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9 - NOMINAL SYSTEM WATER FLOW RATE CONTROL
Refer to the schematic diagram in the "Hydraulic connections"
paragraph for all item references in this chapter.
The water circulation pumps of the units in the range have been
designed to allow the hydraulic modules to operate in all possible
configurations depending on the specific system conditions,
i.e. with water inlet/outlet temperature differences (Delta T) at full
load which vary 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 the control of the system
flow rate:
- For a unit without hydraulic module: nominal pressure drop
at the unit terminals (plate heat exchanger + internal pipe).
This is measured with pressure gauges that must be installed
at the inlet and outlet of the unit (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
differential: nominal temperature difference at the exchanger.
If this information is not available when the system is commissioned,
contact the engineering and design department responsible for
the system 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 information
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 typical hydraulic circuit diagram).
Due to the pressure drop it generates on the hydraulic system,
this flow rate control valve is used to set the system 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 exchanger + 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 as the difference between the unit inlet
and outlet pressures on the pressure gauge (item 21).
- Let the pump run for 2 hours continuously to flush the
system's hydraulic circuit (presence of contaminating solids).
- Perform another reading.
- Compare this value to the initial value.
- A changed value indicates that the filters in 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 then clean (items 1 and 20) 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 exchanger + internal piping).
Compare the value obtained to the theoretic value of the selection
(WARNING: Take into account the pressure drop on the filter if it
is located between the pressure gauges).
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 by successively closing the control valve (item 22)
until the nominal flow rate is achieved at the unit's required
operation point
NOTE:
If the system 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 installation's hydraulic system pressure drop, it is
necessary to:
- Reduce the pressure drops of individual components (bends,
level changes, options, etc.) as much as possible;
- Use the correct pipe diameter;
- Avoid extending the hydraulic systems when possible.
9.2 - Units with hydraulic module and
fixed-speed pump
General information
See the paragraph on "Units without hydraulic module"
Hydraulic circuit cleaning procedure
- Open all control valves completely (item 22).
- Start up the unit's pump.
- Read the flow rate on the user interface.
- Let the pump run for 2 hours continuously to flush the
system's hydraulic circuit (presence of contaminating solids).
- Perform another reading.
- Compare this value to the initial value.
- A decrease in the flow rate value indicates that the filters in
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
39
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