## 2 Research in Sustainable Energy Systems at DTG: Main Results and Discussion
### Energy and Economic Analysis of Direct and Indirect Evaporative Cooling
The relevant parameters of a real WLSC supermarket located in Bologna (Italy) were monitored and recorded over 12 months. In this way, the energy performance of the WLCS plant was compared to those of two traditional multiplex configurations: One equipped with TEV (operated with a fixed suction pressure, MP_TEV_Fixed_suction_p) and one equipped with EEV (operated with lower head pressures and with a floating suction pressure, MP_EEV_Float_suction_p). The three supermarket configurations were modelled to assess both the compressor electricity consumption and the cooling capacity [40]. The MP_EEV_Float_suction_p solution led to 8.1% electric energy savings with respect to the MP_TEV_Fixed_suction_p system. This was due to the lower condensation pressure and the higher evaporation pressure;  
Figure 16: Cycling losses as a function of the load factor (TEV = without solenoid valve; TEV * = with solenoid valve). Figure 17: Layout of the WLSC supermarket. moreover, the higher heat recovered allowed the WLSC to feature 15.8% electric energy saving with respect to the \(\text{MP}_{\text{TEV\_Fixed\_suction\_p}}\) system and 8.4% if compared with the \(\text{MP}_{\text{EEV\_Float\_suction\_p}}\) system (Figure 18). The authors' analysis of the WLSC system allowed to evaluate significantly lower \(\text{CO}_{2}\) emissions (around 56-58%), due to the reduction of both the direct (refrigerant charge and leakages) and indirect (electric energy consumption) warming effect. Finally, the authors focused on the control of the activation of the medium temperature (MT) chiller of the WLSC system [41] (Figure 19a). Measurement of the performance of a real WLSC system allowed evaluating a strong increase in total electric power required with the operation of the MT chiller when the external temperature was between 25 \({}^{\circ}\)C and 30 \({}^{\circ}\)C (Figure 19b). The reason for the activation of the MT chiller was to limit the condensation pressure of the MT cabinets in case of very high external temperature. In this case, the use of a compressor with a low minimum pressure ratio limit limited the inefficiency of the system due to the extra temperature difference in the evaporator. Figure 11:0 _Cont._  
Figure 11:1 Monthly total energy consumed by WLSC refrigeration system and multiplex solutions, and electric energy savings with respect to the \(\text{MP}_{\text{TEV\_Fixed\_suction\_p}}\) system. A further analysis by the authors, based on several tests carried out on a real small experimental WLSC system [42], revealed that the use of a dry cooler should always be preferred to the use of the medium temperature chiller to cool the cold water loop, as it allowed for a 7% energy saving. Furthermore, the solution that implied the exploitation of the evaporative cooling phenomenon by means of direct water evaporation into the air (at the dry cooler inlet) led to appreciable additional energy savings (4%). From an economic perspective, the evaporative cooling solution was revealed to be preferable both in dry and humid climates, due to the possibility to avoid the installation of the MT chiller, thus reducing the initial investment.