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

Artificial Intelligence, Fuzzy Logic and Controlquality from sensor data. DuPont has used them to predict the compositionof chemical mixtures.The inputs to the network are measurements of the mixture. Trainingthe network to determine the network connection weights involvesdata from mixtures whose composition is known. Numerical algorithmsto train the network are used from commercial software packages. Du-Pont has also used neural networking as a virtual sensor to predictperiodically measured concentrations.Historical data on temperature, pressure, and concentration wereused to train a network to predict the concentration from temperatureand pressure measurements. This trained network can then be used toprovide continuous, on-line prediction of concentration.Neural networks are a tool to solve many complex problems. Theymay be embedded in databases or expert system applications or act aspreprocessors or postprocessors to other systems.Neural networks have the ability to adapt, generalize, and extrapolateresults. However, they cannot optimize and need lots of data. Theycan be unpredictable in untrained areas and are not well understood orwidely accepted.Neutral Network GrowthThe basic concepts of the neural network have been known sincethe 1940s. The theoretical foundations were established in the 1960s and1970s. Research of the 1980s-1990s provided the first applications.The researchers included neuroscientists, cognitive psychologists,physicists, computer scientists, mathematicians, and engineers. The increasingpower and inexpensive cost of computing allowed the developmentand deployment of systems for industrial applications.Neural networks obtain their name and some of their associatedterminology from biological systems (Figure 6-6). Neural networks arebuilt of neurons which are also called nodes or processing elements.These nodes are usually arranged in layers or slabs and are oftenconnected to nodes in other layers. A layer is a set of nodes with weightsthat are actively manipulated. These layers serve as a buffer between theinputs or outputs or other layers.A slab is a set of nodes that may be different in their internal specificationsor connectivity but which share the same layer. A single layer©2001 by The Fairmont Press, Inc. All rights reserved.