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A Light at the End of the Wireless Tunnel
BACnet-ZigBee for Building Automation has a Bright Future
The good news is that there is light at the end of the wireless tunnel … and the even better news is that I’m pretty sure it’s not a train. The imminent completion of additions to the BACnet and ZigBee specifications allowing integration of the two technologies means we’re close to delivering on the promise of interoperable wireless systems for building automation. And, when we get there I will finally be able to join the mainstream of industry pundits in promoting a bright future for wireless.
For several years, while many people proclaimed the virtues of wireless and predicted its rapid adoption in building automation, I have ruffled more than a few feathers by quietly suggesting that wireless wasn’t quite ready for prime time … not that it wasn’t coming, mind you – just that it wasn’t there yet. On occasion, this position was puzzling to users who could see widespread use of wireless in homes and offices. It was also a bit annoying to suppliers who were selling wireless components and systems. But my reservations about wireless in building automation had nothing to do with wireless technology itself, but only with the lack of an interoperable, standards-based wireless solution that could deliver the value of open systems to users.
Most people understand enough about BACnet, Information Technology, Open Systems in general or the limitations of proprietary systems to appreciate the value of interoperable networks. However, far fewer understand the concept of layered protocols and the need for standards at each layer in order to achieve interoperability. So, when building automation users hear that a wireless system uses ZigBee they are likely to think it’s “standard” and presume it’s interoperable with other (third-party) ZigBee devices. Unfortunately, that’s not the case because the ZigBee specification doesn’t have an application profile for commercial building automation. ZigBee, as used in BAS devices, only specifies the means of transporting data; it does not provide a definition of the data or the transactions that can occur among devices. As such, today’s BAS “ZigBee” products are not generally interoperable. In applications where wireless connectivity is essential or wiring is prohibitively expensive, they can be good solutions. But, they are not the path to a bright wireless future for the BAS industry. Our wireless future must be founded on fully interoperable products and for that we need a set of layered protocols that standardize wireless data transfer as well as data representations and device interactions.
Fortunately, the need for a layered set of protocols is being addressed by a joint technical effort of the ZigBee and BACnet communities. They have been working hard to align the two specifications so that compliant products can be designed that benefit from ZigBee’s low-power, mesh wireless networking technology as well as BACnet’s BAS data model and communications protocol. The result of the work will be a ZigBee Commercial Building Automation application profile and Addendum Q for the BACnet specification. On the BACnet side the work is complete and awaiting final approval for inclusion in the standard. On the ZigBee side the work is largely complete and ready for system prototyping. As this BACnet/ZigBee combination begins to appear in products in 2009, the potential for standard, interoperable wireless will finally be realized.
In my opinion, interoperable BACnet-ZigBee devices will dramatically accelerate wireless adoption. However, that does not mean that every application will suddenly move to wireless. At Teletrol we have been looking at wireless sensor and controller solutions for a long time. We have been (and continue to be) engaged with suppliers of wireless components and devices and we have installed applications using a variety of wireless technologies. Our experience with wireless leads me to believe there are a couple of areas beyond interoperability that could slow wireless adoption, including:
System architecture can make wireless solutions more or less attractive. Wireless is most attractive when all wiring to a device can be eliminated. For example, a battery operated or energy scavenging wireless space sensor is great because it eliminates all need for wiring related to the sensor. However, in the case where a space sensor with wireless communication requires external power the value of wireless is diminished (in that the senor cannot be readily relocated and the task of wiring it is not fully eliminated). In the same way, a wall-mounted RTU controller allows for lower system cost by eliminating the need for a factory-mounted proprietary controller in the RTU, but making the communications for it wireless does not eliminate all of the wiring effort since the controller still needs to be wired to the RTU. (Of course, when RTUs have standard, built-in wireless things will get more interesting.)
Battery-operated wireless devices create a new maintenance task which is objectionable to some users. The long battery life and automatic notification of low-battery status provided by most ZigBee devices certainly helps, but in some applications and for some users, it will still be an issue. And, even where it is not an issue, over the life of the system it will reduce the net savings gained through elimination of wiring.
Installation and Commissioning
As long as all of the wireless devices on the network are working correctly, installation and commissioning is pretty easy. Mount them and flip the switch. However, when it doesn’t “just work,” an electrician or HVAC technician cannot pull out their voltmeter or continuity checker to debug things. There are wireless commissioning tools but not all of them are “field-ready” and most require knowledge and skill that many contractors today lack. This challenge can be mitigated in the short term by over-designing the system (more mesh nodes than should be needed) and adopting a "replace parts until it works" strategy rather than a "debug" strategy. But, these add cost and in the occasional situation where they don’t solve the problem, it may be expensive to get someone to the site who can.
There are some perceived risks involved in wireless systems that may or may not be warranted, but can still be obstacles to adoption. In spite of encryption technology some users are concerned about unauthorized access by someone walking the building or sitting in the parking lot. This is particularly true where the wireless network is in a retail store and inter-connected with the store's IT backbone network. As some users have explained to me, the issue is not that security technology is inadequate, but more that human error (router mis-configuration, trivial passwords, etc) will compromise the security. I have also heard concerns about whether a system that works today will still work when someone builds a cell tower (or WiMAX node) next door.
A Bright Future
Even with these all of these issues still on the table, users with urgent needs or pioneering spirits are implementing wireless now. As the BACnet and ZigBee communities complete their work and introduce interoperable wireless for BAS, many more users will move forward with implementations. The remaining issues will get addressed as people engineer system architectures to leverage wireless, further develop installation tools and the base experience grows. These developments will reinforce each other so I expect to see more suppliers embedding wireless capability in their equipment and even more users adopting wireless solutions. So many, in fact, that I am beginning to think the light at the end of the wireless tunnel is indeed, not a train, but just a bright future.
As always, the views expressed in this column are mine and do not necessarily reflect the position of BACnet International, Teletrol Systems, ASHRAE, or any other organization. If you want to send comments to me directly, feel free to email me at email@example.com
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