Wireless: The Future of BAS?
Taking a look around, it’s safe to say that wireless communication has permeated our daily lives; not only are cell phones in extensive use, but even church steeples in New England are now supporting cell towers. On college campuses, personal digital assistants (PDAs) are as common as backpacks. There is even a trend among a few high-tech youth to outfit themselves in “computer clothing” that connects them wirelessly to the Internet. Wireless communication is growing so fast in the United States that 24 million new subscribers signed up for cell phones last year. So why not wireless building control as well?
Working without a wire
There are two primary reasons for moving toward wireless in building automation systems (BAS): reducing costs and adding functionality.
Facility managers want to get more out of their buildings by cutting operating and maintenance costs. As a result, developers need to provide state-of-the-art functionality at the best possible price. Buildings that run smarter will fare better as they will incur less operating costs. Real-time monitoring and control of more devices and systems, as well as remote and ready access to the information produced, are valuable advantages of wireless, not only through increased functionality, but also through reduced costs.
And wireless makes a lot of sense simply on the basis that wire pulls can be expensive, especially when retrofitting older buildings where access is limited. The wire, even when it is possible to install, is often premium-priced plenum cable. The advent of low-priced wireless technology presents a more appealing and cost-effective alternative.
Even though exciting developments are taking place, with new applications for wireless being rolled out every day, the use of wireless in commercial as well as industrial applications will evolve gradually, because there are still many technical issues to overcome.
The ultimate goal is to install a system that will transmit over long distances and function in fast-moving vehicles. At present, this is still the stuff of dreams. Users are forced to segment applications and prioritize either bandwidth or distance to keep costs down. In critical applications, both reliability and security requirements need to be addressed. But the use of wireless devices in the industrial arena has begun in earnest.
IT departments, PDA users and consumers are vying for more bandwidth and greater transmission distances, but the wireless requirements for BAS are actually relatively simple. Except for the operator interface—which may be carried by an off-site technician or building manager—building automation systems are generally for stationary, close-proximity systems that have low bandwidth requirements.
Wireless transmission for low-bandwidth local communication has a low cost, resulting in the advent of competitive products for the type of applications required in building automation. For reasons related to price, functionality, distance and bandwidth, these devices use differing standards and technologies.
A wireless operator interface offers one of the most immediate returns for building automation. A communications link can provide mobile computing devices complete access to facility operational data and allow maintenance operators and facility managers—no matter where they are—to see what is happening in real time. Remote access can increase productivity and uptime in critically important operational systems.
The operational staff can be instantly alerted to events, alarms and operational data. They will be able to analyze activities or problems as they occur and can take initial actions by remote control of motors, fans or pumps.
Wireless operator interfaces use standard Internet protocols to send data back and forth. Data from the building system is centralized in an Internet server that serves as the communications link to wireless computing devices carried by the operating staff. Standards such as wireless application protocol (WAP) were developed to allow a mini-browser on a PDA or cell phone to connect to the Internet. This same technology enables a user to monitor or control the building automation systems. Eventually, when cell technology with 2-megabit per second (Mbps) bandwidth is implemented, it will be possible to have real-time video access to cameras placed in the facility from these remote operator interfaces, permitting even higher levels of surveillance and control.
Sensors, controls and switches
A growing number of companies currently manufacture wireless temperature, pressure and flow sensors. Additionally, they have introduced wireless read, verify and change controls for pumps, motors, fans and variable-air-volume controls. These devices use a variety of technologies.
One product, for example, is a small wireless card that can be equipped with analog or digital inputs and outputs and mounted on a power or control panel. It can provide continuous information on the operation of important parameters in the panel. In retrofit projects, installation of such a device is extremely cost effective and can be completed quickly. Equipped with global positioning system technology, this type of wireless card can also be used to track mobile units, such as a service truck.
Low-voltage switches for lighting control have reached a very low cost; because of their relatively higher costs, wireless switches have not been widely used. However, as the price point of wireless devices comes down and the costs of labor and materials increase, wireless switches will become increasingly competitive. Aiding this innovation is the use of line-of-sight, low-cost wireless technology from switches to lights in close proximity.
Metering and monitoring
One technology that has been available for some time now is the wireless utility meter. In earlier years, connected meters required access to a modem and telephone line, making them expensive and relatively rare. But more recently, the ability to use cell phone frequencies to connect to these meters has made their use more cost effective and practical. Additional “smart” features make these meters capable of generating information that cannot be gained from a traditional meter. Building energy-monitoring and -management systems not only read usage; they can also perform demand control, automatic load control, alarming and real-time reading and paging based on the events or data being monitored.
