LED lighting is revolutionising the lighting industry and creating completely new market conditions. However, unlocking its full potential has been hampered by a lack of simple and easy to install industry standard solutions enabling personal control, energy conservation and compliance with increasingly stringent building standards. To fulfil all of these requirements, LED control based on standardised wireless technology is the way forward. By Matthias Kassner, Product Marketing Director, EnOcean
With LEDs replacing old lighting technologies, new control capabilities enable building owners to achieve higher energy efficiency rates and increased comfort. Fulfilling this potential requires selecting a suitable control solution. As the lighting market is still evolving, different standards and architectures exist for lighting control to cover the comprehensive requirements of changing colours, dimming, occupancy-based on/off, demand response or sophisticated daylight harvesting.
Building owners demand reliable systems at reasonable costs, which forces the lighting industry to provide a comprehensive but easy to install control solution. This goes hand in hand with regulations, such as the EU Directive for the Energy Performance of Buildings, which became a vital part of building regulations in a drive for greener buildings. It aims to make energy use in buildings transparent by issuing Energy Performance Certificates (EPC) as well as identifying and developing new opportunities for a reduced carbon footprint.
Besides this, green building certification programmes such as LEED or BREEAM call for integrated control of building areas for the achievement of the maximum number of points. Here, the meaning of lighting control is still significant: 30% of lighting energy consumption is still wasted on average when rooms are not in use.
The limits of wires
One option for installing LED lighting control is a wired system. This is mainly suitable for simple use cases where all lights are connected to the same bus and set to the same light intensity. But wiring complexity grows significantly once the system is required to control a set of lights together. Furthermore, an upgrade from a simple scenario to an advanced control system cannot be implemented without costly changes to the existing wiring and the controller. In addition, it is almost impossible to include sensors, for occupancy detection or daylight harvesting for example, to achieve optimal energy saving rates.
For retrofit projects in particular, the installation of wired controls can be complex, costly and time-consuming. Modernising an existing building with wired control systems requires the addition of dedicated control cabling to each individual lamp. Each element, such as switches, sensors and lights in these systems requires dedicated cabling as well.
An alternative to a wired system is wireless control. It has increased in popularity in the last decade due to advances in radio technology and the emergence of standards which enable seamless communication between different devices. The key advantages of wireless control are the ease of upgrading existing buildings and expanding a system at any time. No new control wiring is required for existing lights; they simply have to be upgraded with wireless control units. Wireless control systems can potentially also provide greater installation flexibility if units within the system do not require dedicated cabling for power.
Several standards already exist for wireless communication in a building automation system. The energy harvesting wireless or so-called EnOcean standard is one of the most established. It is defined by the EnOcean Alliance, a consortium of international companies of the building automation industry. The wireless communication uses the 868 MHz frequency, which delivers a distance of up to 30 metres in buildings and has no interference impacts from local Wi-Fi or Bluetooth devices. RF reliability is assured as wireless signals are less than one millisecond in duration and are transmitted multiple times for redundancy. These characteristics make the standard well suited for wireless lighting control in larger buildings with a few hundred wireless sensor nodes up to several thousands.
Elimination of batteries
The standard is optimised for ultra-low power communication, which allows the use of battery-less, self-powered sensors and switches. For lighting control purposes, the two main energy sources for battery-less, wireless devices are motion and light. Self-powered switches use kinetic energy to generate a wireless signal for controlling and dimming. The second energy source is provided by miniaturised solar cells which harvest ambient light and convert it to electrical energy. This approach is particularly suitable for light level or occupancy sensors. Based on standardised application profiles, energy harvesting wireless devices from different vendors can seamlessly communicate with each other. This approach of open connectivity and interoperability offers the conditions for an integrated LED control.
