B8 B A C n e t ® To d a y | A S u p p l e m e n t t o A S H R A E J o u r n a l N o v e m b e r 2 0 0 3

By Jeff Gollnick

HHHHH eightened homeland security, the increasing

value of information, and the need to com-

municate faster and more accurately are driving

the creation of mission critical data centers. Once

contained in single rooms or floors within exist-

ing structures, data centers now require increased

security, access, functionality, and capability—far

beyond the original purpose or capacity of their

host buildings.

BACnet® Exceeds Needs at‘Because the BMS

needs to perform to

the same standards as

the data systems,

BACnet was used to

integrate and

coordinate all of the

building systems onto

a single network.’

Mission Critical Data Center

The following article was published in ASHRAE Journal, November 2003. © Copyright 2003 American Society of Heating, Refrigerating andAir-Conditioning Engineers, Inc. It is presented for educational purposes only. This article may not be copied and/or distributed electronicallyor in paper form without permission of ASHRAE.

N o v e m b e r 2 0 0 3 B A C n e t ® To d a y | A S u p p l e m e n t t o A S H R A E J o u r n a l B9

Today’s data center is not only housed within a secure build-ing—it is the building. Any company whose business is con-trol of and access to its data must ensure every system in thebuilding—from heating and cooling to lighting and ventila-tion—runs perfectly at all times in conjunction with its dataservice systems. For this reason, companies are placing build-ing management systems (BMSs) and control devices onto theenterprise network to simplify control of all operations.

Atlanta Data CenterAn Atlanta-based identification and credential verification

services company recently built its new data center from theground up to provide mission critical data storage, access, anddistribution. While 99.999% high availability—where annualdowntime doesn’t exceed five minutes per year—may sufficefor most companies, the Atlanta company required 100% highavailability.

The organization handles massive amounts of informationthrough the identification, retrieval, storage, analysis, anddelivery of data. Some of its services include:

• Providing credit check information,• Tracking the results of DNA testing on death row

inmates,• Conducting high level background checks for gov-

ernment and corporate agencies,• Creating biometric and authentication services, and

• Maintaining a fax-based alert system that identi-fies likely communities where a missing/abductedchild might be recovered then transmitting dataand photos of the child to get a search underway.

Because the BMS needs to perform to the same standards asthe data systems, BACnet was used to integrate and coordinateall of the building systems onto a single network.

Mission Critical SystemsThe non-negotiable 24/7/365 operation of the data center

requires a specialized infrastructure to handle its mission criti-cal nature. Because redundancy is the key to 100% uptime,the BMS contractor used BACnet technology to create a solu-tion that met the needs of the mechanical, electrical, HVAC,and data systems to achieve it.

PowerPowerPowerPowerPower

The data center has 4160 vac emergency generators in casemain power ever fails. The generators feature two 20,000gallon fuel tanks and four day tanks, allowing the center tooperate for 50 hours without main power. The company in-stalled power distribution units (PDUs) that clean and distrib-ute the power from an uninterruptible power supply. The PDUscan page data center staff if any alarm is activated within theBACnet BMS. The BMS contractor monitors the PDUs and thestatic transfer switch issues, which transfer one feed to another

B10 B A C n e t ® To d a y | A S u p p l e m e n t t o A S H R A E J o u r n a l N o v e m b e r 2 0 0 3

in the event of a power surge or outage,so that none of the mission critical com-puters ever go down.

WaterWaterWaterWaterWater

The company’s own water well sup-plies its mechanical systems. The well isthe primary source for the data center’smakeup water, with the City of Atlanta’swater well serving as backup. Conversely,if the city’s water supply is disrupted, thewell serves as a source for potable water.

TTTTTying in HVying in HVying in HVying in HVying in HVACACACACAC

Every device running the data center—from the building’s standard HVAC opera-tions to the chillers, generators, utilities,incoming power, breakers, and fuel oil—had to be integrated with the BMS. Thecenter’s HVAC system runs on a nativeBACnet/IP BMS operating on thebuilding’s Ethernet local area network.

System ComponentsSystem ComponentsSystem ComponentsSystem ComponentsSystem Components

The BMS contractor installed threeglobal controllers to manage the 15 es-tablished zones in the building. An MS/TP network connects the global control-lers to nearly 300 field level controllersthat oversee all HVAC devices, includ-ing main air-handling units, coolingtowers, variable air volume terminals, fancoil terminals, and exhaust fans.

For secondary control of the variablefrequency drive (VFD), which controlsthe average of hot and cold duct staticpressures, the contractor installedMODBUS communication wires directlyto the drive so the BMS could retrievedata from the VFD.

BACnet extends redundancy capabili-

ties to the HVAC system’s cooling proto-cols. The center hosts one stand-alonechiller plant with two expandable con-trollers that act as redundant panels. If onepanel fails, the other carries the load andno change is noticed when the switch oc-curs. The BMS monitors all chiller dataand operating information.

BACnet/Software FeaturesBACnet supplies the interface between

the company’s building controls and itsengine and compressor controls by ty-ing many MODBUS points to 12-cylin-der diesel-fueled engines. This wayengineers can see real-time data fromeach engine, including voltage and cur-rent for the entire building.

Using BACnet, the BMS transmits thestatus of each breaker position from 54third-party vendor distribution boardsthroughout the data center.

The BMS tracks the company andother building tenants’ main power us-age to accurately capture and bill energycosts. The additional monitoring capa-bilities of the BMS allows tracking andjustifying the electrical and mechanicalcosts of running their businesses.

BACnet operator workstations allowthe data center’s facility manager to view,monitor, and adjust all system functions,

Screenshot of HVAC control shows an air-handling unit.

including time schedules, trend logs,alarms, and alarm histories. Vivid, ani-mated 3-D graphics display zones downto the deepest levels, allowing completeand detailed views of every zone andmechanical device. Operators can alsocreate global control strategies or modifyexisting control algorithms for any con-troller using graphical DDC logic pro-gramming software, then quicklydownload the program to individual con-trollers on the network.

BACnet, BMS and the FutureThe BACnet BMS within the data cen-

ter is the latest example of how compa-nies are protecting their mission criticaldata within mission critical buildings.New BMS technologies are beginning toconverge with existing enterprise systemsfor exponentially increased benefits tobuilding owners and property managers.By providing interoperability betweendisparate equipment, the BACnet proto-col standard leverages a company’s totaltechnology investment for better systemperformance and a greater return on in-vestment. Already accepted industry-wide, BACnet is proving to be a long-termsolution to building management issues.

Jeff Gollnick is communications man-ager at Alerton, Redmond, Wash.

Screenshot of generators.