HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New Millenniumto the building automation systems in use. The Canadian AutomatedBuilding (CAB) Protocol was supported by Public Works and GovernmentServices Canada (PWGSC) and compatibility with this protocol isnow required for all new building control systems procured by PWGSC.CAB uses a Local Area Network between gateways and workstations.It defines a standard interface console that connects to the LANand communicates to nodes via defined messages. CAB provides user interfacecapabilities across multiple-building systems.CAB is essentially a high-speed network protocol and best usedwhen communicating between devices with good processing capabilities.It is rarely used for field-device communication.MODBUSMODBUS is an Instrument Society of America (ISA) protocol thathas been developed for factory automation. It allows communication betweendifferent manufacturers’ programmable logic controllers (PLCs)and intelligent field devices, such as transmitters and actuators.Devices that use MODBUS typically require healthy processing capabilities,and are usually more expensive than the control devices usedin a typical commercial or institutional building for environmental control.From proprietary to public standard, the proliferation of industrialnetworks offers user benefits, but unfortunately many of the benefits arespread across different networks.Plant-wide network architectures are evolving into three layers.ControlNet fits into the middle automation and control layer for realtimeI/O control, interlocking, and messaging. The upper informationlayer for plant-wide data collection and program maintenance can bedone with Ethernet. The device layer for the integration of individual devicesis handled with the device buses like DeviceNet and FoundationFieldbus.References“A Host of Options at the Device Level,” Worldbus Journal, (Supplementto InTech), Vol. 46 No. 10, October 1999, pp. 38-42.©2001 by The Fairmont Press, Inc. All rights reserved.