Grundfos Control MPC-Serie Installationsanleitung Seite 43

8.7.24 Stop function (4.3.1)
Fig. 64 Stop function
Description
The function is typically used in constant-pressure applications
and allows you to stop the last pump if there is no or a very small
consumption.
Purpose of the function:
• to save energy
• to prevent heating of shaft seal faces due to increased
mechanical friction as a result of reduced cooling by the
pumped liquid
• to prevent heating of the pumped liquid.
When a pilot pump is connected to the system, the
stop function parameters will be valid for the pilot
pump and not the main pump as the pilot pump will
be the last pump in operation.
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
Hset
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 CU 352 detects no or a
low flow rate (Q lower than 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 Hset plus (distribution above setpoint / 100) x
start/stop band. The pump is restarted when the pressure is Hset
minus (100-distribution above setpoint) / 100 x start/stop band.
See fig. 66. The start/stop band can be distributed around the
setpoint.
The flow rate is estimated by CU 352 when the pump is in the
stop period. As long as the flow rate is lower than Qmin, the pump
runs in on/off operation. If the flow rate is increased to above
Qmin, the pump returns to normal operation, Hset. Hset is equal
to the actual setpoint. See section
Detection of low flow rate
Low flow rate can be detected in two ways:
•
•
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.
Diaphragm tank size
Pump type
6. Overview of control
CRI(E) 3
CRI(E) 5
CRI(E) 10
CRI(E) 15
CRI(E) 20
CR(E) 32
CR(E) 45
CR(E) 64
CR(E) 95
CR(E) 125
Q
CR(E) 155
Precharge pressure
Hydro MPC-E and -F: 0.7 x the setpoint.
Hydro MPC-S:
During each flow estimation (every 2 minutes), the estimating
function will disturb the outlet 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, that is 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.
Stop: Hset + 0.5 x start/stop band
Start: Hset - 0.5 x start/stop band
Fig. 66 On/off operation
direct flow measurement with a flowmeter or flow switch
estimation of flow rate by measurement of pressure and
speed.
Recommended diaphragm tank size [litres]
-E
8
12
18
80
80
80
120
120
180
180
180
0.9 x the setpoint.
A: Normal operation
B: Pressure boosting
C: Stop
8.4.4 Setpoint (1.2.2).
-F -S
8 80
12 120
18 180
80 300
80 400
80 600
120 800
120 1000
180 1500
180 1500
180 1500
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