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

HVAC Control in the New MillenniumRecently, some companies have turned to neural network models,which are useful for dealing with complex situations. As plant operatorsgain confidence in this relatively new technology, they are even beginningto use it for real-time plant control.Some industries have used predictive control technology, referredto as model predictive control (MPC), for over 20 years using linearmodeling techniques. The increasing complexity of some plants has ledto the development of nonlinear models.A hybrid alternative to these complex, nonlinear models, is a linearmodel combined with the learning capability of neural networks thathelps the system cope with real-world nonlinearities.A neural network controller does not know how to treat data thatis outside the range of data collected in its training or open-loop mode.The hybrid system provides a linear system that takes over control whenparameters are outside the neural network’s range.A power plant near Warsaw, Poland, recently installed and testedsuch a hybrid system. The Ostroleka power plant near Warsaw, Poland,is one of the first to apply a hybrid neural network MPC system with anAspen Target MPC controller using a nonlinear state-space model integratedwith a neural network model.The plant uses three wall-fired boilers with pulverized coal. Sixsets of low NO x burners are installed in each of four elevations. After aperiod of open-loop training the MPC was placed in closed-loop operationwith the following results:• NO x decreased 15 to 25%,• Boiler efficiency increased 0.1 to 0.5%,• LOI (carbon loss on ignition) decreased from 5% to 3%, and• Cooling water consumption reduced by up to 5%.The controls also demonstrated robust response to extraordinary events.Burner Management SystemsTo ensure that modern power plants have the capability to respondpromptly to any load demand, new burner management systems(BMSs) provide the programmable control needed to operate burnersand igniters for gas or oil firing. They also provide the highest available©2001 by The Fairmont Press, Inc. All rights reserved.