Carrier Aquasnap 30RW Installation, Operation And Maintenance Instructions

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Carrier Aquasnap 30RW Installation, Operation And Maintenance Instructions Manual pdf 24 page image

248 - REFRIgERANT lINE CONNECTIONS (30RWA)(Split units for connection to air-cooled condensers)8.1 - Recommendations for the installation of liquidchillers with remote condensersThe 30RWA units (split units for connection to air-cooledcondensers) have been specially designed to optimise theoperation of split system installations, using air-cooledcondensers as the chiller heat rejection system.The installation of an operational system is limited to theconnection of the air-cooled condenser inlet and outlet tothe 30RWA unit. The components such as the non-returnvalve (in the discharge line), filter drier, moisture sight glassand solenoid valves are installed and wired in the factory.The Pro-Dialog Plus control system of the 30RWA unitsincorporates the logic to permit control of the different fanversions (single-circuit, dual-circuit, fixed and variable-speedfan, separate ventilation or interlaced ventilation, i.e. commonventilation for both refrigerant circuits).To guarantee optimum and reliable performance of the30RWA units (split units for connection to air-cooledcondensers) it is necessary to comply with the regulationsdescribed below, when these units are connected to remotecondensers.1. Size the discharge and liquid line piping according tothe recommendations in the following paragraphs (ifnecessary, install a double riser to ensure correct oilcirculation in the refrigerant circuit).2. Select a condenser with an integrated subcooler toobtain a minimum of 3 K subcooling at the inlet to theexpansion device.3. Connect the fan stages electrically to the accessorycontrol board, using the auxiliary board “AUX 1”,analogue inputs and outputs and discrete remoteair-cooled condenser control outputs.Refer to the paragraph on the description of theana-logue and discrete inputs and outputs for theassign-ment of the fan stages.4. Make the communication bus connection to the masterbasic board of the 30RW unit.5. In the Pro-Dialog Plus control configure the number offan stages and ventilation type in accordance with theair-cooled condenser model used in the installation.A fan speed controller may be required for the firstfan stage for operation at low ambient temperatureand part load.ATTENTION: The air-cooled condenser must always beused with a subcooler, normally with 8 K subcooling.8.2 - generalRefrigerant pipe sizing must be carried out, taking accountof the following constraints:Oil return to the compressor must be ensured for themajo-rity of applications. Oil return is ensured byentrainment. A minimum refrigerant velocity is required toensure entrain-ment. This velocity depends on the pipediameter, the refri-gerant and oil temperature (these aretreated as being the same in most cases). A reduction ofthe pipe diameter per-mits an increase of the refrigerantvelocity. The problem of a minimum entrainment velocitydoes not exist for the pipes that carry liquid refrigerant asthe oil is fully miscible here.The pressure drop at the compressor discharge (pipes linkingthe compressor outlet with the condenser inlet) must belimited to avoid system performance losses (the compressorpower input inceases, and the cooling capacity decreases).As a first estimate and for standard air conditioningappli-cations, a 1 K pressure drop on the discharge sidedecreases the cooling capacity 2% and increases thecompressor power input by 3%.Increasing the pipe diameter permits limiting the pressuredrops.The pressure drop in the liquid line (linking the condenseroutlet to the expansion device) must not result in a changein phase.The estimate of these pressure drops must include thosegenerated by the filter drier, moisture sight glass and thesolenoid valve, integrated into the 30RWA.8.3 - Use of pipe sizing diagramsIn the annex to this document two pipe sizing diagrams areshown. They allow an estimate of the cooling capacity,corresponding to 1.5 K pressure drop for different pipediameters, based on the pipe length.The following procedure can be used for pipe sizing:1. Measure the length (in metres) of the piping underconsideration.2. Add 40 to 50% to take account of special characte-ristics.3. Multiply this length by the appropriate correctionfactor from Table 1 (this correction factor depends onthe saturated suction and discharge temperatures).4. Read the pipe size from diagrams “Discharge piping”and “Liquid line piping”.5. Calculate the equivalent lengths for parts included inthe piping under consideration (such as valves, filters,connections).The equivalent lengths are normally available fromthe component supplier. Add these lengths to thelength caculated in step 3.6. Repeat steps 4 and 5 is necessary.