BAS Flies Standby

Most discussions of building automation systems (BAS) and power are usually about energy efficiency—how to use BAS to monitor and control overall power consumption in a facility, making more efficient use of power, and thereby cutting costs. But often overlooked is the role that BAS plays in centralized control of backup-power systems, which is more of a security issue than energy-efficie...

09/01/2002


Most discussions of building automation systems (BAS) and power are usually about energy efficiency—how to use BAS to monitor and control overall power consumption in a facility, making more efficient use of power, and thereby cutting costs. But often overlooked is the role that BAS plays in centralized control of backup-power systems, which is more of a security issue than energy-efficiency function.

In fact, tying an integrated standby-power system into a facility's central building automation system would provide a vital link between essential backup power during a power event and the systems—HVAC, fire and life-safety and lighting—that will rely on the standby system when the utility-supplied power fails.

To meet this need, manufacturers of standby-power systems have not only developed integrated systems with distributed control functions for local or remote monitoring of these integrated systems, they have also incorporated standard interfaces with leading building management systems and automation packages that are open and interoperable.

Distributed Generation

Another factor driving the interface between BAS and standby power is the rise of distributed generation. As on-site power sources become an integral part of a facility's energy management plan, what was once thought of as backup and emergency equipment is being treated as a primary source of power.

But even if it is only considered in terms of its standby-power function, this type of equipment—generator sets, transfer switches, paralleling controls and switchgear—must be monitored and controlled. And what better way than through the BAS.

For quite some time now, the makers of standby-power systems have been developing the microprocessor-based applications for networked monitoring and control of their equipment, and through strategic alliances, they have developed standard interfaces for connecting into BAS. Centralization of all control functions into a comprehensive and integrated BAS offers many advantages including:

  • Increased productivity by streamlining operations.

  • Greater uniformity of controls that facilitates training.

  • Easier operation that facilitates quicker reaction in emergencies

  • Increased interaction and sharing of data that makes the subsystems work together.

Some recent projects in which integrated standby-power systems were implemented illustrates the possibilities of centralized monitoring and control of emergency and standby power. In each of these projects, integrated systems with the capabilities of interfacing with the overall building management system can be controlled from a central location, or even remotely.

The first project involved a standby power system at an international airport. The other was a link up on-site generators at separate facilities to create what has been called a "virtual power plant."

Uptime at the Airport

According to a recent survey by the International Air Transport Association, the Minneapolis-St. Paul International Airport ranks fifth worldwide for passenger convenience among airports with over 25 million passengers. Airport inconveniences such as long check-in lines or slow baggage claim carousels are the exception not the norm here, and that's good news for the traveling public.

To maintain this high level of service, the airport is in the midst of a major expansion project that, when completed in 2004, will accommodate 40 million travelers. Runways, roads, parking lots, terminals and concourses have already been upgraded or expanded. As the airport grows, so does demand for the myriad of electrical services that keep the airport functioning smoothly. Boilers, chillers, heating, cooling and ventilating systems; security cameras, monitors and computers; elevators, lights, public address, commercial operations and more all rely on uninterrupted electrical service. To ensure continuous service, even during an interruption of electric power, the airport has installed a new standby power system for the airport's Lindbergh Terminal, seven concourses, roadways and parking ramps.

Engineers specified an efficient pre-integrated standby power system. Rated at 6 MW on a standby basis, the system includes four 1,500-kW generator sets, a command network and digital paralleling equipment.

"While the primary function of an airport standby-generator system is to provide power for life-safety systems, these units give us the dependability and performance to provide essential operations now and when the expansion is complete," said Bob Tschida, project engineer, Dunham & Associates, Minneapolis. "In the unlikely event of a power failure, the standby generator will power the exit lights and fire alarms needed to direct people safely out of the buildings. More than that, the system provides standby power so the airport can maintain a basic level of operation during a power interruption."

Although the airport's redundancy system virtually guarantees uninterrupted utility power—three different utilities service the airport—operating without standby power is unthinkable to airport officials. Without essential services to keep flights arriving and departing on time, a domino effect would topple operations at other airports as well. "We would have to close down the airport if we didn't provide essential operations such as heating, cooling, ventilating, lights, security cameras and surveillance, not to mention commercial operations," said Tschida.

The airport's fiber-optic hub and the "smart" technology of integrated digital control allowed designers to install an efficient system—despite the networking obstacles posed by the length of the 2,000-foot concourses.

