Hitachi YUTAKI Series - 6.1.2 Precautions in the Event of Gas Refrigerant Leaks

Controller pack
Service Manual
96
Boiler control functions
SMGB0066 rev.0 - 12/2009

EP2 Integral Factor Required Load - Boiler/Electric Heater Control (default 2.5 %/Kmin.)
EP16 Proportional Band Required Load - Boiler/Electric Heater Control (default 6 K/100%)
EP31 Supply Setpoint Control Offset (default 4 K)
It is not normally recommended to change these parameters. They have been selected during laboratory tests for best
performance in most situations.
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note
Engineering Parameters (EP) are only available for service engineers. -
 

This function helps prevent the boiler operating unless the heat pump is already providing heat. When the heat pump
isin“thermo-off”state(compressoroff)orin“defrost”,thedifferencebetweenthesupplytemperatureTSUPandreturn
temperature TRET will be small (or negative in case of defrost) since no heating is provided. The boiler is prevented
from switching on until this difference is greater than the Supply-Return Difference Limit (P32). A +/-0.5K control
differential is applied.
TSUP-TRET > P32 + 0.5K Boiler is allowed to switch on.
TSUP-TRET < P32 – 0.5K Boiler is not allowed to switch on.
Whentheboilerstartsfromcold,thesupplytemperaturecandropforasmalltimeasthecoldwaterintheheat
exchanger is pumped into the system. This function would then cause the boiler to be switched off. In order to prevent
this,thisfunctiondoesnotoperatewhentheboilerisswitchedonuntilacertaintimehaspassedfromtheboilerstarting.
ThisdelaytimeisdenedbyaparameterBoilerDelayTime(EP36).

This function can be disabled by setting parameter P32=OFF.

P32 Supply-Return Difference Limit (default 3K)
EP36 Boiler Delay Time (default 5min)
A high value of P32 will prevent the boiler switching on until a large temperature difference is seen by the System
Controller.WithalowvalueofP32orwiththefunctiondisabled,theboilermaystartmoreoften,forexampleduring
defrost cycles.
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note
This check is ignored if the Heat Pump is switched off or has a fault -
Engineering Parameters (EP) are only available for service engineers. -