|M.Sc Student||Dagan Yossef|
|Subject||A Study of Air Temptrature Variation in the Space Between|
|Department||Department of Architecture and Town Planning||Supervisor||Mr. Milo-Emil Hoffman|
The purpose of this paper is to present and analyze the results of an empiric study of air temperature variation at different heights in the space between buildings, performed in site, and to contribute to a better understanding of morphological parameters and local climate relation in the urban environment.
An almost closed to the wind, with 10 to 12 meters high 5- stories buildings street was chosen for this purpose in Haifa city. Air temperature sensors (copper constantan thermocouples) were fixed at different heights in an open on both sides aluminium foil truncated cones. Measurements were recorded continuously. In addition manual measurements of wind velocity and direction, air temperature and humidity were carried out at 4 - 5 hours intervals for comparison, near the meteorological booth at about 3 meters over the roof of one of the buildings and along the street. The air temperature recorded at the meteorological booth was considered to represent that of the open space.
Four series of measurements were performed during week-ends, from Friday noon until Sunday morning. Week-ends were chosen because A. C. appliances are generally locked out and almost no human and traffic activities - that contribute additional heat to the street - take place in the site, which is a commercial street.
Three series were performed in summer and one in a winter week end with relatively stable weather conditions: clear during the day, clear and cold during the night and very light winds.
An air temperature variation of 0.5K (which is the measurements device accuracy limit) was observed at the different heights during night hours, except for one night in the winter period, during which a 1K difference was noted for 3 hours.
0.5K can be considered negligible for planning and design purposes in places with similar characteristics design.
During the day, air temperature maximal variation recorded between the different heights was about 3K at noon. This is determined by sun’s altitude and by floor and walls shaded areas.
Air temperature patterns recorded at night in the meteorological booth remained higher then the street section. In winter the picture was reversed. It is possible to infer that cold air drains from the roofs to the streets space in clear sky nights. This phenomenon is more significant in winter, when air temperature values of the open environment (which are, the air temperature values measured at the meteorologic booth above roofs level) are lower compared to the streets space. In addition, air transparency is higher, because the water vapor parcial pressure is low, and cooling by radiation (at the roofs level) is enhanced. This interpretation can also explain the 1K temperature difference along the height, obtained in winter night.
The measurement site represents semi laboratory conditions. It is an extreme example of a narrow street with buildings linked together without lateral space on both sides and partly blocked against the wind entrances. If no significant vertical temperature variance was found under such conservative conditions, this conclusion can be considered certainly true for other open and wider street cases.