The impact of height/width ratio on the microclimate and thermal comfort levels of urban courtyards

Abstract

The outdoor thermal comfort level of urban spaces is an important contributor to pedestrians’ health. The urban microclimate is also important due to its influence on the energy use of buildings. These issues are likely to become more acute as increased urbanisation and climate change increase the urban heat island effect. However, urban planning must be able to provide urban forms that produce various microclimates that result in different comfort situations for pedestrians. This study aims to define various configurations of urban open spaces by analysing the influence of geometrical parameters on outdoor comfort levels. To achieve it, open spaces are simulated for typical hot and cold days in the semi-arid climate of Constantine, Algeria. The sun exposure is estimated using TownScope 3.1, and assorted models are evaluated according to the geometrical indicator of the height to width (H/W) aspect ratio. ENVI-met 3.1 is used to simulate such factors as the outdoor air temperature, mean radiant temperature (Tmrt), wind speed and relative humidity, while RayMan 1.2 is used for converting these data into physiological equivalent temperatures (PETs). The results show that duration of direct sunlight, mean radiant temperature and wind speed are influenced by the urban form and play an important role in attaining optimal thermal comfort levels.

Keywords:

• Urban geometry
• public courtyards
• sun exposure
• thermal comfort
• ENVI-met