The energy harvesting wireless standard enables a complete wireless LED control system for retrofit projects. Solutions based on this standard include LED controllers, solar-powered occupancy and light level sensors, kinetic-powered light switches and a remote commissioning software tool. The controller wirelessly communicates using the energy harvesting radio standard at 868 MHz. Via this protocol, it receives wireless telegrams from all linked self-powered wireless switches and sensors and adjusts its outputs accordingly. It provides a switched output for the supply of connected loads as well as a control output to dim connected loads. Multiple fixtures can be daisy-chained, e.g. 20 each 30W fixtures or 10 each 60W fixtures.
This system can support a wireless daylight harvesting application, for example. Daylighting means that the light level is automatically adapted to the amount of available natural light in a room measured by light level sensors. In a typical commercial building, it is possible to save between 20% and 30% of energy with such an automated control system.
The wireless controller supports several usage scenarios. In a very simple configuration only wireless light switches will be connected for manual control of the lights. If desired, it is possible to configure an auto-off timer which turns the lights off after a certain amount of time as is usually used in stairwells. Another basic installation can be implemented by connecting occupancy sensors, which sense motion in a room and send wireless signals to the controller, which controls LED lighting according to occupancy. Both the standard on/off configuration as well as switching between two dimming levels is possible. The latter case is important in applications where a minimum light level must always be maintained. Instead of an on/off configuration, the occupancy sensors’ signals can also be used to set different dimming levels in the range between 100% and 0%.
The combination of occupancy sensors and rocker switches enables the user to manually turn on the light, whereas the occupancy sensors automatically switch off the light after a pre-configured period of time when the room is unoccupied. Light can be automatically turned back on if occupancy is detected. In this scenario, the occupancy sensor can also be used to switch between a high and a low illumination level and the switch can be used to turn lights off completely.
The addition of a light level sensor allows the implementation of daylight harvesting based on open loop control. This means that the light sensor, positioned facing a skylight or window, measures the amount of available natural light and regulates the output light level accordingly. The lighting controller will then only add as much artificial light as needed. In a simple configuration, the system will change between two levels, a minimum and a maximum dimming level, depending on light levels reported by the light level sensor and signals from occupancy sensors and switches. In addition, it is possible to set up a more sophisticated daylight harvesting scenario which supports continuous dimming based on five sampling points which can be defined via remote commissioning software. In both scenarios, illumination will change smoothly by means of adjustable speeds which can be independently configured for manual changes via rocker switches and automatic changes based on sensor signals.
Configuration over the air
More advanced settings, such as thresholds, dimming levels, ramp speeds, or timers can be changed wirelessly via a remote commissioning interface. By employing a Windows-based laptop computer equipped with a remote commissioning tool, an installer can locate wireless devices throughout the facility, logically connect the controller to switches and sensors, and configure settings in the controller over the air, all completely without physical access. It is also possible to link the LED controller via a central unit or a gateway to a supervisory building automation system like BACnet or KNX.
Low installation effort
Thanks to wireless technology, all of these scenarios can be set up quite easily at low installation costs and only require a minimum of maintenance. Therefore, building operators can fulfil regulatory requirements and achieve immediate energy savings and increased comfort with low investments and a fast return on investment (ROI). The wireless sensors and switches can be flexibly and optimally positioned without requiring repair to walls or ceilings. Due to the self-powered operation they even eliminate the need for changing batteries.
The LED controller’s compact size enables flexible installation inside of or next to electrical boxes and fixtures so it can be easily wired out of sight using standard wiring practices. Wireless lighting control also enables a migration path, starting with simple control and expanding the system with advanced functionalities such as scheduling, demand response or remote commissioning later on. As the LEDs can be digitally addressed, they can also communicate with each other and a central control. This enables the building of groups of light, which create optimised scenes in accordance with changing situations.
Wireless standards offer valuable benefits to LED control by following an integrated approach consisting of accessories, software and easy-to-use commissioning tools. At the same time, they combine control functionalities and networking abilities with a consequently standardised communication. The wireless technology allows users to easily install, retrofit, move and commission LED lighting control even in complex systems achieving large scale economies.