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

Artificial Intelligence, Fuzzy Logic and ControlStructure of Expert SystemsExpert systems encode the relevant knowledge about the problemdomain in a form which is suitable for manipulation. The structure ofthe expert system separates the knowledge from the mechanism formanipulating the knowledge.It is this separation of the knowledge base from the reasoningprocess that makes expert systems different from most other softwarepackages. The type of knowledge in the knowledge base depends on theproblem. Knowledge is stored in the following ways:• Acts As temperature goes up, fuel use increases.• Rules If space temperature is high, then the HVAC systemis faulty.• Data frames Data structures for storing information in a hierarchicalformat.• Objects These perform specific tasks such as an energy balance.Objects may be coded in other programming languages and both theknowledge and the data can be either qualitative or quantitative sinceexpert systems have the ability to deal with qualitative data and knowledge.The problem-solving strategy of the expert system is contained inthe inference engine. The rules in the knowledge base are applied in acertain sequence until a conclusion is reached. This process is called rulechaining.The user interface provides a mechanism for the expert to enterknowledge and the user to enter data for a specific problem. Most expertsystems are programmed using expert systems shells.An expert system shell contains all of the structure, but its knowledgebase is empty. By programming the shell to contain knowledgeabout a domain, an expert system can be built up.Real-time expert systems involve the time element in the reasoningprocess and must be integrated with sensor and data communicationswith the operator (Figure 6-5). Examples of real-time expert systemsinclude G2 from Gensym and Expert 90 from Bailey Controls.©2001 by The Fairmont Press, Inc. All rights reserved.