Hitachi YUTAKI Series - Electric Heater Control Functions; Electric Heater Control

Controller pack
Service Manual
98
Electric heater control functions
SMGB0066 rev.0 - 12/2009

P15 Maximum Outdoor Temperature for Boiler Operation (default 0°C)

Todisablethisfunctionandallowboileroperationatalloutdoortemperatures,settheparameterP15=OFF.

note
The boiler is always available for DHW loading, independent of outdoor temperature. -

 

ElectricHeatercontrolisavailableonlyinconguration2(CONF2).

When the heatpump cannot meet the heating demand the 3-stage electric heater can be switched on to raise the supply
temperature up to a maximum of 65°C. The electric heater control decides whether to switch on one or more of the
electric heater stages based on a proportional plus integral action (P+I) control algorithm and the difference between the
Electric Heater Setpoint and the Supply Water Temperature (TSUP).
The electric heater will only be used when
the outdoor temperature is below the bivalence point (maximum outdoor temperature for electric heater operation) -
or the electric heater has been manually released (after a heat pump fault) -
Inaddition,twofurtherchecksaremadebeforetheelectricheaterisallowedtoswitchon.Thepurposeofthesechecks
are to help ensure that the electric heater only switches on when the heat pump is working at its maximum capacity.
the Supply-Return Difference Check 1.
the Electric Heater Return High Limit Check2.
These checks are not carried out if the heat pump is switched off or has an internal fault.

note
The boiler is always enabled when there is DHW loading required -

Iftheheatpumpisswitchedoff,orhasaninternalfault,theElectricHeaterSetpoint=SupplySetpoint(SSUP)
Iftheheatpumpisswitchedon,thewatersetpointusedfortheelectricheatercontroldependsonthevalueofthe
SupplySetpoint.Whenthesupplysetpointislow,theelectricheaterwillonlybeusediftheactualsupplytemperatureis
muchlowerthanthedesiredsetpoint.Toachievethis,theelectricheatersetpointisoffsetlowerthanthesupplysetpoint.
Whenthesupplysetpointishigherthancanbeachievedbytheheatpumpalone,theelectricheatersetpointisequalto
thesupplysetpoint.Thisfunctionisintendedtohelpreducethenumberoftimestheelectricheaterisused,toemphasise
energy saving operation.