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Siemens Building Technologies Basic Documentation LMU54... / LMU64... CC1P7494en
HVAC Products 3 Functions 07.11.2002
• With speed limitation
When speed limitation is active, disturbing effects on the fan’s speed (voltage variations,
changes in resistance on the flue gas side) will be offset with regard to output limits.
For that purpose, the associated speeds must be matched to the heat output measured
at the boiler. Like without speed limitation, the modulating range or the maximum heat
output can be specified in the form of fan speed.
Heat output
(fan speed)
Output signal of
temperature controller
7494d02E
N_VL
Max. speed without RU
Max. speed with RU
Modulating range with RU
Modulating range without RU
Modulating range DHW
N_TL
Modulating range of the LMU... with speed limitation
The output limits in the case of heat demand are dependent on the connection of an RU.
The following table shows the assignment:
RU Maximum heat output «NhzMaxAkt»
Present See calculations below
Not present NhzMax
Formula to be used for weather compensation without room influence via the RU:
RelModLevSet
NhzMaxAkt = • (NhzMax – N_TL) + N_TL
100 %
RelModLevSet: The relative modulation level setting specifies the maximum degree
of modulation of the RU in % of the modulating range.
If there is demand for DHW, the maximum output is always predetermined by «N_VL».
With regard to heat demand, the following thus applies to the output or speed range:
Demand for space
heating
Demand for DHW heating
Minimum output N_TL N_TL
Maximum output NhzMaxAkt N_VL
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