Units With Hydronic Module And Variable-Speed Pump - Pressure Differential Control - Carrier Aquasnap 30RQS Series Installation, Operation And Maintenance Instructions

13.2 - Units with hydronic module and fixed-speed pump
13.2.1 - General information
See chapter ''Units without hydronic module'' .
13.2.2 - Procedure for cleaning the hydronic circuit
• Open all valves completely (item 19).
• Start-up the system pump.
• Let the pump run for 2 hours consecutively to clean up
the hydronic circuit of the system (presence of
contaminating solids).
• Perform another reading.
• Compare this value to the initial value.
A reducing value of the flow 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 hydronic part of the unit (item 6).
• Remove the air from the circuit (items 5 and 14).
• Repeat until the filter remains clean.
13.2.3 - Procedure for controlling water fow
Once the circuit is cleaned, read the flow value on the user
interface and compare it with design value for the system. If
the value of the flow is greater than the specified value, this
indicates that the overall pressure drop in the system is too
low against the available static pressure generated by the
pump.
In this case, close the control valve and read the flow value.
Repeat as necessary until the pressure drop corresponding
to the design flow rate is achieved.
NOTE: If the network has an excessive pressure drop in relation
to the available static pressure delivered by the unit 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
(bends, level changes, valves etc.) as much as possible
• Use the correct pipe diameter
• Do not extend the piping system.
13.3 - Units with hydronic module and variable-speed
pump - pressure differential control
The system flow is not controlled to a fixed value. The flow
rate will be adjusted, by varying the pump speed, to maintain
a system pressure differential value defined by the user. The
pressure sensor at the unit outlet (item 10 in the typical
hydronic circuit diagram) is used as the means of control.
The system calculates the measured pressure differential
value, compares it with the user-selected set point value and
modulates the pump speed as necessary. The result is:
• an increased flow rate, if a lower value than the set point is
measured,
• an decreased flow rate, if a higher value than the set point
is measured.
This flow rate variation is realised, observing the minimum
and maximum admissible unit flow rates as well as the
minimum and maximum pump supply frequency values.
The pressure differential value maintained can in certain
cases be different from the set point value:
• If the set point value is too high (achieved for a higher flow
rate than the maximum value or a higher frequency than
the maximum value), the system settles at the maximum
flow rate or maximum frequency and this results in a lower
pressure differential than the set point.
• If the set point value is too low (achieved for a lower flow
rate that the minimum value or a lower frequency than the
minimum value), the system settles at the minimum flow
rate or minimum frequency and this results in a higher
pressure differential than the set point.
See with Carrier Service to implement the procedures
described below.
13.3.1 - Procedure for cleaning the hydronic circuit
Before proceeding, it is advisable to remove any possible
contamination from the hydronic circuit.
• Start-up the system pump by using the forced start
command.
• Control the frequency to the maximum value to generate
a higher flow.
• If there is a ''Maximum fow exceeded'' alarm, reduce
the frequency until an acceptable value is reached.
• Read the value of the flow on the user interface.
• Let the pump run for 2 hours consecutively to clean up
the hydronic circuit of the system (presence of
contaminating solids).
• Perform another reading of the flow and compare this
value with the initial value. A reducing value of the flow
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 12 and 1) after draining the hydronic
part of the unit (item 6).
• Remove the air from the circuit (items 5 and 14).
• Repeat if required the filter remains clean.
13.3.2 - Procedure for controlling the pressure differential
setpoint
Once the circuit is cleaned, place the hydronic circuit in the
configuration for which the unit selection was performed
generally (all valves open and all cooling coils active). Read
the value of the !ow on the user interface and compare it with
the theoretical value of the range:
• If the value of the flow is greater than the specified value,
reduce the pressure differential setpoint on the user
interface to reduce the value of the flow.
• If the value of the flow is lower to the specified value,
increase the pressure differential setpoint on the user
interface to increase the value of the flow.
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