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

HVAC Control in the New Millenniumbased DCS (Figure 3-5). These systems generally have CRT-based operatorconsoles and keyboards which are used for monitoring and controllingthe system. Controllers and multifunction control modules are usedto provide the basic control computation or operation.A communication network transfers the information between thecontrol modules and operator consoles. I/O (Input/Output) modulesare used to convert the sensor signals from analog to digital and digitalto analog for the controller modules and console displays. Fieldbus communicationlinks are used for communication between remote I/O devicesand control modules. Historical data storage is used for controldata and is available for on-line data retrieval. A control software packageis used for monitoring, control, reporting, graphics and trending.In most applications, a DCS replaces a conventional control systemfor the purpose of performing basic control. The supervisory controlfunctions performed by the older computer systems plus additionalfunctions such as on-line information evaluation may be performed bya supervisory computer linked to a DCS.Figure 3-5. DCS structure.©2001 by The Fairmont Press, Inc. All rights reserved.