Hitachi YUTAKI Series - Principle of Bi-Valent or Mono-Energetic Operation

Controller pack
Service Manual
76
Systemconguration,settingsandcontrolsystem
SMGB0066 rev.0 - 12/2009

TheSystemControllercanbeusedinasystemwhichhasaDHWstoragetank,witheitheradivertingvalveorpump.
IfthesystemhasaseparateDHWpump,thenahydraulicseparatororbuffertankhastobeusedtoensureproper
hydraulic balancing of the system.
The DHW system type is selected by an installer parameter (P1)

WhenahydraulicseparatororbuffertankisusedinCONF1&2,thesystemwillcontainasecondarypumponthe
distribution side of the separator/buffer. In this case it is necessary to set installer parameter P2 to 1.
Inbi-valentsystems(CONF3,4,5)ahydraulicseparatororbuffertankisalwaysneeded.
 

Bi-valent and mono-energetic systems use an auxiliary heat source (boiler or electric heater respectively) in addition to
the heat pump.
Athigheroutdoortemperatures,theheatpumpcanprovidealltheheatingrequirementsofthesystem,anditisnot
necessarytoswitchontheauxiliaryheatsource.Howeveratloweroutdoortemperatures,theelectricheaterorboileris
used to provide the increased heating demand. The changeover point for bi-valent or mono-energetic operation is called
the balance point. A +/-0.5K control differential is applied to the switching between the operating modes.
Outdoortemperature(TEXT)>BalancePoint(BP)+0.5K,theboilerorelectricheaterisnotused.(Exceptionisthatthe
boiler can be used for DHW loading.)
Outdoortemperature(TEXT)<Balancepoint(BP)-0.5K,thesystemcontrollerdetermineswhethertoswitchontheboiler
or electric heater depending on the heating requirements. Refer to the sections on Boiler Control and Electric Heater
Control for more details.

P15 Maximum Outdoor Temperature for Boiler/Electric Heater Operation = Balance Point (BP) (default 0°C)
P14 MinimumOutdoorTemperatureforHeatPumpOperation(CONF3,4,5only)(default-20°C)

note
Parameter P15 can be set to OFF, in which case the boiler or electric heater is allowed to operate at all outdoor -
temperatures
Parameter P14 can be set to OFF, in which case the heat pump is allowed to operate at all outdoor -
temperatures.

CONF 2 Mono-Energetic Systems -
The electric heater is used to “top-up” the energy required for the system. The System Controller tries to ensure that
theheatpumpisalwaysrunningwhentheelectricheaterisused,buttheremaybesomecircumstanceswherethe
electric heater is providing all the energy for the heating system.
Heating Zone
Heat Pump Capacity (kW)
Heat Demand (kW)
Electric Heater
Heat Pump
Only
Heat Pump
20ºC P15 -20ºC Outside Temp
Heat Pump operates
on it’s own down to the
balance point (installer
parameter )
Heat Pump plus
Electric Heater
operate together