Emergency lighting normally accounts for 25–30% of the luminaires in a typical commercial project. It is the last line of defence when the mains fail and it is essential to effectively light the space so that building occupants can evacuate safely in an emergency. With that in mind FM managers, building owners and suppliers need to be confident that the emergency lighting functions reliably and consistently in what may be a life-threatening situation.
We can’t escape the fact when self-contained emergency luminaires don’t work, it is most commonly due to failure of the battery. Therein lies the problem – emergency lighting batteries need to be kept charged, a function of the associated electronic inverter. They also need to be periodically tested and rules exist for the mandatory function and duration testing by maintenance personnel. Automated DALI monitoring and testing systems offer the best possibility for management and maintenance, reducing the labour burden and ensuring compliance.
Lithium iron phosphate (LiFePo4) is now seen as the new, preferred option. Not only does it have a high-energy density, low self-discharge and high charge efficiency, it also has none of the toxicity of nickel cadmium (Ni-Cad) cells and out performs nickel metal hydride (Ni-MH) in all applications.
But beware: changing the cell chemistry is not the complete answer. The factors that impact the reliability and mortality of emergency batteries still exist; high temperature, short circuit, overcharging or unmanaged discharge will also damage Lithium iron phosphate batteries and these events will still vary depending on the application, the emergency controls (where used) and the care of the maintenance team.
Currently, few systems incorporate battery management in self-contained lighting products. Standard practice is to accept ad hoc failures as a fact of life and to provision for full replacement every three to four years. Adoption of LiFePo4 delivers benefits such as reduced charging requirements, lower power consumption, greater system efficiency, and a higher energy density and longer lifetime. However, like nickel-based batteries, performance and mortality is impacted by high temperature operation.
Other factors that contribute to failure are aged batteries or where the batteries have been subject to excessive testing. In this case, the battery is prematurely aged resulting in an end-of-life condition and limited or no function. DALI emergency lighting systems can reduce this problem by ensuring batteries are tested according to the standards and will highlight where failures have occurred. Normal maintenance and replacement is then required to replace defective batteries and repeat tests until a complete system is shown to be functional. In any project this can be an ongoing and costly proposition. Thus, monitoring and management of the battery is the only way to ensure maximum viability in an emergency.
The LiFeGuard system ensures a lithium iron phosphate battery is constantly monitored and ready to work when it counts. It does this with three discrete layers of protection. On top of the usual mechanical pressure vent in a battery, a device that allows gases to be expelled from within the cell under any condition they occur, LifeGuard also incorporates a dedicated temperature sensor within the battery pack, allied to a monitoring circuit in the dedicated intelligent inverter. This allows for the monitoring of the following battery conditions:
- Over charge
- Over discharge
- Short circuit
- Over current
Thirdly, LiFeGuard discreetly monitors the battery and acts to switch off charging should the cell temperature reach critical values. Normal charging operation resumes once the cell has cooled and throughout which means discharge in emergency operation is assured.
What lies ahead?
With the increased awareness of the benefits of lithium iron phosphate batteries and forthcoming changes to the standards, it seems inevitable that the application of emergency luminaires with LiFeGuard-type battery monitoring will become the norm in new projects. Tridonic has included this protection in its lithium iron phosphate emergency battery products from inception.
The changes to IEC 61347-2-7 and IEC 60598-2-22 are imminent. They will be published by the International Electrotechnical Commission, an international standards organisation for all electrical, electronic and related technologies, meaning that relevant national and international versions will apply and be required. Building owners and facilities managers wanting to ensure the best for their occupiers will no doubt adopt lithium iron phosphate batteries but perhaps without stipulating the use of a protected battery variant. Who wouldn’t insist on the best protection ahead of a mandatory requirement, particularly when it comes to emergency lighting?
Additionally, Tridonic inverters record critical functional parameters, much the same as an aircraft’s black box device. Therefore, in an automated emergency lighting installation, only the use of Tridonic’s EM converterLED PRO and lithium iron batteries can monitor, manage and protect the battery, record operational factors such as the number of tests or hours of battery operation, to maximise performance and longevity.
So, where do the brakes come into this? In 1978, Mercedes-Benz pioneered the use of Anti-lock brakes (ABS) in passenger vehicles by offering it as an option on their S-class model. In 1984, it became a standard fitment across all their models. Since 2004, regulation has ensured that this technology is mandatory on all passenger vehicles in the UK.
Surely the same needs to happen with monitoring of emergency lighting batteries. As with brakes, there is no space for compromise with emergency lighting – shouldn’t constant battery monitoring be the norm rather than the exception?
For more information, go to www.tridonic.com