## 3 Results and Discussion  
### Energy Analysis  
Figure 4 presents the variation of the COP\({}_{\text{opt}}\), cooling capacity (\(\dot{Q}_{cooling}\)), optimal discharge pressure (P\({}_{\text{dis,opt}}\)), outlet pressure of the evaporator (P\({}_{\text{e,out}}\)) and the optimal EEV opening degree (OD\({}_{\text{opt}}\)) with respect to NRC. The values of OD\({}_{\text{opt}}\) as a function of NRC were kept the same at all the selected ambient temperatures, since they were not affected by the latter considerably. The states of sufficient charge showed in Figure 4 (i.e., NRC \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Instrument** & **Accuracy** & **Range** \\ \hline Refrigerant temperature & T-type & \(\pm 0.20\) \({}^{\circ}\)C & \(-50\)-\(200\) \({}^{\circ}\)C \\ Air dry/wet bulb temperature & P100 & \(\pm 0.20\) \({}^{\circ}\)C & \(-200\)-\(450\) \({}^{\circ}\)C \({}^{\circ}\)C \({}^{\circ}\) \\ Refrigerant pressure & Pressure transmitters & \(\pm 0.25\%\) of full range & \(-0.15\) MPa \\ Air volume flow rate & Standard nozzle device & \(\pm 0.50\%\) of reading & \(0\)-\(10\),\(000\) m\({}^{3}\)-\(\mathrm{h}^{-1}\) \\ Power input & Electric power analyzer & \(\pm 0.16\%\) of reading & \(9\)–\(600\) V \\ Charge amount & Electronic mass scale & \(\pm 20.00\) g & \(0.020\)–\(40.000\) A \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Detailed information of the measuring instruments. values between 0.248 and 0.336) refer to the operating conditions at which the COP values are maximized. On the other hand, the excessive and insufficient states in Figure 4 indicate the operating conditions above and below those involving COP\({}_{\text{max}}\) values, respectively. The OD\({}_{\text{opt}}\) reached the minimum value of 0.479 at sufficient charge states, and at the same time, the optimal discharge pressures were 10.9 MPa, 11.5 MPa and 11.63 MPa at 35 \({}^{\circ}\)C, 38 \({}^{\circ}\)C and 40 \({}^{\circ}\)C, respectively. The highest values of COP\({}_{\text{opt}}\) and \(\dot{Q}_{cooling}\) were about 1.716 and 18.97 kW at 35 \({}^{\circ}\)C, 1.543 and 17.69 kW at 38 \({}^{\circ}\)C and 1.441 and 16.90 kW at 40 \({}^{\circ}\)C. As the ambient temperature rose from 35 \({}^{\circ}\)C to 40 \({}^{\circ}\)C, the COP and cooling capacity of the system decreased by 16.03% and 10.90%, respectively. For low values of NRC, the system performance was found to be very poor. As the NRC was 0.204, the COP and \(\dot{Q}_{cooling}\) decreased by 1.39% and 4.06% at 35 \({}^{\circ}\)C, by 3.56% and 5.94% at 38 \({}^{\circ}\)C and by 7.04% and 9.44% at 40 \({}^{\circ}\)C compared to corresponding cases involving NRC values between 0.248 and 0.336, respectively. As the NRC was 0.380, the COP and \(\dot{Q}_{cooling}\) decreased by 2.59% and 3.22% at 35 \({}^{\circ}\)C, by 1.25% and 0.50% at 38 \({}^{\circ}\)C and by 2.91% and 1.51% at 40 \({}^{\circ}\)C compared to the corresponding cases involving NRC values between 0.248 and 0.336. It could be concluded that the effect of insufficient charge on cooling capacity is more penalizing than that of a slight overcharge. Figure 5a shows the variation of COP and \(\dot{Q}_{cooling}\) with discharge pressure when the NRC is 0.137 (insufficient charge condition), 0.248 (sufficient charge condition) and 0.381 (excessive charge condition) at 35 \({}^{\circ}\)C. It was found that as P\({}_{\text{dis}}\) reached the optimal value, both COP and \(\dot{Q}_{cooling}\) reached the maximum values.