3.2. Test conditions
The test conditions followed ASHRAE Standard 116 (2010), and extended conditions of 46.1 #C for cooling and "17.8 #C for heating were added to investigate the system behaviors at severe weather conditions, as shown in Table 5. At the extended condition for heating mode at "17.8 #C, the humidity ratio of the air is quite low, and therefore it is not mandated during the test (Wang, 2008). The volume flow rate of the air circulating the indoor heat exchanger was set to be 0.58m3 s"1 according to the manufacturer specification. The compressor suction port superheating was maintained at 8 K for all tests. The condenser outlet sub-cooling was left to vary freely because the charge in the system is a constant value determined from the refrigerant charge optimization test. Refrigerant charge optimization was performed for both R410A and R32 at the ambient condition of 8 #C (Wang, 2008). Fig. 3 shows the refrigerant charge optimization results. The optimum refrigerant charge amount was determined to be 7.0 kg for R410A and 5.0 kg for R32 by selecting the refrigerant charge amount with the maximum COP values. It should be noted that this is a drop-in test comparison, and therefore the system configuration has remained the same for R410A and R32.