User Manual
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Siemens Universal controllers RMU710B, RMU720B, RMU730B CE1P3150en
Building Technologies Frost protection (basic types A and P) 03.10.2011
17.2.3 2-phased frost protection on water side (passive Ni 1000)
N.X1
x
AI
3140S32
Frost
Reliable frost protection depends on correct sensor placement. The detector
should be located on the water outlet of the heating coil within the air duct
As an additional protective function, the heating circuit pump must automatically
switch on at outside temperatures below 5 °C (setting value "ON according to
the outside temperature", see section "Pump")
Whe
n the temperature drops below the adjusted level, the heating sequences are
continuously opened and the cooling sequences continuously closed. The
temperature is thus prevented from falling below the "risk of frost limit".
If, in spite of this, the temperature does drop below the risk of limit value, the
following actions are triggered:
The fans are switched off
The configured control loop with the relevant heating coil keeps all heating
sequences open and all cooling sequences closed, the heating coil pump
remains on
The step switches remain on if not locked via input "Release external"!
All the other control loops are switched off
The outside air dampers are closed (see section 10.5 "Mixed air damper (basic
types
A, P)")
100 %
0 %
Xp
5 %
Xp/2
2 K
w
FP
OT
3150D21en
On
Off
Heat valve
RFL
PumpsFault
Key:
w
FP
Plant OFF frost protection setp.
RFL Risk of frost limit
FT Temperature measured at the
frost sensor
When the plant is off, a PI controller keeps the temperature of the heating coil at an
adjustable level, ensuring that a certain amount of heat is available when the plant
is started. This function acts on the heating sequences of the configured control
loop, but:
The outside air damper remains closed (see section 10.5 "Mixed air damper
(bas
ic types A, P)")
The heat recovery equipment is switched on (see section 0 "
Heat recovery equipment (basic types A, P)")
Application example
Notes
Caution
Function diagram