Grundfos MAGNA3 Manual page 12

3
Primary and secondary pumps
Due to variations in the cooling demand and flow rate,
we recommend that you use speed-controlled
MAGNA3 pumps in a cooling system, either
single-head pumps connected in parallel or twin-head
pumps. Single-head pumps connected in parallel have
several advantages. In alternating operation, each
pump is sized for 100 % flow. In this operating mode,
the second pump functions as backup for higher
reliability. As the pumps alternate, an equal number of
operating hours is ensured. Cascade operation of
pumps connected in parallel meets demands in
high-flow systems with low differential temperature
(∆t), and 50 % backup is ensured at the same time.
The twin-head pump saves installation time and costs.
By speed-controlling all pumps, you can obtain
maximum energy saving as the pumps will run at their
best efficiency point (BEP).
In a variable-flow system, we recommend that you
control secondary pumps in AUTO
proportional-pressure mode with a
differential-pressure sensor in the flow pipe with the
lowest pressure. This ensures maximum energy
saving.
The built-in heat energy monitor allows monitoring of
the heat energy consumption in the system.
Air handler cooling coils
The performance of cooling surfaces is controlled by
the cooling-water temperature and the flow rate. For
this purpose, we recommend that you install
variable-flow mixing loops at the cooling surfaces. A
speed-controlled mixing-loop pump is ideal for
adaptation to the varying loads in a cooling surface. In
this case, MAGNA3 will have full authority, eliminating
the need for external pump throttling valves. The
FLOW ensures that the rated flow is never
LIMIT
exceeded.
Heat recovery system
The heat recovery system is of paramount importance
for the overall energy efficiency of an air-conditioning
or cooling system. Due to high load and temperature
variations in the system, it is important to use
variable-speed pumps in a heat recovery system.
12
or
ADAPT
Cooling tower
Due to chiller load variations and changes in the
temperature and moisture of the ambient air, the
cooling-tower flow rate is continuously changing. In
order to achieve maximum energy saving,
cooling-tower pumps have to be able to adapt to these
varying conditions. The pumps are controlled by a
temperature setpoint which is measured at the
condenser of the chiller. In this system, MAGNA3 will
have full authority, eliminating the need for pump
throttling valves. The FLOW
rated flow is never exceeded.
Mixing loops
Due to the risk of condensation, the flow-pipe
temperature through a cooling ceiling or floor must
never be lower than the dew point temperature of the
indoor air. The dew point temperature varies due to
variations in indoor moisture load and outdoor thermal
conditions. The result is that the cooling-water setpoint
has to be controlled. A mixing loop is ideal for
obtaining the correct temperature in order to adapt to
the varying setpoint.
Due to continuous cooling-load variations in the
building cooling zones, the cooling performance in
cooling ceilings and floors is controlled by motor
valves via zone control units, and therefore you must
always use a speed-controlled mixing-loop pump.
MAGNA3
ensures that the
LIMIT