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The present study deals with the estimation of human thermal sensation zones in a Mediterranean climate (Athens). Field monitoring along with field surveys leading to a database of 2313 questionnaires were carried out in three open urban areas. Thermal sensation conditions were analysed under the influence of air temperature, relative humidity, solar radiation and wind speed. Thermal sensation zones were first defined using air temperature as a single parameter affecting thermal sensation. Logistic regression was appropriately used to define each thermal sensation zone. The thermal sensation zones were then determined using a combination of the microclimatic parameters to investigate the extent to which these parameters affect thermal sensation. Results showed that the thermal comfort zone is characterized by a quite wide air temperature range, on the order of more than 10°C. In addition, this zone presents always statistical insignificance in theP-values of residuals. These results imply that thermal comfort is a complex situation and adaptation plays an important role as far as this zone is concerned. By contrast, the other thermal sensation zones were found to present statistical significance in theP-values of residuals, implying thus that the examined microclimatic parameters seem quite adequate to define these zones. [ABSTRACT FROM PUBLISHER]

The cooling effect in a courtyard's garden and in the adjoining ground- and first floor verandas, attached to the NNE side of a two-storey building is evaluated with measurements performed during a hot weather summer period in Athens. Results revealed a well defined and strong daytime cool island between the buildings rear garden (with about 85% canopy covering) and an air temperature reduction for the ground floor veranda, as compared with an urban square with low canopy coverage (about 15%), reaching a maximum air temperature reduction of 6.5 K during daytime. Compared with a nearby densely wooded park, the garden and the veranda were found 1–1.5 K cooler during 4 and 8 hours during daytime, respectively. Using the physiologically equivalent temperature thermal index with appropriate adjustments to local conditions, it was found that those two sites, compared with the urban square, were able to mitigate the extreme thermal stress conditions and to decrease the daily number of hours associated with strong thermal stress conditions. It is concluded that appropriately designed semi-open spaces in residential buildings, well known from vernacular architecture for their qualitative benefits, may be considered as positive bioclimatic pedestrian transitional elements in sustainable urban design for Mediterranean climates. [ABSTRACT FROM AUTHOR]

Abstract: This work investigates how to reduce, by appropriate urban design, air temperature at the street level and to improve pedestrian thermal conditions in summer. The case study is a street in Athens with low aspect ratio H/W (H: building height; W: street width), low trees canopy coverage level, and high traffic. Urban variables for design are trees canopy coverage area ratio, traffic load, walls surfaces albedo, and H/W. Their thermal effect is separately and altogether estimated by applying the microclimatic Green-CTTC model whereas thermal stress is assessed using the Physiological Equivalent Temperature (PET) index. The studied day is relatively hot (36.5 °C at midday) with eight hours of heat stress (two and six hours of extreme and strong heat stress, respectively) at street level. Acceptable near-to-discomfort limits for local pedestrians are considered whereas PET classification heat stress levels are adjusted to local conditions by applying a correction equation to obtained PET values. Results show that the examined scenarios are associated with air temperature decrease and improvement of thermal comfort in the shade, especially during the day''s hottest hours. The trees thermal effect is the dominant factor followed by the increase of H/W and of the walls surfaces albedo. All the studied design scenarios are found able to reduce the number of heat stress hours but the trees canopy coverage area ratio increase scenario was found by itself able to be associated only with moderate heat stress for local pedestrians. Alternative local smart controls for thermal comfort (SCAT) options are also discussed. [Copyright &y& Elsevier]

Abstract: The present work investigates the causes of the variability in air temperature patterns among urban streets with trees in Athens, as obtained from in situ measurements, in a suburb area and in the city center. Urban variables studied are: the extent of tree canopy coverage, traffic load, surfaces albedo modification, street deepening aspect and the street’s ventilation. The thermal effect of each variable is estimated by simulations using the Green CTTC analytical microclimate model. The model was first validated with measurements data and consequently used to study the effect of the various urban variables in attenuating the high values of air temperature within the studied streets considering two feasible scenarios for each of the examined streets. Model results revealed that the total attenuation effect in reducing the air temperatures inside the streets may reach as much as 5 K at noontime with a daily average cooling of 3 K. Further, the study demonstrates the potential use of microclimate modeling in assessing the merits of proposed passive cooling strategies in urban streets. [ABSTRACT FROM AUTHOR]

Abstract: Three biometeorological indices were examined in terms of their potential to describe the actual thermal sensation as this is experienced by humans at areas with different climatological characteristics. The thermal comfort scales, as derived from using Physiological Equivalent Temperature (PET), the Temperature-Humidity Index (THI) and the wind chill index (K), were compared to Actual thermal Sensation Votes (ASV) data as expressed on a 5-point scale. These data were collected by surveys that covered all four seasons of the year and were conducted in seven European cities (Athens, Thessaloniki, Milan, Fribourg, Cambridge, Sheffield and Kassel). Results show that, for any given ASV class, the corresponding classes calculated according to PET, THI and K, present a strong correlation with the climatic mean temperature of the survey site, which in turn leads to misclassification of the thermal sensation. Accordingly, an effort was made to apply an adjustment to the indices based on climatic mean temperature. Only small improvements were observed on the performance of the indices. [Copyright &y& Elsevier]