Siemens RVD230 Basic Documentation page 38

Minimum and maximum
pump speed
Control of the heating
circuit pump
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Siemens Building Technologies
HVAC Products
The intermediate circuit pump used in connection with stratification storage tanks and
circulating pump K6 are not speed-controlled.
If the pulse-width-modulated output is assigned to a pump that is not used by the re-
spective plant type, it remains at 0 %.
• The minimum pump speed in % of the nominal speed is to be set on operating line 58.
It should be as low as possible, but high enough to ensure that all consumers get suffi-
cient amounts of heat. The relay assigned to the pump is still connected in parallel and
can be used to fully deactivate the pump when not in use.
The setting range reaches from 0 to the value set on operating line 59
• The maximum pump speed in % of the nominal speed is to be set on operating line 59.
If, due to the hydraulic layout, the maximum pump head must be reduced, this should
be done via a reduction of the maximum pump speed since this saves pumping power.
If the pump may operate at nominal capacity, the maximum speed is to be maintained
at 100 %.
The setting range reaches from the value set on operating line 58 to 100 %
The following illustration shows the control of the heating circuit pump. It shows the pump
speed and the flow and return temperatures as a function of the outside temperature.
In the upper outside temperature range (range 1; in the example T
pump speed is maintained at its minimum until the flow temperature – according to the
heating curve – would exceed the flow temperature setpoint T
In the lower outside temperature range (range 2; in the example T
flow temperature is then maintained at a constant level of T
continuously increased until the selected maximum speed is reached (operating point
A; T = –10 °C).
A
The heating output at operating point A is the same as the heating output that would
result at operating point B (flow temperature according to the heating curve, minimum
pump speed).
T
V
100
90
80
70
60
T
HK m
50
40
30
20
10
0
20 15 10
A Operating point A (maximum pump speed reached)
B Operating point B (theoretical heat output)
C Operating point C (effective heat output)
n Maximum pump speed
max
n Reduced pump speed
red
Notes on the example given in the illustration:
• The heating plant is designed such that it reaches its maximum capacity at an outside
temperature of –10 °C (no more spare capacity for heating up processes). At this
outside temperature, both the pump speed and the flow temperature are at their ma-
ximum
Basic Documentation RVD230
11 Function block Plant configuration
T for n
V max
T for n
V red
T for n
T for n
R max
R
n
red
5 0
Range 1
T
t
RL
T
T
= 20...–5 °C), the
A
(operating point C).
Vmax
= –5...–10 °C), the
A
. But the pump speed is
Vmax
B
T = 70 °C
Vmax
C
A
n
max
red
-5 -10
T
AM
Range 2
Mean radiator temperature
HKm
Return temperature
Flow temperature
V
Maximum limit value of the flow
Vmax
temperature
CE1P2383en
27.05.2004