Diaphragm Tank Size; Start/Stop Band; On/Off Operation; Stop Parameters - Grundfos Control MPC Installation And Operating Instructions Manual

The description of the stop function applies to all booster systems
with variable-speed pumps. MPC-S systems will have on/off
control of all pumps as described in section
variants.
H

Start/stop band

H
set
Qmin
On/off control
Normal operation
Fig. 65 Start/stop band
When the stop function is enabled, the operation is continuously
monitored to detect a low flow rate. When the CU 352 detects no
or a low flow rate (Q < Qmin), it changes from constant-pressure
operation to on/off control of the last pump in operation.
Before stopping, the pump increases the pressure to a value
corresponding to H plus (distribution above setpoint / 100) x
set
start/stop band. The pump is restarted when the pressure is H
minus (100-distribution above setpoint) / 100 x start/stop band.
See fig. 66. The start/stop band can be distributed around the
setpoint.
H [m]
A B C
Stop
Start
Stop: H + 0.5 x start/stop band
set
Start: H - 0.5 x start/stop band
set
Fig. 66 On/off operation
The flow rate is estimated by the CU 352 when the pump is in the
stop period. As long as the flow rate is lower than Qmin, the pump
will run on/off. If the flow rate is increased to above Qmin, the
pump returns to normal operation, H
setpoint. See section
8.4.4 Setpoint
Detection of low flow rate
Low flow rate can be detected in two ways:
• direct flow measurement with a flowmeter or flow switch
• estimation of flow rate by measurement of pressure and
speed.
If the booster system is not connected to a flowmeter or flow
switch, the stop function will use the estimating function.
If the detection of low flow rate is based on flow estimation, a
diaphragm tank of a certain size and with a certain precharge
pressure is required.
38
5. Overview of control
Q
set
A: Normal operation
B: Pressure boosting
C: Stop
B C
Time [sec]
. H is equal to the actual
set set
(1.2.2).

Diaphragm tank size

Recommended diaphragm tank size [litres]
Pump type
-E
CRI(E) 3 8
CRI(E) 5 12
CRI(E) 10 18
CRI(E) 15 80
CRI(E) 20 80
CR(E) 32 80
CR(E) 45 120
CR(E) 64 120
CR(E) 90 180
CR(E) 120 180
CR(E) 150 180
Precharge pressure
Hydro MPC-E and -F: 0.7 x setpoint.
Hydro MPC-S: 0.9 x setpoint.
During each flow estimation (every 2 minutes), the estimating
function will disturb the discharge pressure by ±10 % of the
setpoint. If this disturbance is not acceptable, the stop function
must be based on direct flow measurement with a flowmeter or
flow switch.
The minimum flow rate can be set, i.e. the flow rate at which the
booster system changes to on/off control of the last pump in
operation.
If both a flowmeter and a flow switch are connected, the
changeover to on/off control will be determined by the unit first
indicating low flow rate.
Setting range
Start/stop band: 5-30 %
2-50 % of the rated flow rate (Qnom) of
one of the pumps. (Can only be set if
Min. flow rate:
direct flow measurement by means of
flowmeter has been selected.)
Distribution above
0-100 %.
setpoint:
Setting via control panel
System without flow switch or flowmeter
• Settings > Secondary functions > Stop function.
• Select: Enabled.
1. Set: Start/stop band.
2. Select: Go to setting of flow stop parameters.
The display below appears.
Fig. 67 Stop parameters
-F -S
8 80
12 120
18 180
80 300
80 400
80 600
120 800
120 1000
180 1500
180 1500
180 1500