# Experimental Study of a Novel Prototype of Dual-Cycle Two-Phase Cooling System for a Data Cabinet
## 3 Results and Discussion
### Cooling System Energy Consumption Analysis
#### 3.3.2 Energy Consumption Analysis of the PBTCS  
Figure 11 presents the impact of varying outdoor temperatures on the COP of the backplane cooling system, while maintaining the outlet air temperature of the backplane at 24 \({}^{\circ}\)C. Analysis of the data in this table reveals that as outdoor temperatures rise, the COP of the cooling system gradually decreases. In natural cooling mode, when the outdoor temperature is below 17.5 \({}^{\circ}\)C, the system can effectively maintain the outlet air temperature of the backplane at 24\({}^{\circ}\)C, with the overall COP of the cooling system remaining at a high level, demonstrating excellent heat dissipation performance. However, this mode is relatively sensitive to fluctuations in outdoor temperature, and a slight increase in outdoor temperature can lead to a rapid decrease in the system's COP.  
When the outdoor temperature is between 18 \({}^{\circ}\)C and 20 \({}^{\circ}\)C, the system switches to hybrid cooling mode, where the condenser and refrigerant work together to provide the required cooling for the data center. Compared to the single refrigerant cooling mode, the hybrid mode exhibits a better energy-saving performance within this temperature range. However, as the outdoor ambient temperature continues to rise, the energy-saving advantage of the hybrid cooling mode compared to the refrigerant cooling mode gradually diminishes.  
When the outdoor temperature exceeds 20 \({}^{\circ}\)C, due to the decreased temperature difference between the condenser and the outdoor environment, the cooling effect of  
Figure 11: Cooling system and IT power at different outdoor ambient temperatures.  
continuing to operate the condenser becomes limited. Therefore, the system enters chiller cooling mode, where the condenser is bypassed by a three-way valve, and the cooling for the data center is solely provided by the chiller. In this mode, the COP of the cooling system gradually decreases as outdoor temperatures continue to rise.  
Based on experimental data, a simulation study was conducted to investigate the effect of the data cabinet outlet temperature on the cooling system, with the results shown in Figure 12. High energy consumption periods are mainly concentrated in summer. Raising the outlet temperature can significantly reduce peak pPUE during high outdoor temperatures, while the reduction in pPUE during low outdoor temperatures is less pronounced, primarily due to the minimum power limitation of the cooling system. Increasing the outlet temperature results in a clear downward trend in the annual pPUE distribution. The annual average pPUE values at 24 \({}^{\circ}\)C, 27 \({}^{\circ}\)C, 30 \({}^{\circ}\)C, and 33 \({}^{\circ}\)C were 1.078, 1.063, 1.052, and 1.044, respectively. Therefore, on the basis of ensuring that the chip temperature is effectively controlled, moderately increasing the room temperature of the data center will be able to greatly reduce the energy consumption level of the cooling system.  
Figure 12: Influence of cabinet outlet air temperature on the cooling system pPUE: (**a**) cabinet outlet air temperature 24 \({}^{\circ}\)C; (**b**) cabinet outlet air temperature 27 \({}^{\circ}\)C; (**c**) cabinet outlet air temperature 30 \({}^{\circ}\)C; (**d**) cabinet outlet air temperature 33 \({}^{\circ}\)C.