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What is BACnet, KNX and Modbus and how do they work together and for which applications?

BACnet:  BACnet was designed to allow communication of building automation and control systems for applications such as heating, ventilating, and air-conditioning control (HVAC), lighting control, access control, and fire detection systems and their associated equipment. The BACnet protocol provides mechanisms for computerized building automation devices to exchange information, regardless of the specific building service they perform. BACnet is a communication protocol for Building Automation and Control (BAC) networks that leverage the ASHRAE, ANSI, and ISO 16484-5 standard protocol. The development of the BACnet protocol began in June, 1987, in Nashville, Tennessee, at the inaugural meeting of the ASHRAE BACnet committee, known at that time as SPC 135P, "EMCS Message Protocol". The committee worked at reaching consensus using an initial three working groups: Data Type and Attribute Working Group, Primitive Data Format Working Group, and the Application Services Working Group. 

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KNX:  is an open standard (see EN 50090, ISO/IEC 14543) for commercial and domestic building automation. KNX devices can manage lighting, blinds and shutters, HVAC, security systems, energy management, audio video, white goods, displays, remote control, etc. It can use twisted pair (in a tree, line or star topology), powerline, RF, or IP links . On this network, the devices form distributed applications and tight interaction is possible. This is implemented via interworking models with standardized datapoint types and objects, modeling logical device channels.

Modbus:  Modbus is a data communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). The development and update of Modbus protocols have been managed by the Modbus Organization since April 2004, when Schneider Electric transferred rights to that organization. The Modbus Organization is an association of users and suppliers of Modbus-compliant devices that advocates for the continued use of the technology.

Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices. Modbus is popular in industrial environments because it is openly published and royalty-free. It was developed for industrial applications, is relatively easy to deploy and maintain compared to other standards and places few restrictions - other than the datagram (packet) size - on the format of the data to be transmitted. Modbus uses the RS485 or Ethernet as its wiring type. Modbus supports communication to and from multiple devices connected to the same cable or Ethernet network. For example, a device that measures temperature and a different device to measure humidity, both of which communicates the measurements to a computer. Modbus is often used to connect a plant/system supervisory computer with a remote terminal unit (RTU) in Supervisory Control and Data Acquisition (SCADA) systems in the electric power industry. Many of the data types are named from industrial control of factory devices, such as Ladder logic because of its use in driving relays: A single physical output is called a coil, and a single physical input is called a discrete input or a contact.

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  What do the protocol abbreviations stand for? BACnet, Modbus, KNX?

BACnet – Building Automation Controls network.

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Modbus - Modbus is a data communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices.

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KNX   KNX evolved from three earlier standards; the European Home Systems Protocol (EHS), BatiBUS,
nd the European Installation Bus (EIB or Instabus).

3

What is the difference between a “standard” and a “protocol” like KNX ?

A protocol is a communication language used in data communications, more specifically are field controls communication protocols e.g., KNX, BACnet, Modbus, M-bus, SNMP, etc. A standard, technical in our context, is a specific level of performance expected on either a piece of equipment or all-inclusive system based on proven, established engineering or technical principles. However, that said, both the BACnet and KNX protocols became a standard in ASHRAE/ANSI Standard 135 in 1995, and ISO 16484-5 in 2003. The Method of Test for Conformance to BACnet was published in 2003 as BSR/ASHRAE Standard 135.1. BACnet is under continuous maintenance by the ASHRAE Standing Standard Project Committee 135. Protocols and standards are not one in the same i.e., the former does not automatically apply to the latter, respectively.

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What is the significance and associated benefits (e.g., cost savings) of standardizing on a protocol like KNX?

Standardizing on a protocol has the following benefits:

• Streamlined design and commissioning. The KNX building technology platform is truly inter-operable; the fixed standard data communication structure, which all manufacturers based their products/SW on, to streamline data transfer between components. This saves significant engineering, programming time on your projects

• Manufacturer-Agnostic i.e. multiple market options, proven and future-proof. When a protocol is adopted as standard, such as BACnet and KNX, you can “connect” between manufacturers, leaving you multiple options when selecting your product suppliers and system integrators/installers. Therefore, there is no cost for protocol gateways or additional isolated (siloed) systems. There is also a global network of knowledge and expertise to draw upon, therefore no problem too large to solve in the market.

• Backwards- and Forwards-Compatible.

• Installation material and labor savings.  There are cost savings on material due to less power and control wiring required for LED lighting, daylighting (blinds) and HVAC when compared to standard analog control. This also saves on the amount of installation labor to install all of those wire runs for of all three trades and also material savings by using only one room sensor/switch instead of three. The robust KNX control signal in the KNX rated cable allows for installation in traditional raceways, trunking, conduit and modern prefabricated wiring systems. This means that the KNX wire can be installed with the power wiring, alleviating the requirement for a separate raceway for low voltage (e.g., BACnet) saving significant time and money.

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  What types of markets and their associated buildings would I find these types of protocols?

Construction and (Light) Industrial (C&I) key markets: Education (K12, Universities), Commercial Offices, Light Industrial (e.g., GRR), Hospitals.

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Generally, what protocol works best for which application and why?

The KNX protocol is an ideal platform for the occupant/room i.e., field level (e.g., lighting switching, VAV, blinds) with BACnet ideal for HVAC central and room automation in commercial buildings. Modbus would be for the Industrial sector mainly, however it is used as the primary protocol, along with M-Bus and SNMP, for electrical distribution control system (EDCS) in commercial and light industrial buildings.