The First Facility Management Blog

At ASHRAE’s 2010 Winter Conference held recently in Orlando, the BACnet committee approved final publication of eight addenda to the ANSI/ASHRAE Standard 135, A Data Communication Protocol for Building Automation and Control Networks. The addenda are expected to be available by the end of February.

The addenda include a specification for a standard way of representing data in XML that will give BACnet new capabilities for communications between a wide range of applications. The Extensible Markup Language (XML) is a popular technology in the data processing and communications worlds, due to its capability to model complex data and its flexibility to be transformed and extended.

“With this new IT-friendly way of representing building data, BACnet will open up new ways to communicate. XML can be used for exchanging files between systems, communicating with the Smart Grid, and expanding enterprise integration with richer Web services,” said Dave Robin, chair of the BACnet committee.

The XML syntax is intended to be the core data representation for a variety of uses:

• New Web services that are capable of efficient exchange of complex structured data.
• An electronic version of a BACnet PICS document, consumable by workstations and other tools, to describe the capabilities of a device.
• An “as built” description of a deployed device, distributed either as a separate file or as a BACnet File object resident in the device itself.
• Descriptions of proprietary objects, properties, and data types, which may be simple for basic data sharing purposes, or extremely rich, providing complete descriptions of the meaning and usage of the data in multiple human languages.
• An export/import format for tools and workstations to publish their knowledge of a complete system of devices and networks.
• An XML version of an EPICS, including the complete test database and other test-oriented data.

In addition to the new “computer language” of XML, another addendum has added an important new capability for human languages as well. When the Unicode character set was created many years ago, it was constructed to be universal set of characters to support most of the world’s languages together in one stream. However, its original 2-byte encoding caused trouble with many existing systems that were designed to process only the 1-byte characters common in Western languages. The “UTF-8″ encoding was created to solve this problem and quickly became a very popular method of conveying international text on the World Wide Web. BACnet has also embraced this standard and uses it in a way that fully takes advantage of its compatibility with the existing and ubiquitous ANSI/ASCII character set.

BACnet has also added support for more data types as well. A set of new “Value” objects rounds out BACnet’s ability to represent different data types in a uniform and standard way. Added to the original Analog, Binary and Multi State Value objects, are new Value objects for every primitive datatype that BACnet supports, including support for character strings and large numerics.

By Eddie Hickerson, lighting control specialist, Schneider Electric

As facility managers (fms), consulting and specifying engineers, and other members of the building industry focus more intently on energy consumption and resultant cost, finding ways to reduce product lifecycle and maintenance costs has become an hot topic industry-wide. Effectively integrating building automation systems directly results in lower costs and gained efficiencies. Considering nuances, such as using only one data communications protocol in these efforts, can not only drive these results but other benefits as well.

Developed by the building automation industry for the purpose of building system integration, Building Automation and Control network (or BACnet®)—an open data communications protocol for building automation and control networks—facilitates integration of HVAC, lighting, security, and other commercial building systems. It can work toward enhancing energy savings, lowering design, and lifecycle costs, facilitating commissioning, and providing improved flexibility, scalability, reliability, and control.

BACnet’s ultimate objective is to achieve interoperability of building control devices that may differ by application, manufacturer, and vintage. While there are other open protocols widely used and supported within the building automation industry, BACnet was the first protocol developed by the industry purely for building system integration, and has been widely adopted by manufacturers of building control devices. Therefore, a plentiful and growing supply of BACnet devices virtually guarantees that interoperability can be achieved and maintained now and in the future.

Making The Case For BACnet
Consider this scenario: A building’s fm programs a schedule-based lighting control system to turn lights on at 6 am, the anticipated arrival time for the company’s first employee. However, the first employee typically doesn’t arrive until 6:30 am, which results in 10 hours each month that lights are on in a vacant building.

