Hitachi YUTAKI Series - Refrigerant and Water Piping

95
Boiler control functions
SMGB0066 rev.0 - 12/2009
Controller pack
Service Manual
4

 

Boilercontrolisavailableonlyincongurations3,4,5(CONF3,CONF4,CONF5)

The boiler control decides whether to switch the boiler on or off based on a proportional plus integral action (P+I) control
algorithm and the difference between the Boiler Setpoint and the Supply Water Temperature (TSUP).
The boiler will only be used when
the outdoor temperature is below the bivalence point (maximum outdoor temperature for boiler operation) -
or the boiler has been manually released (after a heat pump fault). -
InadditiontheSupply-ReturnDifferenceCheckisperformedbeforeallowingtheboilertoswitchon,unlesstheheat
pump is switched off or has an internal fault.

ParameterP33shouldbeset=OFFincongurations3,4,and5.P33relatestoafunction“ReturnLimitOffset”for
electricheatercontrol.Itisnotrecommendedtousethisfunctionforboilercontrol.IfP33isnotsettoOFF,thenthe
boiler will be prevented from starting until this special condition is met.

note
The boiler is always enabled when there is DHW loading required, or when the Heat Pump is blocked by the -
Tariff/Timer input.

Iftheheatpumpisswitchedoff,orhasaninternalfault,theBoilerSetpoint=SupplySetpoint(SSUP)
Iftheheatpumpisswitchedon,thewatersetpointusedfortheboilercontroldependsonthevalueoftheSupply
Setpoint. When the supply setpoint is low the boiler will only be used if the actual supply temperature is much lower than
thedesiredsetpoint.Toachievethis,theboilersetpointisoffsetlowerthanthesupplysetpoint.Whenthesupplysetpoint
ishigherthancanbeachievedbytheheatpumpalone,theboilersetpointisequaltothesupplysetpoint.Thisfunctionis
intendedtohelpreducethenumberoftimestheboilerisused,toemphasiseenergysavingoperation.
IfSupplySetpoint>HeatPumpmaximumsupplytemperature–HeatPumpSensorOffset+0.5K,
then Boiler Setpoint = Supply Setpoint (SSUP)
IfSupplySetpoint<HeatPumpmaximumsupplytemperature–HeatPumpSensorOffset-0.5K,
then Boiler Setpoint = Supply Setpoint (SSUP) – Supply Setpoint Control Offset (EP31)
The heat pump maximum supply temperature depends on the outdoor temperature and the heat pump operating limits.

The P+I algorithm calculates a “Load factor” from 0% to 100%. The boiler is switched on when the Load Factor reaches
100% and switched off when the Load Factor reaches 0%.
Required Load Factor = PI function ( Boiler Setpoint – TSUP )
ON
BOILER
CONTROL
100%
0%
Required Load Factor