Engineering Manual o.. - HVAC.Amickracing

CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONSTOWER FREE COOLING, DUAL CHILLERSFUNCTIONAL DESCRIPTION1000667226 2641 22 2342405P336 ONCOOLINGTOWER 166CURRENTSETPOINTOPEN TOCHILLER146COOLINGTOWER 2681003243044383CHILLERMINIMUMSETPOINT-+OUTSIDEAIR55492166.0DRY BULBWET BULB42.0CONDENSER WATER SETPOINTSPHX 183031FREE COOLING OA WB SETPOINT = CHILLED WATERTEMPERATURE SETPOINT MINUSDEGREES50.260.0CHILLER/ FREECOOLING SETPOINT41WET BULBFREE COOLINGMINIMUMSETPOINT15410.09CHILLER/ FREECOOLINGCURRENT MODECHILLERTOWERCONTROLCHILLERCONTROL26464724CURRENTSETPOINTCHILLER/ FREECOOLINGCURRENT MODE11 = CHILLER2 = AUTO3 = TOWERMINIMUMSETPOINT4551512572037P411OFF56 00163476OPEN TOCHILLER72104539CHILLER 178 ONLOAD STATUS00 OFF1819281ONP1OPEN602760OPEN56 0013 3576761233CHILLER 2-PHX 260 29 60+ONP2217M15049Fig. 36. Graphic for Tower Free Cooling System with Dual Chillers.Item No. Function1,2 Chilled water pumps produce flow throughchillers or plate/frame heat exchangers.3,4 Free cooling mode initiated when OA WBdrops to setpoint.5 Tower water entering temperature, operatorinformation.6,7 Setpoints indicate need for cooling tower andchilled water.8 Minimum condenser water temperature setpointprovides free cooling low limit.9 In free cooling mode, tower will produce waterabout 7F above OA wet-bulb temperature, andHX will cool chilled water to within 2 to 3F ofcondenser water temperature, so the sum ofthese dictates when to activate free cooling.10-13 Maintains condenser water temperature enteringchiller during period when tower is pullingwater temperature down to free cooling setpointvalue and the temperature is too low for chiller.14-17 Valves direct water from chiller/condenser toHX when condenser water reaches setpoint.18,19 Chiller Status.20 Operator information.21 Prevents tower from cooling water belowminimum value that chiller can tolerate (duringchiller cooling mode).22,23 Tower fans modulate to maintain condenserwater setpoint.24 CHILLER-AUTO-TOWER software modeselection function.25 Prevents chilled water temperature setpointfrom dropping below the design minimum.26-45 Operator information (see chiller control andcooling tower control examples).46 Icon, to display cooling tower control data.47 Icon, to display chiller control data.ENGINEERING MANUAL OF AUTOMATIC CONTROL302