Engineering Manual o.. - HVAC.Amickracing

AIR HANDLING SYSTEM CONTROL APPLICATIONSIn the following chart it is assumed that:1. Desired space condition is 24°C DB and a maximum of50% RH.2. OA condition is 27°C DB and 26°C WB.3. Air entering the system is from the ECONOMIZERCYCLE DECISION application. The system operates on25 percent OA during the cooling cycle.4. Cooling coil leaving air temperature is 13°C.COOLING COILDISCHARGE13°C DB3245OA 27°C DB,26°C WBMA1RA 24°C DB,50% RHC3253The following results are obtained:ItemNo.Explanation1 Mixed air temperature at cooling designcondition.2 Air entering the cooling coil is cooled along aline of constant moisture content until saturationis approached. Near saturation the moisture contentis reduced as the air is cooled. This processinvolves both latent and sensible cooling.3 The final leaving air temperature necessary tosatisfy space requirements will be maintainedby reheating along a constant moisture line.4 Heating coil discharge.5 This process line represents the increase intemperature and humidity that occurs due tothe sensible and latent heat gains in the space.WATER COIL FACE AND BYPASS SYSTEM CONTROLFunctional DescriptionCOOL2HEAT32523.522411CONTROLPROGRAM650505COOL ORDEHUMIDIFIERDEMAND010CHWVALVE0FACEDAMPER708732SA601010001100100MASUPPLYFANON909M15174ItemNo.Function1 Control system energizes when fan is turnedon (See FAN SYSTEM START-STOPCONTROL).2-4 Space temperature PI control loops have heatand cool setpoints with deadband.5,6 Space humidity sensor and setpoint enabledehumidification.7-9 Heating and cooling valves and face andbypass dampers position for heating, cooling,and dehumidifying cycles.10 Stages chilled water and face-and-bypassdamper loading.11 Control program coordinates cooling, heating,dehumidifying, and fan and hot waterinterlock control.244ENGINEERING MANUAL OF AUTOMATIC CONTROL