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Frequently Asked Questions (FAQs)

 What is BACnet?

 

 How can I learn more about BACnet?


 Why was the BACnet protocol developed?

♦ What do BACnet products look like?

♦ Do BACnet systems provide anything special that traditional DDC systems do not?

♦ Is a BACnet system easily expandable?

♦ What types and sizes of buildings are best suited for BACnet product installation?

♦ Does a BACnet system provide better building HVAC control than traditional DDC systems?

♦ What's the upside for the building owner if a BACnet system is used?

♦ Will a property management company see any benefits from having BACnet controls in buildings it manages?

♦ Are there cost benefits to using BACnet?

♦ Can BACnet products be used for building retrofits?

♦ How does BACnet affect consulting engineers?

♦ Will the system operator require retraining in order to efficiently monitor and control a BACnet equipped system?

♦ Does BACnet provide a means for networking more than one building?

♦ Is there an independent testing agency to certify BACnet products?

 Do proprietary extensions to BACnet make devices incompatible?

♦ Are standard objects preferable to proprietary objects?

♦ Are there any advantages or drawbacks to combining BACnet & KNX or LonWorks in a single system?

♦ Why should we use BACnet and not other protocols?

♦ Should I use BACnet Gateways?

♦ How has BACnet impacted availability of third party resources to support device, functional and application integration?

♦ 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?

♦ Considering the current state of the controls market and BACnet, what are the odds of getting a control loop with equipment made by six different manufacturers (chosen at random) to work properly?

♦ Is it possible to create Fire and Life Safety systems with BACnet?

♦ I work for a government agency and therefore must go out for bids for any new product. Do you have many government entities as customers? Is compliance an issue regarding your standard?

 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.

♦ What is the difference between the terms "BACnet" and "true BACnet?"

 Is there a BACnet Interest Group in the US?

Over time we've designed several different BAS systems in our buildings. Does BACnet allow us the option to operate them and to talk to them all?

Is BACnet Plug & Play?

Does using BACnet mean that my technician can use the same tools and methods to program devices from multiple suppliers?

What's the difference between BACnet and Ethernet?

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?

Is BACnet involved in the Smart Grid standardization work?

Who makes up "the BACnet council?" DDC vendors? How can I contact them?

 

♦ What is a Certificate of Conformance?

 

Does a Product Need a Certificate of Conformance?

 

Why would a Product not have a Certificate of Conformance?

 

Is a BTL Listed Product with a Certificate better than a BTL Listed Product without one?

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.

 

How can I learn more about BACnet?

There is a lot of information available about BACnet. One place to start for education and information is The BACnet Institute. The Institute includes an online, self-paced introductory BACnet course called BACnet Basics. It also has a curated, searchable library of white papers, conference presentations and videos on various BACnet-related topics. For answers to specific questions the Institute includes an “Ask the Expert” section and also includes a community forum for discussion. The Institute can be found at TheBACnetInstitute.com where the registration and content are free of charge.


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.

How does BACnet affect consulting engineers?
There is a strong need for professionals who can accurately specify BACnet interoperability requirements to achieve specific system objectives. Consulting engineers can provide substantial value by ensuring the BACnet portion of specifications are clear and complete. They can be the front line in saying that a specification that simply states "system should be BACnet compliant" is not sufficient. To do this, engineers need to be educated on BACnet, BACnet products and networks.

Because of BACnet's inherent approach to communications, many BACnet devices are being designed with extensive remote access capabilities. Web-based access to a building's control systems from the engineer's office is already commonplace. This access to supervising BACnet installations translates into saved time and money for consultants responsible for monitoring installations.

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.

Is there an independent testing agency to certify BACnet products?

Yes. There is an organization called the BACnet Testing Laboratories (BTL) for testing and certifying BACnet products. This organization is administered by BACnet International to provide independent oversight of BACnet product testing and certification.  The list of BACnet tested products is available on the BTL website (bacnetlabs.org) along with the information on the BACnet product testing process.


