Integrated thermal effects of generic built forms and vegetation on the UCL microclimate

Abstract

This paper presents a tool for quantifying the integrated thermal effect of built forms and of vegetation on the urban canopy layer (UCL) climate in design built-up alternatives. Three generic models were studied, representing the most common types of residential urban street: (a) the street form, a conventional type, with spacing between the houses, (b) the canyon form—a limiting case of the street form, (c) the courtyard house form. Recessed colonnades in streets and courtyards were considered in this study as the fourth generic model. The four models were analyzed hierarchically from shallow open spaces to deep ones. For each studied case, the built form effect, the vegetation effect and the colonnade effect were estimated using simulated data generated by the analytical Green CTTC model recently developed by the authors. Emphasis in this study is on the UCL air temperature variation at midday, in summer, in a hot-humid region, near the Mediterranean Sea coast (31–32 °N). Eighty-six simulations were generated for estimating the various thermal effects. In addition, 100 experimental observations at 11 urban wooded sites were analyzed to confirm the simulated effect of the trees. Statistical analysis indicates that each of the thermal effects of the built form, vegetation and of the colonnade can be explained each by one linear relationship, common to all the studied built-up generic models, to a high degree of accuracy and confidence level. This provides a useful general design tool, as opposed to the analysis of a particular simulated case, to assess the potential thermal effects of control variables in different building configurations. The study also considers the extent of the thermal effects of built form, vegetation and colonnades, in streets and in courtyards. These effects are shown to depend, each on the envelope ratio, an overall geometry factor, and thus are interdependent.