Siemens LMU54 Series - Third Stage ∆T Supervision; PWM Pump Control; H-Q Chart (Example)

63/171
Siemens Building Technologies Basic Documentation LMU54... / LMU64... CC1P7494en
HVAC Products 3 Functions 07.11.2002
Like the first stage plus limitation of the minimum volumetric flow to ensure the
measured ∆T will not exceed the adjusted ∆Tmax (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]
20 10 0 -10 -20
Acquired return
temperature
0
100
Modgrad [%]
NqmodNenn
(= 18)
corresponding to 100 %
TiAussenNorm
(= -20)
Range in which the delta-T controller
adjusts the volumetric flow
TkSNorm
(= 70)
7494d36E/0102
NqmodMin
(= 40)
dTkTrNenn
(= 20)
dTkTrMax
(= 30)
Required flow temperature
Required flow temperature
at NqmodNenn
Outside temperature [°C]
Outside temperature [°C]
Theoretical return
temperature at NqmodNenn
Range of reduced volumetric flow
(= NqmodMin)
∆T supervision
Condensing boilers with return temperature sensor to increase the efficiency of
condensation and when there are limitations with regard to the heat exchanger’s
maximum ∆T.
No bypass allowed.
• As before, the pump is activated and deactivated via the AC 230 V line. The pump’s
speed is adjusted via a separate control line
• The pump is controlled by means of a pulse width-modulated DC signal (PWM =
Pulse Width Modulation)
• Automatic maximum operation should the control line become faulty
FoerderMax
(= 5.9)
FoerderMin
(= 0.6)
Speed = 1
6
5
4
3
2
1
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
7494d37E/0102
Speed = QmodDrehzStufen
Pump head [m]
Q [m
3
/ H]
H-Q chart of PWM pump
Third stage
∆T supervision
Application
PWM pump control
H-Q chart
(example)