Carrier 30KAV-ZE Series Installation, Operation And Maintenance Instructions page 71

12 - OPTIONS
12.1.5.4 - Variable-speed pump - Pressure differential control
The system flow rate has not been set to a nominal value.
This will be adjusted by the system, by varying the pump speed,
to maintain a constant Delta P value defined by the user.
This is checked by the pressure sensors at the hydraulic module
inlet and outlet.
The system calculates the value for the measured pressure
difference, compares it with the setpoint value set by the user and
then modulates the pump speed module accordingly.
■ This results in an increase in the flow rate if the measurement
is below the setpoint,
■ This results in a decrease in the flow rate if the measurement
exceeds the setpoint.
This modulation is limited only by the maximum and minimum flow
rates for the unit and by the maximum and minimum allowable
pump speeds.
The maintained Delta P may, in certain cases, differ from the
setpoint value:
■ If the setpoint value is too high (corresponding to a flow rate
higher than the maximum value or a frequency greater than
the maximum value), the system will be limited to the maximum
flow rate or maximum frequency, which will result in a Delta P
below the setpoint.
■ If the setpoint value is too low (corresponding to a flow rate
lower than the minimum value or a frequency less than the
minimum value), the system will be limited to the minimum flow
rate or minimum frequency, which will result in a Delta P above
the setpoint,
Contact the manufacturer's service department to implement the
procedures described below
Hydraulic circuit cleaning procedure
Refer to the water circuit cleaning procedure.
Procedure for controlling the pressure differential setpoint
Once the circuit is cleaned, place the hydraulic 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 flow on the user interface and compare it
with the theoretical value of the range:
■ If the flow rate read is greater than the specified value, reduce
the Delta P setpoint on the user interface to decrease the flow
rate value.
■ If the flow rate read is less than the specified value, increase
the Delta P setpoint on the user interface to increase the flow
rate value.
Repeat until the unit's nominal flow rate at the required operation
point is achieved.
Stop the forced operation of the pump and proceed to the
configuration of the unit for the required control mode.
Modify the control parameters:
■ Water flow rate control method (Delta P),
■ Required Delta P set point.
■ If necessary, the control PID parameters can also be adjusted
(refer to the control manual).
NOTE: If, during adjustment, the low or high frequency limits
are reached before reaching the specified flow rate, keep the
pressure differential value at its lower or higher limit as the
control set point.
If the user knows in advance the pressure differential value
at the unit outlet, this value can be entered directly. You should
not, however, avoid the sequence of cleaning the hydraulic
circuit.
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