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 harnessed 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.
Sensors such as the Omron D6T can resolve temperature changes of as little as 0.15°, and could be used for many other applications. For example, by measuring the floor temperature across the room, they 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 challenge for designers of these circuits are 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. Omron, for example, uses a Silver-Indium-Tin alloy, which is extremely hard, has a high melting point, and exhibits excellent resistance to arcing and welding, making it ideal for high inrush loads. A further advantage is that the alloy is cadmium-free so meets RoHS requirements. Omron’s high inrush current relay G5RL-HR uses these contacts for example, and also has 90% less bounce time than earlier Omron devices, ensuring a clean switching action. AgInSn contacts are naturally resistant to contact welding, but the relay is designed with a rolling/wiping break action to tear any welding that does occur. Using this design, Omron has achieved 40,000 switching operations controlling a 2400W light bulb. A latching version such as the forthcoming G5-RL U/K requires no power when to maintain its on position to provide a further energy saving.
These AgInSn contacts 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 use of LEDs is spreading, driven by legislation as well as energy costs, and with such power saving lamps there is less need for 16A capability. Here, lighting control systems can take advantage of the size-reduction innovations that come with lower power consumption. Compact and slim line relays are especially useful in the switching modules used to control LED lights: 6,5mm devices like the Omron G6D-ASI 5A relay, also using a Silver-Indium-Tin alloy contact, leads to space as well as cost reductions.
Switching noise is a major negative in automatic lighting control circuits – users in a room don’t want to hear a click each time the lights go on or off. The patented silent mechanisms of the 16A low profile G5RL-LN relay can reduce switching noise by more than 10dB, making the sound of releasing the relay all-but inaudible, even in a quiet office.
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. As a result ‘domotics’ control systems present a significant opportunity for the European electronics industry, and one that, using the best available sensor and switching technologies, can be readily addressed.
Figure 1 – to meet the EU Energy Performance in buildings directive, all buildings will require control systems
Figure 2: the architecture of a lighting control system
Figure 3: Omron D16T MEMS IR sensor has a 16x16 array of detectors, allowing it to monitor where in a room the occupant is
Figure 4 – relays like the Omron G5RL family can handle the very high inrush currents associated with energy saving lighting
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