6-2
6.2.1
Automatic alternate operation type
In automatic alternate operation, two pumps
alternately start automatically when the pressure in
the pipe drops to a certain level, and the running
pump stops automatically when the water usage
drops to a certain level.
(1) When the water tap is opened and water is used,
the pressure in the discharge piping drops. If the
pressure in the discharge piping drops to a value
close to the preset minimum sustained head (P
L
),
the pressure transmitter detects the drop and the
system starts up a pump.
(2) For constant control of estimated terminal
pressure until the flow rate reaches the
maximum water supply rate (Q
2
), the inverter controls the rotation speed according to the
increase/decrease in water usage to change the discharge pressure from P
L
to P
H
.
(3) If the water usage drops to the stop flow rate (Q
1
), the flow switch detects the drop and the system
stops the pump. The operation indicator light blinks while the system checks that the pump is being
stopped. If the energy-saving operation is enabled, the period for checking the pump-stop changes
depending on the operation conditions. (
ĺ
see 7.5.3)
(4) When the water tap is opened and water is used again, the system starts up the pump which was not
running last time.
6.2.2
Automatic alternate parallel operation type
In automatic alternate parallel operation, two pumps run alternately when the water usage does not
exceed the maximum water supply rate of one pump, and they run in parallel (simultaneous operation of
the two pumps) when the usage exceeds the maximum water supply rate of one pump.
(1) When the water tap is opened and water is used, the pressure in the discharge piping drops. If the
pressure in the discharge piping drops to a value close to the preset minimum sustained head (P
L
),
the pressure transmitter detects the drop
and the system starts up a pump.
(2) For constant control of estimated terminal
pressure until the flow rate reaches the
maximum water supply rate (Q
3
), the
inverter controls the rotation speed
according to the increase/decrease in
water usage to change the discharge
pressure from P
L
to P
H
.
(3) If the water usage increases to a value
close to the parallel water flow rate (Q
2
),
the system starts up the inactive pump at
rest (“the subsequent pump”) to follow
the operation of the first-started pump.
(4) If the water supply rate changes also in
parallel operation, the pumps continuously run at a pressure along the discharge curve of the unit.
(5) If the water usage drops to the parallel water flow rate (Q
2
), the system stops the subsequent pump
and keeps only the first-started pump running.
(6) If the water usage further drops to the stop flow rate (Q
1
), the flow switch detects the drop and the
system stops the pump. The operation indicator light blinks while the system checks that the pump is
being stopped. If the energy-saving operation is enabled, the period for checking the pump-stop
changes depending on the operation conditions. (
ĺ
see 7.5.3)
(7) When the water tap is opened and water is used again, the system starts up the pump which stopped
first.
Discharge pressure
P
H
: Total head
P
L
: Minimum sustained head
Q
1
: Stop flow rate
Q
2
: Maximum water supply rate
Specified point
Performance curve at
maximum frequency
Water supply rate
Discharge
curve of unit
Fig. 6-2-1 Automatic alternate operation
Discharge
pressure
P
H
: Total head
P
L
: Minimum sustained head
Q
1
: Stop flow rate
Q
2
: Parallel water flow rate
Q
3
: Maximum water supply rate (Operation of two pumps)
Specified point
Performance curve at
maximum frequency
(Two pumps)
Water supply rate
Discharge
curve of unit
Fig. 6-2-2 Automatic alternate parallel operation
Performance curve at
maximum frequency
(One pump)
