Daylighting sensors and controls

Daylight harvesting is an energy-saving tactic that relies on sensors and lighting controls to optimize natural light through a building’s windows and skylights.

By Joshua Slobin, Daintree Networks, Mountain View, Calif. April 15, 2011

While the core concepts and benefits of daylight harvesting in commercial buildings have been widely discussed, the adoption and success of large-scale daylighting systems have been hindered by technology difficulties and drawbacks. New wireless lighting control technologies are reducing the cost and commissioning complexity of daylighting systems within commercial buildings while helping ensure measurable sustainable energy savings are realized.

This article will focus on the enhanced benefits of wirelessly controlled daylighting, discussing new technology developments, building standards that drive adoption of lighting controls, success factors, and recommendations for proper selection and installation of daylight harvesting systems. Automated control systems that detect daylight levels using photosensors will be explained, with a special focus on systems that use wireless mesh networking to monitor and improve energy usage.

As technological advances enable the adoption of energy-efficiency measures in commercial buildings, it is important to not lose sight of one of the most common-sense ways to minimize electricity usage: using light from the sun. By incorporating automated daylight harvesting, natural light can be used in place of or in conjunction with electric lighting to reduce overall energy load. Through advancements in dimmable luminaires, photosensors, and lighting control software, it is now possible to detect available light from windows and skylights, and automatically dim or brighten electric lights.

Typically, photosensors are equipped with a photoelectric “eye” that measures the illumination in the zone where they are placed, in some cases taking into account variables such as the weather and window coverings. Real-time illumination information is then transmitted to lighting control software, which is programmed with threshold levels. If illumination levels fall outside those thresholds, the software sends a command to dim or brighten the luminaires as required. Throughout any given day, the amount of available natural light in a space will ebb and flow, following a curve. A good daylighting system can use electric light to “fill” that curve, maintaining consistent occupant experience with less electricity consumption.

In addition to reducing energy usage, daylight harvesting systems are increasingly used or even required to meet national and statewide building codes, regulations, and green building standards. ASHRAE/IESNA 90.1, for example, has included evolving requirements for daylighting that have become more stringent with each update, as has California’s Title 24.

While daylighting can yield energy reductions of 10% to 30%, the widespread adoption of large-scale daylighting systems in commercial buildings has been hindered by the cost and complexity of installing lighting components and advanced lighting control systems. This is especially true for older buildings, where retrofit photocell sensor placement may not be possible. However, new lighting control technologies that use the power of wireless networking are reducing these barriers and further enhancing the benefits of daylighting.

Wireless mesh networking applications

Most traditional lighting control systems are fully wired with lights, sensors, and switches hard-wired to a central controller that facilitates communication between the lighting network and lighting control software. Because of the cost of the wiring and the complexity of covering a large area or a variety of areas, traditional systems often operate individually, with one self-contained system per room, rather than allowing each unit to be networked together.

In today’s networking world, it is possible to effectively combine wireless mesh networking with lighting controls, allowing the lights, switches, photocells, and other sensors to communicate with each other without the need for dedicated control wiring. Mesh networks (such as the popular ZigBee protocol and others based on IEEE 802.15.4) enable each lighting device to route messages from other devices, providing multiple paths for network communications. The route between two end devices (such as a photocell sensor and a ballast) can pass through multiple “hops” if necessary, with reliable and quick communication.

In the case of a wirelessly controlled daylight harvesting system, photosensors transmit light intensity information wirelessly to a central controller, which uses a software algorithm to determine the appropriate light level based on a facility manager’s input. The software discovers which lights are in the appropriate daylighting zone (e.g., those located closest to the window or other natural light source). The command is then communicated wirelessly with the fixture’s power source to adjust illumination levels appropriately. Using a wireless mesh network for lighting sensors and controls presents several opportunities for optimizing daylighting capabilities and benefits.

Enhanced daylighting benefits

Levels of natural light fluctuate throughout a building, and photosensors are affected by variables such as orientation, proximity to windows or skylights, and the colors of walls, ceilings, and furnishings. Therefore, achieving the best results in daylighting applications requires a solution with flexible placement based on the room layout, as well as one that allows luminaires to be dimmed in different zones at different times, rates, and levels. Wireless mesh technology enables this flexibility and also yields daylighting systems that are scalable and reliable. Wireless systems can also be more cost effective due to the reduction of some cabling and installation costs associated with wired systems.

