# Transcritical R744 Supermarket Refrigeration System Integrated with a Heat-Driven Ejector Chiller
## 3 Results and Discussion
### Economic Analysis of the Investigated Systems  
The economic performance of the proposed system was also evaluated in terms of the additional investment incurred upon the integration of the HEC system with the pre-existing R744 refrigeration unit. The savings achieved by the R717-, R718-, and R600a-based systems in terms of energy cost are depicted in Figure 19. Although the proposed system was able to achieve the highest energy savings in Riyadh (Figure 18), the savings in the electricity cost were relatively higher in Chennai. This was due to the higher electricity tariff structure prevailing in Chennai (0.103 $/kWh) compared to Riyadh (0.048 $/kWh). Among all the locations, the cost savings obtained by the proposed system were found to be the highest in Phoenix due to relatively higher tariff (0.166 $/kWh) compared to the other locations. Even though the tariff structure was found to be the highest in the U.S. locations, the savings achieved by the system installed in Tucson and Las Vegas were found to be lower compared to Chennai. This was attributed to the fact that the energy savings achieved in Chennai were comparatively higher than in these U.S. locations (Figure 18). Although the energy savings obtained by the proposed system operating in Delhi were relatively higher, the savings in the electricity cost in Bangkok were higher due to the higher tariff (0.12 $/kWh). As expected, the savings in the electricity cost achieved by the R718- and R600a-based HEC were found to be significantly lower compared to the R717-based HEC unit. However, savings with the R600a-based HEC were found to be higher compared to the R718 unit due to its higher energy-saving potential (Figure 18).  
Figure 18: Comparison of the energy savings obtained by the various systems.  
Figure 20 compares the AIRT of the investigated systems at the selected locations. The installation cost of the R717-based HEC unit was found to be significantly higher compared to the R718-based HEC. For instance, the installation of the R717 unit in Riyadh cost around $23,436, while installation of the R718 unit accounted for about $8246. This was attributed to the fact that the capacity of the R717-based HEC unit (55 kW) was relatively higher compared to the R718 unit (\(\sim\)18 kW) at the design condition (Figure 8). The higher the capacity of the HEC unit, the higher its installation cost [25]. It was interesting to observe that the AIRT of the R718 units in Riyadh, Phoenix, and Las Vegas were lower compared to the R717 unit even though its energy saving potential was much lower (Figure 18). However, the recovery time associated with the additional investment made on the R717-based HEC in the remaining locations was found to be relatively lower than that of the R718 unit. The lower installation cost of the R718-based HEC played a key role in lowering the AIRT in Riyadh, Phoenix, and Las Vegas. However, due to significantly lower savings in the electricity cost at the remaining locations (Figure 19), the AIRT associated with the R718 unit was found to be higher than the R717-based HEC. Even though the energy savings obtained by the R717 system were higher compared to the R600a system, the AIRT of the R600a-based HEC was found to be relatively lower in all the selected locations. This was primarily attributed to the lower cost of the R600a-based HEC compared to the R717 unit and significantly higher savings in the electricity cost compared to the R718 unit.  
Figure 19: Savings on the electricity cost by the investigated systems.