Open systems — the way forward
Anders Norén explains how using a number of open protocols to bring together a host of building services is the key to interoperability.Interoperability in a typical commercial office building means bringing together a host of building services and their diverse range of communication systems. Here are some examples. • BACnet over RS485 or IP is supported by most HVAC control systems. • Meters, chillers and inverters commonly use Modbus in the UK. • M-bus is also used in the metering of utilities. • Two protocols used in lighting are EIB/KNX and DALI. • Moving on to the management and interpretation of data, XML is used for the exchange of data between web-based applications and devices. • LonWorks typically serves HVAC, lighting and process devices on a network. • OPC server and OPC client enables PC-to-PC applications. • TCP/IP is used to transmit data across communications networks, such as an organisation’s IT network or the Internet. Currently, the end-user (facilities manager, financial director etc.) is offered front-end solutions that, in combination with intelligent outstations, manage and control the connected building services at management level. These front-end solutions are normally web-based and provide the end-user with communication and access to the various building services from many locations using nothing more than a web browser. Communication between the web-based solution and the system itself is based on OPC, BACnet, XML or proprietary systems. The network connections are achieved using the building’s IT network via TCP/IP or the traditional building management system (BMS) network wiring (i.e. RS485 over a single twisted network cable). To such a network, the industry can add and combine different third-party sub-systems (metering, security, fire alarm etc.) that, together with the HVAC main plant, will result in an integrated BMS automation and control. These sub-systems are accessed from a common front-end and can be built up using products from various suppliers employing the communications protocols as mentioned above. The communications network may comprise RS485, LonWorks or TCP/IP, or a combination thereof. Open-system examples
Here are three examples that clearly demonstrate the advantages of open systems. Metering: Traditionally, meters have been read manually or connected to the BMS by counting pulses. A much more cost effective solution is to network the meters using Modbus or M-bus.
From a web browser at management level, a variety of protocols are widely used to connect the wide range of equipment that services a modern building — and no single one is likely to become the de facto standard.
Inverters: Danfoss and ABB drives both support Modbus, and ABB also supports BACnet — making it possible to interface their inverters to a BMS using a bus connection to the controller/outstation, rather than hard-wired using physical inputs and outputs. With a bus connection, extensive additional data can be recorded, such as speed, frequency output, current, torque, voltage, energy consumption, and faults with error codes. VRV systems: Variable refrigerant volume (VRV) systems for air-conditioning have grown in popularity in recent years and offer easy communications with a BMS via Modbus, BACnet or LonWorks — either over RS485 or IP. Open-system checklist
Most companies have an IT network infrastructure based on TCP/IP, so why not make use of it. It would be a missed opportunity and a waste of financial resources not to let the building control system utilise that investment by either offering access to the BMS across the IT network or allowing the BMS to communicate between its outstations via the network. Involve the people responsible for IT and show them what the building-control system can do, how easy it can be to connect a device on the network with an address and how that device can be accessed from any PC. Concerns voiced over network security are often the result of lack of knowledge; in reality the BMS will have little influence. Indeed, the security measures applied to modern IT infrastructures will prove beneficial to the BMS as well as its network. When specifying a BMS, make sure that it can interface using open and universally available protocols. Also, make sure that this applies to third-party products and systems. Select meters with Modbus or M-bus, VRV systems that can communicate over Modbus or BACnet. Ensure that users can access the whole system from any PC on the IT network, enabling the day-to-day running of the building to be more effective and efficient. Standardisation or open system?
There are at least eight different types of open protocol actively used in today’s building-control projects, even without counting wireless standards. These protocols are often complementary and used to integrate different sections of the system. The question, therefore is not which of them will be the one and only de facto standard but, rather, the opposite. The more likely event is that the client will ask for, and suppliers and installers will offer, the integration of a multitude of different systems and sub-systems using a number of these open protocols, rather than trying to agree on one specific protocol. Anders Norén is managing director of Priva Building Intelligence Ltd.