Engineering Manual o.. - HVAC.Amickracing

AIR HANDLING SYSTEM CONTROL APPLICATIONSOUTDOOR AIR TEMPERATURE RESET OF SUPPLY AIR TEMPERATUREFunctional DescriptionOA223 NORMAL5MASA70081ONCONTROLPROGRAM2436RESET SCHEDULEOUTDOORAIRSUPPLY AIRSETPOINT16-151638416SETPOINTM15161ItemNo.Function1,2 Control system energizes when fan is turned on(See FAN SYSTEM START-STOP CONTROL).3,4 SA temperature setpoint, as adjusted by resetschedule, maintained by modulating hotwater valve.5,6 OA temperature resets the SA temperature setpointaccording to a reset schedule.7 Hot water valve modulates flow, opens upon lossof motive force, and closes upon fan shutdown.8 Control program coordinates SA temperature,valve, and fan interlock control.PSYCHROMETRIC ASPECTSThe SA condition depends on the entering air condition andthe temperature rise needed to satisfy the space heatingrequirements.In the following chart it is assumed that:1. The MA system is set to maintain 16°C DB MAtemperature.2. The OA temperature reset controller increases thesetpoint of the discharge PID control loop linearly from16°C to 38°C DB as OA temperature falls from 16°C to–15°C DB.FEATURESThe SA temperature rises as the OA temperature fallsaccording to a predetermined reset schedule.ENTERINGAIR1 24 3CONDITIONS FOR SUCCESSFUL OPERATIONUse multiple inline coil arrangement should be used if a hightemperature rise is required.The following results are obtained:C2550-2SPECIFICATIONSItemNo.ExplanationSee FAN SYSTEM START-STOP CONTROL.Anytime the supply fan runs, heating control shall be enabled.A SA PID control loop shall modulate the hot water valve tomaintain the SA temperature setpoint. The SA temperaturesetpoint shall be reset from 16°C to 38°C as the OA temperaturevaries from 16°C to –15°C.1 MA temperature.2 SA at the beginning of the reset schedule.3 SA heated to 38°C at outdoor designtemperature.4 Between –18°C and 16°C OA temperature,SA temperatures are between Points 2 and 3.ENGINEERING MANUAL OF AUTOMATIC CONTROL225