Hitachi YUTAKI Series - Supply-Return Difference Check

99
Electric heater control functions
SMGB0066 rev.0 - 12/2009
Controller pack
Service Manual
4
IfSupplySetpoint>HeatPumpmaximumsupplytemperature–HeatPumpSensorOffset+0.5K,
then Electric Heater Setpoint = Supply Setpoint (SSUP)
IfSupplySetpoint<HeatPumpmaximumsupplytemperature–HeatPumpSensorOffset-0.5K,
then Electric Heater Setpoint = Supply Setpoint (SSUP) – Supply Setpoint Control Offset (EP31)
The heat pump maximum supply temperature depends on the outdoor temperature and the heat pump operating limits.

The P+I algorithm calculates a “Load factor” from 0% to 100%. The electric heater stages are switched on depending on
the load factor
Required Load Factor = PI function ( Electric Heater Setpoint – TSUP )
Beforeswitchinginmoreorfewerstages(forexamplebetweenstage1andstage2),theSystemControllerwaitsfora
certaintimetopreventtoofastswitching.ThistimeistheInter-StageWaitingTime,parameterEP20.

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%)
EP20 Inter-Stage Waiting Time (default 10 sec.)
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. Correct positioning of the Supply Temperature Sensor close to the outlet of the Electric
Heatershouldresultingoodcontrolperformance.Ifnecessary,adjustingtheseparameterscancorrectunstablecontrol
behaviour in certain circumstances.

note
Engineering Parameters (EP) are only available for service engineers -
 

This function helps prevent the electric heater 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 electric heater
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 Electric Heater is allowed to switch on.
TSUP-TRET < P32 – 0.5K Electric Heater is not allowed to switch on.