Evaporator Water Flow Recirculation - Carrier 30KAV-ZE Series Installation, Operation And Maintenance Instructions

4 - WATER CONNECTIONS
General information
The nominal flow rate of the installation will be set using a manual
valve that should be installed on the leaving water piping (item
18).
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 will be checked using the reading for the pressure drop in
the unit (evaporator).
As the exact total installation pressure drop is not known prior to
commissioning, it is necessary to adjust the water flow rate with
the control valve (item 18) to obtain the installation's specific flow
rate.
Hydraulic circuit cleaning procedure
■ Open all control valves completely (item 18).
■ Start up the system pump.
■ Read the evaporator pressure drop as the difference on the
pressure gauge connected to the unit inlet then the outlet (item
16).
■ 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.
An increasing Delta P value indicates that the filters on the
installation needs to be removed and cleaned. In this case, close
the shut-off valves on the water inlet and outlet (item 19). Remove
then clean the filters (item 1) after draining the hydraulic part of
the unit (item 9).
Purge the air from the circuit (item 10).
Repeat until all fouling is removed from the filter.
Water flow rate adjustment procedure
Once the circuit is cleaned, read the pressures on the pressure
gauges (water inlet and outlet pressure) to determine the pressure
drop at the evaporator terminals. 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
(item 18) and read the new pressure difference. Repeat as
necessary, closing the control valve until the specific pressure
drop corresponding to the unit's nominal flow rate at the design
point is achieved.
NOTE: If the network has an excessive pressure drop in
relation to the available static pressure delivered by the
system pump, the nominal water flow cannot be obtained
(lower resulting flow) and the difference in temperature
between the water inlet and outlet of the evaporator will be
increased.
To reduce the hydraulic system pressure drop:
■ Reduce the pressure drops of individual components (elbows,
level changes, options, etc.) as much as possible,
■ Use the correct pipe diameter,
■ Do not extend the hydraulic systems.

4.7 - Evaporator water flow recirculation

If the installation flow rate is less than the minimum unit flow rate,
the evaporator flow can be recirculated, as shown in the diagram.
For minimum chilled water flow rate
Legend:
B Evaporator
C Recirculation
B
C
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