Fire and security systems
Wireless technology has also made advances in fire and security systems. In fact, many European countries already have the relevant codes in place. The United States, however, has been slow to accept this particular use of wireless technology. There are commercial installations in the United States that operate on licensed, rather than unlicensed frequencies. One vendor, for instance, claims good results with FCC-approved equipment tuned to various frequencies in the 134 to 174 MHz range. The design engineer, however, must be prudent and research local codes before specifying wireless fire or security products.
RF tagging, also known as radio frequency identification or RFID, is a fast-growing area with widely varying applications. RF tagging is an economical way to tag, identify and track assets and their movement in and out of a facility.
With the use of RF tags, large databases of assets can be maintained. RF tags are manufactured in a variety of sizes and configurations. They can be as small as a grain of rice and can be given unique unalterable identities during manufacture. Passive units require no battery or power and typically have read distances of less than three feet. Active RF tags use low amounts of power and can have batteries with lives as long as five years. Active units have larger read distances, but because they are much more expensive, are not generally used in asset management systems unless the assets are of a high value.
Similar to RF tagging systems used for asset tracking, RF tagging systems and transponders used for security systems monitor and control movement of personnel and vehicles in and out of facilities. Security system transponders are generally powered devices, which increase the cost but allow for readings over much greater distances than can be achieved with less expensive passive units.
Currently, there are no generally accepted industry standards for RF tags. Systems are built around proprietary standards; once systems are installed, a user is forced to buy service, parts and expansion units from the original manufacturer. Once avoided because swipe cards could fill the same functions at a much lower cost, RF units are becoming more common as technology improves and costs decrease.
Frequencies, costs, features
There are many devices that operate wirelessly, ranging from simple RF-tagging systems to cell phones with built-in, fully-digital PDA functionality. Between these two extremes, there are the sensors, transmitters and controlling devices that are needed to fully integrate a building automation system. Table 1 (page 26) lists a subset of wireless standards and technologies to help BAS designers identify some of the differences among protocols and devices.
Because the value added by wireless technology has not always been recognized by major BAS suppliers, it is generally smaller, innovative companies that provide wireless technology today. It can take some determination on the part of an engineer to write specifications for wireless devices. Fast-moving technical innovations means that engineers won’t be able to copy specifications from one project to the next—a difficulty that won’t be resolved soon.
As wireless BAS applications mature, standardization will occur. But even though there appears to be no standards planned for wireless BAS in the near future, a lack of standards is not reason enough to miss out on the enormous potential of these devices (see “BACnet and the Wireless Connection”).
Users of building automation systems are poised to reap the rewards of wireless technology advances. Lower material and labor costs for installation and faster retrofitting of facilities are only a few of the advantages.
Once a facility is up and functioning, portable, wireless operator interfaces built into PDAs will allow maintenance staff and facilities managers to have real-time links to critical equipment and alarms. Crisis intervention will be carried out quickly and effectively, reducing operating costs. And in time, standards will be developed to allow the variety of hierarchical devices to be effectively integrated.
Wireless Standards and Technology
|BAS Application||Other Applications||Bandwith or Speed||Relative Cost||Standards or Protocol|
|Asset management||RF tagging||n/a||Very low||Proprietary typically &125 Mhz|
|Security and identification||EZPass, animal tracking, railcar tracking||n/a||Low||Proprietary up to 900 Mhz|
|Light and device-switching||Personal area networks||9,600 baud||Very low||Infrared transmission|
|Real-time utility alarms and controls||Personal area networks||1 Mbps||Low||Bluetooth 2.4Gh (IEEE 802.11b)|
|Low priority events||n/a||Low||Internet e-mail|
|Security fire alarms and info||WAN||9,600 baud||Low||IEEE 802.11|
|WLAN||Wireless LAN||11 Mbps||Mid-range||IEEE 802.11b|
|Mobile operator interfaces for data||Cellular phone/PDA||14.4 Kbps for 2G||High||GSM|
|Mobile operator interfaces for data||PDA/Video on demand||2 Mbps for 3G||High||3G|
BACnet and the Wireless Connection
When ASHRAE first introduced the BACnet protocol in 1995 to allow interoperability of building-automation products, the standard was limited in usefulness because it lacked complete definitions of connectivity.
This shortcoming has been corrected in recent addenda (see August 2001 issue, p. 50), and for some functions, the BACnet protocol does cover wireless technology for building automation.
BACnet tunneling routers (BTR) and BACnet building maintenance devices (BBMD) are both Internet interfaces that allow use of the Internet to connect IP messaging for building automation.
In time, more changes will be made to BACnet to cover wider offerings in wireless, but presently there are only limited standards available for wireless technology and little, if any, interchangeability or interoperability among manufacturers. Care on the part of the engineer, however, will allow designers to interface the wireless part of the system with wired systems that are defined more completely by the BACnet protocol.