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8 - NOMINAL SYSTEM WATER FLOW CONTROL
Refer to the diagram in the "Hydraulic connections" section
for all references points mentioned in this chapter.
The water circulation pumps of 30RQM/30RQP units have been
designed to allow the hydraulic modules to operate over a range
of possible configurations based on specific installation
conditions, i.e. with temperature differences between the water
inlet and outlet (Delta T) at full load from 3 to 10 K.
This temperature difference required between the water inlet
and outlet determines the system's nominal flow.
Use the specification provided while 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:
•
Units without hydraulic module: the nominal pressure drop
at the unit connections (plate heat exchanger + internal water
pipe work). This is measured with pressure differential gauges
that must be installed at the inlet and outlet connections
of the unit (item 18).
•
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 30RQM/30RQP control manual).
•
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: heat exchanger T° Delta.
•
Units with variable speed pump – controlling a fixed system
flow: nominal flow rate (see units with fixed speed pumps).
If this information is not available when the system is started
up, contact the technical service 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
DT is 5 K) or from the Carrier Electronic Catalogue selection
program for all other applicable DT's.
8.1 - Units without hydraulic module
8.1.1 - General information
The nominal flow of the system will be set using a manual valve
that should be installed on the water outlet pipe (item 19 on the
hydraulic circuit schematic diagram).
By causing the pressure in the water system to drop, this flow
control valve aligns the system pressure/flow curve with that of
the pump so that the nominal flow rate corresponding to the
desired operating point is obtained.
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.
8.1.2 - Cleaning procedure for the water circuit
•
Open the valve completely (item 19).
•
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 18).
•
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 decrease in the
pressure drop 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 16) and
remove the filters (item 17) after draining the hydraulic
part of the unit (item 6).
•
Remove the air from the circuit (item 5).
•
Repeat until all fouling is removed from the filter.
8.1.3 - Procedure for controlling the water flow
Once the circuit is cleaned, read the pressures on the pressure
differential gauges (water inlet and outlet pressure) to determine
the pressure drop within the unit (plate heat exchanger + internal
pipe work).
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 installation) is too high. In this case, close
the control valve and read the new difference in pressure.
Repeat as necessary until the specific pressure drop corresponding
to the unit's design 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 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 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 hydraulic systems.
35
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