Carrier 30RBM 160 Installation, Operation And Maintenance Instructions

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Carrier 30RBM 160 Installation, Operation And Maintenance Instructions Manual pdf 34 page image

349.3 - Units with hydronic module and variable speedpump – Pressure differential controlThe system flow rate is not set at a nominal value.The flow rate will be adjusted, by varying the pump speed, tomaintain a system pressure differential value defined by theuser.This is checked by the pressure sensor at the water exchangeroutlet (item 10 on the main water circuit diagram).The system calculates the measured pressure difference,compares it with the setpoint value set by the user and thenmodulates the pump speed module, resulting in:• an increase in the flow rate if the measurement is belowthe setpoint,• a decrease in the flow rate if the measurement exceedsthe setpoint.This modulation is limited only by the maximum and minimumflow rates for the unit and by the maximum and minimumallowable pump speeds.The maintained pressure difference value may, in certain cases,differ from the setpoint value:• if the setpoint value is too high (obtained for a flow rate higherthan the maximum value or a frequency greater than themaximum value), the system will stop once it reaches themaximum flow rate or maximum frequency, which will resultin a pressure difference below the setpoint,• if the setpoint value is too low (obtained for a flow ratelower than the minimum value or a frequency less thanthe minimum value), the system will stop once it reachesthe minimum flow rate or minimum frequency, which willresult in a pressure difference greater than the setpoint.Contact the manufacturer's service department to implementthe procedures described belowHydronic circuit cleaning procedureBefore proceeding, it is advisable to remove any possiblecontamination from the hydronic circuit.• Start up the unit pump by using the override command.• Control the frequency to the maximum value to generatea higher flow.• If there is a ‘‘Maximum flow exceeded’’ alarm, reduce thefrequency until an acceptable value is reached.• Read the value of the flow on the user interface.• Let the pump run for 2 hours continuously to clean upthe system's hydraulic circuit (presence of contaminatingsolids).• Perform another reading of the flow and compare thisvalue with the initial value. A reducing value of the flowindicates that the filters on the system need to be removedand cleaned. In this case, close the shut-off valves on thewater inlet and outlet (item 19) and remove the filters(items 20 and 1) after draining the hydronic part of theunit (items 6).• Remove the air from the circuit (items 5 and 17).• Repeat until all fouling is removed from the filterProcedure for controlling the pressure differential setpointOnce the circuit is cleaned, place the water circuit in theconfiguration for which the unit selection was performed(generally, this will be all valves open and all cooling coilsactive)Read the value of the flow on the user interface and compareit with the theoretical value of the range:• If the flow rate read is greater than the specified value,reduce the pressure differential setpoint on the userinterface to reduce the flow rate value;• If the value read is lower than the specified value, increasethe pressure differential setpoint on the user interface toincrease the flow rate valueRepeat until you obtain the flow rate corresponding to thenominal flow rate at the unit's requisite operating point.Stop the forced operation of the pump and proceed to theconfiguration of the unit for the required control mode. Modifythe control parameters:• Set water flow control to ‘pressure differential’• Set the value of the required pressure differential.The unit's default factory configuration is the minimum speed(frequency: 30 Hz).NOTE:If during adjustment, the low or high frequency limits arereached before reaching the specified flow rate, keep thepressure differential value at its lower or higher limit as thecontrol parameter value.If the user knows in advance the pressure differential valueat the unit outlet to be maintained, this value can be entereddirectly as data to be declared. You should not, however, omitthe water circuit cleaning sequence