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Delta Controls & BACnet®


What is BACnet?

BACnet is a data communication protocol for Building Automation and Control Networks. Developed under the auspices of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), its purpose is to standardize communication between building automation devices and systems from different manufacturers. The protocol is supported and maintained by ASHRAE Standing Standard Project Committee 135.


What are the benefits of BACnet?

BACnet affords facility owners and managers maximum flexibility and cost-effectiveness by allowing control products made by different manufacturers to be integrated into a single, uniform system. It is designed to allow HVAC/R, lighting, fire, access and security devices to interoperate. Owners can select the best technologies and services available, with the investment protection of being able to competitively expand current systems, without being “locked in” or having to replace them in the event that an original supplier loses favor. BACnet also facilitates single workstation control in campus/multi-building environments composed of a variety of different manufacturer’s control systems.


Why was BACnet developed?

Before BACnet was developed, every manufacturer’s control equipment line was based on its own proprietary protocol. Any time equipment from different manufacturers needed to share information, custom software and hardware had to be developed and maintain at considerable time and cost.


How was BACnet developed?

BACnet was developed by a cross-section of industry professionals, comprising manufacturers, consulting engineers, end-users, government agencies and the academic community. It took over nine years to develop, was publicly reviewed and was adopted in 1995 as ANSI/ASHRAE Standard 135-1995.


Has BACnet been adopted as a public standard internationally?

Yes. In addition to being an American national standard (ANSI), BACnet is an established European pre-standard (CEN) and in the final stages of becoming a world standard (ISO). There are now thousands of BACnet projects installed and operating across more than eighty countries worldwide.


What is interoperability?

Interoperability is the result of different manufacturers’ devices using a common set of rules for data structure and transmission, allowing them to exchange data and execute commands.


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

BACnet can be implemented in any building or set of buildings, regardless of size. These systems can be very simple, with few devices, or very complex, with practically any number of devices and manufacturers.


Does BACnet apply to all system levels?

Yes. From front-end workstations to network controllers and routers, central plant controllers, unitary controllers, actuators and sensors, BACnet is designed to be scaleable and provides a complete, cost-effective communication standard from top to bottom.


What networks does BACnet specify?

BACnet specifies six network types to accommodate different project and system requirements. These networks use widely accepted LAN standards, including Ethernet (IEEE 802.3/ISO 8802-3), ARCNET (ANSI/ATA 878.1), master slave/token passing (MS/TP, a twisted-pair RS-485 network created by BACnet), point-to-point (PTP, also created by BACnet) and LonTalk. The sixth option, BACnet/IP, was added later on to allow BACnet messages to be transported across the Internet and other IP-based wide area networks.


What is native BACnet?

Native BACnet typically refers to a device that inherently represents data in BACnet format and communicates utilizing BACnet messaging. Native BACnet devices can be connected to a BACnet system without requiring a gateway device or software driver to translate to and from any proprietary protocols. Typical examples of native BACnet devices would be a native BACnet VAV application controller at the field level, and a native BACnet general system controller for central mechanical systems (e.g. air handing units) at the automation level.


What are the advantages of native BACnet?

Systems incorporating native BACnet devices at all levels provide facility owners and managers with superior system performance and interoperability. They are not compromised by proprietary software drivers and/or external gateways, which typically degrade system performance (throughput) and limit functional scope. Rather, BACnet messaging is utilized to communicate through all system levels, providing a consistent and seamless system-wide communications infrastructure. This also ensures owners with maximum investment protection and freedom of selection for future system expansion and upgrades, since they are not bound by the technical and commercial restrictions of proprietary drivers/gateways, as well as their potentially high maintenance costs.


When does it make sense to consider specifying a gateway?

It may be appropriate to specify an available gateway product for cost-effectively upgrading or expanding an existing facility with a BACnet system. The gateway bi-directionally translates the messages of the proprietary legacy system to and from the BACnet protocol, allowing them to interoperate. Another case is when integrating building systems that do not yet have native BACnet devices available (e.g. fire). Various gateways are available on the market for connecting proprietary equipment and systems to a BACnet system. Specifiers should carefully review the gateway performance specifications (including PICS) to verify that the system interoperability requirements can be met.


What is PICS?

PICS stands for Protocol Implementation Conformance Statement. It is a detailed description for a given BACnet device stating its inherent BACnet capabilities. The level of BACnet functionality are typically scaled to suit the type of building automation device, ranging from simple intelligent peripheral devices to sophisticated operator workstations. Thus PIC statements are important for specifiers and users to ensure that the various devices will satisfy the desired interoperability requirements when designing and implementing integrated BACnet systems.


What are BIBB’s?

BIBB stands for BACnet Interoperability Building Block. BIBB’s represent specific individual function blocks for data exchange between interoperable devices. They are designed to be a simplifying tool for engineers to be able to write concise specifications describing the interoperability requirements of the various devices comprising a BACnet system. The various BIBB’s that have been defined to date are divided into five categories: data sharing; alarm & event management; scheduling; trending; device & network management.


Where can I get more information about writing specifications for BACnet systems?

A document published by the National Institute of Standards and Technology (NIST) - Internal Report 6392, GSA Guide to Specifying Interoperable Building Automation and Control Systems Using ANSI/ASHRAE Standard 135-1995, BACnet - may be particularly helpful. This report is available to the public at (located in the bibliography section).


What is BACnet International?

The BACnet Interest Group – North America (BIG-NA) and the BACnet Manufacturers Association (BMA) have joined to form BACnet International - a non-profit organization of companies that design, market, and install building automation products. It includes various manufacturers of BACnet products, all of which are committed to ensuring that their BACnet products will interoperate.


What is the purpose of BACnet International?

BACnet International’s mandate is to encourage the successful and widespread use of BACnet in building automation and control systems through interoperability testing, educational programs, and promotional activities.


What is the BACnet Testing Laboratory (BTL)?

The BACnet Testing Laboratories was formed by BACnet International to perform BACnet compliance & interoperability testing of building automation products utilizing BACnet. A product-listing program identifies the products tested by BTL that have passed the necessary requirements.


Why is BACnet compliance testing important?

Compliance testing provides assurance of interoperability between different manufacturers' products by verifying that the products correctly implement BACnet.


Why specify products listed by BACnet International?

Listed products are authorized to display the “BTL” logo, and are presented on BACnet International's web site. This enables specifying engineers and end users to specify and purchase listed products with the assurance that these products have passed extensive BACnet interoperability testing and comply with the BACnet standard.


Where can I get more information about BACnet?

BACnet International:

ASHRAE BACnet Committee:

European BACnet Interest Group:

Publications (incl. the BACnet standard):

Delta Controls Summary:


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