Generating The Demands For Heat - Siemens LMU54 Series Basic Documentation

With QAA73...
Generating the
demands for heat
Legend
Siemens Building Technologies
HVAC Products
Calculation of the heating curve is based on a maximum pump flow rate, which means
that the pump's degree of modulation is 100 %.
When using a variable speed pump, a certain extra temperature is added.
RU QAA73... calculates weather compensation completely (referred to a degree of
pump modulation of 100 %). Input data from the RU's perspective are the following:
Toutside: Actual outside temperature
As the results of weather compensation, the LMU... receives from the RU:
TSet: Boiler temperature setpoint of HC1 of the RU
TSet2: Boiler temperature setpoint of HC2 of the RU
CH1 enable: Heat demand HC1 of the RU
CH1 enable: Heat demand HC2 of the RU
To maintain the room temperature level with pump modulation, the LMU... calculates an
extra temperature, which is added to the value of the RU.
If there are several sources that call for heat, the following priorities apply:
1. Demand for heat via the RU.
2. Room thermostat or time switch with / without weather compensation.
For the different plant components that act on the demand for heat, refer to the table in
chapter «Combinations of RU and room thermostat / time switch».
The → ECO functions also have an impact on the demand for heat.
In general, the heating circuits' demand for heat is that shown by the following diagram:
S / W auto
&
S / W switch =
Auto
S / W switch =
winter (1)
RT / SU
&
Sab
HgS
RU
Heat demand
per Parameter
Only Rh1:
Warm air curtain
Generation of heat demand by heating circuits 1 and 2
RT / SU Room thermostat / time switch
HgS Heating limit switch
RU Room unit
S / W auto S / W changeover by LMU...
S / W switch S / W changeover on HMI
Sab Quick setback
If certain plant components are not present (e.g. no S / W changeover), the input will
enable the demand for heat.
Basic Documentation LMU54... / LMU64...
3 Functions
≥
1
&
≥
1
Heat demand
≥
1
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CC1P7494en
07.11.2002