Web Exclusive Article: Building Automation With BACnet
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.
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.
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.
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.
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