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Siemens Building Technologies
Basic Documentation LMU54... / LMU64...
CC1P7494en
HVAC Products
3 Functions
07.11.2002
In the case of systems using a time switch (external clock connected to the room
thermostat or QAA73... input), there are 2 choices to determine the demand for heat.
Changeover takes place via setting parameter «dTrAbsenk»:
dTrAbsenk = 0:
Time switch acts directly on the demand for heat
dTrAbsenk
≠
0:
Time switch acts on the room temperature setpoint
In this case, the switching state of the time switch contact is directly passed on. The
time switch can be connected either to the room thermostat or to the QAA73... input.
The following assignment applies:
Time switch contact open:
SU = 0
Time switch contact closed:
SU = 1
If
no
time switch is connected, the demand for heat will stay locked (SU = 0)
The assignment to the heating circuits is as follows:
Time switch connected to …
Impact on …
RT input
Heating circuit 1, SU1 = RT
QAA73 input
Heating circuit 2, SU2 = OT
If a RU is connected to the QAA73... input, the following assignment applies:
Time switch connected to …
Impact on …
RT input
Heating circuit 1, SU1 = RT,
if not controlled by the RU
Heating circuit 2, SU2 = RT,
if not controlled by the RU
If SU2 is derived from the QAA73... input (no RU connected), SU2 will act on heating
circuit 2 only when parameter «KonfigRg1.Schaltuhr2Bw» = 0 and
«KonfigRg1.Schaltuhr2» = 1, that is, if a change to heating circuit 2 was made.
Otherwise, SU2 acts on the DHW circuit.
If, by contrast, SU2 is derived from the RT input (RU connected), the RU always acts on
heating circuit 2.
When AGU2.310... is connected, following applies : Time switch is inactive. It will be
replaced by the time switch program of the AGU2.310... (
→
CC1
B
7494).
In this operating mode, the time switch produces a reduction of the room temperature
setpoint when the time switch contact is open. The room temperature setpoint changed
in this way is included in the calculation made by the heating limit switch. Hence, in this
case, the time switch only acts indirectly on the demand for heat.
If weather compensation is used, reduction of the room temperature setpoint also leads
to a reduction of the boiler temperature setpoint.
TsRaumAkt:
Current room temperature setpoint
TsRaum:
Room temperature setpoint from HMI or RU
dTrAbsenk:
Temperature by which the room temperature setpoint shall be
lowered in reduced mode (setting parameter)
The room temperature setpoint «TsRaumAkt» changed in this way is included in the
calculation of the boiler temperature setpoint if weather compensation is used. The time
switch can be connected either to the room thermostat’s input or to the QAA73... inputs.
With regard to the time switch signal, the following applies, independent of the contact
position:
SU = 1
With this variant, the demand for heat is generated based on S / W changeover, heating
limit switch and quick setback.
Time switch
Time switch acting directly
on heat demand
Time switch acting on the
room temperature setpoint
U
