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Making Wireless Work
Wireless technology is making its way into building automation systems. While wireless technology has been widely used for such functions as connecting computers and communications, its use to monitor and operate building controls is relatively new, yet rapidly expanding. The development of standards for its use, as well as falling device costs, are increasing the benefits of using the technology for building automation applications by engineering and maintenance managers.
Since the inception of the building automation system, engineering and maintenance managers have been looking for easier and less expensive ways to connect the hundreds or thousands of sensors and control points that make up these systems. Connecting cables to each of these devices has always been expensive, accounting for as much as one-third to one-half of the installation cost of a new system in large facilities.
In some cases, limitations imposed by the design of the building, its historic nature, or changes to its configuration limited the extent to which the systems could be installed. Wireless devices can be placed where maintenance personnel can easily access them for service or for relocation.
Today, the application of wireless technology is helping to reduce installation costs while overcoming many of the obstacles to the traditional, wired system. Wireless offers all of the advantages found in wired systems, such as centralization of controls and data, interoperability, and energy efficiency.
But wireless offers the additional advantage of convenience. System users are no longer tied to a centrally located computer. With a laptop, they can access system information from anywhere. Information concerning the operation, configuration or status of any device located anywhere in the facility can be accessed or changed from anywhere within the system’s operating range.
Just as it was with the development and adoption of a number of standards that led to the widespread use of interoperable building automation systems, standards are driving the growth of the wireless building controls industry.
One that is having a particular high impact is known as ZigBee. ZigBee is a wireless personal-area networking standard that conforms to the IEE wireless standard, 802.15.4-2003. By adhering to the standard, different controls manufacturers can produce modules that are relatively inexpensive and can be easily incorporated into the wireless network.
Each module is about the size of a paper matchbook and includes the radio chip, a microprocessor and the necessary software for the application. By design, each module draws very little power from its internal battery, resulting in years of service before battery replacement is required.
One advantage of ZigBee is its reliability. Most networks operate on a hub format that requires each device to communicate directly with the central equipment. ZigBee uses a mesh format, where each device in the network can communicate with any other device in the network.
If a communications path between two particular devices is interrupted for any reason or if a device fails, the system finds and uses a new path. This ability to establish new communications paths overcomes the two most common problems found in any wireless system: interference and single-point failures.
The mesh network configuration also offers managers another advantage: scalability. In hub systems, the signal must be strong enough to reach the farthest device connected to the system. But in a mesh system, the signal only needs to be strong enough to reach another device. This feature can reliably connect very large networks of up to 65,000 devices. The ability to use lower signal strengths also improves the system’s security by limiting the range that data inadvertently travels outside of a facility.
Managers must carefully consider security when setting up and operating any network. Without solid network security, hackers and others intent on doing harm could gain access to sensitive data or disrupt operations. In a building automation system, unauthorized access to the system also could result in changes being made to system-operating parameters or damage to building systems.
Security requirements for a wireless network are similar to those for a wired network but are more complicated. Wireless signals typically travel well beyond the boundary of the facility, particularly if the signal strength has been set high enough to reach the client at the most distant point within the facility.
As a result, anyone with a laptop computer can access the system, even if they are not physically located within the facility. Unless managers address security issues when developing the wireless network, unauthorized access to the system can result in problems ranging from data theft to endless hours of troubleshooting network problems.
Moving Toward Wireless
One important factor in ensuring system performance after it has been installed is the level of planning that goes into the installation. Radio frequency (RF) propagation within buildings is an essential consideration. RF sources, such as cordless phones, wi-fi hotspots, rotating machinery, computers, and office equipment, can generate high levels of interference.
Similarly, common building materials, such as concrete, electrical wiring, rebar, and building piping systems, can attenuate signals. And since any of these sources of interference or attenuation can increase in number or be relocated, any wireless system must be designed to take them into consideration.
The first step is to survey the building to locate sources of interference and attenuation. By identifying these locations, the system designer will have a better understanding of how many routers are needed, where to locate them, and how to aim the antennas. Planning at this level is particularly important in avoiding performance problems once the network has been installed.
Another critical step in avoiding future problems is planning only future needs. Based on the number of connected points, the system will require a certain minimum bandwidth for performance. That bandwidth might be acceptable today, but it might be insufficient for the future, even the near future.
As managers have seen with nearly every other application of technology in a facility, capabilities installed today identify new possibilities tomorrow, and those possibilities place new demands on the infrastructure being installed today. As a rule of thumb, the network should be designed with the assumption that in the near future it will be required to carry three times the traffic than currently being contemplated.
When Things Go Wrong
One factor that has prevented many engineering and maintenance managers from implementing a wireless system is the belief that tracking down problems in a wireless system is next to impossible. With so many potential sources of interference and the lack of wiring that could be physically traced, managers have shied away from installing the networks.
All networks need troubleshooting, and wireless networks are no exception. But those who have installed the systems have learned that troubleshooting a wireless network is not that much different than troubleshooting a wired one.
Wireless systems do offer some unique challenges, but the troubleshooting techniques are very similar. They start with forming hypotheses about the causes of the problem, then following a testing routine until the cause is identified and can be eliminated.
As with wired systems, technicians should maintain a log of everything that they try in eliminating a problem. This log will help in solving future problems by identifying steps that worked, as well as those that didn’t work. It also will allow personnel to reverse measures if they find that the corrective action makes the overall problems worse.
In general, technicians can start by eliminating user errors. Determine exactly what the user was doing when the problem first appeared.
The law of unintended consequences is alive and well in building networks. Frequently, a seemingly minor change implemented by one user can result in an apparent network error to that user or other users. Identifying and undoing that change often will correct the reported problem.
Next, move on to the network connections. Use a handheld wireless analyzer to confirm the network’s signal is present and strong enough.
Don’t forget security. Even with a well-protected wireless system, opportunities remain for a determined hacker to gain access. Scan the network on a regular basis for known threats.
Managers and front-line technicians have a range of hardware and software tools at their disposal for troubleshooting problems, such as configuration errors, IP address assignments, and signal strength. Some are specific to the type of system installed, while others will work with nearly any wireless system.
All of them can help troubleshoot a misbehaving system. But in the end, it might come down to trial and error. That is where experience and a well-maintained troubleshooting logbook become important tools.
James Piper is a national facilities consultant based in Bowie, Md., with more than 25 years’ experience in facilities management and maintenance.