This paper describes work that was carried out by CRES, in the frame of the EU-funded Joule project``PRECis: assessing the potential for renewable energy in cities.'' The main aim of the project is to develop simpli®ed parameters that describe the microclimate and environmental performance of different urban textures. One of the roles of CRES within the team was to describe simpli®ed parameters for the use of vegetation in the urban context, which can eventually be used irrespective of site-speci®c characteristics for different climatic contexts and urban textures. Of particular interest is the effect of vegetation on microclimate: thermal effects, as well as the effect of vegetation on solar and daylight access. These affect the microclimate of the existing open spaces as well as the energy use of the surrounding buildings for heating, cooling and lighting, through shading, evapotranspiration, etc. Simple parametric studies were examined, to identify the thermal impact of vegetation in the urban environment, at the scale of the urban block, particularly as far as the reduction of air temperature is concerned.

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The role of urban green areas in the microclimatic conditions of cities, during summer, is investigated in this paper through monitoring campaigns carried out at the National garden, at the city centre of Athens. Two types of investigations were carried out: i) a microscopic one that investigated the thermal conditions inside the Garden and the immediate surrounding urban area and ii) a macroscopic one that compared the temperature profile of the Garden with that of the greater city centre area. It was concluded that in microscopic level, the temperature profile inside the National Garden and the immediate surrounding urban area did not showed a clear evidence of the influence of the Garden and it was dependent on the characteristics of each location. In a macroscopic scale, the Garden was found cooler than the other monitored urban locations and temperature differences were mainly greater during the night, especially in streets with high building height to street width (H/W) ratio and low traffic, while in streets with high anthropogenic heat during the day, the biggest temperature differences were recorded during the day.

One of the greatest environmental challenges for the sustainability of future cities is the mitigation of the urban heat island phenomenon and thus, improvement of outdoor comfort conditions for people. The emphasis of this work is to analyze how mitigation techniques in a dense urban environment affect microclimate parameters and outdoor thermal comfort. The quantitative differentiation of outdoor thermal comfort conditions through bioclimatic urban redevelopment for an area in the city of Serres, Greece is investigated. The main bioclimatic interventions concern the application of cool paving materials, the increase of vegetated areas and the creation of water surfaces. The analysis and comparison are performed for a hot summer day with the ENVI-met model. Software simulations regarding microclimatic and outdoor thermal comfort conditions are performed for the daytime period 06.00 to 20.00 (14 hours) at the height of 1.8m from the ground. The examined parameters are air temperature, surface temperature and mean radiant temperature (T mrt). The evaluation of outdoor thermal comfort conditions is conducted using the index PMV (Predicted Mean Vote), adapted for outdoor conditions. The results of simulations are discussed regarding the assessment of bioclimatic interventions.