Heat Output Limits - Siemens LMU54 Series Basic Documentation

Heat output limits

Siemens Building Technologies
HVAC Products
The PWM setting range of the temperature controller depends on the speed limitation
and the heat demand.
• With inactive speed limitation:
The modulating range must be parameterized while giving consideration to voltage
variations.
LmodTL:
This limit must be set such that the heat output will not fall below the minimum
permissible output while taking into account voltage variations (undervoltage).
PhzMax, LmodVL:
This limit must be set such that the heat output will not exceed the maximum
permissible output while taking into account voltage variations (overvoltage).
Output limits with speed
limitation inactive
In addition, the following requirement must be met: PhzMax ≤ LmodVL
• When speed limitation is active:
The modulating range of the temperature controller remains as wide as possible and
speed limitation limits the heat output to the required value.
- Upper limitation:
- Lower limitation:
To ensure a maximum modulating range will be reached and voltage variations in the
fan's power supply can be offset, it is recommended to set the setting parameters of
output adjustment as follows:
LmodTL:
Minimum PWM value at which the flame is not yet lost (while giving consideration to
voltage variations).
PhzMax, LmodVL:
100 % (makes possible the maximum fan setting range).
If the associated speeds «NhzMax» and «N_VL» deviate too much from these PWM
values, there will be more and more overshoot when the fan speed attempts to adjust
itself on reaching the maximum heat output.
If such overshoot is not desired, the values can be reduced.
With the following operating modes, the heat output is statically predefined, that is, the
boiler controller's results will be ignored and a value in accordance with the function is
delivered to the burner control.
Function
Chimney sweep function
Controller stop function
Controller delay
Basic Documentation LMU54... / LMU64...
3 Functions
Heating mode
LmodTL, PhzMax
«NhzMaxAkt» in the case of heating demand, «N_VL» in the
case of DHW demand
«N_TL» in the case of heating and DHW demand
Required heat output
PhzMaxAkt
Set on the HMI or QAA73...
LmodRgVerz
DHW mode
LmodTL, LmodVL
51/171
CC1P7494en
07.11.2002