Urban sustainability development offers improvements on the quality of human life and helps decrease the environmental impact in cities and use of energy sources, in terms of both the residual production (heat, pollutants) and the consumption of resources outside the city (energy, water). Climatic conditions can contribute positively to all these aspects and provide comfortable, healthy and secure environments, promoting also the use of outdoor spaces. Local climate does not necessarily interfere with economical interests; on the contrary, appropriate environmental urban design can contribute to cost reductions, for instance, decreasing energy consumption in buildings and decreasing costs and damages related to various types of accidents, such as those associated to the occurrence of strong wind speeds.

Taking climatic and design factors into account, the present project aims to provide solutions, which can improve the microclimate of urban spaces, transforming them into more comfortable and secure spaces, and which will lead to energy savings in urban areas.

The main goal of this project is to contribute to the planning and design of safer and more comfortable urban outdoor open and transitional spaces, by analysing occupant’s thermal and mechanical comfort on the use of those spaces as objectively as possible. Furthermore, the improvement of the environmental performance of urban spaces can ameliorate visual and thermal conditions in adjacent buildings, thus helping to reduce energy consumption and, consequently, environmental impacts in town.

Comfort may be viewed from the thermal or mechanical point of view.
Most of the thermal comfort models have been developed referring to indoor conditions (the “two-node model” of the JB Pierce Laboratories (New Haven) and Fanger´s “heat balance equation” (1970, 1982)); on the other hand, in most of them deterministic models have been adopted; in most cases “thermal optimum” is associated with “thermal neutrality” and most of them are “static” models (Fanger, 1972; Gagge et al., 1986; Parsons, 1993; Givoni, 1999).

Some authors have shown that these kinds of models are not adequate to the study of outdoor conditions, which are much more changeable than indoor conditions, and where psychological aspects such as thermal expectation and motivation are important factors that influence thermal preference (Auliciems and DeDear, 1997; DeDear and Brager, 2001; Cadima, 2000; Nikolopoulos et al., 2003).

The studies referring to outdoor thermal environment, based on questionnaires, are quite recent (Nikolopoulou et al., 2003; Givoni, 2003; Ahmed, 2003; Thorsson et al, 2004). In these studies, “real” environmental perception of the individuals in different thermal contexts are analysed as objectively as possible. Results are complementary to the ones obtained through the use of different comfort indices. In a study undertaken inLisbon on the use of transitional urban spaces, it was found that as criteria, thermal comfort is less important than views and air pollution, as important as smells and more important than noise and availability of sun (Cadima, 2000).

Wind affects human comfort in two ways. On the one hand, it enhances convective heat exchanges and interferes on sweating rates; on the other hand, it may cause mechanical discomfort. Criteria used to classify the effects of wind are mainly based on wind mean speed or, in more specific cases, to gusts (Penwarden, 1973; Lawson and Penwarden, 1975; Hunt,J.C., E.C. Poulton and J.C. Mumfort, 1976). The thresholds commonly used are not always those of the individuals, subjected to the wind. For example, a wind speed of 5m/s is frequently referred to as an upper limit of an “agreeable” wind. The owners of commercial establishments located in areas of strong winds, may ask the authorities to take measures to reduce wind speed, when its speed exceeds 5m/s during more than 20% of the time (Penwarden and Wise, 1975).