Temperature was controlled via a central panel in the electrical room. If a teacher turned on one override for a zone, he or she might also have turned on 12 or 15 heat pumps. To check temperature and humidity levels after hours, a member of the facility staff would have to drive to the school and go into individual classrooms. Another problem was that the county's infrastructure-improvement budget did not support the construction costs associated with cutting through walls to run new cable and busway.

The goal was to move from an electromechanical control system to a direct-digital-control system that managed the heating, air-conditioning, lighting, and energy use of the entire building. The challenge — install and deploy the new BAS in only three weeks (to work around the summer-school schedule) while minimizing the impact on the existing structure — was significant. The solution? A wireless ASC network.

The school district completed the installation in one week and within its limited budget. Additionally, the number of wall and ceiling penetrations was significantly lower than it would have been with a hard-wired network.

Post-installation checkout revealed that two radios located at the end of a wing had not established robust communications with the rest of the network. A “repeater radio” installed between the two radios corrected the problem immediately.

More efficient control is saving the district money by reducing energy costs. Engineers now can perform remote monitoring of day-cooling set points, night-cooling set points, night-heating data, and numerous other points via the room controllers. Moreover, with the wireless system, the district can add a room controller, move a classroom, or add a water heater without having to run cable; all that it has to do is install a wireless device exactly where it is needed.

As with the assembly plant and hospital, various RF systems and devices — including wireless LANs, security systems, inventory-control systems, microwaves, and cell phones — were in use in the school. However, at no point have there been any interference issues.

FOR BEST RESULTS

When the “RF-friendliness” of an existing facility is unclear, consider an informal site survey. Such a survey might consist of simply powering up a few radios and locating them throughout the facility in a manner approximating their positions in support of a mesh-controller network.

If, during final deployment, a system cannot establish an adequate number of communication links, install additional “repeater radios” in “holes” in the mesh, or reposition existing radios and/or antennas.

ABOUT THE AUTHOR

Jeff Raimo is a product manager focused on the integration of new wireless technologies. He has a bachelor's degree in aerospace engineering and a master's degree in business administration from the University of Illinois.

Wireless-Mesh-Network Primer

In a wireless mesh network, messages are passed from device to device without having to be routed through a central switch point. The network is smart enough to determine the optimal route for messages; if that route is obstructed, the network automatically shifts to the next-most-efficient path.

Once devices are installed and communication is established, a wireless mesh network essentially becomes “invisible” to a building-automation system (BAS) — that is, the BAS does not distinguish between hard-wired and wireless devices; all are recognized as integral components.

Key Considerations

Through evaluation of certain project characteristics, an engineer can determine whether a wireless mesh network is appropriate for his or her application. Key questions include:

• Will wireless devices be in a grid-like arrangement or a long, narrow configuration? A grid-like arrangement is more conducive to mesh topology.

• Will wireless devices be in a dense configuration without radio-frequency (RF) obstructions between them so that each wireless device is within communications range of two or three other wireless devices? Generally, the denser the configuration and the fewer the RF obstructions the better.

• Are other wireless devices used in the facility? If yes, what frequencies are being used? An engineer may want to consult with the information-technology department to determine if a frequency-channel-management plan is in effect.