Flexible and scalable: Wireless mesh solutions provide flexibility in terms of where switches and sensors can be placed, allow for the simple addition of sensors in the network for more granular information, and also support easier control of larger systems with more devices. For photocell sensors, flexible placement is especially critical, as a change of even a few inches can drastically affect the measured light level.

With a wireless mesh network, lighting controls can be run as a single system that covers an entire building, different sections of buildings, or even multiple buildings. This approach provides a centralized, system-wide view of operations, current power usage, savings, and more, and enables light level targets to be set individually from a single interface for more granular daylighting applications. This also simplifies continuous commissioning (or recommissioning) of the daylighting system. Mesh networks provide self-configuration: when a new device—such as a photosensor, ballast, or fixture—is added, removed, or relocated, the network automatically recognizes what type of device it is and continues to operate without interruption.

Reliable: Another significant benefit of wireless mesh architecture for daylighting is that mesh networks look for the most efficient path between endpoints and automatically re-route messages to avoid failures in case an intermediary device fails for any reason. The built-in redundancy of multiple pathways helps make the mesh network both robust and reliable. The network’s self-configuring and self-healing capabilities improve reliability and help reduce the manual maintenance required—often a major concern in the lifecycle of daylighting systems.

Cost-effective: Eliminating dedicated control wiring can reduce the expense and time involved in installing each device within the network. In retrofit environments, adding new control wiring can cost as much as $2/sq ft (depending on the type of system being added), and a typical 48-ballast control area requires up to 5 miles of dedicated control wiring. A variety of automated commissioning techniques, using existing wiring, location-based sensing, and other methods to create automated association, can make it easier to get the network up and running once it has formed, further reducing installation costs.

Investing in open technology

Wireless communications standards are used to define and structure the messages between devices in a wireless network—telling networks which radio frequencies to monitor, how to read the messages they receive, and how to provide security and reliability.

Wireless networking standards, such as WiFi, Bluetooth, EnOcean, and ZigBee, are aimed at different applications and types of communications. For example, wireless Internet access requires high data rates to enable large amounts of data to be uploaded and downloaded, and is able to accept minor connection delays. The WiFi standard (based on IEEE 802.11) meets these needs as it was designed with high maximum bandwidth and high signal intensity that is resistant to signal interference from outside sources.

On the other hand, daylight harvesting systems transmit relatively simple messages (e.g., light level readings, on/off, and dimming commands) that do not require high data rates yet require a near-instant connection speed to ensure immediacy when a command is given. The ZigBee standard (based on IEEE 802.15.4) was created to address this market need for a cost-effective, standards-based wireless networking solution that supports low data-rates, low power consumption, security, and reliability. Many of the wireless lighting controls solutions being developed today use ZigBee for large-scale systems, or the EnOcean protocol for room-based solutions.

To ensure compatibility and interoperability with current and future technologies and network devices, it is important to consider whether the communications in a lighting control system are based on an open standard that enables interoperability or on a proprietary protocol. Interoperability is especially important in large-scale, mixed-device networks such as wireless lighting systems with daylighting control. As the network grows and adds devices, the use of an open standard ensures seamless connection between switches, ballasts, sensors, etc., from various manufacturers. This provides greater choice and flexibility for the buyer, and results in lower device costs due to the use of standard components.

Additional Information: Success factors and recommendations

Daylight harvesting systems are typically complex and often not well understood. Below are some critical success factors in the installation and use of such systems:

  • Proper commissioning and placement of sensors is often the key to success.
  • As interior spaces change over time, complex systems tend to “fall out” of commissioning. Systems that can automatically recalibrate or perform continuous commissioning can help.
  • Most individual ballasts and sensors will interact differently. It is important to investigate in advance whether the sensors and ballasts chosen will work together, or use a system with an algorithm that can adjust for differences.
  • “Open-loop” and “closed-loop” daylight harvesting systems each have pros and cons; it is important to understand which is more appropriate for a given space prior to installation.
  • Daylighting algorithms differ in how they handle frequent light changes, gradual dimming, and so on. These settings can have a major effect on occupant comfort.
  • As with all energy-efficiency projects, ongoing measurement of energy savings should be used to validate success and find areas for improvement.
  • Another way to measure success (or lack thereof) is the frequency of manual user override, where it is available.

Slobin is director of solutions marketing for Daintree Networks, where he is responsible for developing the company’s industry solutions, ecosystem partnerships, and marketing strategy. In addition to the cleantech industry, he has held leadership roles in wireless technology and enterprise networking, at both startups and established market leaders.