Hitachi YUTAKI Series - Boiler Minimum on; off Times; Boiler Waiting Time; Maximum Outdoor Temperature for Boiler Operation

97
Boiler control functions
SMGB0066 rev.0 - 12/2009
Controller pack
Service Manual
4
 

Inordertopreventinefcientshort-cyclingoftheboiler,thisfunctionpreventstheboilerfromswitchingonorswitchingoff
until either the boiler minimum off time or boiler minimum on time,respectively,haselapsed.

P17 Boiler minimum ON time (default 2 min.)
P18 Boiler minimum OFF time (default 5 min.)
HighvaluesofminimumONandOFFtimesmaycauselargeuctuationsinwatertemperatureandshouldusuallybe
avoided.

note
If the boiler is disabled, rather than off due to normal control (load=0%), then the boiler minimum ON time does -
not apply
 

Itisimportantwithbi-valentsystemsthattheHeatpumpshouldrsttrytosatisfytheheatingdemandbyitself.Forthis
reasonaboilerwaitingtimeapplies.Thismeansthatwhentheheatpumpcannotmeettheheatingdemand,thenthe
boiler is switched on only after the waiting time has elapsed.
The waiting time starts:
Whentheheatpumpisswitchedon,or -
When the boiler 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boiler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 Boiler (default 30min.)
AhighervalueofP19willreducethenumberoftimesthattheboiler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boilerisusedatlowersupplysetpoints,butensurethatthedesired
supply temperature is reached more quickly (better response).
 

This function disables the boiler control when the outdoor temperature is above the boiler maximum outdoor temperature
setting. Above this setting it is assumed that the heat-pump is able to deliver all the requested heat by itself and the boiler
is therefore not required.