Experimental assessment of a resilient air-cooling system under extreme heat events in southern European climate conditions

The global rise in average outdoor air temperatures has led to a significant increase in the demand for cooling energy in recent years. The development of resilient air-cooling systems capable of handling extreme heat events is essential to achieve the aim of Nearly Zero Energy Buildings. Ventilative cooling technologies based on indirect evaporative cooling systems are considered a sustainable solution in terms of indoor air quality and energy performance. 
In this study, the daily energy performance of a renewable air-cooling unit (RACU) based on a dew-point indirect evaporative cooler (DIEC) and a desiccant wheel (DW) was experimentally evaluated under the real extreme heat events in southern Europe. The RACU prototype has been developed to be integrated into renewable District Heating and Cooling Networks. This air-cooling system allows controlling air humidity through the DW and air temperature and carbon dioxide emissions through the DIEC. The RACU system works with two inlet air streams: outdoor air (OA) and outdoor air for regeneration (ROA) to thermally activate DW. For the purposes of this work, both inlet air streams were 100% outdoor air. The RACU prototype does not use refrigerants.  
The daily energy performance of the RACU was obtained in terms of Daily Energy Efficiency Ratio (DEER). The RACU system operated during four different days under the severe heat weather conditions in Cordoba, Spain, during office hours. Therefore, four different case studies were established to analyse the supply air conditions, sensible and latent capacities and DEER values for the RACU in this work.  
Results indicated high DEER values for the RACU, ranged between 7.0 and 14.8. High values of daily sensible cooling energy, up to 177.0 MJ/day, and daily total latent capacity, up to 38.6 MJ/day, were also evident for the RACU. These results suggest that the use of resilient air-cooling systems as the RACU could be interesting under southern European climatic conditions of extreme heat, demonstrating high daily energy efficiency performance.