*3.2. Electric Energy Consumption*

For each configuration, Figure 6 shows the annual electric energy consumption of the whole system (i.e., including cabin cooling as well as waste heat managemen<sup>t</sup> from the WCD within the system boundaries). In Figures 6–9, the results are represented as histograms for each climate zone, in two rows (sub-figures) depending on the condenser used (with DC above and CT below). The bars labelled as BASE, FC, and ABS corresponding to the traditional MVC, free cooling, and absorption cooling configurations, respectively.

In Figure 6, the electricity demand by auxiliaries (AUX) is represented in green scale at the base of the bars, the demand for cabin refrigeration (REF) is represented by the intermediate bars in blue scale, while the top bars in yellow scale correspond to the electricity demand for heat dissipation from the WCD of the EAF. The relative reduction of electricity consumption in the ABS cooling mode compared with the baseline was on the order of 40% to 60%, and was more evident in CT configurations, which inherently require less electric power than DC to dissipate the same heat flows. In the FC configuration, which does not include waste heat recovery, the electricity consumption for heat dissipation at the WCD remained unchanged from baseline.

The reduction in electricity consumption for refrigeration was more pronounced in FC than in ABS configuration in several climatic regions, but almost exclusively when DCs were used. In fact, the overall balance resulted in a slight to remarkable advantage for ABS in all but the last climates in CT configurations, whereas in DC configurations FC outperformed the ABS configuration in climate zones 4C (mixed-marine), 5A (cool-humid), 5C (cool-marine) and 7. Interestingly enough, in continental dry climates such as in Dunhuang (5B) and Helena (6B), prolonged high-temperature periods in summer reduced the contribution of FC to electric energy saving over the year, making ABS cooling more attractive in terms of electricity demand.

**Figure 6.** Electricity consumption based on climate zone and case study. AUX: electricity demand by auxiliaries; REF: demand for cabin refrigeration.

#### *3.3. Direct and Indirect Water Consumption*

Water consumption is illustrated in Figure 7. DC configurations imply only indirect water consumption, which was small and basically mirrored electricity consumption patterns, in a more or less pronounced way depending on the water intensity of the local electricity generation mix (see Table 2). In other words, this means that when DCs were used as heat dissipation systems, ABS configurations were mostly preferable to FC configurations also as to their impact on freshwater consumption.

For CT configurations, the direct water consumption (at the base of bars, in blue) was several orders of magnitude larger than the indirect consumption. Nevertheless, their overall balance was significantly affected by the indirect water footprint: for instance, although the direct water consumption of CTs evidently decreased in colder climates, the total water footprint of the baseline CT configuration in Östersund (climate region 7) equalled the baseline in Cairo (climate region 2B) due to the high indirect water footprint of electricity in Sweden.

For CT configurations, FCs were usually best performers in terms of direct freshwater footprint. In fact, the direct water consumption of FC configurations was always lower than that of corresponding ABS systems, except in very hot humid climates (1A). Indeed, the ABS configuration generally had a direct water consumption lower than or equal to the baseline, and its total (i.e., direct plus indirect) freshwater footprint was always lower than the baseline. However, FC configurations, in spite of their higher electricity demand, generally outperformed ABS cooling in terms of overall freshwater footprint, which was lower for the ABS configuration only in Singapore (1A) and New Delhi (1B). For New Delhi, this was mainly due to the high indirect water consumption associated with the national electricity mix, which is rich in water-intensive solid-fuel-based power generation (Table 2).

**Figure 7.** Direct and indirect water consumption based on climate zone and case study.

#### *3.4. Direct and Indirect CO2 Emissions*

CO2 footprints are compared in Figure 8. Only indirect CO2 emissions associated with electricity consumption characterized the systems of interest. Hence, the CO2 emission performance of configurations reflects electricity consumption both for DC and CT configurations. Indeed, the influence of the national energy mix on carbon emission was remarkable: for instance, baseline DC configurations achieved similar performance in Birmingham and Cairo, although their electricity consumption would be about 15% higher in the latter city (see Figure 6). Nevertheless, the climate dependence trend demonstrated for electricity (Figure 6) was basically conserved for CO2 emissions (Figure 8): heat-recovery-based ABS cooling outperformed FC in all but the last CT configuration and in very hot to mixed climate zones, as well as in cool climates with hot summers, for DC configurations.

**Figure 8.** Indirect CO2 emission based on climate zone and case study.