To counter this issue, the fm uses a card reader for employees to disarm the security system and turn lights on when the first employee enters the building, essentially linking the security and lighting systems that must communicate properly to facilitate desired results. Seeking further energy savings, the fm employs occupancy sensors to turn off lighting, and then links that process with the HVAC system to simultaneously set back thermostats or close vents feeding unoccupied spaces.

Typically, in order for building systems like lighting, HVAC, and security to share an input, such as a card reader or occupancy sensor, the input device must be physically connected to each system separately. On a small scale, this is a simple task, but on a large scale, physically connecting every input to every system is a daunting task. Imagine trying to connect 50 sensors, 12 card readers, and 40 keypads to multiple systems—for three systems; that is more than 300 pairs of wire. Such a configuration would require a tremendous amount of time and effort to troubleshoot and correct if a problem occurs.

BACnet efficiently supports both small and very large systems, but is particularly effective for the latter. What if miles of wire could be replaced with a single network over which all devices can report status, share information, and work together to control building systems, much like a single control system? Using common and often pre-existing Ethernet networks, BACnet systems are fast, reliable, and better understood and managed by maintenance personnel.

Figure 1

Implementing a BACnet system can also reduce risk. The prevalence of native BACnet building control devices provides fms with the flexibility to upgrade the existing BACnet system to meet future needs.

Primary Benefits
BACnet simplifies the task of designing systems by providing a common language that various devices can understand. BACnet control devices may differ by application, manufacturer, and vintage, but they share a common language through which they communicate and work together without the need for communication gateways and network bridges (see Figure 1). As a result, building system integration begets substantial savings. For example:

• Lower design cost. From a consulting engineer’s perspective, designing one control system that encompasses all the major building systems (HVAC, lighting, and security) takes less time than designing three or four separate systems.
• Quicker commissioning. In an integrated building control system, all building control devices are connected to a common network and communicate using a common protocol—BACnet. This is a simple system to install and even simpler to commission. From a single PC, the building automation system installer can verify the system performs as specified. If changes are required, reconfigurations can be generated via the same PC.
• Reduced lifecycle costs. Integration minimizes the number of devices required to achieve overall system functionality and allows all building control devices to share a single communications network. Maintenance of fewer devices and networks lessens lifecycle maintenance costs.
• Monitoring. With an integrated solution, fms can more easily monitor critical metrics like energy consumption and occupancy patterns. The data available for reports is richer in detail and can often be analyzed for greater energy savings opportunities.
• Improved flexibility. Designing around BACnet simplifies building system integration in that designers can choose from a great array of native BACnet devices from a multitude of manufacturers. As systems age and change, BACnet hardware can be added with the assurance that new devices will communicate reliably with existing equipment.

Energy Code Compliance

The most prevalent energy codes and standards in the United States require automatic shutoff of all interior lighting in commercial buildings greater than 5,000 square feet. A lighting control system is usually required by local building codes to shut off lighting based on a pre-set schedule, or a signal from another system indicating an unoccupied area. Used effectively, BACnet simplifies the use of other systems, like security, to shut off interior lights; for example, when the security system is armed, interior lights are shut off. Employing BACnet controls allows the security controller to signal the lighting controller over a common network, rather than requiring a hard connection between the security system and the lighting control systems.

Figure 2

Spaces having schedule-based lighting control are usually required by code to have a way for occupants to override the schedule (usually for not more than four hours), turning the lights on when they would otherwise be off. With a BACnet-enabled lighting control solution, an override initiated from a keypad button-press to turn on lights can also be shared with the building control system. In response, the building controller commands the HVAC system to heat or cool the area while the lights are on (see Figure 2). Events like schedule overrides and tripped circuit breakers, for example, can be logged for later reporting to facility management (FM).

Ultimately, consulting engineers must address how their recommendations have positively affected the bottom line for FM staff. Maximizing energy savings involves taking control of major building systems that consume the majority of energy. When these systems are controlled together in a coordinated way using BACnet as a universal data communications protocol, it can become easier for fms to automate control, manage time and dollars required for updates, and maximize savings.