BACnet

What is BACnet, and who maintains it?

BACnet is a data communication protocol that lets controllers, sensors and other equipment in a building exchange information over a network. Its name is short for Building and Control Network. The committee SSPC 135 of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) developed it and now maintains it. The committee publishes the protocol as ANSI/ASHRAE 135. Its website announces the 2024 edition, which includes 17 addenda to the 2020 edition. The committee calls BACnet the global data communication standard for building automation and control networks.

The purpose is interoperability between makers. A 1990s article on the committee website says BACnet ends the frustration of proprietary control systems that cannot talk to each other. It names heating, ventilation and air conditioning (HVAC), lighting, security, fire, access control and maintenance among the controls it handles. A building management system can use that shared language to show data from equipment bought from several suppliers.

Why does ISO 16484-5 matter in Slovakia?

ISO 16484-5 is the data communication part of the series on building automation and control systems (BACS). The BSI catalogue entry for the 2008 British edition lists sections titled BACnet protocol architecture, BACnet procedures and encoding BACnet protocol data units. This shows that the ISO part contains the BACnet protocol itself. That BSI edition was withdrawn in 2011, so this page uses it only to show the structure of the standard.

In Slovakia the standards office adopted it as STN EN ISO 16484-5, catalogue number 74 7400. Its Slovak title is Automatizácia v budovách a riadiace systémy (BACS), Časť 5: Dátový komunikačný protokol. The cover sheet shows the January 2023 edition, based on ISO 16484-5:2022. It includes the English version of the European standard. It withdraws the January 2018 edition of the same standard. The full text is sold by the standards office, so this page relies on the catalogue cover sheet for the number, title and edition.

Designation	Issued by	What the sources read show
ANSI/ASHRAE 135	BACnet Committee, ASHRAE SSPC 135	2024 edition announced, with 17 addenda to the 2020 edition
ISO 16484-5:2022	International Organization for Standardization	Data communication protocol part of the BACS series
STN EN ISO 16484-5 (74 7400)	ÚNMS SR	Slovak edition of January 2023, which withdraws the January 2018 edition

How does BACnet describe a device on the network?

BACnet does not use the general word point for every sensor input or control output. It defines a standard set of objects, and each object has a standard set of properties. The properties describe the object and its current state to other devices on the network. Other devices can then read them and, where the device allows it, control the object through them. An analog input object, for example, stands for an analog sensor input such as a thermistor.

Every BACnet device has a device object. Its properties describe the device to the network. One property lists every object inside the device, and others give the maker name and the model. Properties of the device object also tell which objects and services the device supports.

The protocol also lets makers add proprietary objects and properties. Another maker's equipment will not necessarily understand them. That is why a tender should ask for the objects the building management system needs, and not only for BACnet.

How is BACnet different from KNX?

BACnet and KNX both aim to make equipment from different manufacturers work together. They have different maintainers and different audiences. The KNX Association describes KNX as an open standard. It says that more than 8,000 certified devices come from more than 500 manufacturers. It shows apartments, family homes, villas, hotels and office buildings among its project categories. The KNX entry explains how a KNX installation works. The table sets out what the sources read show.

Question	BACnet	KNX
Who maintains it	BACnet Committee, ASHRAE SSPC 135	KNX Association
How the maintainer describes it	Global data communication standard for building automation and control networks	Open standard
Equipment it names	HVAC, lighting, security, fire, access control and maintenance	More than 8,000 certified devices from more than 500 manufacturers
Project types the maintainer shows	Not stated on the committee page	Apartments, family homes, villas, hotels, office buildings

Neither source gives a market share for Slovakia, so this page makes no claim about which protocol is more common in Slovak houses.

How is BACnet different from Modbus?

Modbus is a separate and older protocol with its own entry. Modbus defines message formats, function codes and data tables, and the meaning of each register comes from the device maker's register list. BACnet defines objects with standard properties, so a device can describe its own data. A device that speaks only one of the two needs a gateway or controller that speaks both. Only then can it appear in the other's front end. Ask which protocol each device speaks, and where you need a gateway.

Is BACnet a practical choice for a family house in Slovakia?

Usually it is not the first thing to ask about. BACnet suits networks where a management system joins equipment from several suppliers. A family house often has one heat pump, one ventilation unit and a set of lighting circuits. It needs little of that kind of integration. This is the design judgement of this practice, not a market statistic. For whole-house control in a family house, read the KNX entry and the smart home automation entry first.

BACnet can still matter if the plot also holds a small commercial space or a rental unit that an operator runs as a larger building. In that case the operator may ask for BACnet. Agree the boundary between the two systems at the start of design.

What should a client check before specifying BACnet?

A specification that asks only for BACnet compliance leaves too much open. These steps make a tender more precise:

• Which objects and services each controller supports, taken from the manufacturer's documentation and not from a general claim.
• Which building management system will read the data, and whether it can read every object the controllers expose.
• Whether the controllers use proprietary objects or properties that the building management system may not understand.
• Who will commission the network, and whether that person can read the device list and trace a missing sensor.