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2.2 Test matrix and baseline results The systems were tested at steady-state under dry conditions at indoor/outdoor temperatures specified in ARI standards. Those temperatures are a constant indoor temperature of 21oC (70oF) and outdoor temperatures of 16.7, 8.3, 1.7 and –8.3oC (62, 47, 35 and 17oF respectively). Results of the baseline R410A data were compared to data supplied by the manufacturer at the 8.3 and -8.3oC conditions. Dry conditions were run so that an easier comparison between the refrigerants could be made, and so that the results could be compared with computer models . Experiments were conducted at two compressor speeds. First, the capacity of the R410A and R744 systems were matched in heating mode at the 8.3oC outdoor condition. The objective was to compare the performance of a system sized to provide the same heat pump capacity. Second, the capacity of the compressor was set so that the R744 system would have the same cooling capacity as the R410A system operating in air conditioning mode at 26.5oC indoors and outdoors at 34.9oC and 50% relative humidity. The objective of the second test was to simulate the operation of a combined air conditioning/heat pump system, having a single speed compressor sized for the cooling capacity rating condition. The appropriate compressor speed was calculated from the refrigerant mass flow rate and pressure ratio measured by Beaver et al. (1999) at the a/c rating condition using a different compressor, and the experimentally-determined volumetric efficiency of the Dorin heat pump compressor (84% at that operating condition). COPh = WQindoor (2.1) compressor Results of the tests are compared on the basis of cycle capacity and heating COP. Heating COP is defined as: Fan power is not included in this cycle efficiency calculation, which tends to favor R410A. Beaver et al. (1999a) showed the pressure drop over microchannel heat exchangers to be as much as 40% lower than the conventional round-tube, flat-fin heat exchangers used in the R410A system. 2.3 Experimental heat pump results for R744 compared to R410A The results of the tests run with the capacity of the system matched in heat pump operation are shown in Figure 2.1. The results show that the heating COP of R744 is slightly lower than R410A at higher temperatures, but is matched at the lowest outdoor temperature tested. Additionally, the reduction of capacity at lower outdoor temperatures is not as significant for R744 as for R410A, resulting in a higher capacity for the R744 system at lower temperatures. Figure 2.2 shows the results of the tests run at matched air conditioning capacity. The heating COP of R410A is matched only at the lowest outdoor temperature by R744, however, the capacity of R744 is considerably higher. 5PDF Image | Comparison of R744 and R410A
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