Discussions about building controls and sensors usually revolve around function, but just as important is how these devices speak to each other.
One class of devices develops its own network as soon as each one determines that a compatible counterpart is nearby, allowing the network to extend like a web across every similar device in the building. Called a wireless mesh network, this phenomenon enables a new dimension of control over building systems with minimal supervision after installation.
How It Works
Wireless mesh networks function like a low-energy version of a Wi-Fi network. Multiple nodes – tiny wireless radio chips embedded in fixtures and sensors – exchange signals with a wired router or access point to determine which actions to take, such as dimming lighting or measuring carbon dioxide. A gateway or bridge then publishes the resulting data to the internet or a local area network (LAN) for remote access.
However, the network’s communication style, or topology, is different from Wi-Fi (see above). Wi-Fi utilizes a star topology with each laptop receiving signals from one central router. If the router malfunctions, the laptops can’t receive signals. The mesh topology, on the other hand, uses a spread of intermediate nodes that relay messages. If a signal traveling from point A to point B encounters a node that isn’t functioning, the network will route the signal along another path so the message isn’t lost.
“You can get information across the network without having to do any external management if there’s a problem,” says Charlie Huizenga, chief scientist, CTO, and cofounder of Adura Technologies, a lighting control system developer.
Virtually any building system that lends itself to sensor-based measurement is a candidate for a mesh network connecting wireless devices, explains Bob Heile, chairman and CEO of the ZigBee Alliance, a nonprofit that develops standards for building control devices. Security and centralized building management especially stand to benefit due to the nature of their requirements.
“In a commercial building, you have a security center with video feeds going into cameras, plus other security elements, and you expect this data to be brought back to a central location,” Heile explains. “The way mesh networks are structured means there’s nothing you have to do to get the data there.”
Customized Control for Your Building
The system’s granular control and ease of use appealed to the owners of San Francisco’s 221 Main, a 17-floor, multi-tenant Class A office tower. The management team was unsatisfied with the wired sensors and scheduled sweeps they previously used. Most of the building was controlled by one circuit, so if anyone remained at work after the scheduled sweep, the lights would go back on in most of the structure.
Using a mesh network of 84 sensors to control 400 fixtures across five suites, the management team implemented occupancy detection, daylight harvesting, demand response, and task tuning to cut energy use by roughly 58% across the participating suites.
The network approach allows the use of a predictive lighting strategy – when the occupancy sensors detect someone entering a suite, they illuminate not only the occupied area, but also the area ahead of the occupant.
The nodes’ ability to interact with each other has also paid off through a synergistic relationship between the occupancy sensors and daylight-detecting photocells. If the occupancy sensor signals that the space is occupied but the photocell determines that daylight is adequate, the light won’t turn on. Conversely, if the photocell detects inadequate daylight and signals the light to turn on but the occupancy sensor doesn’t detect a presence in the space, the light stays off.
This level of control is possible for any building, not just a Class A tower. Knowing your building’s occupancy patterns and tenant needs will make it easier to advise the installer and IT on the optimal presets.
Also know any existing legacy systems inside and out, Huizenga recommends. Some facilities still have functioning control systems that can cause problems when the new wireless control system is installed.
“You might have an old building with relays and circuit breakers that turned off whole floors,” Huizenga explains. “If we put in more fine-grained control but the legacy system is still in place, the system will power down. Understanding what’s in a building is important because it changes over time.”
Janelle Penny ([email protected]) is associate editor of BUILDINGS.