Effects of vegetation, urban density, building height, and atmospheric conditions on local temperatures and thermal comfort

This paper shows the effects of several variables, which co-cause the Urban Heat Island effect on temperature distribution and outdoor thermal comfort (by using the Predicted Mean Vote, PMV) on dense urban environments. The study is conducted by means of a three-dimensional microclimate model, ENVI-met 3.1, which forecasts the microclimatic changes within urban environments. The effects of building density (% of built area) and canyon effect (building height) on potential temperature, mean radiant temperature, and Predicted Mean Vote distribution are quantified. The influence of several types of green areas (vegetation on the ground and on roofs) on temperature mitigation and on comfort improvements is investigated for different atmospheric conditions and latitudes in a Mediterranean climate. The research quantifies the effects of the variables investigated on temperature distributions and in determining outdoor comfort conditions. Vegetation on the ground and on roofs mitigates summer temperatures, decreases the indoor cooling load demand, and improves outdoor comfort. The results of the study demonstrate that density and height of buildings in a city area influence potential temperature, mean radiant temperature, and Predicted Mean Vote distribution; for most of the cases examined higher density causes higher temperatures and with taller buildings vegetation has higher cooling effects. Considering the cooling effect of vegetation, a difference can be noticed depending on the amount of green areas and vegetation type. The results of this study show also that vegetation is more effective with higher temperatures and lower relative humidity values in mitigating potential temperatures, mean radiant temperatures, and PMV and in decreasing the cooling load demand.