Lighting Controls
Strategies for Wireless Systems
Minimizing the energy consumption for lighting can only be achieved when the lighting is controlled in an efficient manner. The better this goal is achieved, the greater the energy savings.
Hard wired lighting control systems include occupancy sensing, individual control and daylight-dependent control configured in either open-loop or closed-loop setups. Emerging wireless controls offer similar features and could tap into existing wireless communication networks. Therefore, they have the potential of being implemented in a more cost-effective manner.
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Opportunities and Constraints for Wireless Lighting Control Systems
Lighting controls are the nerve centre of a lighting system. Spectacular technological advances have propelled control applications to a level of practicality and affordability that seemed a distant prospect just a decade ago.
What once was a switch and a dimmer combination is now a pre-programmed lighting control system designed to support multiple work tasks and activities. Centralized building lighting systems integrate daylighting and allow entire building complexes to be controlled on-line from anywhere in the world. Occupancy sensors can be employed more liberally throughout both open plan and private offices to save energy and money.
Wireless control systems may soon replace the conventional, wired systems while offering much greater flexibility and convenience in building installations.
Benefits of Wireless Lighting Controls
Wireless control systems can be applied to a wide variety of building types, both new and existing. The benefits include:
• Ease of installation. With fewer wires to run, installation takes less time, costs less, is less disruptive to ongoing activities, and results in fewer wiring errors. Wireless controls can save as much as 30-40% on installation and material costs compared to a hard-wired control system.
• Reduced maintenance. In a conventional installation, wires and connectors can crack and fail over time.
• Increased flexibility. Because there are no wires to move around, it’s easy to regroup fixtures and relocate sensors and switches as spaces are reconfigured.
• True building integration. The same sensor can easily feed HVAC, lighting and other building systems that incorporate equipment and environment monitoring.
• Scalability. Devices can be easily added to and removed from the system to account for future needs.
• Centralized and decentralized intelligence. Controls can receive commands from a central computer and can also interact with each other independently, increasing responsiveness. Devices can also engage in two-way communication.
• Personal control. Wireless control permits each occupant to control his/her local lighting and temperature [where available].
Wireless Control Options
Wireless control networks do not need dedicated communications wiring. Control devices address their signals using radio-frequency [RF] waves or along existing line-voltage power wiring [power line carrier or PLC]. Today, a new, leading approach to wireless building controls is the “mesh network”.
In a wireless mesh network, multiple nodes [which may be sensors, switches, or other addressable devices] cooperate to relay a message to its destination. Like the Internet, a mesh network offers multiple redundant communication paths throughout the network. If one link fails for any reason [including the introduction of obstructions from construction materials or strong RF interference], the network automatically reroutes messages through alternate paths. It also makes it possible to cover large distances with limited transmitting power because the nodes can hand off data to each other.
Mesh networks are also scalable to larger sizes; one can extend the reach, add redundancy, and improve the general reliability of the network simply by adding more nodes. Another important thing to consider for wireless controls is the bandwidth and the data volume. However, most automated lighting functions in a building [switching, transmitting the information of wireless sensors like photocells and occupancy] only require short-term wireless transmission of small amounts of information. This benefit enables the use of low energy devices for mesh lighting control networks.
Using a frequency band that is less crowded makes for a faster and more reliable mesh network. For example, given that the two major license-free world wireless communications frequencies, 868 [or 900] MHz radio waves [used for building automation] have twice the range of 2.4 GHz signals [used worldwide for PC and IT devices] and double the penetration through materials like walls and furniture. A 2.4 GHz system consequently requires about four times more receiving nodes over its area, so increasing its cost compared to 900 MHz [used in the Americas] or 868 MHz solutions [used in Europe].
Wireless networks are also defined by what communication protocol they use. A protocol provides a common language for control devices, thus enabling communication between control devices from different manufacturers. There are a number of competing protocols which are distinguishable in their topology, maximum number of nodes, range, and bandwidth and power consumption. [See full version of this article for more details.]
One area of concern with these wireless control networks, particularly for the home, is RF interference from other devices such as security cameras and baby monitors that may operate in the same frequency range. Manufacturers are increasingly taking such potential issues into account.
Battery-free Wireless Devices
To date, wireless control systems have experienced some resistance from building owners and operators because of their reliance on batteries as a source of power.
In time, battery-free technology may overcome this resistance. What makes this technology possible is the extremely low energy need and extremely short signal duration. What powers the technology is the energy present in the environment around us [light, vibration, temperature gradients or motion].
The wireless protocol requires only about 0.12 µWs to securely transmit one bit of information over a distance of 300 metres in free space. A battery-less wireless switch consumes about 50 µWs for a complete radio command [100 times less than the more usual, battery-powered wireless switch].
With existing technologies, engineers can now expect transmission distances of up to 30 meters indoors, with signal strengths sufficient to transmit reliably through walls and other structural elements. The battery-less, world-leading supplier is EnOcean GmbH whose products successfully power the network devices by converting the kinetic energy of pushing on a switch, the energy in ambient daylight, or the energy in small temperature differences, to electrical energy.
