English (GB)
16
11.2 Functions for constant-pressure systems
11.2.1 Pump cascade control
The cascade function ensures that only the required number of
pumps is running. This means that the number of running pumps
always corresponds to the required flow at the entered setpoint.
The first pump is started if the pressure at the discharge manifold
is below the setpoint.
If the first pump is not able to keep the discharge pressure at the
setpoint, and the minimum time between start/stop has passed,
another pump is started.
During the start and stop of a pump, the speed of the
speed-controlled pump is controlled in such way that the pressure
disturbance is kept as low as possible.
At decreasing demand, pumps will be stopped if the pressure
rises above the setpoint. Pumps will not be stopped until the
minimum time between start/stop has passed.
The last pump in operation
If only one pump is operating, this pump can be operated in
energy-saving on/off mode.
See section
.
The number of possible starts/stops per hour for all pumps is
limited by the maximum number of starts per hour.
11.2.2 Standby pumps
This function is optional and available on request. The function
makes it possible to limit the maximum performance of the
booster system by selecting one or more pumps as standby
pumps.
If a three-pump system has one standby pump, maximum two
pumps are allowed to operate at a time.
If one of the two pumps in operation has a fault and is stopped,
the standby pump will be started. The performance of the booster
system is thus not reduced.
The status as standby pump alternates between all pumps.
Contact Grundfos for further information.
11.2.3 Maximum pressure exceeded
This function protects the piping on the discharge side of the
booster system against damaging high pressures. The pressure
is monitored, and if the pressure is higher than 1.5 bar above the
setpoint for more than 5 seconds, the pumps are stopped, the
indicator light
illuminates, and the display indicates high limit
.
When the pressure falls below the setpoint, the system will
automatically restart.
11.2.4 Low-flow operation
When only one pump is operating due to cascade, the booster
system will regularly check for low flow by decreasing the pump
speed.
When low flow is detected, the booster system will change its
mode of operation to "low-flow operation" and run in on/off mode
as described below.
In on/off mode, the system has two phases:
• Off phase
Water is drawn from the diaphragm tank until the pressure of
the system reaches the lower limit of the on/off band (P
set
- 0.5
x on/off band).
• Boosting phase
The pump runs at 100 % speed until the pressure reaches the
upper limit of the on/off band (P
set
+ 0.5 x on/off band).
Fig. 12
On/off operation
11.2.5 S-system mode (start/stop band)
S-system mode is only auto-enabled in an ES-system if the CME
pump is out of operation due to a fault.
Fig. 13
Start/stop band
PT
H
.
L
TM
03
92
92
48
07
TM
03
92
05
36
07
Stop = H
set
+ 0.5 x on/off band
Start = H
set
- 0.5 x on/off band
Stop
Start
H [m]
Time [sec.]
A
B
C
B
C
A: Normal operation
B: Pressure boosting
C: Stop
Start/stop band
H
set
Time [sec.]
H [m]
Pump stops
Pump starts
