Hitachi YUTAKI Series - Electric Heater Waiting Time; Electric Heater Return High Limit Check

Controller pack
Service Manual
100
Electric heater control functions
SMGB0066 rev.0 - 12/2009

This function can be disabled by setting parameter P32=OFF.

P32 Supply-Return Difference Limit (default 3K)
A high value will prevent the electric heater switching on until a large temperature difference is seen by the System
Controller.Withalowvalueorwiththefunctiondisabled,theelectricheatermaystartmoreoften,forexampleduring
defrost cycles.

note
This check is ignored if the Heat Pump is switched off or has an internal fault. -
 

Itisimportantwithmono-energeticsystemsthattheHeatpumpshouldrsttrytosatisfytheheatingdemandbyitself.
For this reason an electric heater waiting time applies. This means that when the heatpump cannot meet the heating
demand,thentheelectricheaterisswitchedononlyafterthewaitingtimehaselapsed.
The waiting time starts:
Whentheheatpumpisswitchedon,or
When the electric heater switches off (but only also when the Supply Setpoint SSUP < heat pump maximum temperature
– heat pump sensor offset).
Thismeansthatwhentheheatpumpshouldnormallybeabletomeettheheatingdemandonitsown,theelectricheater
waitingtimeapplies,butwhenthesupplysetpointissohighthattheheatpumpcannotmeettheheatingdemandonits
own,thewaitingtimedoesnotapply.

P19 Waiting Time for Electric Heater (default 30min.)
AhighervalueofP19willreducethenumberoftimesthattheelectricheaterisusedatlowersupplysetpoints,butthe
desiredsupplytemperaturemaynotbereachedquicklyifthereisahighheatingload(slowerresponse).Conversely,a
lowervalueofP19willincreasethenumberoftimestheelectricheaterisusedatlowersupplysetpoints,butensurethat
the desired supply temperature is reached more quickly (better response).
 

The return high limit check is used to help ensure that the heat pump operates as much as possible even when higher
supplytemperaturesarerequired,thusemphasisingenergyeconomyoperation.Theelectricheaterisdisabledwhenthe
return water temperature (TRET) rises above the maximum heat pump outlet temperature minus the return limit offset
(P33). A +/-0.5K control differential applies.
TRET > Heat Pump maximum supply temperature – P33 + 0.5K Electric Heater disabled
TRET < Heat Pump maximum supply temperature – P33 - 0.5K Electric Heater enabled
Sincetheelectricheaterisswitchedoffthenthereturntemperaturerisestoohigh,theeffectwillbethatinsomesystem
conditionsitwillnotbepossibletoreach65°Csupplytemperature.Ifitisimportanttoallow65°Coperation,thenthe
parametercanbereducedorsettoOFF,buttheresultisthatinsomesituationstheelectricheaterwilloperateonits
own and the heat pump will not be used. This will cause higher energy costs.