12
VI.KT.F2.02
© Danfoss 06/2008
DH-SMT/DK
DH-SMT/DK
VI.KT.F2.02
© Danfoss 06/2008
13
The controller automatically changes the desired flow temperature to obtain an
acceptable return temperature when the return temperature falls below or gets higher
than the set limit.
Influence
‘Gain - min.’ > 0
‘Limit’
‘Gain max.’ > 0
Return temperature
‘Gain - max.’ < 0
‘Gain - min.’ < 0
This limitation is based on a PI regulation where P (Gain) responds quickly to deviations
and I (Intgr. time) responds slower and over time removes the small offsets between the
reference and actual measured values. This is done by changing the flow temperature
reference.
If the ‘Gain’ is too high and / or the ‘Intgr. time’ too low, there is a risk of unstable control.
Limit (return temp. limitation)
4030
Setting range
Factory setting
10 ... 110 °C
50 °C
Set the return temperature you accept for the system.
Set the acceptable return temperature limit.
When the return temperature falls below or gets higher than the set value, the controller
automatically changes the desired flow temperature to obtain an acceptable return
temperature. The influence is set in lines 4035 and 4036.
Return T limit (return temp. limitation)
4000
Gain - max. (return temp. limitation - max. influence)
4035
Setting range
Factory setting
-9.9 ... 9.9
0.0
Determines how much the flow(DHW) temperature will be influenced if the return temperature is
higher than the desired ‘Limit’ (line 4030) (P control).
Influence higher than 0:
The desired flow temperature is increased, when the return temperature gets higher
than the set limit.
Influence lower than 0:
The desired flow temperature is decreased, when the return temperature gets higher
than the set limit.
Example
The return limit is active above 50 °C.
The influence is set to -2.0.
The actual return temperature is 2 degrees too high.
Result:
The desired flow temperature is changed by -2.0 x 2 = -4.0 degrees.
Normally, the setting in line 4035 is lower than 0 in district heating systems to avoid a too
high return temperature.
Typically, the setting in line 4035 is 0 in boiler systems because a higher return temperature
is acceptable (see also line 4036).