Do proprietary extensions to BACnet make devices incompatible?
Not necessarily. There are essentially three areas where BACnet can be extended: Object Properties, Services, and certain Enumerated Values. If a device implements any of these extensions, it is still interoperable with other BACnet devices that share the standard objects, properties and services that it implements.

If a device implements non-standard objects, or non-standard properties of standard objects, it may still be possible to interoperate effectively with those objects and properties. BACnet object properties have values that are said to be of a particular "datatype." BACnet defines a number of so-called "primitive" or "application" datatypes including real (floating point) numbers, signed and unsigned integers, character strings, bit strings and so forth. BACnet also allows "constructed" datatypes that are collections of primitive and other constructed types. Devices using non-standard objects that have only simple (primitive) datatypes for their properties are more universally interoperable than those that do not.

Extended enumerations can appear in several places in BACnet communications. A common area is in the reporting of Alarm and Event notifications. Devices may be designed to report extended "event types" that are not defined in BACnet using so-called proprietary event types. This doesn't necessarily inhibit interoperability but it may be less than optimal in some instances. For example, an operator workstation might receive and report an alarm that is "Event Type 456" if it does not know what the "human readable" interpretation of that proprietary event type should be.


Are standard objects preferable to proprietary objects?
Generally yes. Standard objects have the advantage that they exhibit behavior that is already documented in the BACnet standard. Proprietary ("non-standard") objects can't be used unless you know of their existence and you have a description of their behavior as well. Assuming that you know what a non-standard object's properties are and what they are intended to do, it is possible to take advantage of them.

It is important to keep in mind that if a vendor has designed their non-standard object with interoperability in mind, then it may be easier and more efficient to use than standard objects. Consider, for example, a special type of controller that contains 50 parameters that might be of interest. One way to implement BACnet in this controller might be to represent each parameter value as the Present_Value property of a BACnet Analog Value object. This has the advantage that everyone knows how to use Analog Value objects. However, even with the minimum set of required properties, Analog Value objects have a lot of additional overhead in terms of memory and required functionality. In contrast, those 50 parameters might be more efficiently represented as 50 properties of a non-standard object (or 5 objects with 10 properties, or 2 with 25 and so on). In this case, there is no overhead, and the explanation of how these parameters work might be greatly simplified.


Are there any advantages or drawbacks to combining BACnet & KNX or LonWorks in a single system?
There may be some advantages but also some drawbacks. A mixed system with both BACnet and other components would require more complex commissioning, maintenance, training and may lose some degree of interoperability. However, it might be the preferred solution in situations where there is already an installed base of functioning LonWorks or KNX equipment that can be accessed from the BACnet network using an appropriate gateway device. It may also be the preferred solution in a new application where the required devices have KNX or LonWorks, but do not have an available BACnet interface.

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

Should I use BACnet Gateways?

As a general statement, BACnet gateways are not a preferred solution because they introduce additional configuration and system maintenance complexity as well as adding cost.  Instead, the trend for at least the past ten years has been to implement BACnet capabilities directly in controllers and devices.


How has BACnet impacted availability of third party resources to support device, functional and application integration?
Unlike proprietary technology, which by definition can really only be supported by the vendor’s own employees or factory-trained representatives, BACnet has created a market for third parties who can offer support, training and hardware/software resources on a par with, or even surpassing, traditional vendor-sourced services. There are a growing number of sources for third party BACnet applications and support. This creates additional options for users and drives the improvement of support products and services throughout the industry.

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.

Considering the current state of the controls market and BACnet, what are the odds of getting a control loop with equipment made by six different manufacturers (chosen at random) to work properly?

This is a question that can't be answered with certainty but assuming the products have BTL Certification it is highly likely all six devices would interoperate and work properly using standard BACnet objects and services. This conclusion is based on BACnet's flexibility and the community’s global testing and certification process plus broad supplier participation in BACnet PlugFest interoperability events.

