Siemens LMU54 Series - First Stage Maximum Limitation of the Flow Temperature; Second Stage ∆T Limitation

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Siemens Building Technologies Basic Documentation LMU54... / LMU64... CC1P7494en
HVAC Products 3 Functions 07.11.2002
Operation with the minimum volumetric flow (NqmodMin) and calculation of the
associated flow tempeature boost to keep the amount of heat delivered by the heating
system at a constant level.
Limitation ot the maximum flow temperature (TkSnorm) by a stepwise increase of the
volumetric flow until the maximum volumetric flow is reached (NqmodNenn).
20 15 10 5 0 -5 -10 -15 -20
20
30
40
50
60
70
80
90
100
Temperature [°C]
Outside temperature [°C]
Outside temperature [°C]
20 10 0 -10 -20
Required flow temperature
at NqmodMin
Theoretical return
temperature at NqmodMin
Theoretical return
temperature at NqmodNenn
Range of reduced volumetric flow
(= NqmodMin)
0
100
Modgrad [%]
NqmodNenn
(= 18)
corresponding to 100 %
TiAussenNorm
(= -20)
Range in which the
volumetric flow
must be increased
from NqmodMin
to 100 %
TkSNorm
(= 70)
7494d34E/0102
NqmodMin
(= 40)
Required flow temperature
at NqmodNenn
Maximum limitation of the flow temperature
Condensing boilers with no return temperature sensor to increase the efficiency of
condensation and when there are no limitations with regard to the heat exchanger’s
maximum ∆T. There should be no bypass, if possible.
Like the first stage plus limitation of the minimum volumetric flow to ensure the
expected ∆T will not exceed the adjusted ∆T (dTkTrMax)
→ Control of ∆Tmax via the volumetric flow.
20 15 10 5 0 -5 -10 -15 -20
20
30
40
50
60
70
80
90
100
Temperature [°C]
Outside temperature [°C]
20 10 0 -10 -20
Required flow temperature
0
100
Modgrad [%]
NqmodNenn
(= 18)
corresponding to 100 %
TiAussenNorm
(= -20)
TkSNorm
(= 70)
7494d35E/0102
NqmodMin
(= 40)
dTkTrNenn
(= 20)
dTkTrMax
(= 30)
Required flow temperature
at NqmodNenn
Range of reduced volumetric flow
(= NqmodMin)
Range in which the
volumetric flow
must be increased
from NqmodMin
to 100 %
Outside temperature [°C]
Theoretical return
temperature at NqmodNenn
Theoretical return
temperature at NqmodMin
∆T limitation
Condensing boilers with no return temperature sensor to increase the efficiency of
condensation and when there are limitations with regard to the heat exchanger’s
maximum ∆T. There should be no bypass, if possible.
First stage
Maximum limitation of the
flow temperature
Application
Second stage
∆T limitation
Application