Engineering Manual o.. - HVAC.Amickracing

ELECTRIC CONTROL FUNDAMENTALSCONTROL COMBINATIONSThe following are representative Series 60 two-positioncontrol circuits. Notice that many of these functions can bedone with Series 40 or 80 systems. If spring-return action isrequired when power fails, use Series 40 or 80.TWO-POSITION CONTROL OF STEAM VALVEFigure 15 illustrates two-position control of a steam valve.During the day when the temperature sensed by the Series 60controller drops below the setpoint, contacts R to B close andthe actuator opens the valve allowing the steam to flow to thecoil. On a rise in temperature, contacts R to W close and theactuator closes the valve stopping the flow of steam. At nightthe time clock overrides the temperature controller and drivesthe actuator/valve closed.TIME CLOCKDAYNIGHTSTEAMTEMPERATURECONTROLLERW R BW R BT2T1VALVEACTUATORTRANSFORMERTOCOILLINE VOLTAGEC2516-1Fig. 15. Series 60 Two-Position Control of SteamValve with Time clock Override.HIGH-LIMITCONTROLLERCAPILLARYWATERSENSINGELEMENTSOUTDOORCONTROLLERW R BW R BT1T2TO CHILLERLOW-LIMITCONTROLLERTRANSFORMERTO BOILERACTUATORC2517LINEVOLTAGEFig. 16. Series 60 Summer/Winter ChangeoverControl of Diverting Valve.When the outdoor air temperature rises above the setpointof the controller, contacts R to B open and R to W closecalling for summer operation. If the water temperature isbelow the setting of the high limit, the R to W circuitcompletes, and the actuator positions the diverting valve tosend the return water to the chiller. If the high-limit controllersenses that the return water is too warm, the contacts open,and the valve remains in a position to divert the return waterthrough the boiler. This circuit protects the chiller by notallowing hot water into the chiller.SUMMER/WINTER CHANGEOVER CONTROL OF ATHREE-WAY DIVERTING VALVEFigure 16 illustrates summer/winter changeover control ofa three-way diverting valve. A Series 60 controller sensesoutdoor air temperature to determine when to change overfrom heating to cooling. When the outdoor air temperaturedrops below the setpoint of the controller, contacts R to Wopen and R to B close calling for winter operation. The lowlimitcontroller, located in the return water line, senses the returnwatertemperature. If the water temperature is above the setpointof the low limit controller, the R to B circuit completes, and theactuator positions the diverting valve to send the return waterto the boiler. If the low-limit controller senses that the returnwater is too cool, the contacts open, and the valve remains in aposition to divert the return water through the chiller. This circuitprotects the boiler from thermal shock by not allowing chilledwater into the hot boiler.OPEN-CLOSED CONTROL OF DAMPERFigure 17 illustrates open-closed control of a damper. ASeries 60 actuator is linked to a ventilating damper. When thecontroller senses that the temperature in the interior of thebuilding is above the controller setpoint, contacts R to B openand R to W close. This powers the R to B actuator terminalscausing the actuator shaft to turn, opening the dampers. Whenthe controller senses that the temperature is below the setpoint,contacts R to W open and R to B close causing the actuatorshaft to close the damper.DAMPERTEMPERATURECONTROLLERBRW R BWT1T2TRANSFORMERLINEVOLTAGEACTUATORC2518Fig. 17. Series 60 Open-Closed Control of Damper.ENGINEERING MANUAL OF AUTOMATIC CONTROL 101