## 2 Research in Sustainable Energy Systems at DTG: Main Results and Discussion
### Energy and Economic Analysis of Direct and Indirect Evaporative Cooling
as a free cooling effect is also present in case external air enthalpy \(\rm{h_{E}}\) should be greater than the inside air \(\rm{h_{A}}\) (Figure 12c);
* Indirect Evaporative Cooling (Double Stage) (IEC_DS): Internal air is humidified and flows through two cross-flow heat exchangers before being discharged. Such a system emphasizes the adiabatic cooling, and so increases the free cooling effect with respect to the IEC single stage. However, it also increases the pressure drop of the AHU; therefore, overall performance must be carefully evaluated (Figure 12d). Figure 12: _Cont._  
Four resorts were selected at different latitudes to represent the main European climates. According to the Koppen classification: Berlin, Germany (52.47\({}^{\circ}\) N) and Paris, France (48.73\({}^{\circ}\) N) as representative for the Cfb climate, Venice, Italy (45.50\({}^{\circ}\) N) for the Cfa climate and Seville, Spain (37.42\({}^{\circ}\) N) for the Csa climate. The percentages of the psychrometric zones are reported in Figure 13: The most suitable zones for a free cooling effect (D2 and U2) were wider with IEC technology (even more with double stage), also highlighting a reduction of D1 and U1 (the least favorable zones). Figure 12: Schemes of the different plant solutions compared (grey lines represent equipment not used in that solution). (**a**) Heat recovery only (if h\({}_{\rm E}\) > h\({}_{\rm A}\) damper A closed, dampers B, C and D operating; if h\({}_{\rm E}\) < h\({}_{\rm A}\) dampers B and C closed, dampers A and D operating allowing free cooling); (**b**) DEC (damper B closed, dampers A, C and D operating); (**c**) IEC_SS (damper A closed, dampers B, C and D operating); (**d**) IEC_DS (damper A closed, dampers B, C and D operating). Figure 13: Percentage of psychrometric zones (the U1 zone is not reported as negligible). In Berlin and Paris, that is, in climates where D1 and U1 zones were relatively less frequent than D2, U2 and U3, both DEC and IEC featured very effective cooling energy savings with respect to the total cooling and ventilation air load (Figure 14). IEC savings were greater than DEC, especially in Venice and Seville (that is, in climates with a high frequency of the D1 zone). Where the climate was mainly colder (wider U4 zone), both IEC_SS and IEC_DS allowed for basically the same advantage of DEC (Figure 14). Such figures were found to be emphasized when the comparison was done with respect to HR. Furthermore, free cooling also had a positive effect on the reduction of the chiller capacity, which the authors evaluated at around 11 kW in most situations for the case considered. While energy savings by evaporative techniques were appreciable in all European climates, the economic analysis carried out by the authors revealed some drawbacks. In fact, the higher costs were compensated by savings in cooling capacity and electricity costs only in Cfb climates. Instead, the economic advantage had to be carefully evaluated in warmer climates (Cfa and Csa), due to its great dependence on the extra investment costs in evaporative cooling equipment. As a main conclusion of this study, the authors highlighted that evaporative cooling can be a sustainable energy saving technique in many types of climates, especially in buildings with high internal heat gain. This will be more and more common in the next years due to the increased thermal insulation of new and retrofitted buildings. However, economic profit should be carefully evaluated in each situation, considering the extent of outdoor ventilation, air flow (so the presence of people) and internal heat gain. An Experimental and Theoretical Approach to Energy Saving for Refrigeration and Air Conditioning in Supermarkets  
First, the advantages of using an electronic expansion valve (EEV) instead of a thermostatic expansion valve (TEV) were evaluated.