What is BACnet? BACnet stands for Building Automation Control network. BACnet is a data communication protocol developed by ASHRAE. BACnet is known as “ANSI/ASHRAE standard 135-2016” and also as the international standard “ISO 16484-5.” Its purpose is to standardize communications between building automation devices from different manufacturers, allowing data to be shared and equipment to work together easily.
Why was the BACnet protocol developed? By 1987 ASHRAE realized that automation systems for buildings needed a standard method of communications. Because of the proprietary nature of the industry, existing systems, for the most part, did not permit interconnection between different manufacturers’ equipment. At that time ASHRAE undertook the challenge to develop and put forth a standard set of rules (BACnet) governing communication between various devices used in building control systems. BACnet is now an accepted standard by ASHRAE, ANSI and ISO and it serves as the foundation for thousands of building automation systems around the world.
What do BACnet products look like? BACnet devices physically resemble other standard control devices you may have seen, but their physical form isn’t important. Because BACnet is simply a set of rules for communicating between building automation devices, the microprocessors of these devices are programmed so they will understand the same language and conform to BACnet requirements. The physical nature of the device itself remains unchanged.
Do BACnet systems provide anything special that traditional DDC systems do not? Absolutely. BACnet gives you options to choose the right piece of equipment for the right job, from any manufacturer you want, instead of being limited to the brand of the system that’s already in place. An increased set of choices permits finer tuning of the installation for better operation. For new installations and retrofits, BACnet offers a future of easy expansions and modifications. When carefully selected, new devices will interface easily with the BACnet system already in place. As a wider variety of BACnet devices have been developed, more comprehensive system integration of services such as access control, security, fire and life safety, and direct utility company cooperation has become commonplace and easier to implement.
Is a BACnet system easily expandable? System expansion was the major guiding force when the BACnet protocol was developed. As a result, BACnet is very open-ended. It allows you to choose from a large range of devices. By selecting the right equipment, not only can a system be expanded, but it can also become even more efficient. The building automation industry can easily develop and integrate new products into today’s BACnet systems, while providing the means to accommodate tomorrow’s needs.
What types and sizes of buildings are best suited for BACnet product installation? Buildings of all sizes are capable of being controlled by BACnet systems. BACnet control systems may be simple, with very few devices, or they may be very complex. The BACnet standard is open-ended, yet has stringent criteria for device interoperation. It is very comprehensive, but does not require all devices to implement all capabilities. Thus, BACnet is robust enough for large, complex facilities, yet economically viable for small buildings.
Does a BACnet system provide better building HVAC control than traditional DDC systems? Because BACnet is basically a system of communication rules for building automation equipment, it will not automatically provide better control. However, BACnet simplifies the system integration process making it cost-effective to build more sophisticated systems tailored to the specific facility, complete with better monitoring capabilities. In many cases this enables better results than less capable, traditional systems. In addition, the BACnet standard is designed to be open for future expansions, even to the point of allowing devices to contain exclusive proprietary functions, yet overall, retain their BACnet conformance. This leaves open the possibility of future system improvements even when they require equipment from suppliers that were not used in the original implementation.
What’s the upside for the building owner if a BACnet system is used? If an owner becomes unhappy with product availability, service, replacement cost, or any other aspect of a specific vendor’s installed BACnet compatible product, chances are there’s a suitable replacement readily available from another company. The owner can be assured that matched BACnet products will perform in the system regardless of the manufacturer. Additionally, if a specific BACnet product is no longer manufactured, the owner won’t have to replace the entire system or keep repairing old devices. Some of the other benefits for owners and building operators include:
- choice of adding more sophisticated devices to their system as they become available,
- potential savings through reduced equipment cost,
- simple integration of BACnet controllers pre-installed on purchased equipment like boilers and chillers.
Will a property management company see any benefits from having BACnet controls in buildings it manages? Yes. BACnet continues to make the industry more competitive, allows more choices, and provides capability for future expansion. It enables the property management company to minimize dependence on any single vendor, as well as allowing for the capability of remote monitoring. For smaller installations, this off-site service results in cost savings because the company can monitor many sites from one or more central property management locations. One operator interface can be used for many systems. Another potential benefit to a property management company is that it will be able to have a common operator interface across equipment from multiple vendors. This lowers staff training costs and reduces operator errors.
