various items of the system and also results in improved lighting. Simple payback periods of one to three years are typically achieved. 10.1 HOW IT CAN BE ACHIEVED Lighting installation - The purpose of every lighting installation is to provide the right amount and the right quality of light at the right time for the people to effectively carry out their tasks within the work space. The emphasis on energy saving must not compromise the definite relationship that exists between the lighting and the productivity of the people under the lighting system. The lighting system must enhance sales in a retail environment, it must not create headaches for office workers and it must allow warehouse operators to efficiently identify and pick products. Safety factors must not be compromised. 10.2 LIGHT SOURCE To achieve an energy efficient installation the lighting designer must carefully choose the appropriate light source to give the highest possible lumen per watt output whilst considering the illuminance level, glare requirements and the demands of the task to be illuminated. It is not simply a matter of choosing fluorescent tubes over incandescent, for example. Choosing the most energy efficient type of fluorescent is also important. For example, triphosphor tubes have a 15% higher light output than standard tubes, together with a better depreciation curve. This allows less energy to be consumed over the life of the installation while achieving the same light levels. The modern T5 lamps are very energy efficient light sources. The designer should also ensure that the luminaires chosen not only meet the aesthetic and dimensional requirements of the installation but that they have the highest light output ratio (LOR) suitable for the task and that they also meet all the other lighting requirements, such as glare and spacing to mounting height ratio limitations. Individual tube switching (to provide 0% - 50% - 100% control) should also be considered when choosing luminaires and associated wiring. 10.3 DESIGN The IS:3646 (Pt. II), indicates recommended light levels for certain tasks in offices. The lighting system should be designed so that these levels are maintained throughout the life of the installation with as little excess as possible. Some over-design will always exist. Area and office grid layouts restrict luminaire layouts, whilst higher light levels are evident when the lamps are new. By ensuring that respective tasks are only illuminated to the recommended levels, and proper maintenance is carried out, the minimum amount of luminaires can be installed in the space to be illuminated. In new buildings this will mean cheaper capital costs, cheaper installation costs and lower energy costs. 54 10.4 MAINTENANCE Regular maintenance is an important function in keeping the lighting system operating efficiently and therefore cost effectively. Dirt and dust accumulate on luminaire reflectors and diffusers whilst the lumen output of the lamps decreases with age. Keeping the luminaires clean and reducing the time between lamp changes means a higher maintenance factor when considering the design of the lighting system. A higher maintenance factor consequently results in less luminaires (and energy) to provide the required task illuminance. The maintenance procedures in graph A include cleaning of luminaires and changing lamps every three years. The maintenance procedures in graph B include cleaning of luminaires annually and changing lamps every two years. Less luminaires are therefore needed in situation B to achieve the same minimum illuminance levels. 10.5 AUTOMATIC SWITCHING SYSTEMS One of the most cost-effective measures for lighting energy management is the implementation of appropriate light switching. A proper energy effective switching system comprises many parts, but can lead to substantial energy savings. Some of its components are as discussed below. 10.5.1 Location of switches In commercial office applications, the simple multi-gang switch plate by the door way is the most inefficient switching method used as it leads to every light on the entire floor being switched on even if only one occupant is present on that floor. This is a huge waste of energy. The entrance switch should provide background lighting only, with local switches being strategically located throughout the floor to enable occupants to turn on lights in their own area. Open plan offices should ideally have one light switch within each 100m2 of space whilst individual offices, stores, meeting rooms and so on, should be provided with their own control. 10.5.2 Automatic switching - auto off/manual on Automatic 'on' light switching systems, such as those provided by a building management system should be avoided as it creates considerable wastage to have lights turned on when occupants are not present. On the other hand, it is important that an automatic system be installed to set automatic switching ‘off’ of lights after normal office hours because people simply do not bother to switch lighting off when they leave their workplace. Convenient local switches for after hours over-ride is imperative. 55 10.5.3 Luminaire wiring Lighting designs should allow for variation in tasks, occupancy and light levels. This can be achieved by having individual switching in all luminaires. 10.5.4 Occupancy control of offices There are always offices that are not occupied - staff are away at meetings, visiting clients, or on holidays or sick leave. Occupancy detectors should be installed in these rooms so that/ lighting is only activated when the room is occupied. Detectors should be chosen that has sufficient sensitivity to continuously detect the small hand movements that people make while doing routine office tasks.. As with all switching equipment, detectors should be suitably rated to switch the inductive load of fluorescent fittings by having in built inrush current protection for fluorescent tube start up. 10.5.5 Timer switching Rooms such as stores need lighting only occasionally. Savings arise by providing controls so that lights are turned on manually through a local switch while being turned 'off’ automatically on a time basis by an electronic timer The correct setting of the time delay on these timers is important. 10.5.6 Utilizing daylight Circuit arrangements should allow switching of the outer row of luminaires (or individual tubes in outer luminaires) along perimeter faces of a building to compensate for natural lighting. This switching should be carried out automatically using photocell technology or on a time base. Manual local switching must be provided to allow the user to override the system if so desired. To ensure that sufficient daylight exists for implementation of this type of strategy, daylight linking should be limited to a maximum of approximately 1.5 times the window height. 10.6 BALLASTS Various electronic ballasts can be used for the control of the same lamp or lamp types. It is the responsibility of the designer to select the appropriate ballast to successfully control the lamp and at the same time results in the lowest energy losses. High frequency electronic ballasts are now available in both dimmable and non- dimmable types. A standard non-dimmable HF ballast can increase the light output of a standard tube by up to 10% and reduce the energy consumption of the luminaire as a whole due to the lower ballast losses. HF dimmable ballasts can add further energy savings on top of these already mentioned. The quality of light from a luminaire fitted with HF ballasts is also better than that of its iron core counterpart. Stroboscopic effects, flicker and annoying off/on start ups are almost eliminated. 10.7 DIMMING There are instances where over-design cannot be eliminated for one reason or another. One way of compensating for this is to overlay lighting with a dimming system. The two main energy-saving dimming systems currently available are high frequency electronic dimmable ballasts and wave chopping dimming. Dimming may also be used to compensate for daylight. Careful consideration must be given to blinds on windows, the orientation of the building, individual offices and local over-ride facilities. Energy effective dimming of fluorescent luminaires is relatively new and several possible technical problems must be 56 addressed when selecting dimming equipment. These include power factor correction, harmonic distortion, selection of lamp type and the withdrawal of lamp life warranties with certain wave chopping dimming equipment. 10.8 STRATEGY Some of the important steps for cost-effective energy efficient lighting are Choose the right light source, including luminaire Choose the right number of luminaires and lamps. Implement proper maintenance procedures. Centralised off control with local on/off switches. Install presence detectors Consider daylight control. Consider HF ballasts or dimming. 10.9 SUMMARY The lighting standards of existing installations and the design of new installations should be checked to ensure that most energy efficient lighting system possible is installed or is to be installed The quality and quantity of light must be sufficient in order to meet the requirements of the visual task and to maximise productivity whilst not unnecessarily exceeding standards, Maintenance procedures should be put in place in order to ensure the system continuously operates to maximum efficiency. An energy effective switching system should be installed to allow good house- keeping and to correlate the number of lights which are switched ‘ON’ with the actual people carrying out useful work in the building. Essentially it means that the lights shall be switched off in areas where people are not present. -------------------------------------- 57