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12.8  Indoor Back-Up Heater Control 
12.8.1  Indoor Electric Heater Control 
1  Normal Heating Mode 
o Heater On condition: 
a.  Heater switch is ON 
b.  After Heatpump thermo ON for [30] mins 
c.  After water pump operate [9] mins 
d.  Outdoor air temperature < Outdoor set temperature for heater 
e.  When water outlet temperature < Water set temperature + [-8°C] 
f.  [20] minutes since previous Backup heater Off 
*  When heatpump cannot operate due to error happens during normal operation, heater will go into 
force mode automatic 
* Heater need to operate during deice operation 
 
o  Heater Stop Condition: 
a.  When outdoor set temperature > outdoor set temperature + [+2°C] for continuous 15 secs OR 
b.  When water out temp> water set temperature + [-2°C]  for continuous 15 secs OR 
c.  Heater switch is Off OR 
d.  Heatpump thermo-off or OFF condition 
 
2 Force Heater Mode 
o Heater On condition: 
a.  After water pump operate [9] mins 
b.  When water outlet temperature < water set temperature + [-8°C] 
c.  [20] minutes since previous Backup heater Off 
 
o  Heater Stop condition 
a.  Force mode off OR 
b.  When water outlet temperature > water set temperature + [-2°C] for continuous 15 secs 
 
* Do not operate heater at the following situation 
1  Water outlet temperature sensor, and water inlet sensor abnormal 
2  Flow switch abnormal 
3  Circulation pump stop condition 
4  During Heatpump switch to tank side