Basic Documentation

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Siemens Modular Heating Controller RMH760B CE1P3133en
Building Technologies 9 Heating circuit control 2017-09-29
SetPTFlDe
SetPTFlHi
SetPTRN
TFl
TOeff
TODe
sHC
TOHi
B
D
A
C
1
2
3131D24
The nonlinear heat transmission is considered by the radiator exponent nH. The
following table gives an overview of the different types of heating systems normally
used:
Heat transmission via…
Radiator exponent nH
Underfloor heating system
1.05…1.1
Flat radiators
1.26…1.33
Radiators to DIN 4703
1.3
Convectors
1.25…1.45
With a radiator exponent between 1…1.5, the heating curve is only slightly deflected
and can therefore be replaced by linearized sections. This is achieved by setting
another curvepoint, the so-called inflection point.
The inflection point lies 30 % below the outside temperature at which the flow
temperature setpoint is 20 °C and the outside temperature
A
at curvepoint .
This means that curvepoint
 (usually set at the heating limit) does not directly
determine the location of the inflection point.
The basic heating curve applies to a room temperature setpoint of 20 °C. At lower or
higher setpoints, the heating curve is appropriately displaced (also refer to subsection
9.5.3 "Influences on the flow temperature setpoint").
Outside temperature at a flow temperature setpoint of 20 °C = 20 °C
Outside temperature
A
= –10 °C
30 % of that range = 9 K
Hence, the inflection point is at an outside temperature of 11 °C.
nH = 1.5
nH = 1.0
30 K = 100 %
9 K = 30 %
-10
-5
0 5
10
15
20
25
60
50
40
30
20
10
0
TFl
TO
3131D34
38 °C
32 °C
"20/20 °C"
The lift at the point of inflection is dependent on the flow temperature setpoint and the
radiator exponent.
Radiator exponent
Inflection point
Note
Example