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Appendix B: Effect of Suction Accumulator Configuration/Indoor Heat Exchanger Orientation on RAC1 R744 Heat Pump Performance B.1 System configuration It is likely that the full benefit of the suction accumulator and suction line heat exchanger in the R744 heat pump system was not realized in the experimental comparison of R744 and R410A. This can be attributed to the placement of the suction line/vapor line intersection after the suction accumulator below the liquid level in the suction accumulator, as shown in Figure B.1. As a result, the intersection of the vapor and liquid lines may have been flooded, neutralizing the effect of the suction accumulator and allowing refrigerant with a low exit quality to pass into the internal heat exchanger. Further testing (after raising the intersection above the liquid level) suggested that better control over the exit quality from the evaporator may result in a 5-10% improvement in system efficiency at the ARI rating condition, matching and slightly surpassing the efficiency of R410 for matched heating capacity. Suction line to compressor Inlet from evaporator Suction Accumulator Liquid- vapor line intersection Vapor Liquid By-pass Valve Figure B.1 Arrangement of suction accumulator for R744 RAC1 comparison with R410A: liquid-vapor lines intersect below level in accumulator A study by Song et al. (2001) showed that the angle of attack of the indoor coil has little effect on the heat transfer performance of the coil, but has considerable effect on the air pressure drop over the coil. As a result, placing the indoor coil perpendicular to the airflow has the potential of reducing the fan power required by the system while not affecting the capacity of the coil. Based on these results, the R744 indoor oil was rotated 90o and placed perpendicular to the airflow. Subsequent testing showed as much as a 10% improvement in the efficiency of the system, with the efficiency calculated independent of the fan power. This was an unexpected result, as, based on Kim's work, orientation of the coil should not have influenced the capacity of the coil. Further testing of the system indicated that the improved results were dependent on the charging conditions of the system. The presence of the suction accumulator should reduce performance dependence on charging, which indicates that the suction accumulator was not functioning properly. The following results compare the original R744 data which was used in the comparison with R410A with later results with the indoor coil vertical both with the suction accumulator the same as it was during the R410A 59PDF Image | Comparison of R744 and R410A
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