Thermal Effect Of City Buildings And Influence To The Urban Heat Island Formation

The urban buildings' thermal effect has influence to the urban climate and urban heat island. In order to discuss the influence, this paper took low latitude plateau city - Kunming's building as the research object, used the data of the building thermal parameter obtained by real-time observation method, and analyzed the data. Result as follows:1. the air temperature over the rooftop and the ground is higher than the air temperature over the lawn in daytime, while the air temperature over the rooftop and the ground is lower than the air temperature over the lawn in nighttime. The current is more obvious in the dry season comparing the rainy season. The difference is the biggest in the morning and the noon. The air temperature over the rooftop is some lower than the air temperature over the ground in daytime, but some bigger in nighttime. The difference is the biggest in the noon, and is not obvious seasonal variation. The rooftop is different to the ground, it's thermal effect is situated between the ground and the lawn.2. the vertical variations of air temperature show the differences that exist in different seasons and different hours of a day. The vertical variation of air temperature is more obvious in early morning and in the afternoon, while the temporal variation is more evident in midnight and in the morning. In winter air temperature inversion appears at the rooftop height because the rooftop shows the heat source to nearby air. Concrete underlying surface emits heat while lawn underlying surface absorbs heat, and these effects are obvious in winter.3. the interaction of buildings and courtyard atmosphere, with the walls of different direction, different seasons, and time differences, the discrepancy is significant; building and the courtyard atmosphere interact each other, building's external walls surfaces heats the courtyard atmosphere in daytime, the courtyard atmospheric heats buildings in nighttime; with the high increasing, the transferring heat of building's walls surfaces to the courtyard atmospheric reduced, the transferring heat of courtyard atmospheric to the building increased in nighttime; the temperature of air near buildings (distance is 0.5m) also has heating interaction to the temperature of courtyard atmosphere.4. (1) the characteristic of heat flux between the building surfaces and its ambient atmosphere is respectively different because of different seasons, different orientations of walls, different hours, or different heights. Generally speaking, the heat flux intensity in dry season is greater than in rainy season; the heat flux intensity of the east and south walls is higher than of west and north walls; the heat flux in daytime is greater than in nighttime, and the change of heat flux changes prominently among daytime, comparatively gentle at nighttime. (2) the height rate of heat flux between the building's walls external surfaces and its ambient atmosphere is whole negative value, the value of the height rate does not have obvious change among daytime and nighttime. But the height rate is respectively different because of different seasons, and different orientations of walls. The absolute value of height rate in dry season is greater than in rainy season, that of east and south walls is greater than west and north walls. (3) in every orientations walls, most of them show as heat source in daytime, and show as heat sink in nighttime. And according to a whole day, all are show as heat sink except of south wall in dry season and west wall in rainy season. (4) the characteristic of heat flux between the building's ambient atmosphere and the courtyard atmosphere is similar to the characteristic of heat flux between the building's walls external surfaces and its ambient atmosphere. But the heat flux value of the latter is several times as the heat flux value of the former, the former's thermal effect is not obvious. (5) the seasonal variation of heat flux between the building's roof and its ambient atmosphere is not obvious. Among the building's every surfaces, its heat effect is the most prominent in daytime, and is relatively small at nighttime, the change is relatively gentle.5. In the city, the heating contribution of the building rooftop to the atmosphere is greater than that of courtyard air mass in the same height. The heat flux of rooftop to the atmosphere is greater than that of court yard air mass to the atmosphere, being more notable in January than in July , more notable at night than in daytime. In the research of urban heat island, building group density and altitude are also a very important factor.