Sensor Sensibility: When Going Wireless Pays
A demonstration project is under way at a 70,000-square-foot office building at the Pacific Northwest National Laboratory (PNNL) that could demonstrate how wireless sensing systems can provide a cost advantage over wired systems. The three-story, heavy steel-and-concrete building has been retrofitted with wireless HVAC sensors to measure zone-air temperatures. The sensors feeds temperature data to a chilled-water-reset algorithm and is designed to improve chiller energy efficiency. The project’s goal is to make sensor technology practical for facility operations.
“Generally, there’s a lack of information about building operation because owners are only willing to pay for rudimentary sensing,” says Michael Brambley, a researcher at PNNL who manages the project. “When you have more data available, it leads to better system operation. Our goal is to improve operations and maintenance.” But Brambley says building operators need not equate wireless technology with higher cost. Wireless sensor systems are comprised of three main parts:
- sensors, which include integrated signal conditioners and transmitters
- repeaters, which amplify and send digital signals further
- receivers, which are connected to an intranet, computer or other control network.
Using generic, off-the-shelf technology, Brambley and his colleagues constructed a wireless sensor system for the PNNL office building that cost about $200 per sensor point, including installation. Estimates to retrofit a wired system, including installation labor for wiring and conduits, was a $220 per point for the 30-sensor system. Wireless systems for packaged rooftop HVAC components can be even more cost effective.
“Transmission distances can be further because lines of sight can be preserved on a rooftop,” he says. Brambley’s estimates for a wireless monitoring system for three rooftop units are as low as $163 per point, compared to about $315 per point for a similar wired system.
On the Horizon
Brambley expects that the first users of wireless sensing will be in retrofit projects, in which wired systems would require installing cabling conduits or opening up walls or ceilings to route cabling. Costs for wired sensing can sometimes exceed $1000 per point; in such an environment, wireless systems are currently cost-competitive.
“We’ve also found that once the wireless network is in the building, the facility and operations guys start thinking about other ways they can use the wireless network,” Brambley says. “They want to add more sensors because they don’t cost much.”
Brambley also says that future buildings might have a wired network — like a backbone — to which sensors could be attached.
“We want to bring buildings along to ubiquitous sensing,” he says. “With occupancy sensors that don’t go just to the lights but that also send signals back to the building automation system.”