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Building Technologies
Modular Heating Controller RMH760B
CE1P3133en
HVAC Products
10 DHW heating
05.02.2007
The pulses are delivered via the meter inputs of function block “Meter”. For more
detailed information about this function block, refer to chapter 11 “Function block me-
ter”.
After one or several meter inputs have been configured, pulse limitation can be set up.
Main menu > Commissioning > Settings > …
or
Main menu > Settings > DHW > Limitations > Pulse limitation
Operating line
Range
Factory setting
Meter input
--- / 1…4
---
Type of limitation
Absolute / Scaled
Absolute
Limit value
5…4000 pulses/min
75 pulses/min
Integral action time Tn
0…255 min
60 min
The meter input is an input of function block “Meter” and used for the limitation of
pulses. Only inputs configured to a terminal can be selected for pulse limitation.
2 limitation choices are available:
•
Absolute: Limitation will be activated when the limit value is crossed
•
Scaled: The limit value is fixed at 75 pulses/min. The limit value can be set, but this
has no effect. If less than 5 pulses/min are received, fault status message
No signal
meter 1
(or
…2
) will be delivered. Heat meters with a scaled output deliver
120 pulses/min if there is no supply of heat or no volumetric flow. Together with
pulse limitation, this prevents hydraulic creep.
From the limit value, pulse limitation starts throttling the actuating device (mixing valve).
The setting is only active when the limitation is absolute. In the case of scaled limita-
tion, the limit value can be set, but the function works with 75 pulses/min (fixed value).
The setting value determines the rate at which the flow temperature setpoint will be
lowered:
•
Short integral action times lead to a faster reduction
•
Long integral action times lead to a slower reduction
10.8.5 Pump overrun and mixing valve overrun
To protect the boiler against overtemperatures on burner shutdown because there may
be no more consumers drawing heat, a consumer overrun time can be set on the boiler
controller.
When the burner has shut down, overrun ensures that the heating circuits and DHW
heating will still draw a certain amount of heat during that period of time, provided they
were consuming heat up to one minute before shutdown occurred. In any case, pumps
and mixing valves have an overrun time of 60 seconds.
For more detailed information, refer to section 5.4 “Pump overrun and mixing valve
overrun”.
In the case of direct DHW heating, overrun is not possible since there is no pump on
the secondary side. Overrun does not act on the circulating pump.
Overrun applies to both the primary and the secondary pump.
To carry the residual heat away from the heat exchanger, plant types DHW 4 and DHW
5 (with heat exchanger and primary pump) offer a setting for an additional overrun time
of the secondary pump:
Meter inputs
Settings
Meter input
Type of limitation
Limit value
Integral action time (Tn)
Consumer overrun
Direct DHW heating
Primary pump and secon-
dary pump
