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Building Technologies
Modular Heating Controller RMH760B
CE1P3133en
HVAC Products
10 DHW heating
05.02.2007
can be set for both load ranges. For the medium load ranges, the values will be aver-
aged in a continuous process.
When commissioning direct DHW heating for the first time, the default values of Xp, Tn
and Tv should be used. To optimize and check the control parameters, it is recom-
mended to follow the procedure detailed below under ”Checking the control function…”.
To check the control behavior with the preset control parameters, the following proce-
dure is recommended:
1. With
maximum load,
the controller shall maintain the setpoint for a certain period
of time.
2. Then, increase or decrease the setpoint by 5…10 %. During this period of time, the
controller ascertains the connection conditions and adjusts the PID controller. For
this reason, it is important to start with the maximum load.
•
Maximum load means the highest velocity of flow on the DHW side at the highest
setpoint (usually, this is the legionella protection setpoint)
•
Basically, stable control behavior is called for, which should rather be fast than slow,
meaning that the DHW temperature should reach the new setpoint as quickly as
possible
If the correcting action does not produce the required result, the control parameters
should be readjusted as follows:
Setting parameters Xp, Tv and Tn must be
decreased
in steps while the load is at its
maximum. A new readjustment should be made only after the correcting action result-
ing from the previous readjustment is completed.
t
TDhw
TDhwSetpt
31
33
D
13
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 con-
troller 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 read-
justment should be made only after the correcting action resulting from the previous
readjustment is completed.
t
TDhw
TDhwSetpt
31
32
D
11
1. Decrease Xp in steps of about 25 % of the previous value while the load is at its
maximum.
Tip
Checking the control
function with maximum
loads
Note on maximum load
Control action is
too slow
Control action is
too fast
