Lighting control — and beyond
Lighting is the second biggest use of energy in London, making it a prime target for energy-efficient control. Darren Burford takes up the story.
According to a study commissioned by the office of the Mayor of London, lighting accounted for 26% of emissions from the London area commercial and public sectors in 2006 — second only to heating.
In the UK lighting consumes around 58 000 GWh a year, which is about 20% of all electricity generated. Reduced energy consumption and lower carbon emissions are therefore the obvious benefits for any commercial organisation implementing a lighting-control strategy. Effective lighting controls also help to ensure compliance with statutory requirements, including the latest revisions to Part L of the Building Regulations, which have put even more emphasis on reducing carbon emissions.
One of the most effective lighting-control solutions that can be implemented for energy-saving strategies is based around the worldwide KNX open-protocol. Using KNX and DALI (Digital Addressable Lighting Interface) provides one of the best lighting-control offerings in terms of reliability, functionality and simple installation. A correctly designed KNX system integrated to provide a complete solution utilising intelligent KNX presence detectors with constant daylight control combined with DALI dimming technology within modern high-efficiency luminaires can achieve energy savings of around 60%.
The requirements for lighting within a modern building development will vary throughout a working day and at different times of the year, particularly with our current appetite for highly glazed buildings. A typical control strategy for an office would include constant daylight control measuring light reflected from the working area along with room or zoned presence control. KNX detectors are designed as true presence detectors and will out-perform the low-end PIRs that you sometimes have to wave at to get your lights on. A KNX presence detector will also start the ‘room-occupied’ strategy and set fan-coil units to occupied mode or automatically set the blinds to the right position for the angle of sunlight
Maximising the use of daylight is an essential element of a lighting-control strategy. Most organisations do not take natural light into consideration when specifying the lighting for a building. The result is that far too many buildings are over specified in terms of lighting, resulting in unnecessary electrical consumption. Lighting-control systems that consider natural daylight levels can, and should, be specified as part of the building's original specification. They can also be retrofitted to existing installations.
One of the features of KNX/DALI lighting control is that the DALI gateways can be set to a maximum percentage output of the luminaire when energised. This is an excellent way to remove any lighting over-design or margins for light-loss factors. Typically a lighting scheme could run at 80% of the full lamp output and still achieve the design level of illuminance specified by a simple adjustment within the KNX system. As the lighting scheme ages, the maximum percentage output could be raised to increase the light output.
Such digital dimming of lamps can increase the overall life of the lamp; running lamps at 80% of their total output could increase lamp life by as much as 50% (more information is available from manufacturers).
Integrated lighting-control systems also have a number of other benefits such as the contribution they can make to a comfortable working environment. This is an important consideration as it is widely acknowledged that visual comfort is a major contributory factor to a person’s well being and productivity. Automatic window blinds can also form a major part of the overall strategy by controlling glare and as solar irradiation. The automatic control of blinds can reduce internal cooling load by up to 40%. This space control strategy based around the total room solution is in line with the recommendations and guidelines of BS EN 15232 for achieving Class A building performance.
KNX/DALI control for lighting offers real-time monitoring of lighting failures so that immediate action can be taken to counteract both individual problems or to identify developing trends. DALI can provide instantaneous detection of lamp and ballast failure. In the event of a complete failure of the control system, lighting will default to 100%, or other required standby levels.
The KNX/DALI approach to lighting control is suitable for both self-contained and central-battery emergency-lighting systems, offering automated testing and monitoring functions. When connected to one of the many available head-end PC packages or wall-mounted touch-screen options, many hours of labour can be saved compared to the traditional methods of manual testing of emergency lighting.
For the end-user or facilities-management team, KNX can also offer the possibility of energy-management dashboards and other related management tools as part of the integrated-systems approach.
The KNX protocol for intelligent building control is independent from any one manufacturer and is totally interoperable between products from different manufacturers. Only one bus network is required for complete intelligent building control, not just lighting control.
KNX is based on event-driven, distributed-intelligence architecture — so there is no central computer or controller. Each device, such as a light switch, has a micro-controller that can send and receive commands when an event occurs, such as a light being switched on or off.
A 2-core KNX cable is used to link KNX devices using a free topology. Thousands of devices can be linked on the same system. Most devices in a system are powered from the same bus cable (29 V DC).
A vast variety of lighting-control products from many manufacturers is available on the open KNX platform. If a certain product is no longer being available, there will always be an alternative to replace it.
Many manufacturers of KNX products have also developed ‘gateways’ to other control protocols, including DALI, the open protocol supported by all the major lighting manufacturers. With just two wires at the output, the interface has the same functionality as 16 switching/dimming actuators.
Consultants, specifiers and end users looking for an open solution for lighting control are increasing turning to KNX and recognising the drawbacks of proprietary solutions or hardware-based controls.
Darren Burford is a KNX UK board member and managing director of Andromeda Telematics.
