First Stage Maximum Limitation Of The Flow Temperature; Second Stage ∆T Limitation - Siemens LMU54 Series Basic Documentation

First stage
Maximum limitation of the
flow temperature
Application
Second stage
∆T limitation
Application
62/171
Siemens Building Technologies
HVAC Products
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).
100
90
80
70
60
Required flow temperature
50
at NqmodMin
40
30
20
20 15 10
Range of reduced volumetric flow
Modgrad [%]
100
NqmodMin
(= 40)
0
20 10
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.
100
90
80
70
60
50
Required flow temperature
40
30
20
20 15 10
Range of reduced volumetric flow
Modgrad [%]
100
NqmodMin
(= 40)
0
20 10
∆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.
Basic Documentation LMU54... / LMU64...
3 Functions
Required flow temperature
at NqmodNenn
Theoretical return
temperature at NqmodMin
5 0 -5 -10
Outside temperature [°C]
(= NqmodMin)
0 -10
Outside temperature [°C]
Required flow temperature
at NqmodNenn
dTkTrMax
(= 30)
Theoretical return
temperature at NqmodMin
5 0 -5 -10
Outside temperature [°C]
Range in which the
(= NqmodMin) volumetric flow
must be increased
from NqmodMin
to 100 %
0 -10
Outside temperature [°C]
TkSNorm
(= 70)
Theoretical return
temperature at NqmodNenn
TiAussenNorm
(= -20)
-15 -20
Range in which the
volumetric flow
must be increased
from NqmodMin
NqmodNenn
to 100 %
(= 18)
corresponding to 100 %
-20
TkSNorm
(= 70)
dTkTrNenn
(= 20)
Theoretical return
temperature at NqmodNenn
TiAussenNorm
(= -20)
-15 -20
NqmodNenn
(= 18)
corresponding to 100 %
-20
CC1P7494en
07.11.2002