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经典：BACnet® and LonWorks®

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吴志扬  2002-03-25 12:00

BACnet® and LonWorks®: A White Paper By David Fisher, PolarSoft® Inc. Introduction Over the course of the past fifteen years, building owners, managers and consulting/specifying engineers have become increasingly frustrated by incompatibilities and limited opportunities for the integration of building automation and control systems. Although the sophistication and flexibility of networking and communications technologies in general have been increasing geometrically, controls systems for buildings have carried forward a legacy of proprietary thinking which has impeded the natural migration of many of the benefits of open networking technology into building systems. The bottom line effect has been that, while many modern building automation and control systems incorporate some of the latest advances in networking technology, the benefits of interoperability, configuration flexibility, and performance-based pricing have yet to be realized by building owners and operators. Through accident or intent, building automation and controls systems have simply failed to embrace true open systems concepts effectively for building owners. Several solutions have become available recently which promise to change this situation permanently and dramatically. One such solution is called BACnet™;: The Building Automation and Controls Network. BACnet is a standard for computers used in building automation and controls systems that has been developed over the past nine years by ASHRAE. In December of 1995, BACnet was also adopted by ANSI, and is now an American National Standard (ANSI/ASHRAE 135-1995). Nearly every major vendor of building automation and controls systems in North America has demonstrated support for BACnet in the form of new products, many of which have been displayed at the annual AHR/ASHRAE show in Atlanta this year. Another completely different solution is called LonWorks(r) which is a proprietary communications technology which has been marketed for several years by the Echelon Corporation in partnership with Motorola. Various vendors have used LonWorks successfully in recent years to provide solutions for small controls systems applications, in some cases involving multiple vendors. This paper will explore both of these systems in some detail to help bring into focus the substantial differences between each approach. We will also focus on various popular myths in order to dispel some of the confusion and misinformation that has surfaced as these different solutions have been introduced to the marketplace. WHAT IS BACNET? BACnet is an American National Standard. This is literally a book which describes in great detail how to create an automation and controls system which may interoperate with other BACnet systems. In BACnet terms, interoperate means that two or more BACnet-speaking computer systems may share the same communications networks, and ask each other to perform various functions on a peer-to-peer basis. Although BACnet does not require every system to have equal capabilities, it is possible for designers of system components at every level of complexity to have access to functions of other automation system peers. In the BACnet world, there is no class distinction between large controllers, small controllers, sensors, actuators and operator workstations or host computers. There are two key concepts in BACnet that are critical to understand. First, is the idea that BACnet is applicable to all types of building systems: HVAC, Security, Access Control, Fire, Vertical Transport, Maintenance, Waste Management, Lighting, and so forth. The same mechanism that gives BACnet this flexibility has two other important benefits: vendor-independence and forward-compatibility with future generations of systems. This is accomplished using an object-oriented approach for representing all information within each controller. The second key idea is that BACnet uses any combination of five types
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