outdoor microclimate and pavement material - case study in university site

pavement materials have great impact on heat island control under the urban canyon layer. understanding the properties of pavement materials can help to reduce the heat island effect. introducing the main properties of pavement surfaces affecting sol-air temperature and mean radiant temperature - such as albedo, permeability, conductivity, thickness, emissivity, irradiation and convective air flow – is the main scope of this article. the result of an outdoor microclimate case study that was done in the site of kashan university in summit summer and winter is introduced in this regard. using climatology equipment`s such as portable weather station, wet bulb globe temperature and infrared camera, the local and microclimate weather condition and surface temperature was measured in shaded and sunny walkways with different pavement surfaces. a weather station was fixed on the roof of a building in the site to represent the local climate condition. a portable weather station and other equipment`s where moved in the walkways in different paths of the university site. the data of surface temperature, mean radiant temperature, dry bulb temperature and wet bulb globe temperature (wbgt) in different points of the walkways were gathered in morning, noon and afternoon in two days of hot summer and cold winters. the observed points where chosen according to their different conditions such as coffee shops, rest places, bus stations, building entrances and so on. the gathered data were analyzed using microsoft excel and were compared with heat stress cards of wbgt to show thermal condition for pedestrians. the information of each observed point is presented in tables to show the place condition, time and date of observation, weather temperature, surface temperature of the surrounding materials, and local climate temperature at the observed time in each place. the results show the important effect of the sunlit pavement surfaces to increase ambient temperature comparing with local temperature. it was clear that sunshades are the most important parameters to moderate ambient temperature. sunshades prepare favorite shadow in summer days while they have ability to reduce night irradiation in winters. therefore they can decrease daily and yearly temperature swing. in summer midday the difference between sunny and shaded places reached to 12-14°c in asphalt surfaces. in all shaded pavements except asphalt under white iron shades, the ambient weather was 2-7°c less than local temperature. green surfaces as heat sink materials will modify the ambient temperature in hot and cold conditions. in grass surfaces the ambient temperature was 10-13°c less than local climate in summer midday in sunny and shaded condition respectively. it was only 2°c less than local climate in winter day in shaded condition and 2°c more in sunny condition. therewith green surfaces, cobblestone with permeability property and soil surface showed the best heat sink ability. dark asphalt and soil surfaces in sunlit vast areas produce the worst condition in summer and winter by increasing the temperature swing rang. wet surfaces will modify thermal condition by reducing absorption factor and increasing evaporative cooling effect.