9 - NOMINAL SYSTEM WATER FLOW CONTROL
Refer to the diagram in the "Hydraulic connections" section
for all reference points mentioned in this chapter.
The water circulation pumps of unit range have been designed
to allow the hydronic 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 of the system. Use the
specification provided while selecting the unit to determine the
operating conditions of the system.
In particular, collect the data to be used for setting the installation
flow rate:
-
For a unit without hydronic 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
difference: pressure difference at the hydronic module
terminals; the buffer tank module option is not taken into
account.
-
Units with variable speed pumps - control on temperature
difference: nominal temperature delta at the exchanger.
-
Units with variable speed pumps – setting of a fixed flow rate
for the system: nominal flow rate (see units with fixed speed
pumps).
If this information is not available when the system is started up,
contact the engineering and design department responsible for
the system to obtain it.
These data can be obtained either from the performance tables
included in the technical documentation (for cases where the
water 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 hydronic 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 at start-up,
it is necessary to adjust the water flow with the control valve to
obtain the system'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 consecutively to clean up the
hydraulic circuit of the system (presence of contaminating
solids).
-
Perform another reading.
-
Compare this value to the initial value.
-
A decrease in the flow 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 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 control procedure
Once the circuit is cleaned, read the pressures on the pressure
gauges (water inlet and outlet pressure) to determine the
pressure drop within the unit (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 preset value, this
indicates that the flow rate at the terminals of the unit (and
therefore within the installation) 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 at
the required operation point 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 cannot be obtained (lower resulting flow) and
the difference in temperature between the water inlet and outlet
of the water heat exchanger will be increased.
To reduce the system's hydronic 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.
9.2 -
Units with hydronic module and fixed
speed pump
General
See the paragraph on "Units without hydronic module"
Hydraulic circuit cleaning procedure
-
Open all control valves completely (item 22).
-
Start up the unit's pump.
-
Read the value of the flow on the user interface.
-
Let the pump run for 2 hours consecutively to clean up the
hydraulic circuit of the system (presence of contaminating
solids).
-
Perform another reading.
-
Compare this value to the initial value.
-
A decrease in the flow 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 hydronic
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
AQUACIAT
POWER
ILD
EN-36
