Grundfos MAGNA3 25-80 Installation And Operating Instructions Manual page 24

7.3.5 Constant pressure
A constant pressure is advantageous in systems with relatively
small pressure losses in the distribution pipes:
• Two-pipe heating systems with thermostatic valves:
– dimensioned for natural circulation
– small pressure losses in those parts of the system where the
total quantity of water flows (for example boiler, heat
exchanger and distribution pipe up to the first branching)
– modified to a high differential temperature between flow pipe
and return pipe (for example district heating).
• Underfloor heating systems with thermostatic valves.
• One-pipe heating systems with thermostatic valves or pipe
balancing valves.
• Primary circuit pumps in systems with small pressure losses in
the primary circuit.
Characteristics and key benefits
• The pump pressure is kept constant, independent of the flow
in the system.
Technical specifications
H
Fig. 29 Constant-pressure control
7.3.6 Constant temperature
This control mode is suitable in heating systems with a fixed
system characteristic, for example domestic hot-water systems,
where control of the pump according to a constant return-pipe
temperature is relevant.
Characteristics and key benefits
• The temperature is kept constant.
• Use FLOW to control the maximum circulation flow.
LIMIT
Technical specifications
H
Fig. 30 Constant-temperature control
When you use this control mode, do not install any balancing
valves in the system.
The inverse control for cooling application is available from model
B.
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Temperature sensor
If the pump is installed in the flow pipe, install an external
temperature sensor in the return pipe of the system. See fig. 31.
Install the sensor as close as possible to the consumer (radiator,
heat exchanger, etc.).
Fig. 31 Pump with external sensor
We recommend that you install the pump in the flow pipe.
If the pump is installed in the return pipe of the system, you can
use the internal temperature sensor. In this case, install the pump
as close as possible to the consumer (radiator, heat exchanger,
etc.).
Q
Fig. 32 Pump with internal sensor
Sensor range:
• minimum -10 °C
• maximum +130 °C
To ensure that the pump is able to control the temperature, we
recommend that you set the sensor range between -5 and +125
°C.
Q
t
F
t
R
t
F
t
R