Is it possible to create Fire and Life Safety systems with BACnet?
Fire and Life Safety systems have some unique regulatory requirements that may include local jurisdictional requirements. So, while BACnet was designed from the very beginning to make this possible, in many cases UL listed Fire and Life Safety systems provide BACnet interfaces to simplify integration and enhance interoperability even when using some other technology internally.


I work for a government agency and therefore must go out for bids for any new product. Do you have many government entities as customers? Is compliance an issue regarding your standard?
BACnet is an international standard (ISO-16848-5) as well as an ANSI standard. One of the key motivators behind the creation of BACnet was to assist government and municipal entities in specifying and procuring equipment that was able to interoperate in standardized ways. BACnet has been very successful in this regard; today there are literally millions of BACnet devices in use worldwide, many of them in government facilities. Producing interoperability specifications requires some consideration though because the whole point of interoperability is being able to perform specific interoperations. Just like pressures, diameters, lengths and sequences of operation, interoperability must be specified in some detail. A specification that just says "shall be BACnet" does not achieve very much as this is not sufficiently detailed.

BACnet allows devices to implement subsets of the standard and includes many options so the specifier must decide what their system requires and include that in their specification. Many specifiers have realized that it pays to become educated about BACnet and how to specify and apply it successfully. There are, in fact, some consulting engineers who specialize in BACnet.


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.

What is the difference between the terms "BACnet" and "true BACnet?"

The BACnet standard does not define any such term as "true BACnet." By design and intent, BACnet defines a broad set of capabilities and a particular BACnet device typically implements only some of them. A device that implements capabilities A, B and C isn't "inferior to" or "less true" than a device that implements capabilities A, B, C and D.

Is there a BACnet Interest Group in the US?

Yes. BACnet International provides a wide range of information, education and services to support the BACnet community in the US and the rest of North America.

Over time we've designed several different BAS systems in our buildings. Does BACnet allow us the option to operate them and to talk to them all?
If the buildings use controllers based on BACnet, then you could use a wide area network (WAN), the public Internet, or even dialed telephone access to connect a central workstation or management center to each building. If some buildings do not have BACnet devices installed, it may still be possible if a gateway can be added to those buildings to bring them into the BACnet network architecture. In either case, the central monitoring station could generally be supplied by any BACnet workstation vendor, not necessarily the same as the vendor of controllers in the buildings.

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.

Is BACnet involved in the Smart Grid standardization work?
Yes. BACnet has been identified as a Smart Grid standard important in the customer domain. Members of the BACnet committee have been active in the NIST standards coordination effort in the Smart Grid Interoperability Panel and specifically within the Building-to-Grid (B2G) domain expert working group. Also, within BACnet, the Smart Grid-Working Group (SG-WG) is working to take these external activities and translate them to BACnet constructs for effective smart grid integration of the facility.

Who makes up "the BACnet council?" DDC vendors? How can I contact them?

There is no "BACnet council." There is a Standing Standards Project Committee (SSPC-135) that is organized by ASHRAE and has 13 voting and 13 non-voting members, each with a four-year term. The selection of committee members represents a balance of vendors, end-users, consulting engineers, government, and interested third parties. Voting is by a consensus process, not simple majority.

 

The SSPC has a number of Working Groups that deliberate and propose new additions and changes to the standard, each with its own convener. The SSPC and Working Groups meet four times per year; twice in conjunction with ASHRAE Summer and Winter meetings, and two Spring/Fall interim meetings. All four meetings are open to anyone who wishes to attend. Although formal votes are restricted to voting members, many votes are informal "straw polls" and discussion is open. Anyone can have a voice by coming to a meeting.

Additional information on the SSPC  can be found at
bacnet.org.

In addition to the SSPC, BACnet International administers the BTL Working Group (BTL-WG), which is composed of technical experts that meet separately from the SSPC. The BTL-WG defines the test procedures and policies for the BTL Certification program which operates under BTL Laboratories. The test procedures are closely aligned with, but not always the same as, the SSPC's test standard 135.1. BTL-WG has a formal liaison with the SSPC.

 

Additional information on BTL Laboratories can be found at bacnetlabs.org

 

 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.

 

 














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