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Central battery systems for emergency lighting

Feb 15, 2006
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Self-contained 8W emergency luminaires are a popular choice for emergency-lighting installations, but central battery systems can offer a number of significant advantages, especially in medium-to-large projects. Peter Cook takes a closer look at the technology.

All emergency lighting systems are designed to achieve the same three basic objectives in the event of a mains power failure: to provide clear indication of the escape routes, to provide illumination along those routes enabling safe movement through the exits, and to ensure that essential safety items such as first-aid points and fire-alarm and fire-fighting equipment can be readily located.

That being said, there are different ways of achieving those objectives, and the type of emergency lighting system chosen will be affected by the size and function of the premises, economic factors, operational requirements and aesthetic considerations.

Self-contained luminaires

Self-contained emergency luminaires generally provide the simplest and quickest solution as they contain their own batteries and operate independently. They are easy to install, easy to extend or alter at a later date, and are usually the most cost-effective solution for small-to-medium projects.

Normally using 8W fluorescent lamps as their light source, the luminaires automatically monitor the local lighting circuit, charging the battery when the mains is healthy and running the lamp from the battery in an emergency. However, due to the physical constraints of the luminaires, relatively small batteries have to be used, which means that only a limited amount of energy can be stored. Consequently, the typical light output from self-contained luminaires is between 70 and 200 lumens, which makes them suitable for escape routes through corridors and open areas with low ceilings.

In addition, the optical design of the luminaires’ diffusers varies, so there are considerable differences in the spacings that can be achieved. Some provide a spacing of over 11m, while others will only cover 5m. Of course, luminaire spacing not only determines the number of fittings needed but also the installation costs.

Another disadvantage is that self-contained emergency luminaires have a battery life of only 3-5 years. With battery replacement taking approximately one hour per fitting, this can represent a significant ongoing cost for the building operator.

Central battery systems

From an aesthetics point of view, the self-contained emergency luminaire is often frowned upon by architects and building users, who prefer to see a single type of luminaire utilised for both normal and emergency lighting. Probably the most elegant way of achieving this goal is to select a number of mains luminaires for emergency use and power them from a central battery system.

The output from such systems can be controlled and used exactly like the normal mains supply, so different types of system can be configured to match customers’ requirements. In the case of AC/AC systems, the output can be connected directly to suitably designed mains luminaires so that, without having to make any modification to the luminaires, they operate at full light output under both ‘mains healthy’ and ‘mains failed’ conditions. This enables the emergency lighting system to be extremely unobtrusive and versatile.

Although their prime function is to provide luminaires with power during emergency operation, central battery systems can also be considered as an alternative lighting circuit which, in many cases, makes a valuable contribution to the operation of the building. Maintained outputs can be provided for minimal extra cost, and as the whole circuit can be isolated very simply, control of maintained lights or signs is much easier than with individually switched, self-contained luminaires.

Central battery systems can be used to supply either normal mains luminaires or special low-voltage luminaires. Because many of these systems power the luminaires either at full light output or at levels only slightly lower than the lamps’ nominal rating, they are particularly suitable for use when higher light outputs are required, e.g. open areas and when ceilings are more than 2.5m high.

Slave luminaires operating from AC/DC or AC/AC central systems offer a higher light output and improved spacing characteristics than comparable self-contained versions of the same luminaire. In addition, slave fittings can be sited in hotter or colder environments than self-contained luminaires as there is no temperature-sensitive battery inside the fitting.

Another inherent benefit of central systems is ease of testing and maintenance. Luminaire operation can be checked either manually via the system’s control panel or as part of an automatic testing regime, which is designed to save valuable staff time and ensure that tests are correctly and regularly performed.

Unlike self-contained emergency luminaires, whose ‘system monitoring facilities’ are limited to a single LED charge indicator, central battery systems provide an LCD display with comprehensive alarms, monitors and clearly presented status messages.

Battery life in a central system is maximised by sophisticated charging techniques and is usually at least 10 years. When replacement is eventually necessary, this is a quick and simple operation that avoids the disruption caused by having to dismantle numerous fittings in public areas.

Choosing a system

In determining which is the most suitable emergency lighting system for a particular project, the layout of the building is the most important consideration. Large open areas tend to favour centrally powered systems because existing luminaires can be used to great effect, while the higher cost of wiring each point is nullified by the fact that fewer fittings are needed. Buildings with a combination of different types of spaces, e.g. hotels, also tend to favour central systems – especially if maintained operation is required.

Applications that are mainly corridors with no open areas, e.g. student accommodation, favour the use of 8W self-contained luminaires because their optimised light distribution maximises spacing performance. However, analysis of long-term costs still tends to favour central systems due to the simplicity of battery replacement and reduced energy costs.

Conclusion

Whereas self-contained emergency luminaires have a low initial cost, are simple to install and can be easily added at a later date, central systems are simple to test, simple to maintain, provide completely unobtrusive emergency lighting with high light outputs, and offer long-term cost advantages. The final decision on which type of system to use will depend on the relative priorities attached to these different factors.

Biography

Peter Cook is product marketing manager at Cooper Lighting and Security, with responsibility for product development and marketing of the company’s Menvier and JSB ranges of central battery systems, emergency lighting and fire detection systems. He has over 20 years’ experience with the company.