Assessing Artificial Shading and Evaporative Cooling for Enhanced Outdoor Thermal Comfort at the American University of Beirut ^†

Urban environments, especially university campuses, are increasingly exposed to thermal discomfort due to the Urban Heat Island (UHI) effect and extensive solar radiation. These conditions pose significant challenges to achieving acceptable outdoor thermal comfort (OTC) in pedestrian zones. This study aims to evaluate the effectiveness of passive and hybrid cooling strategies, specifically sun-sail shading and mist cooling, in enhancing thermal comfort in an outdoor university courtyard. The Van Dyck courtyard at the American University of Beirut, located on the East Mediterranean coast, is selected as the study site due to its heavy use by students between 10 a.m. and 2 p.m. during summer times. During these hours, ambient temperatures ranged between 32 and 36 °C, while relative humidity varied from 21% to 33%. To capture thermal variation within the outdoor space, four distinct seating areas are analyzed throughout the day using ENVI-met version 5.6.1, a high-resolution microscale model. The model was validated against on-site weather station data, achieving a Mean Absolute Percentage Error (MAPE) of 4% for air temperature and 5.2% for relative humidity. Under baseline conditions, Physiological Equivalent Temperature (PET) values exceeded 58 °C, highlighting the severity of thermal stress in the absence of mitigation measures. Sustainable mitigation strategies are proposed and evaluated, including artificial sun-sail shading and mist cooling, aimed at reducing air temperatures and improving OTC. Multiple scenarios are analyzed: a baseline case, three shading configurations (seated-only, full coverage, and double-layer), two mist-cooling setups (6 and 10 nozzles at a flow rate of 0.9 L/min per nozzle), and a combined system integrating both shading and mist.

Results indicate that mist cooling with 10 nozzles reduced PET by a maximum of 1.2 °C, while double-layer shading achieved reductions of up to 17.1 °C. The combined intervention (double-layer shading and mist cooling) yielded the most substantial improvement in thermal comfort, with PET reductions reaching 20.7 °C during peak heat conditions as each strategy compensates for the limitations of the other. Shading effectively reduces radiant heat gain, while mist cooling enhances evaporative cooling, resulting in a combined effect that maximizes PET reduction under peak thermal stress conditions. Compared to the baseline PET, this combined approach brought thermal conditions significantly closer to a thermal sensation classified as slightly warm to comfortable, aligning more closely with accepted outdoor thermal comfort thresholds.