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Siemens Building Technologies
HVAC Products
6.7.3
Function description of variant 2
(according to the heating curve)
Figure 1 shows an example of the evolution of pump speed, flow and return tempera-
ture versus the outside temperature. In the upper outside temperature range (range 1),
the pump speed is maintained at the reduced level n
cording to the heating curve calculation would exceed the maximum flow temperature
setpoint T
at point C. In Figure 1, this applies to outside temperatures in the range
Vmax
of T
= 20...-5 °C. In range 2, the flow temperature will then be maintained at T
A
that purpose, the pump speed is continuously increased until the selected maximum
speed is reached at point A. In Figure 1, this is the case at T
output at operating point A is the same as the heating output that would result at oper-
ating point (T
according to the heating curve, speed n
V
Heating curve T
reduced pump speed n
Mean radiator
temperature
Reduced pump speed n
20
15
Figure 1: Progression of pump speed, flow temperature T
Notes on the example shown in Figure 1:
•
The heating system is designed such that it reaches its maximum capacity at an
outside temperature of -10 °C (no spare capacity for heating up processes). At this
outside temperature, both the pump speed and the flow temperature are at their
maximum
•
With this kind of plant design, it is assumed that the outside temperature hardly
ever drops below -5 °C. But the pump speed will also be increased above the re-
duced speed in the case of heating up processes, whenever the outside tempera-
ture is above -5 °C
6.7.4
Setting the parameters at the time of commissioning
•
Reduced speed n
Red
The reduced speed should be set at the lowest possible level, but high enough to
ensure that all consumers will still receive sufficient amounts of heat. The minimum
setting is 40 %.
•
Maximum speed n
Max
If a reduction of the maximum pump head is required (due to the hydraulic layout),
this should be done by reducing the maximum pump speed since this also saves
pumping power. If the pump may operate at nominal capacity, the maximum speed
is to be maintained at 100 %.
Basic Documentation RVP540 / RVP550
General control processes
Heating curve T
maximum pump speed n
at
V
red
T
at n
Maximum pump speed
RL
red
red
Range 1
10
5
Outside temperature T
[°C]
A
and T
V
of the circulating pump
of the circulating pump
until the flow temperature ac-
red
= -10 °C. The heating
A
).
red
at
V
T
=70 °C
VMax
max
B
C
A
T
at n
RL
max
Range 2
0
-5
-10
versus the outside temperature (example)
RL
. For
VMax
100
90
80
70
60
50
40
30
20
10
0
CE1P2488en
04.11.2009
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