Is evaporative cooling an efficient solution for ensuring air quality and thermal comfort in overheated classrooms in a dry Mediterranean climate?

• A direct evaporative cooling model was validated using on-site measurements. • Natural ventilation is ineffective for thermal comfort when outdoor temperatures exceed 25 °C. • Direct evaporative cooling becomes effective from outdoor temperatures of 20–25 °C. • The results show that evaporative cooling at a rate of ≥12.5 l/s·p keeps discomfort hours below 1%. • In the 2050 scenario, an evaporative cooling rate of ≥30 l/s·p is needed to keep discomfort hours < 1%. A large percentage of school buildings in Mediterranean climates that rely solely on natural ventilation face critical issues related to indoor overheating and poor air quality. Despite the severity of these challenges, there is limited research quantifying the problem and exploring viable cooling solutions that align with nearly zero-energy building (nZEB) standards. This study aims to fill that gap by presenting a case study on the environmental performance of a classroom with a direct evaporative cooling system. The school is located in southern Spain, a region characterised by a hot and dry Mediterranean climate. The primary objective is to assess whether such a system can ensure both thermal comfort and adequate indoor air quality during periods of overheating. Based on on-site monitoring data, an EnergyPlus simulation model was calibrated and validated. This model was then used to test a range of current and future climate conditions, as well as different ventilation strategies, including natural ventilation and evaporative cooling with different air change rates. The results demonstrate the effectiveness of the direct evaporative cooling system compared to conventional natural ventilation, reducing overheating hours by up to 26% and lowering indoor temperatures by as much as 6 °C.