Are there cost benefits to using BACnet? Absolutely. With faster, smoother integration of various building systems, implementation costs, as well as facility monitoring and operation costs, will fall. Here’s what you can expect:
- Higher quantity and quality of building operational data.
- Tighter evaluations and analysis.
- Better fiscal planning and operation of the facility.
As closer ties with utility providers are forged, more accurate energy provision and consumption data will be available to all. As an end result, there will be more cost-effective energy management and better utility and consumer cooperation.
Can BACnet products be used for building retrofits? Yes. One of BACnet’s major strengths is open-ended, multiple interfaces. Some BACnet devices allow existing non-BACnet systems to interface with BACnet devices. Once the proper interface has been selected, other BACnet compliant products may be matched, selected and used in conjunction with existing facility components.
Will the system operator require retraining in order to efficiently monitor and control a BACnet-equipped system? Probably not. If an operator is familiar with a company’s front-end products, there should be little retraining when moving up to a BACnet conforming system. The communications part of a BACnet installation will be nearly transparent to the system operator. The system will display information at the front-end just as it does now for any given manufacturer. Typically, monitoring and control points with corresponding values will be displayed along with some identifying nomenclature. Also, a given manufacturer’s operator terminal may communicate with other manufacturers’ control systems. This means once an operator is familiar with one front end, he can continue to use it even if controllers from other manufacturers are used. However, as various products reach the market for any given BACnet manufacturer, an operator may need more in-depth training since installation and programming requirements may differ. Of course, this would be true of any new control system.
Does BACnet provide a means for networking more than one building? Yes, internetworking has been designed into current BACnet products. Campus buildings on a site may be networked with existing or new LAN systems. Buildings not directly connected by LANs may be remotely monitored and controlled using Internet-enabled network routing equipment.
Why should we use BACnet and not other protocols? BACnet is designed specifically for building automation systems so the object, properties and messaging are tailored to this application. In addition, all the major building controls manufacturers offer BACnet controllers so you will have a broad supplier base from which to choose components for your system. BACnet is a global standard with extensive test and certification processes to help ensure minimum system integration time and cost.
The principal benefits of BACnet include:
- Practical interoperability between building automation and controls systems from multiple vendors
- Real choices for scalability between cost, performance and size
- Systems based on a single, unified ANSI and international standard and testing standard
- Endorsement and adoption by nearly every major building automation and controls vendor
- Capability for integration with, and use of, existing LANs and LAN infrastructure
- Robust internetworking including multiple LAN types and robust scalability from very small to enormous system sizes
- Unrestricted growth and the ability to add new innovations and new features anytime
- An open, transparent, no fee, consensus process for ongoing use and maintenance of the standard where every interested party has a voice
Why is it that in some products a point is read only, whereas in others it is read-write. Should not “BACnet compliant” mean that everything is the same? BACnet uses the term “conformant” and generally it means “to conform to what the standard says is required, or if optional to behave as the standard says when you choose to implement it.”
The BACnet standard allows for a lot of options so that it can be used to cost-effectively implement a wide range of systems. For systems where cost is the dominant consideration, it is important to avoid requiring non-essential features because they add cost. Other systems are more complex, and therefore require a richer feature set. These applications can afford the cost of providing those features. Each buyer or specifier can specify the specific features and options they require. In fact, to get the most cost-effective system it is important to accurately specify the BACnet interoperability requirements.
Speaking directly to the read/write question, not all properties are meaningful to write to, and, besides requiring a more non-volatile storage, actually make the system harder to use or easier to compromise. So it is not surprising that suppliers have taken different approaches on where to implement read-write vs. read-only capabilities. Again, each buyer or specifier can select the capabilities they need and include them in their specification.
I have experienced mechanical technicians who are not always familiar with BACnet infrastructure and are quick to blame the technology as the main point of failure and put the responsibility back on us to contact a vendor. A part of the solution is better education, which is one of the reasons why BACnet International developed The BACnet Institute. By including online courses, a curated information library and community forums, the Institute is a valuable resource available at no cost to everyone. In addition to education, diagnostics tools can help in clarifying the source of problems. One of the best things about BACnet is that as an international standard it has created a market for third party tools and competition in that area has resulted in some very powerful, easy to use diagnostic tools.
