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

HVAC Control in the New MillenniumFigure 6-11. Internal mode controlFigure 6-12. Internal mode control with first-order plus dead time controllerSetpoint biasing is the feedback adjustment method. To eliminatespikes in from measurement noise and setpoint changes, the biased setpointis filtered.The function blocks are leads, lags, delays, summations, and gains,and they can be configured by most distributed control systems (DCS),single-loop controller or programmable logic controller (PLC). The usualtuning parameter is the filter time constant. Lower values of the timeconstant make the controller more aggressive and higher values make itgentler.In internal modeling control the model is linear and stationary. Ifthe process gain or time constants change, the model-based calculationsbecome either too aggressive or sluggish and retuning may be required.©2001 by The Fairmont Press, Inc. All rights reserved.