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Siemens Building Technologies
Basic Documentation RVP540 / RVP550
CE1P2488en
HVAC Products
General control processes
04.11.2009
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
red
until the flow temperature ac-
cording to the heating curve calculation would exceed the maximum flow temperature
setpoint T
Vmax
at point C. In Figure 1, this applies to outside temperatures in the range
of
T
A
= 20…-5 °C. In range 2, the flow temperature will then be maintained at
T
VMax
. For
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
A
= -10 °C. The heating
output at operating point A is the same as the heating output that would result at oper-
ating point (
T
V
according to the heating curve, speed
n
red
).
0
10
20
30
40
50
60
70
80
90
100
-10
-5
0
5
10
15
20
Outside temperature T
A
[°C]
Flow a
nd r
e
tu
rn
t
e
mpe
ra
tur
e
T
V
, T
RL
[°C]
Heating curve T
V
at
reduced pump speed n
red
Reduced pump speed n
red
T
VMax
=70 °C
Range 1
Range 2
Heating curve T
V
at
maximum pump speed n
max
T
RL
at n
max
T
RL
at n
red
C
B
A
Maximum pump speed
Mean radiator
temperature
2392
Z
43en
Figure 1:
Progression of pump speed, flow temperature T
V
and T
RL
versus the outside temperature (example)
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
of the circulating pump
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
of the circulating pump
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 %.