Is BACnet Plug & Play?
If plug & play is defined as just connecting the devices and having them automatically do everything you want them to do together, then the answer is “probably not.” Only for the simplest of operations will that be possible. For real-world systems, there will be a need for configuration and human intervention. In fact, there is no general purpose plug & play standard for building automation for some very good reasons.
When you buy a DVD player and take it home, there is nearly 100% certainty that you can plug it into your TV and it will work. This is because the interoperation that needs to take place is restricted to one operation (sending a TV signal) and the plugs, cable and signal format are rigidly defined, with only one sender (the DVD player). This is a “plug & play” system. You’ll note, however, that the DVD player doesn’t automatically turn on your TV when you press play, or automatically change from 4:3 to 16:9 aspect ratio, or automatically select the right input, or automatically reprogram your remote control to know how to talk to the DVD player either! These, and dozens more parameters and options, are a “local matter” meaning that some human has to read the manual and figure these things out, usually using a proprietary method to configure the remote controls and settings. And that’s just one basic interoperation.
A large building automation system contains hundreds, if not thousands or tens of thousands, of these kinds of unique interoperations. The number of combinations alone is in the millions. So how can it ever be made to work? The answer, for BACnet anyway, is that the standard defines fairly robust methods for making these kinds of connections, but not all of them are automatic. One of the reasons for this is that humans sometimes have to be involved in the decision making because the individual controllers don’t (and can’t) see the big picture.
Does using BACnet mean that my technician can use the same tools and methods to program devices from multiple suppliers? Generally no. Although BACnet defines many kinds of interoperations between devices, it does not define any standardized programming capability. However, while programming tools are unique to each supplier, a variety of BACnet system diagnostic tools are available that allow technicians to identify problems with BACnet devices, networks and configurations regardless of the equipment supplier. These tools allow technicians to readily support systems incorporating multiple brands of equipment.
What’s the difference between BACnet and Ethernet? Ethernet is a standard for transporting messages from place to place across a network. This is necessary but not sufficient for ensuring building automation equipment can interoperate. In addition to transporting messages, it is necessary to ensure that both the sending and receiving equipment understand the content and context for each message. BACnet provides a standardized set of communications concepts and rules to ensure both pieces of equipment have the necessary understanding. BACnet is designed to serve as a cost-effective basis for a wide variety of building automation systems. To achieve that goal, BACnet supports different methods for transporting messages. Ethernet is one of the methods BACnet supports, but it is not the only one.
When multiple vendors supply equipment, who determines what information is available to the owner and the BACnet operator workstation? Is all the information available to the BACnet operator workstation without reprogramming each vendor interface if changes are needed? As a rule, the specifier provides a detailed list of what information is to be made available through BACnet according to their perception of what is needed for each portion of a system. Left unspecified, the resulting system may or may not meet the needs of the user. In cases where the specification does not include information that is later deemed to be necessary, it may or may not be easy for the vendor to provide access to it, depending on their system design. For example, if the specification says “provide BACnet standard analog input for lobby space temperature” but does not specify that the optional property “Description” must be provided, then it would be very hard to add it later if the installed device does not support the optional “Description” property. So in any particular case, it could be that unspecified information is readily available but not necessarily. This is one reason why it is important to correctly and fully specify the interoperable information up front.
What is a Certificate of Conformance? A Certificate of Conformance is a formal document attesting to the fact that a product has been independently tested and has passed all BTL testing requirements. It was created because it is required as a part of project submittals in some regions of the world.
Does a Product Need a Certificate of Conformance? No. All BTL Listed products have successfully completed testing at a recognized test organization according to the requirements of BTL whether they have a Certificate or not.
Why would a Product not have a Certificate of Conformance? BTL Listings did not automatically come with Certificates of Conformance until January of 2017. Products listed prior to that date may not have Certificates if the regions of the world where they were typically used did not require them.
Is a BTL Listed Product with a Certificate better than a BTL Listed Product without one? No. The testing required for products with Certificates and without Certificates is the same.
Reprinted in part from the BACnet International Website; bacnetinternational.org