Lighting Research Center Lighting Research Center
Volume 2 Number 2 
Copyright @1997 Rensselaer Polytechnic Institute

Interoperable Systems: The Future of Lighting Control

The once-fanciful notion of the intelligent building is becoming both feasible and affordable.

By Robert Wolsey

A few decades ago, the idea of lights that turned on automatically when you entered a room seemed like science fiction. Now, the installation of occupancy sensors for lighting control is commonplace - and with the development of newer, less expensive computer technologies, the once-fanciful notion of an interoperable building (capable of sharing information such as temperature, security, and lighting among building systems) is becoming both feasible and affordable.

A building automation system (BAS) offers advantages such as interoperability and extendibility, over even the most sophisticated lighting control system. For example, an occupancy sensor connected to a BAS can control lights, and it can also control temperature and airflow, alert security staff to intruders, help rescue crews locate occupants in an emergency, and even determine the floors at which empty elevators should wait to pick up passengers. The BAS can span several buildings, no matter how far apart, so that an entire college campus, or even all the worldwide facilities of a multinational corporation can be monitored and controlled from a single workstation.

The technology that makes a BAS possible is direct digital control (DDC), the use of special control modules, sensors, and actuators that communicate over a high-speed network. DDC components are available for virtually every type of electrical or mechanical system, and DDC signals can be transmitted via anything from radio signals to the Internet.

Tomorrow - or today?

One emerging application for a BAS is electrical load shifting - reducing energy use during utility peak demand hours to take advantage of reduced electrical rates during off-peak hours.

Utilities promote load shifting to reduce total peak demand. For example, a utility in Laredo, Texas, Central and South West Corporation (CSW), has begun installing DDC modules in its customers' buildings. Through the use of the modules, companies and homeowners can program their buildings to save energy, and the utility can send and receive DDC signals over the power distribution system to moderate electrical demand interactively, which, in turn, can save customers about 10 percent on electric bills.

Xerox Corporation's Palo Alto Research Center has come up with a novel way to allocate heat and air conditioning to its offices. Researchers at the company developed a software-based system that continuously monitors existing temperatures in office spaces and sends signals through what are dubbed "agents" to bid for cooler or warmer air. The agents are computer representatives for office areas. They are built into the software, and they can bid against agents in other areas.

For example, perhaps offices on both the first and second floors are becoming warm. Agents for each office will bid (without knowing what the other bids are) for cooler air. The system then evaluates each office area, determines the greatest need and allows one agent to "win" the bid. The area that the winning agent represents will then get the cooler air that might have been diverted elsewhere in an unregulated system.

Agents are allotted "money" for bidding purposes based on several factors such as the size of the area, the time of day that the sun warms that area, and the amount of shade. Because bids occur more than once per minute, the building operates efficiently with little or no noticeable change in temperature, and at an energy savings of more than 10 percent.

Brain power

The key to direct digital control lies within the programmable microprocessors (computer chips) contained in DDC control modules. Collectively, the microprocessors distributed throughout a BAS act as a very powerful computer.

DDC modules connect to devices such as sensors, switches, relays, dimmers, actuators, thermostats, pumps, and drives. Many of these devices, including occupancy sensors, are now available with a DDC microprocessor built-in. The modules send out status information about the devices to which they are connected (this light is on, this space is occupied, this space is at 72 ºF, for example), and they execute commands based on their programming (turn on the lights if the room is occupied, dim the lights if it is sunny, etc.).

A building automation system is really a network of computers not much different from a typical local area network (LAN) of office personal computers (PCs). The nodes of the network are simply DDC components, instead of PCs. In fact, data networks such as LANs can be connected by a router to DDC networks.

Distributed control networks

Before DDC, every device on a control network had to be wired directly to a central control panel. With DDC, installation costs are reduced and the process of expanding the network is greatly simplified because each node can be wired to the next closest node. Power-line carrier signaling (sending coded high- frequency signals over the existing supply voltage wiring) can also be used, eliminating the need for any additional wiring. If one of the DDC modules fails, or if the network's wiring is somehow severed, the rest of the network continues to function. For example, even though messages can't get all the way across a severed network, an occupancy sensor node and a luminaire node that are both on the same side of the break will continue to work together properly.

Interoperability: Talking the talk

One of the greatest concerns when putting together a building automation system is the availability of compatible products for controlling the numerous and disparate types of devices used throughout a building. Unfortunately, the history of direct digital control has been one of several competing standards that are not necessarily compatible with each other.

