Basic Documentation

162/256
Siemens Modular Heating Controller RMH760B CE1P3133en
Building Technologies 10 DHW heating 2017-09-29
1. Decrease Xp in steps of about 25 % of the previous value while the load is at its
maximum.
2. Decrease Tv in steps of 1 to 2 seconds (when the value of 0 is reached, the
controller operates as a PI controller).
If this is not sufficient:
3. Decrease Tn in steps of 10 to 20 seconds while the load is at its maximum.
If there is significant overshoot or even continuous oscillations, setting parameters Xp,
Tv and Tn must be increased in steps while the load is at its maximum. A new
readjustment should be made only after the correcting action resulting from the
previous readjustment is completed.
t
TDhw
TDhwSetpt
3132D11
1. Decrease Xp in steps of about 25 % of the previous value while the load is at its
maximum.
2. Increase Tv in steps of 2 to 5 seconds while the load is at its maximum.
If this is not sufficient:
3. Increase Tn in steps of 10 to 20 seconds while the load is at its maximum.
To check the control, the start is made again with the preset control parameters, but
this time under minimum load conditions.
Minimum load means the lowest velocity of flow on the DHW side (e.g. circulation
load) at the reduced setpoint
For the control system, the load under frost protection conditions is only of minor
importance; for this reason, the frost protection setpoint should not be selected
Under these minimum load conditions, the controller should maintain the setpoint for
a certain period of time. Then, increase or decrease the setpoint by 5…10 %
If the correcting action does not produce the desired result, control parameters Xp, Tv
and Tn should be readjusted this time under minimum load conditions according to the
above paragraphs "Control action is too slow" and "Control action is too fast". When
readjusting the parameters, "…while the load is at its maximum" should be replaced
here by "… when the load is at its minimum".
10.5.2 Requirements for the plant
The correct location of the secondary flow sensor is very important! If no flow switch is
used, it must be made certain that the flow sensor immerses into the heat exchanger.
If the flow sensor is not correc
tly sited, there is a risk of excessive heat exchanger
temperatures
.
Apart from certain hydraulic prerequisites, good control performance can only be
achieved under the following conditions:
1. Use of a fast-acting actuator having a running time of ≤15 seconds
2. The time constant of the secondary flow temperature sensor as an immersion sensor
should be about 2 seconds
3. The secondary flow temperature sensor should be located about 100 to 200 mm
outside the heat exchanger (item 4. must be satisfied; otherwise, refer to items 1.
and 2.)
4. Use of a flow switch
5. The circulation pipe joins the DHW supply line by the heat exchanger
Control action is
too fast
Checking the control
function at minimum
load
Notes on minimum load