Downdraft Compensation - Siemens Desigo RXB Technical Manual

K N X
CO
R
Note
Function
Note
Controller output
LTHW radiators with
motorized valve actuators
Siemens
Building Technologies
For test purposes, the radiator valve actuator can be overridden via the following
communication objects:
Heating surface output override (Input communication object)
Flags Type
R W K T U
0 1 1 0 0 8.010
DPT_Percent_V16
Before the radiator valve actuator can be overridden, "Test" mode must be activated via
the communication object Application mode (see page 128).
8.5.5

Downdraft compensation

This function is only active in Comfort mode.
In situations where (owing to large internal heat gains) there is no heating demand from
the room despite a low outdoor temperature (supplied via the bus), large window
surfaces can impair indoor comfort (through radiated cold and the downward flow of
cold air).
A radiator located under the window can be used to "brake" the downward flow of cold
air and compensate for cold radiation.
To achieve this, the radiator is switched on whenever the outdoor temperature drops
below a predefined value (the Outdoor temp. 0% valve position ).
The maximum heating output (set under Max. Valve Position ) is reached at the "coldest
outdoor temperature" (which can be set under Outdoor temp. max. valve position).
100%
Max. valve position
25%
0%
Outdoor temp.
max. valve position
The controller adds the values representing the valve position for downdraft
compensation and the valve position for the heating sequence.
– If the room temperature rises as a result of the downdraft compensation feature, the
heating sequence reduces the opening of the associated valve, so correcting the
room temperature.
– When the sequence reaches zero, the room temperature is increased by the residual
heat from the downdraft compensation feature.
The heat output calculated by the controller is achieved as follows:
The valve is opened to the heat output value [%].
RXB (KNX) application library
Control sequences
Receive timeout
no
Heating output
Thermic
Motoric
Outdoor temp.
0% valve position
FNC Description of functions for FC-10, FC-11, FC-12
Value
00...100% 0 =
+100 = +100%
+32767 = invalid
T
OA
CM110385en_05
28 Feb 2009
0%
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