RBI FlexCore CK 850 Control Manual

Also see for FlexCore CK 1000: Installation and operation instructions

Contents

RBI FlexCore CK 850 Control Manual Manual pdf 24 page image

CONTROL METHODS HeatNet Control V3Page 24Heating Control MethodsAn overview of the (5) methods for controlling the FlexCoreCK -Series boiler are presented here. They are outlined inmore detail at the end of this section.Heating Method 1The first method is to use the FlexCore CK -Series boiler inits stand-alone modulating method. This method uses a PIDalgorithm to maintain a setpoint and is enabled using theHEAT DEMAND input. Closing a relay contact or switchacross the HEAT DEMAND input will cause the Masterboiler to control all member boilers using H-Net.A member boiler may also be controlled by the HEATDEMAND input (LOCAL mode). The member boiler willthen ignore commands from the Master and maintain itsLOCAL SETPOINT at the supply sensor.Basic Single BoilerMASTERSystem Header SensorSystem ReturnSensorLocal PumpSystem PumpExpansion TankBackflowPreventionPressureReducingBall ValveSystem PumpSupply Header SensorHeatNet Outdoor Air SensorMIN 3X PIPE DIAMETERSMAX 10X PIPE DIAMETERSBETWEEN CENTERSWM Water MeterSystem SupplySystem Return SensorNote: The example drawings in this section are simplified.They are meant to illustrate connections to the HeatNet V3control. Only major components are illustrated. The systemengineer must ensure additional safeties, piping,maintenance valves, and components meet coderequirements and safe operation.Heating Method 2The second method is to view the FlexCore CK -Seriesboiler as two separate boilers or as a HIGH/LOW boilerusing T1 & T2.Heating Method 3The third method is to allow a remote 4-20 mA or 0-10VDC signal to control the firing rate (modulation) of theboiler using the 4-20 mA input, along with the 4-20 mAREMOTE ENABLE input.Heating Method 4The fourth method turns the boiler ON and OFF @ 100%modulation using the AA terminal.Heating Method 5The fifth method uses an RS485 digital communicationscable with the MODBUS protocol. The boiler is controlledby writing and reading registers using MODBUScommands. A bridge module may also be used to convertBACnet or LonWorks protocols to MODBUS.Short cycling may occur when a firing rate issent to a member boiler that would cause thesupply temperature to raise high enough totrip the operating limit (low flow rate). Afterthe supply temperature falls, the boiler wouldrestart and the process may continue. Amember boiler would use its supply (outlet)sensor to protect itself from short cycling bylimiting the firing rate coming from theMaster. This occurs in the event that themember’s supply temperature increases abovethe (OPERATE LIMIT- OPERATE LIMITBAND).Operating LimitWhen the Master boiler or an external control input is usedto control a member boiler (i.e. AA, T1-T2, 4-20 mA, H-Net), a software operating limit on the member boiler willbe used to limit the maximum output of the member boiler.This operating limit can be adjusted in the SETTINGS:SETPOINTS: OPERATE LIMIT.There is also an associated operating limit band that must beset in conjunction with the operating limit to help preventthis LIMIT from being reached. Its purpose, is to limit theoutput of the boiler as it approaches the operating limit. Ifthe band is set to 10 degrees, then for every degree that itapproaches the operating limit, the maximum output will belessened by 10%. With a band of 20 degrees, for everydegree that it approaches the band, the maximum output willbe lessened by 5%. You can think of this operating limit asa smart Aquastat which prevents the High Limit fromtripping. This method minimizes boiler short cycling whenusing external inputs. The minimum setting is 1 degree andeffectively turns the limit band OFF. The default setting is20F.