Engineering Manual o.. - HVAC.Amickracing

AIR HANDLING SYSTEM CONTROL APPLICATIONSCONTROL FROM SPACE WITH SUPPLY TEMPERATURE RESETFunctional Description822NORMAL2922SPACETEMPERATUREMASASUPPLY AIRTEMPERATURERESET SCHEDULE300N.O.10ON1 4CONTROLPROGRAMCURRENT SUPPLY AIRTEMPERATURE SETPOINT5353576SUPPLY AIRTEMPERATURESETPOINT3813SPACEHEATINGDEMAND1000M15160ItemNo.Function1-2 Control system energizes when fan is turnedon (See FAN SYSTEM START-STOPCONTROL).3 Hot water valve modulates heating medium.4,5 SA temperature controlled to maintain setpoint.6,7 SA temperature setpoint determined by spaceheating load.8,9 Space temperature is compared to spacetemperature setpoint to determine SAtemperature setpoint.10 Control program coordinates temperaturecontrol and fan interlock.FEATURESshall be reset from no lower than 13°C to no greater than38°C as the space temperature PID demand for heatingvaries from 0% to 100%.2. The N.O. hot water valve shall close upon fan shutdown.PSYCHROMETRIC ASPECTSThe supply condition of the air depends on the condition ofthe entering air and the temperature rise needed to satisfy thespace heating requirements.In the following chart it is assumed that:1. The space temperature control loop is set at 24°C.2. MA condition is 10°C DB and 9°C WB.3. A space heating load exists which is large enough to require35°C DB SA to meet the design condition heat loss.1. Air is supplied at a temperature necessary to make up thesensible heat loss in the space.2. The SA temperature will not fall below a desiredminimum or rise above a desired maximum (unlessheating coil entering air rises).CONDITIONS FOR SUCCESSFUL OPERATIONA multiple inline coil arrangement if a high temperature riseis required.The following results are obtained:MA10°C DB, 9°C WBSPACE24°C12SA 35°C DBC3239SPECIFICATIONSSee FAN SYSTEM START-STOP CONTROL.1. Anytime the supply fan runs, the hot water valve shall bemodulated by an SA PID control loop to maintain theSA temperature setpoint. The SA temperature setpointItemNo.Explanation1 The heating of the MA to the supply temperatureoccurs along a line of constant moisture content.2 Space air picks up moisture from theoccupants and contents of the space.224ENGINEERING MANUAL OF AUTOMATIC CONTROL