Sensors to detect occupancy and switches to control lighting in response to their output are essential elements of such systems, and considerable strides have been made in their design.
To comply with the Kyoto Protocol, the European Union issued the Directive of Energy Performance of Buildings in 2002, to promote improvement in the energy performance of buildings in the community. Member states had until January 2006 to comply with it.
More recently, Directive 2010/31/EU strengthens the EPBD, introducing specific requirements for the use and measurement of energy in buildings, especially the nearly zero emission buildings. It stipulates that by 31 December 2020 all new buildings are nearly zero energy buildings and that by 31st December 2018 all new buildings occupied and owned by public authorities are nearly zero energy buildings.
Lighting control plays a central part in reducing the energy consumption in a building. To comply with the new EU regulations it will be necessary to have an automated lighting system to save power. Such systems are already having a considerable impact on energy use, providing savings of 50-70% in conference rooms and open plan offices, 40-60% in corridors and 40-60% in warehouse racking aisles. The best lighting control systems integrate HVAC control, allowing the same sensors to manage all of the building’s energy using services.
Lighting system architecture
An automatic lighting system can be broken down into three basic areas: input, communications and control. Inputs into the system are provided by sensors such as human presence detectors and potentially some kind of timing device or control panel that manages for example the delay before the light is turned off after the last person has left the room.
These sensors need a means of communication with the lighting device, which may be overridden by a master wall switch. Finally, the lighting device itself needs to be switched on and off by a control device, which may be a relay terminal. We will focus on the design challenges in two areas: input and control.
Pyroelectric and microwave are the traditional technologies for human detection, but these are passive, only able to detect people in a room while they are moving. The relatively new technology of micro electromechanical systems, MEMS, is being adopted to overcome this drawback.
An infrared MEMS sensor monitors the temperature of a room and by measuring areas that are warmer than the ambient surroundings, it can detect the presence of a person, without relying on movement.
A typical installation involves IR sensor with a matrix array structure, making it possible not only to distinguish an empty room from one that is occupied, but also to gain an indication of where the person is in the room. For example, a ceiling mounted central sensor unit with a 16 x 16 sensor array would be able to cover a 6m x 6m area and locate a person precisely within it.
These sensors have a wide field of view and a fast response, allowing large areas to be covered with a small number of sensors, and even fast moving individuals to be detected and potentially tracked across a building, activating and deactivating services as they relocate.
For example, sensors such as the Omron D6T, which can resolve temperature changes of as little as 0.15°, can measure changes in floor temperature across a room. This can be used to control the heating, ensuring that heat sources are turned on and off to maintain an even temperature across the whole area. They can also be integrated with the security system to sound an alarm and activate cameras when the presence of an individual is detected in an area that should be unoccupied.
In an automatic lighting system, these sensors will be connected to control circuits that actually switch the lighting devices on or off. The major design challenge of these circuits is the very high inrush currents associated in particular with fluorescent and CCFL lamps.
Capacitive loads are even more critical: a capacitor connected in parallel with a lamp driver is a very common circuit configuration, also for LEDs, and the peak of current generated from its discharge can easily exceed 10 to 15 times the rated current.
Designing-in the wrong relay can drastically reduce the life of the whole system. These circuits should be designed to comply with the UL TV standards: TV-5 (78A inrush, 5A break, 25,000 operations) or TV-8 (117A inrush, 8A break, 25,000 operations).
Relay manufacturers are rising to the challenge with innovations such as advanced materials for contacts. For example, silver-indium-tin contacts used by Omron will enable relays, depending on the models, to handle up to 100A inrush current, even for fluorescent or tungsten lamps. A 16A relay is suitable for all types of lamps available in the market, from fluorescent to LEDs, though lower-capacity relays can be specified for some lighting applications.
The buildings sector represents 40% of the European Union’s (EU) total energy consumption. Clearly, to meet its Kyoto Protocol commitments the EU needs to control this area of energy use.
By 2020, we will all be used to the idea that lights and other building services come on automatically as we enter and leave rooms in the workplace and the home.
Fabrizio Petris is global application oriented team manager for building automation at Omron Electronic Components Europe