The communication protocol and the networking media determine the compatibility of DDC products. The communication protocol is the networking language in which DDC components speak to each other. Although some building automation systems use Ethernet or Token Ring communication protocols, these protocols were designed for data networks and are not optimized for control networks, either because they do not work well with consistently heavy traffic or because they become too slow when large numbers of nodes are required.

In addition, many manufacturers of control equipment use one of the proprietary communication protocols, so that their components cannot be used with any other manufacturer's and cannot communicate with other building systems. However, the trend in the industry is toward the adoption of open standards for DDC communication protocols. The open standards will allow products for different building systems and from different manufacturers to interoperate and share information with each other. Currently, the two leading BAS open standards are BACnet (which stands for Building Automation and Control network) and Echelon's LonWorks.

BACnet was developed by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), and was originally intended to control only heating, ventilation, and air conditioning (HVAC) systems. It was later expanded to include other building systems, but according to Honeywell, Inc., one of BACnet's founding organizations, it is not well-suited to control other systems, such as fire alarms and security, or applications requiring heavy or very rapid information processing.

LonWorks was intended from its beginning for use with virtually all types of control systems. Indeed, it is currently in use with control systems for satellite communications, automotive electronics, utility meter reading, and theme-park rides.

Although it was initiated later than BACnet, LonWorks has begun to dominate the DDC market for several reasons. For example, it was implemented on computer chips called Neuron chips which have made it easy for other manufacturers to design and build DDC components for applications within their industries. Over 800 companies worldwide have already adopted the LonWorks standard. Many components for lighting systems, including multi-circuit switching panels, occupancy sensors, photosensors, window-shade actuators, and dimming electronic ballasts for fluorescent lighting systems are available with LonWorks DDC built in. Even routers that allow a LonWorks control network to operate as a subset of a BACnet network are available.

Another big advantage of LonWorks is that the same twisted pair wiring used to carry the signals between the nodes can also be used to supply low-voltage power for the control modules, further simplifying installation. Also, LonWorks is a more extensive control protocol; it allows the optional communication of much more than simply status and command information between modules. Error correction, data compression, sender verification (for security purposes), and advanced network management are all possible. Further, Echelon has offered training and support for LonWorks developers since its inception.

Even BACnet founder Honeywell, Inc. has announced its intention to support the LonWorks protocol in its products and now recommends using BACnet and LonWorks together, with BACnet controlling existing HVAC systems and interfacing with the Ethernet PC LAN, while a LonWorks subnetwork controls other building systems. However, BACnet has strong support from the members of ASHRAE, and since most BAS installations are initiated to control HVAC, it is likely that BACnet, and LonWorks will exist as co-standards in building automation in the foreseeable future.

The media is the message

Virtually any media that LANs use to transmit information can be used for control networks. BACnet was designed to use the same media as the popular data networking protocols, Ethernet and Arcnet, and can be transmitted over twisted pair wiring, coaxial cable, and fiber optic cable.

In addition to those media, LonWorks can be transmitted by power-line carrier; radio frequency, using radio transmitters to send signals through the air over distances up to 20 miles; and infrared signals, such as those used for television remote controls. Routers are also available to extend the network over long distances by modem, or via either the Internet or a corporate intranet. Any number of these media can be mixed throughout a single network.

To integrate a building's control network and data network, routers that link a BACnet network or a LonWorks network to an Ethernet network are available. Alternatively, individual PCs can be connected to the control network by an interface device. Figure 1 shows the schematic for a possible multi-building control network using all these media.

What can it really do?

Although a myriad of lighting control options are possible using off-the-shelf DDC components, most building automation system installations do not yet tap the full potential of lighting control possibilities. For the most part, operating schedules, occupancy sensors, and photosensors are used with a BAS to control lighting in much the same way that they would without the BAS, and they yield similar energy savings. The main advantages the BAS provides are interoperability among systems, extendibility, and monitoring capabilities.

Let your fingers do the controlling

One way to maximize the potential of a BAS would be to provide each workstation with a virtual control panel with which occupants could control their own environment, including their lighting, air temperature and air quality. The facility manager would determine which equipment each workstation could control, and could override any individual's settings, if necessary. IEC Intelligent Technologies, Metra Corporation, and Microsoft are among the companies that currently offer software for developing LonWorks' client applications to provide limited control and monitoring capabilities for building occupants. David Gaw, of Coactive Aesthetics, says his company's Internet/ intranet router, available in early 1997, will allow building occupants to use any World Wide Web browser, such as Netscape Navigator or Microsoft Internet Explorer to access the BAS.

