Building Automation Protocol selecting
Each of the competing protocols claims to be the best. So how do facility executives select the one that is best suited for the facility?
Data is communicated between devices through a Communication Protocol. It is the language that a particular device is able to interpret and forward to other devices on the network. Some common protocols are BACnet, Lon, and Modbus.
Protocols must be selected based on the needs of the facility and its ability to support a particular protocol. Each has been used many times to implement an interoperable system. Each has its advantages and disadvantages. Involve your information technology department. They generally are the controlling agency for the facility’s network infrastructure.
When selecting a control system choose one where the front end is compatible with a number of protocols. This will give greater flexibility as building equipment and devices change over time.
Why you want a BMS with open protocols
A BMS with proprietary protocols locks the system owner into using a single BMS vendor. For example, you can’t remotely change the set points of a proprietary BMS unless you use the vendor’s software.
In contrast, with open and standard BMS protocols you can shop for alternative providers of digital devices and enterprise software.
Building Automation Controls Network (BACnet): BACnet is a network protocol specifically used for multiple devices to communicate across building automation systems by system users and building system manufacturers
Modbus: Modbus is a network protocol best used for industrial automation systems specifically for connecting electronic equipment. Although Modbus is best for industrial applications, its simplicity allows it to be a useful tool for building automation as well.
LonWorks: LonWorks is a communication network protocol useful for building automation applications designed on a low bandwidth, for networking devices through power lines, fiber optics, and other media.
Protocol | BACnet | Modbus | LonWorks |
Full Name | Building Automation Controls | Serial Communication Protocol | Local Operational Networks |
Developed By: | ASHRAE | Modicon Inc. | Echelon Corporation/ Motorola |
Use | Communication across devices | Connection between devices | Networking devices through power lines, fiber optics, and other media |
Markets | Industrial, Transportation, Energy Management, Building Automation, Regulatory and health and safety | HVAC, Lighting, Life Safety, Access Controls, transportation and maintenance | Home automation, industrial, transportation, and public utility control networks. |
Examples | Boiler Control, Tank Level Measurements | Tasks such as request temperature reading, send status alarm, or fan schedule | Security, lighting systems, HVAC, machine control, manufacturing, metering |
Proprietary | No | No | Yes |
Transmission Modes | Ethernet, IP, MS/TP, Zigbee | ASCII, RTU, TCP/IP | MS/TP, network, SNVT |
Standards | ANSI/ASHRAE Standard 185 ;ISO-16484-5; ISO-16484-6 | IEC 61158 | ANSI/EIA 709.1; ISO/IEC 14908-1, 14908-2, 14908-3, 14908-4 |
Costs | Low; No charge for usage or licensing fees | Low; No charge for usage or licensing fees | High (proprietary); Limited users (exclusive to actual members; mostly manufacturers) |
Network Interfaces | Existing LANs and LANs infrastructure | Traditional serial and Ethernet protocols | U10/U20 USB Network Interface; i.LON SmartServer; i.LON 600 |
Testing | BACnet Testing Labs | Modbus TCP Conformance Testing Program | Products must conform to LonWorks protocol |
Advantages | - Scalability between cost, performance and system size | - Easy connection to Modicon | - Web based tool; saves time and cost |
- Endorsement and adoption by nearly every major vendor in North America and many other countries | - Suitable for small/medium volumes of data (≤255 bytes) | - Numerous developers of LonWorks products in the market | |
- Robust internetworking including multiple LAN types and dial-up | - Data transfer designed for industrial applications | - Less Architecture at device level | |
- Unrestricted growth and the ability to add new innovations and new features anytime | - Openly published and royalty-free | ||
- Easy to deploy and maintain | |||
- Moves raw bits or words without placing restrictions on vendors | |||
Disadvantages | - Limited the number of field devices that can connect to a master station except Ethernet TCP/IP | - Limited the number of data types; Large binary objects are not supported. | - Outdated |
- MT/TP-Wire Length | - No standard method for a node to find the description of a data object, i.e. finding a register value represents a temperature between 30◦ and 175◦. | - Controlled devices & variables are connected to a separate control device. (Not recommended due to network interruptions producing system failures) | |
- Ethernet-Infrastructure | - No security against unauthorized commands or interception of data | - Extensions are allowed only through the LonMark Consortium. | |
- New standard has security standard but not implemented in all devices | - Transmissions must be contiguous which limits the types of remote communications devices to those that can buffer data to avoid gaps in the transmission. | - Hardware specific, and requires the Neuron chip for network movement of the protocol. | |
- Great amount of configuration and programming required | - Close to “plug & play” ability, yet still far from achieving interconnectivity using Microsoft Windows. | ||
- Protocol is not common in the SIMATIC family |
To determine whether a BMS protocol is open, ask the vendor two simple questions:
1. Can your competitors exchange data with your BMS?
2. Is the system’s protocol published in such a way that it’s easily accessible to everyone (including competitors)?
Even the ASHRAE BACNet committee has convened a working group to define use of XML with BACnet systems. The group is also working to define web services that will enable data exchange between building automation and control systems and various enterprise management systems.
Use these criteria when you’re choosing devices and BMS:
1. For devices such as RTUs and refrigeration controllers, look for ones that use open protocols such as BACnet or Modbus.
2. Make sure these devices give you both “read” and “write” capabilities so you can change set points.
3. For easy enterprise access, choose a BMS with web services and XML capabilities.
4. Make sure the web services of the BMS allow both read and write capabilities.
5. Be sure the BMS supplier provides the XML dictionary and definitions of web services to anyone, including competitors.
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