Study of thermal comfort in courtyards in a hot arid climate

The outdoor thermal comfort in an enclosed courtyard has been studied numerically by the three dimensional prognostic microclimate model, Envi-met 3.1. The effect of wind, and shading by different means - galleries, horizontal shading or trees - has been examined. The effect of wind is evaluated by allowing cross-ventilation through openings at 3 and 5. m height above ground level, designed according to the prevalent wind direction. The study was conducted for the hours 11-17 LT during June assuming average climate conditions. The thermal comfort is evaluated by the Predicted Mean Vote (PMV) index. During hot summer days, outdoor comfort is mainly dependent on solar radiation; hence, shading is the best means to improve comfort, while the contribution of wind under all configurations studied was limited and much smaller than the shade contribution. The amount of shade is mainly determined by the courtyard orientation. Inspection of empty enclosed courtyards has shown that an elongated E-W rectangular courtyard has the least shade, and therefore it is the most uncomfortable. When the courtyard is ventilated by openings, hot air and radiation penetrate through them increasing the air temperature and the radiation temperature in the courtyard relative to the conditions obtained in a closed courtyard. Higher openings are less comfortable to stay under, and further decrease the comfort in the courtyard. The addition of trees or/and galleries to the closed courtyard significantly improves the outdoor comfort. Under the assumption of constant building temperature of 25°, the addition of galleries is the most efficient shading strategy. Quantitative results exhibiting these trends are presented for specific configurations and orientations of ventilated and/or shaded courtyards.