Engineering Manual o.. - HVAC.Amickracing

AIR HANDLING SYSTEM CONTROL APPLICATIONSCONDITIONS FOR SUCCESSFUL OPERATIONLocal weather data analysis needed to determine the optimumchangeover setpoint. The analysis need only consider data when theOA is between approximately 60°F and 78°F, and during the occupancyperiod.NOTE:The dry bulb economizer decision is best on small systems(where the cost of a good humidity sensor cannot bejustified), where maintenance cannot be relied upon, orwhere there are not frequent wide variations in OA RHduring the decision window (when the OA is betweenapproximately 60°F and 78°F).SPECIFICATIONSA global economizer function shall be provided to switch all AHUsfrom OA cooling to minimum OA based upon an OA temperaturesetpoint. Software shall also be provided to allow the user to overridethe decision from being based upon OA dry bulb (with an appropriatecommandable setpoint), to manually lock the system into or out of theeconomizer mode.ECONOMIZER CYCLE DECISION—OUTDOOR AIR ENTHALPY CONTROLFunctional DescriptionEARA883OA1 2MA49 5216.8ENTHALPYBTU PER POUND837ECONOMIZERSTATUSCONTROLPROGRAMON95OTHER INPUTSAND OUTPUTS3 622OA MINIMUM SETPOINT(NOTE: THE TEST AND BALANCE INITIALVALUE FOR PROPER VENTILATION IS 22)4ECONOMIZER MODE SELECTOR11 = AUTO BASED UPON OAENTHALPY BELOW 27.0BTU PER POUND2 = AUTO BASED UPON OA DBTEMPERATURE BELOW 72.03 = MANUAL, ECONOMIZER ON.4 = MANUAL, ECONOMIZER OFF.DEGREESNOTE:THE SYSTEM IS LOCKED OUT OFTHE ECONOMIZER MODE ANYTIMETHE OA DRY BULB ISABOVE 81.0 DEGREES.M10455ItemNo.Function1 Sensor senses OA temperature.2 Sensor senses OA humidity.3 OA enthalpy calculated from OA temperatureand humidity.4 Economizer mode decision selector, includingOA enthalpy setpoint below which theeconomizer decision is invoked, and commandschedule.5 Economizer decision status (operatorinformation).6 Setpoint for minimum OA damper position.7 Actuator positions OA and RA dampers.8 Actuator positions EA dampers.9 Control program coordinates occupancy,temperature, smoke, and ventilation controls.ENGINEERING MANUAL OF AUTOMATIC CONTROL199