The integrated power system consists of generator sets, transfer switches, the paralleling equipment and controls to coordinate all the demands placed on an electrical system. These components are designed and manufactured to work together interactively. The power control systems feature "smart" components that are capable of communicating with one another and that facilitate remote monitoring and control along with the PC network. This feature is intended to improve the functionality, enable easier installation and reduce operating and maintenance costs.

In the airport's main generator control room, a PC-based control console monitors the status of 30 automatic transfer switches, allowing engineers to control and segment the load to distribution panels located throughout the airport.

Gateway modules convert data on twisted pairs into fiber optic signals to allow monitoring and diagnostics at remote locations thousands of feet away. Eleven routers located throughout the airport, and monitored from the main control room, provide overall control of the transfer switches.

The system also provides an important maintenance function over the network, even while the generators are not operating. From the control console, technicians can monitor the actual power consumption in each area of the airport. If a current load is lower than normal, they know something is wrong. "We can identify a trouble spot before it's identified by the user," said Tschida. "This feature provides us with unlimited capability for maintenance."

Although the standby power generator system will be exercised monthly, it is seeing more regular use during the current construction project. During utility service upgrades, the generators provide the airport's electric service. "We occasionally need to switch off our power from the utility. Switching to the standby generators lets us continue construction without inconveniencing the airport," said Tschida. "The standby generators play an important role in providing uninterrupted service even during construction."

When there is a loss of utility power, the power system senses it, and starts all four generator sets after a three-second delay. The first generator set that gets up to rated speed picks up high priority loads. The remaining three generator sets synchronize to the generator bus and as they connect, additional loads are added to the system. The entire start-up and synchronization sequence takes less than 15 seconds. All four generators run for 15 minutes, after which the system analyzes actual load requirements. If the load can be handled by fewer generator sets, the command system automatically shuts down the unneeded generator sets. If additional load is added to the system, it automatically reconnects required generator sets.

When utility power is restored, the generator system will continue to run for a selected stabilization period. Once utility power remains steady throughout this period, load is re-transferred back to the utility.

Backing Up Chicago's Finest

In November 2001, Mayor Richard M. Daley of Chicago suggested that the city could help "private companies generate more of their own electricity through gas-powered generators."

Daley's 2001 Energy Plan called for linking on-site generators to create a "virtual power plant," and one of the city's first initiatives was the creation of a 10-megawatt power plant by linking backup generators at a number of police stations and senior citizen cooling centers.

The $400,000 system was in part inspired by the utility ComEd's failure to keep the lights on during the summer of 1999. System integrators worked with the project contractor to retrofit six critical emergency backup generators—four at police stations and two at senior citizen cooling centers. Engineers designed an integrated control system that enabled complete remote start/stop, power-quality monitoring, energy/electrical metering and data logging, as well as automated troubleshooting of multiple generators. It also allows communication directly with a central operations center for real-time control and data transfer.

Enterprise-wide monitoring and metering assist building managers by using technology like an Ethernet or the Internet to remotely monitor buildings and equipment, and make it possible to correct any problems faster and less expensively. The metering works in conjunction with monitoring to provide energy usage, demand and power quality measurements to benchmark against similar facilities. Demand side management can reduce demand charges, which constitute 60 % of energy costs, and off-peak and time-of-use rates allow processes that can be performed off-peak to realize energy savings for agencies.

Now, following the terrorist attacks of Sept. 11 and concerns about energy security, the city's power plant has taken on a greater significance. Rather than relying on engineers at each location to switch on the on-site generators, the power plant links all the generators with the flick of a switch from one central spot.

Commonwealth Edison, Chicago's main supplier of electric energy, spearheaded the effort to contract for negotiable interruptible power, which provides the utility and the City of Chicago economic savings during times of peak power demand. In addition, generators retrofitted with controlling equipment can run independent of the ComEd power grid, thus ensuring the police department's critical equipment, such as telephones and computers, are supplied electrical power even during a power outage. The control equipment enables the Chicago Police Department to monitor and control its on-site power generation system remotely.

Now complete, the installation allows the police department's backup emergency generators, each producing nearly one megawatt of power, to be remotely dispatched, monitored and controlled. This means that if Chicago power shortages are eminent, the police department can easily switch from utility-supplied to on-site generated power. The advantages—no downtime, no 911 glitches and no additional costs for expensive peak electricity.

BAS and Backup

What the two projects described above have in common is that they illustrate the potential of linking fully-integrated standby-power systems to a central point of control. While these systems offer their own functions for monitoring and controlling power systems, they are being designed with the interfaces that make possible their incorporation into the management systems that control an entire facility or group of facilities.

From Pure Power, Fall 2002





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