When the sensors or switches are not transmitting, they revert to an ultralow-energy sleep mode. When signaled, the devices quickly wake up to transmit a burst of data, and then go back to sleep - all in a split-second. The most common applications specified today are solar-powered room temperature sensors and wall-mounted light switches that operate off the energy harvested when somebody pushes them.
The battery-less EnOcean wireless technology has raised the interest of key control manufacturing companies across Europe and North America. To date, some 50 manufacturers [Siemens, Osram Sylvania, Texas Instruments, Echoflex Solutions, etc.] are now forming the EnOcean Alliance and have incorporated the battery-free technologies in over 200 compatible devices. This consortium is a nonprofit, mutual benefit corporation whose purpose is to establish the EnOcean wireless technology as a wireless standard for broad ranges of interoperable wireless products for sustainable buildings.
This arrangement allows designers and contractors to create maintenance-free systems for every building size using many transmitting devices from different manufacturers on the same wireless interface in one radio cell.
BC Hydro Pilot Projects
To verify the performance of wireless control systems, BC Hydro conducted a pilot project in which it installed and monitored systems in a variety of spaces within its own facilities. The spaces included open office cubicles, a meeting room, gym/fitness area and a lunchroom. The lighting control was varied based on the size of the space, the requirement for individual lighting control and daylight availability. This enabled the testing of various combinations of these wireless devices to check the effectiveness of the interaction between them.
The control strategies depended on the space use as well as the location within a building [e.g. daylight access].
The gym has access to daylight via a large window in the front wall. The control system chosen for this area combined the occupancy sensors with a daylight dependent switch. The electric lighting system is divided into two zones [close by the window and far away from the window] to increase the energy-efficiency of this solution. This required two daylight sensors so that the zones could be controlled independently from each other.
In the open office area, the placement of the wireless controls allowed the testing of Individual occupancy sensors. The challenge in the design of this control situation was to select and place the individual sensors so that they did not interfere with each other leading to false ‘ons’ or avoiding switch off in an unoccupied space when an adjacent space was still occupied.
The meeting room serves several purposes which have to be reflected in the control strategy. Besides the occupancy sensor, there was a need to select various scenarios based on the activity in the room. The wireless control system consists of a 360° occupancy sensor as well as a scene selection panel. Scenes can be programmed easily and include a setting for general discussion events as well as presentation using data projection.
The lunchroom had access to daylight via two large windows, with southern and western exposure. The control strategy used the combination of a 360° occupancy sensor and daylight-dependent dimming controls. The space is divided into three zones each of which is controlled individually by a dimming control. The zones are close by the south window, close by the west window, and closer to the core of the building, i.e. the northeastern corner of the space.
More than a year after the installation, all systems are still functional and none has been tampered with. Random interviews with occupants have revealed that they are happy with the control strategies for their spaces and unanimously agree that the wireless control system works as it was predicted. Often the occupants add that it outperforms the system that was in place before the redesign.
All current indicators show that the energy savings will meet the predicted levels of 30% as there was no control system in place prior to the installation. The systems work reliably and show that the wireless solutions are robust enough to be used in a variety of space types. [Note: A second pilot project, in which a wireless system was used to control the lighting for a sports field, is included on the full version of this article at www.sabmagazine.com.]
Summary
Since wireless systems have the potential to revolutionize lighting controls there is considerable interest among large lighting and buildings systems manufacturers to develop such an opportunity, but further research, testing, and demonstrations are needed to overcome security and reliability concerns.
The benefits of wireless control systems easily outweigh those of wired control systems. The system can be commissioned and re-commissioned without major changes in the installation - this is the minimum requirement for a positive cost-benefit analysis relative to wired systems. This technology can be adapted widely if the cost for these systems does not provide a major barrier.
Pilot projects have verified the ease of installation, the simple commissioning process and the proper operation of the control system. In all cases, the system performed to the design intentions and there was only limited need to adjust the initial set-up.
The indoor demonstration project has successfully shown the applicability of the wireless controls for various requirements. The preliminary data shows that an average of 30% energy savings can be achieved if the space is controlled by an occupancy sensor [auto-off, manual on]. Additional savings can be achieved if daylight-dependent lighting controls are added in applicable spaces.
With these benefits, the existing barriers can be overcome and allow for future res-earch and development of wireless sensors for lighting and building automation systems.
For the moment, hardwired and wireless control systems have begun to co-exist complementing each others’ benefits, minimizing risk management and reduce capital and maintenance costs. To date, few luminaire and control manufacturers have developed hybrid integrated lighting systems based on digital ballasts/boards and a combination of hard-wired/wireless transmitters, repeaters, sensors and actuators.
Dr. Alexander Rosemann, P.Eng. is a codes and Standards Specialist, and
Dr. Cristian Suvagau, P.Eng. is a Senior Lighting Engineer – both with BC Hydro.
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