## 3 Results
### Mode 3: Simultaneous Charging and Discharging
In this mode, part of the cooling capacity of the refrigerant is initially used to charge the PCM until steady state conditions are reached, and the RPW-HEX acts as a cold energy storage component. It is observed that the slope of the instantaneous cold energy curve is higher for higher compressor powers during the transient part of the process. When steady state conditions are achieved, the value of the cold energy remains constant. However, at compressor power of 60%, the evaporation temperature reaches at the set-point (\(-10\)\({}^{\circ}\)C) before thermal equilibrium was achieved. Figure 19 shows the influence of compressor power in Mode 3a with an HTF flow rate of 100 L h\({}^{-1}\) and inlet temperature at 12 \({}^{\circ}\)C. Hereby the total cold energy stored at compressor powers of 15%, 30%, and 45% when steady state conditions are attained is about 5 kJ, 140 kJ, and 145 kJ, respectively. The time required to partially charge the PCM and attain thermal equilibrium was about 27 min, 28 min, 45 min for compressor powers of 15%, 30%, and 45%, respectively. As mentioned above, thermal equilibrium was not attained at 60% compressor power, while experimentation at compressor power of 75% was not feasible. The instantaneous cold energy and the final cold energy stored in the PCM at thermal equilibrium are shown in Figures 20 and 21, respectively. Both figures show the influence of the HTF flow rate on  
Figure 19: Influence of compressor power on the total cold energy stored in the PCM and time to reach thermal equilibrium for HTF inlet temperature of 12 \({}^{\circ}\)C and at a flow rate of 100 L h\({}^{-1}\). Figure 18: Influence of compressor power on the instantaneous cold energy stored in the PCM in Mode 3a with HTF inlet temperature at 12 \({}^{\circ}\)C and at a flow rate of 100 L h\({}^{-1}\). the PCM in Mode 3a with compressor power at 30% and HTF inlet temperature at 12 \({}^{\circ}\)C. It is observed that the higher the flow rate the faster the thermal equilibrium is attained. Moreover, the cold energy stored in the PCM at equilibrium is observed to be lower for higher HTF flow rates. 3.2 Mode 3b: Simultaneous Charging and Discharging of the RPW-HEX with the PCM Initially Completely Charged  
Temperature Profiles during the Simultaneous Charging and Discharging of the PCM  
Regarding Mode 3b, the experimental conditions were similar to those in Mode 3a, except that the PCM was initially completely charged at -4 \({}^{\circ}\)C. Only experiments performed at compressor power at 15% were feasible, as shown in Table 9. Figure 22 shows the temperature profile in Mode 3b for the experiments performed at compressor power of 15%, with the HTF inlet temperature at 12 \({}^{\circ}\)C, and for HTF flow rates at 50 L-h-1, 100 L-h-1, and 150 L-h-1. In this case, the whole cooling capacity of the refrigerant is used right from the beginning to cool down the HTF. Moreover, the HTF  
Figure 21: Influence of HTF flow rate on the total cold energy storage in the PCM and time to reach equilibrium for HTF inlet temperature at 12 \({}^{\circ}\)C.  
Figure 20: Influence of HTF flow rate on the instantaneous cold energy stored in the PCM in Mode 3a for HTF inlet temperature of 12 \({}^{\circ}\)C.  
was also cooled down by the PCM that also discharges part of the cold energy initially stored until steady state conditions are reached. At low HTF flow rates, PCM located at the top and middle parts of the RPW-HEX undergoes phase change and attains a temperature well above the phase change temperature, while PCM at the bottom part of the RPW-HEX remains completely or partially charged when thermal equilibrium is reached.