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9 - NOMINAL SYSTEM WATER FLOW RATE CONTROL
Refer to the schematic diagram in the "Water connections"
paragraph for all item references in this chapter.
The water circulation pumps of unit range have been designed
to allow the hydraulic modules to operate at each possible
conditions, i.e. with chilled water temperature differences at full
load from 3 to 10 K.
This temperature difference required between the water inlet
and outlet determines the nominal flow rate of the system. Use
the specification provided when selecting the unit to determine
the system's operating conditions.
In particular, collect the data to be used for setting the
installation flow rate:
•
For a unit without hydraulic module: nominal pressure
drop at the unit terminals (plate heat exc internal
water pipe). This is measured with pressure differential
gauges that must be installed at the unit's inlet and outlet
(item 21).
•
Units with fixed speed pumps: nominal flow rate . The
pressure of the fluid is measured by sensors installed at
the inlet of the pump and outlet of the unit (items 7 and
10). The system calculates the flow rate associated with
this differential pressure. The flow rate can be read directly
on the user interface (refer to the control manual for the
range).
•
Units with variable speed pumps - control on pressure
differential: pressure differential at the hydraulic module
terminals,
•
Units with variable speed pumps - control on temperature
difference: nominal temperature delta at the exchanger.
If this information is not available when activating the system,
contact the design office responsible for the installation to
obtain it.
This data can be obtained either from the performance tables
included in the technical documentation (for cases where the
water type heat exchanger temperature delta is 5 K) or from
the "Electronic Catalogue" selection program for all other
applicable temperature delta in the range of 3 to 10 K.
9.1 - Units without hydraulic module
General
The nominal flow rate of the system will be set using a manual
valve that should be installed on the water outlet pipe (item
22 on the water circuit schematic diagram).
Due to the pressure drop it generates on the hydraulic network,
this flow control valve is used to set the network pressure/flow
rate curve to the pump pressure/flow rate curve, to obtain the
nominal flow rate at the desired operation point.
This is checked by reading the pressure drop on the unit (plate
heat exc internal piping).
As the exact total system pressure drop is not known upon
commissioning, it is necessary to adjust the water flow rate
with the control valve to obtain the installation's specific flow
rate.
Hydraulic circuit cleaning procedure
•
Open all control valves completely (item 22).
•
Start up the system pump.
•
Read the pressure drop of the plate heat exchanger using
the pressure differential gauge to find the difference
between the unit inlet and outlet (item 21).
•
Let the pump run for 2 hours continuously to clean up
the system's hydraulic circuit (presence of contaminating
solids).
•
Perform another reading.
•
Compare this value to the initial value.
•
A reducing value of the flow rate indicates that the filters
on the system need to be removed and cleaned. In this
case, close the shut-off valves on the water inlet and outlet
(item 19) and remove the filters (items 20 and 1) after
draining the hydraulic part of the unit (items 6).
•
Remove the air from the circuit (items 5 and 17).
•
Repeat until all fouling is removed from the filter.
Water flow rate adjustment procedure
Once the circuit has been decontaminated, read the pressures
on the pressure gauges (water inlet pressure - outlet pressure)
to determine the pressure drop across the unit terminals (plate
heat exc internal pipework).
Compare the value obtained with the design value predicted
by the selection software.
If the pressure drop reading is above the specified value, this
indicates that the flow rate at the terminals of the unit (and
therefore within the system) is too high. In this case, close the
control valve and read the new difference in pressure.
Repeat as necessary, closing the control valve until the specific
pressure drop corresponding to the unit's nominal flow rate
is achieved.
NOTE:
If the network has an excessive pressure drop in relation to
the available static pressure delivered by the system's pump,
the nominal water flow rate cannot be obtained (lower
resulting flow rate) and the temperature difference between
the water inlet and outlet of the water type heat exchanger
will be increased.
To reduce the system's hydraulic network pressure drop:
•
Reduce the pressure drops of individual components
(bends, level changes, options, etc.) as much as possible;
•
Use the correct pipe diameter;
•
Do not extend the piping system.
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