Carrier Aquasnap 30RW Installation, Operation And Maintenance Instructions

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Carrier Aquasnap 30RW Installation, Operation And Maintenance Instructions Manual pdf 25 page image

25The diagrams in the appendix can obviously be used tocalculate the actual pressure drops for the piping underconsideration:7. Based on the pipe diameter and the cooling capacityfind the equivalent length, producing 1.5 K pressuredrop in he graphs “Discharge piping” and “Liquid linepiping”.8. Calculate the equivalent pipe length as described insteps 1, 2, 3 and 5.9. Calculate the length ratio from steps 8 and 7 (equiva-lent length from step 8 DIVIDED by the equivalentlength from step 7).10. Multiply this ratio by 1.5 to find the equivalent pressuredrops in K.8.4 - Discharge pipe sizingThe discharge piping must be sized to achieve reasonablepressure drops: a variation of 1.5 K of the saturatedtempe-rature is normally accepted (approx. 60 kPavariation for a condensing temperature of 50°C).For most applications the refrigerant gas velocity is suffi-cient to entrain the liquid refrigerant/oil mixture. Neverthe-less, Table 2 shows the minimum required cooling capacitiesfor different pipe diameters and different saturateddis-charge temperatures.This table is based on 8 K superheat, a saturated suctiontemperature of 4°C and 8 K subcooling. Table 3 shows thecorrection factors to be applied to the values from Table 2, ifthe operating conditions are different from those previouslystated.8.5 - liquid pipe sizingThe 30RWA compressors are supplied with an oil that isfully miscible with refrigerant R-407C in the liquid phase.Consequently low refrigerant velocities in the liquid linesare not a problem.The 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.Special attention must be paid to the liquid line sizing whenthe expansion device ist positioned higher than the conden-ser. It may now be necessary to increase the pipe diameterto compensate for the additional pressure of the liquidrefrigerant column. If the liquid refrigerant head ist veryhigh, it may even be necessary to increase the subcoolingto prevent an phase change in the liquid line. This can bedone e.g. by a liquid-vapour heat exchanger or an additionalcoil.At 45°C the volume mass of refrigerant R-407C in the liquidphase is approximately 1050 kg/m3. A pressure of 1 barcorresponds to a liquid head of: 100 000/(1050 x 9.81) = 9.7 m.