With control at the workstation level, individuals could program certain BAS functions themselves. For example, they could program the luminaire above their workstation to flash at predetermined times to remind them of appointments. They could flash the lights throughout their department, or use some other signal, to remind everyone of a staff meeting, and then have the lights in the conference room flash when the meeting is scheduled to conclude.

Users could program the BAS to associate certain software applications with preset lighting conditions, so that, for example, the lights behind the worker would dim whenever a data entry application was launched. On suitably equipped PCs, the lighting and HVAC could even be controlled by voice commands.

Benefits help balance the books

According to manufacturers of LonWorks components, the biggest obstacle to widespread acceptance of this technology is cost. Installation costs are low compared to the installation of a new centralized control system, but DDC components are still relatively expensive and network administration personnel costs must also be considered. For components, installation, set-up (in-field commissioning), and a year's maintenance, a DDC network can cost more than $300 per circuit controlled.

Although highly-trained personnel are required to administer and maintain the system, reductions in occupant complaints and early identification of equipment malfunctions and inefficiencies can result in lower overall maintenance costs. Most BAS installers offer system administration service contracts. Typically, system problems can be resolved by remotely located technicians connected to the system via modem.

Brian Hogan of the BAS design company, Advanced Control Technologies, estimates an expense of $500 to $1000 for the minimum hardware (a 386-based PC with a BAS interface card) and software (such as IEC Intelligent Technologies Inc.'s ICELAN-G®), and set-up costs of approximately $50 per node. For a commercial facility, 24-hour monitoring of the system by someone with the necessary technical expertise will probably be required-a significant expense to consider.

Metra Corporation has claimed a 25 percent building-wide utility-bill reduction through the use of a BAS; this is typical of other manufacturers' estimates. The Center for Analysis and Dissemination of Demonstrated Energy Technologies estimates typical lighting energy savings from a BAS in an office at 30 to 50 percent.

However, most of these savings are possible using programmable timers, occupancy sensors, and photosensors without a BAS. The incremental energy savings are the result of system integration features such as occupancy sensor control of the HVAC system. Additional savings come from reduced maintenance costs and equipment downtime. The monitoring and reporting capabilities that a BAS provides help to quickly identify and address building inefficiencies. Also, if a BAS provides enhanced communication and cooperation between the building and the electric utility, advanced load management strategies could reduce energy bills further.

Although the term BAS emphasizes automated control, the eventual success of such systems may lie in the manual control options that they make possible. Professor Walter Kroner of Rensselaer Polytechnic Institute's Center for Architectural Research notes that manual controls increase employee satisfaction and productivity. His own study revealed a three percent increase in productivity when office workers were given individual workstation HVAC and lighting controls. "With human resources accounting for the great majority of any office's operating expenses, the payback on individual controls from increased productivity alone can be as quick as two years," Kroner said.


That a computer system can have so much control and access to information can be troubling. For example, if someone outside the company breaks into the system, could they disable the security system or the fire safety systems? To address this concern, both BACnet and LonWorks were designed with a sender authentication security feature. Nodes can be assigned unique keys that are used with an algorithm to verify the identity of other nodes sending commands. BACnet also supports the encryption of data packets.

Another concern among employees is that their employers might use the information gathered by the BAS to scrutinize their activities. Building automation systems are capable of generating detailed reports which could be used, for example, to examine the occupancy patterns of a particular office. If the BAS also controls the access to the building, the system could theoretically track occupant whereabouts throughout the day. Good communication between employers and employees should resolve any privacy issues.


Computers continue to transform the way we live and work. As we approach the next millennium, it appears that predictions of intelligent buildings are coming true right on schedule. The flexibility, convenience, energy, and cost savings attributed to building automation systems are fast becoming a fact of life. As technology advances, our workplaces can make us happier, healthier, and more productive, - unless, of course, they become so intelligent that they can do our jobs without us.

About the author
Robert Wolsey is a technical writer with the Lighting Research Center. He is an author of several publications for the LRC's National Lighting Product Information Program, including Lighting Answers: Power Quality, Lighting Answers: T5FT Fluorescent Lamps and Ballasts, and Specifier Reports: Dimming Electronic Ballasts.

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