Carrier 61WG 020 Installation, Operation And Maintenance Instructions

Contents

33For most applications the refrigerant gas velocity is sufficientto entrain the liquid refrigerant/oil mixture. Neverthe-less,table 3 shows the minimum required cooling capacities fordifferent pipe diameters and different saturated dischargetemperatures.Table 3 - Minimum capacity (kW) to ensure oil returnfor different pipe diameters30WGA Outside pipe diameter, inSaturatedcondensingtemperature, °C3/4 7/8 1-1/8 1-3/8 1-5/8 2-1/8 2-5/830 3.8 5.6 11.5 19.7 31.0 48.9 86.535 3.8 5.7 11.7 19.9 31.5 49.5 87.740 3.9 5.8 11.8 20.2 31.9 50.2 88.945 3.9 5.9 12.0 20.5 32.3 50.9 90.150 4.0 5.9 12.1 20.8 32.7 51.5 91.255 4.0 6.0 12.3 21.0 33.1 52.2 92.460 4.1 6.1 12.4 21.3 33.5 52.8 93.6Correction factor, oil entrainment in the discharge linesSaturated evaporating temperature, °C -7 -1 4 10 16Correction factor 0.94 0.97 1 1.03 1.06Table 1 "Discharge line piping" shows the different pipediameters based on the unit size and the equivalent circuitlength. These recommended diameters allow oil return withinthe application range.IMPORTANT: Siphon traps must be inserted in the verticalriser pipes:• • at the bottom of the piping• • every 3 m of vertical length• • at the top of the piping (counter-siphon).•ExamplesThe siphon must be correctly sized to avoid trapping toomuch of the liquid oil/refrigérant mixture.It is advisable to include a slight slope (10 to 20 mm/m) inthe refrigerant flow direction in the horizontal piping betweenthe 30WGA unit and the condenser.8.4 - Liquid line sizingThe 30WGA compressors are supplied with an oil that isfully miscible with refrigerant R-410A in the liquid phase.Consequently low refrigerant velocities in the liquid linesare not a problem.Table 2 “Liquid line piping” shows the different pipe diame-tersbased on the unit size and the equivalent circuit length.To determine the equivalent liquid line length the filter drierand the solenoid valve pressure drops must be taken intoconsideration. Table 4 below shows the equivalent length foreach unit based on the diameter used.Bottom of piping Riser pipe Counter-siphonTable 4 - Equivalent length (m) for filter drier, solenoidvalves, moisture sight-glass (standard supply)30WGA 020 025 030 035 040 045 050 060 070 080 0901/2” diameter 4.2 4.2 4.2 4.2 4.2 4.2 2.2 - - - -5/8'' diameter 12.3 12.3 12.3 12.3 12.3 12.3 5.4 5.4 5.4 5.4 5.43/4'' diameter - - - - 29.9 29.9 12.4 12.4 12.4 12.4 12.47/8'' diameter - - - - - - - - 25.1 25.1 25.1The admissible pressure drops in the liquid lines dependmainly on the subcooling level of the liquid refrigerant atthe condenser outlet. Pressure drops corresponding to 1.5 °Csaturated temperature must not be exceeded.If the liquid refrigerant head is very high, it may be necessaryto increase the subcooling to prevent a phase change in theliquid line. A liquid-vapour heat exchanger or an additionalcoil can be used for this purpose.It is advisable to include a slight slope (10 to 20 mm/m) in therefrigerant flow direction in the horizontal piping betweenthe remote condenser and the 30WGA unit.9 - WATER CONNECTIONSFor size and position of the heat exchanger water inlet andoutlet connections refer to the certified dimensional drawingssupplied with the unit. The water pipes must not transmit anyradial or axial force to the heat exchangers nor any vibration.The water supply must be analysed and appropriate filtering,treatment, control devices, isolation and bleed valves andcircuits built in, to prevent corrosion, fouling and deteriorationof the pump fittings. Consult either a water treatmentspecialist or appropriate literature on the subject.9.1 - Operating precautionsDesign the water circuit with the least number of elbows andhorizontal pipe runs at different levels. The main points to bechecked for the connection are:• Comply with the water inlet and outlet connectionsshown on the unit.• Install manual or automatic air purge valves at all highpoints in the circuit(s).• Use a pressure reducer to maintain pressure in thecircuit(s) and install a safety valve as well as an expansiontank. Units with hydronic module and option 293 or293A include the safety valve and expansion tank.• Install drain connections at all low points to allow thewhole circuit to be drained.• Install stop valves, close to the entering and leaving waterconnections.• Use flexible connections to reduce vibration transmission.• If the insulation provided is not sufficient, insulate thecold-water piping, after testing for leaks, both to reduceheat loss and to prevent condensation.• Cover the insulation with a vapour barrier.• If the external water piping to the unit is in an area wherethe ambient temperature can fall below 0 °C, insulatethe piping and install an electric heater on the piping.NOTE: For units without option 293 or 293A, a screen filtermust be installed as close as possible to the heat exchangerand in a position that is easily accessible for removal andcleaning. Units with a hydronic module include this filter.The mesh size of the filter must be 1.2 mm. If this filter is