ASHRAE Journal - November 2011 - B7

facturer who wanted to provide a simple keypad interface to a single piece of BACnet equipment. The BACnet committee spent more than 10 years in Deep Thought about this question before specifying operator interfaces in 2009. (To be fair, they weren’t just pondering this one question during those 10 years. They were also reﬁning and expanding the rest of the BACnet standard, developing speciﬁcations for all other BACnet devices, and creating test standards for everything BACnet.) In the meantime, vendors were providing many interfaces to meet the needs of different operators. The BACnet committee recognized the wisdom of this approach, so rather than combining everyone’s requirements into one unwieldy device they created three different kinds of operator interfaces. A BACnet Operator Display (B-OD), a BACnet Operator Workstation (BOWS), and a BACnet Advanced Workstation (B-AWS).

system on a daily basis. In addition to viewing and editing selected BACnet objects, an Operator Workstation can display trends, schedules, and other specialized objects. It can also display reports and graphics. Alarms provide a good example of how a BACnet Operator Workstation provides more features than a BACnet Operator Display. Both interfaces will notify an operator that an alarm has occurred, but an Operator Workstation will also allow the operator to acknowledge the alarm. It will provide a summary of alarms as well, and will allow the operator to adjust the alarm thresholds of analog objects. Examples of BACnet Operator Workstations are shown in Figures 3 and 4. Note how the use of graphics enhances the presentation of information. Links on these pages will navigate to other pages, provide more details, display trends, etc.

BACnet Operator Display (B-OD)

BACnet Advanced Workstation (B-AWS)

If a BACnet Operator Workstation is designed to provide an A BACnet Operator Display provides an operator with the abil- operator with all the information needed to manage the system ity to view a limited set of BACnet objects and make changes to on a day-to-day basis, what more can an Advanced Workstation setpoints and other parameters. These interface requirements are do? The answer is, a BACnet Advanced Workstation can be used simple enough that they can be met by a keypad display mounted to conﬁgure and commission a BACnet system, and it can also directly on the equipment, or they could be included in a portable provide advanced network troubleshooting services. This does device that the operator plugs into not mean that if a vendor does not a BACnet controller. A B-OD can provide a B-AWS you will have discover other BACnet devices, so no way to commission the system. it could “learn” which device it No vendor could stay in business was plugged into, but it’s not reif they did not provide the tools quired to discover all the BACnet needed to conﬁgure, commisobjects within a device. Instead, it sion, and troubleshoot its system. would probably use preconﬁgured The difference is that a BACnet screens designed to provide acAdvanced Workstation provides cess to the most important BACBACnet tools for completing these net objects in the devices, which it tasks. That means you can use it expected to discover. (I say “probto commission and reconﬁgure a ably” because at the moment there Figure 2: A text-based operator display. system with components supplied are no BACnet Testing Lab (BTL) listed BACnet Operator Dis- by multiple BACnet vendors, as the happy operator in Figure plays.) It’s also not required to display graphics and reports, so a 1 illustrated. If your system comes from a single vendor, or if text-based display would meet the requirements. Figure 2 shows you manage a combined system that’s installed and modiﬁed a simple text-based equipment mounted display that is similar to by contractors with the appropriate vendor tools, then a BACa B-OD, although it is not a BTL-listed device. net Operator Workstation may be ideally suited to your needs. Of course, a manufacturer could make an Operator Display If, on the other hand, you need to conﬁgure controllers made by with a graphic interface if it chose to, but it would still provide an multiple vendors, then you may need BACnet Advanced Workinterface that was much more limited than a workstation. Opera- station features. tor Displays have only limited alarming capabilities, and are not A B-AWS gives the operator the tools needed to manage a required to provide any scheduling or trending capabilities. They system on a daily basis. If that sounds suspiciously like the also provide only limited network support, with no requirement to functionality provided by a B-OWS it’s because a B-AWS probroadcast time syncs or provide any backup and restore capabili- vides all of the features of a B-OWS, plus the additional featies. tures needed to go beyond daily operations. Figures 5 and 6 show screenshots of BACnet Advanced Workstations. BACnet Operator Workstation (B-OWS) At an equipment summary level, the screenshots of the AdA BACnet Operator Workstation provides a much richer user vanced Workstations look very similar to the Standard Workenvironment. It’s designed to provide an operator with all the stations. There are obvious style and presentation differences information and editing ability he or she needs to manage a between vendors, but they all show information a user would
November 2011 B A C n e t ® To d a y & t h e S m a r t G r i d | 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 B7

ASHRAE Journal - November 2011

Table of Contents for the Digital Edition of ASHRAE Journal - November 2011