The impact of built form on the urban microclimate at the scale of city blocks

In the aftermath of the first oil crisis, Philip Steadman concluded that as a result of twentieth-century developments in architectural design "the means for environmental control within and around buildings which was formerly achieved through effects of mutual shading, enclosure and wind protection, [were] lost" (1975). Since then, building regulations introduced primarily focused on wintertime energy conservation measures in countries with mild to moderate climates. Yet, climate change models increasingly project a warming trend and prolonged heat waves in these parts of the world. As a consequence architects and urban designers find themselves ill equipped to address the challenges of the changing climate.

The aim of this paper is to assess the microclimatic performance of built form at the scale of city blocks. The study takes four metropolitan urban block typologies from Budapest as models. The purpose of this analysis is to obtain basic understanding regarding the interaction between built forms and microclimates in general, and to gain knowledge regarding the microclimatic behavior of these existing typologies in particular. The understanding of the performance of these forms is the first step towards climate-sensitive design and is necessary for developing effective climate mitigation and adaptation strategies in the future.

The comparative numerical simulation study utilizes ENVI-met and MATLAB. The models are compared on the basis of their diurnal air temperature, mean radiant temperature and Predicted Mean Vote cycles. The analysis found mean radiant temperature a good indicator of the built form's influence on the thermal environment. It is sensitive to directionalities in the model and signals problematic periods and areas with high surface and air temperatures. Therefore, mean radian temperature — the most important variable in governing outdoor thermal comfort on typical summer days — is also helpful in analyzing and understanding the effects of mutual shading.

Steadman, P., 1975. Energy, Environment and Building, Cambridge, UK: Cambridge University Press.