System Sizing - Grundfos CU 301 Notice D'installation Et De Fonctionnement

Flow detection
During pump operation, meaning when water is
consumed, CU 301 adjusts the pump speed to
maintain a constant pressure. In order to stop the
pump when no water is consumed, CU 301 performs
flow detection every 10 seconds.
The pump speed is reduced until a small pressure
drop is registered. This pressure drop indicates that
water is consumed and the pump speed is resumed.
See fig. 8.
If the pump speed reduces without any pressure
drop being registered, this indicates that no water is
consumed. The diaphragm tank is filled with water
and the pump stops.
Pressure
Flow detection
10 s
Fig. 8
System limits
Even though, CU 301 controls the pressure within ±
0.2 bar, bigger pressure variations may occur in the
system. If the consumption is suddenly changed, for
example if a tap is opened, the water must start
flowing before the pressure can be made constant
again. Such dynamic variations depend on the pipes,
but, typically, they will lie between 0.5 and 1 bar.
If the desired consumption is higher than the quantity
the pump is able to deliver at the desired pressure,
the pressure follows the pump curve as illustrated in
fig. 9.
Pressure
Stop
+ 0.5 bar
A
Controlling
Start
± 0.2 bar
- 0.5 bar
0.18
Fig. 9
A = Pressure set
10 s
Time
Dynamic
variations
± 0.5 bar
Flow
3
m /h

3.2 System sizing

To ensure the correct function of the system, it is
important that the pump is of the right type.
During operation, CU 301 controls the pump speed
within the range from 3000 min
See fig. 10.
We recommend that you follow the guidelines below:
H [m]
Pump curve at
3000 min
Fig. 10
The following must be fulfilled:
1. Minimum head at no flow < static head + system
pressure.
2. Maximum head at maximum flow > dynamic head
+ system pressure.
-1 -1
to 10,700 min .
Pump curve at
-1
10,700 min
-1
Q 3
Q [m /h]
max
9