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

Energy and Power Management, Distributed Control Trendspriate zone level controllers to provide building-wide functions.Equipment level applications are energy intensive and include airhandlers, chillers and boilers. The characteristics of the control includedata point monitoring and multiple control sequences such as reset andwarm-up.Control LoopsBuilding-wide control systems depend on control loops to regulatethe different parts of the control hardware. These can be categorized intotwo types, closed and open loops.An open loop uses a controller that starts and stops the HVACequipment at given times. There is no feedback to the controller abouttemperature or other controlled variables.In a closed loop the controller responds to continuous environmentaldata and compares them to a programmed environmental setpoint(temperature, humidity, air quality).In a closed-loop system, the sensing element provides feedbackinformation to the controller. These data are compared by the controllerto the setpoint that has been adjusted by the user.The controller sends a corrective signal to the controlled hardware.The sensing element continuously monitors the environment and outputsnew data to the controller. The controller monitors the sensors andactivates or controls the devices to compensate for any needed environmentaladjustments.Digital LogicThe logic circuits in digital computers think and respond in termsof on and off logic. This may be a yes or no, one or zero, open or closedor true or false logic state. This binary logic is converted into electricalsignals which are defined as a true or false digital signal.The digital signal in a HVAC relay is represented by a set of openor closed contacts. The controller may interpret an input device signal asa request or non-request for heating.A digital signal on the output of a microprocessor usually activatesa contactor (relay) to either open or close. The system can use this open©2001 by The Fairmont Press, Inc. All rights reserved.