Grundfos LCSE Installation And Operating Instructions Manual page 48

Factory setting
See section
10. Technical data.
"Low-flow detection"
Low flow can be detected in two ways:
1. A built-in low-flow detection function which is active if none of
the digital inputs are set for flow switch.
2. A flow switch connected to one of the digital inputs.
1. Low-flow detection function:
The pump checks the flow regularly by reducing the speed for
a short time. If there is no or only a small change in pressure,
this means that there is low flow. The speed is increased until
the stop pressure (actual setpoint + 0.5 x ΔH) is reached and
the pump stops. When the pressure has fallen to the start
pressure (actual setpoint - 0.5 x ΔH), the pump restarts.
– If the flow is higher than the set minimum flow, the pump
returns to continuous operation at constant pressure.
– If the flow is still lower than the set minimum flow (Q
pump continues in start-stop operation until the flow is
higher than the set minimum flow (Q
higher than the set minimum flow rate (Q
returns to continuous operation.
2. Flow switch:
When the digital input is activated for more than 5 seconds
because there is low flow, the speed is increased until the
stop pressure (actual setpoint + 0.5 x ΔH) is reached, and the
pump stops. When the pressure has fallen to start pressure,
the pump restarts. If there is still no flow, the pump quickly
reaches the stop pressure and stops. If there is flow, the pump
continues operating according to the setpoint.
Operating conditions for the low-flow stop function
You can only use the stop function if the system incorporates a
pressure sensor, a non-return valve and a diaphragm tank.
Always install the non-return valve before the
Caution
pressure sensor. See figs
Pressure sensor
Non-return
valve
Fig. 68 Position of the non-return valve and pressure sensor in
system with suction lift operation
Diaphragm tank
Pressure sensor
Pump Non-return valve
Fig. 69 Position of the non-return valve and pressure sensor in
a system with a positive inlet pressure
48
), the
min
). When the flow is
min
), the pump
min
68 and 69.
Diaphragm tank
Pump
"Set minimum flow"
Set the minimum flow (Q ) in this display. This setting
min
determines at which flow rate the system is to change from
continuous operation at constant pressure to start-stop operation.
The setting range is 5 to 30 % of rated flow.
Factory setting
See section
10. Technical data.
"Diaphragm tank volume"
The stop function requires a diaphragm tank of a certain minimum
size. Set the size of the installed tank in this display.
In order to reduce the number of start-stops per hour or to reduce
the ∆H, install a larger tank.
Install the tank immediately after the pump. The precharge
pressure must be 0.7 x actual setpoint.
Recommended diaphragm tank size:
Rated flow rate
of pump CRE pump
3
[gpm (m /h)]
0-26
1s, 1, 3
(0 - 5.9)
27-105
5, 10, 15
(6.1 - 23.8)
106-176
20, 32
(24.2 - 40)
177-308
45
(40.2 - 70.0)
309-440
64, 90
(70.2 - 99.9)
441-750
120, 150
(100-170)
Factory setting
See section
10. Technical data.
Typical diaphragm
tank size
[gal (liters)]
2 (7.6)
4.4 (16.7)
14 (53.0)
34 (128.7)
62 (234.7)
86 (325.5)