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

HVAC Control in the New Millenniumsame challenges found elsewhere in the enterprise. Communication andnetworking standards abound. Programmable logic controllers (PLCs),temperature controllers and PCs all have well-defined but sometimesoverlapping roles. The longevity of the equipment means that controllersand software do not always reflect the latest technologies, especiallyin the area of communication capability.Often, replacing expensive equipment just to improve the controllercapability is not practical. So, while PCs are recycled quite rapidly,equipment controllers, or at least the underlying designs of the controller,may be 5 or more years old which is aged in computing years.Enhanced communications capability might justify adding features toexisting equipment, such as tracking energy or fuel use.Using Internet technologies on a local network to create a localIntranet allows you to integrate many of these systems without a significantimpact on operation (Figure 9-1). Networking allows the display ofnew information, as well as the addition of new control features. TheIntranet servers are Web servers with off-the-shelf Web browsers, suchas Netscape’s Navigator or Microsoft’s Internet Explorer, combined withnew Java-based technology to provide better access.The use of Web techniques is fairly straightforward. Information isprovided to clients by a Web server. On the Internet, a server may receivemany millions of requests for information every day and Webservers are typically dedicated and high-powered computers. For a facilityIntranet, the number of requests for information is relatively small,so a Web server can run on a standard off-the-shelf PC system equippedwith a network interface. These systems can run the user interfaces.They can also function as real-time controllers.Web enabling equipment allows anyone with a Web browser andthe appropriate permissions can access the information. This makesaccess to control information uncommonly simple. Once the client computeris set up and networked, you just need the familiar Internet address,or URL. This address might take the same basic form as an externalURL, such as www.ibm.com. Internally, an address such asheatingSystem/status.html might provide access to the status of a localsystem.In a typical Internet Web site, most of the information is static sinceit does not change until someone physically changes it. Dynamic applicationson the Web need to advance this concept by displaying rapidlychanging information in near real time. To create, transport, and view©2001 by The Fairmont Press, Inc. All rights reserved.