urban canyon

Heat island is a big issue for large cities especially located in hot and moist climate in Asian countries. The phenomenon is severer in an urban canyon because of surrounding highrise buildings causing little ventilation and heat dissipation from traffic. The first purpose of this study is to investigate thermal environment of a main street in Osaka by intensive  measurement in the summer of 2006. Osaka is the second largest city and suffers from the most severe heat island in Japan.

The urban climate of high-density areas is often affected by an increase of the air temperature known as Urban Heat Island (UHI) phenomenon. 
UHI is strongly influenced by the solar reflectance of conventional materials used for building envelope and urban coatings, i.e. streets and square pavings. 
The present work proposes an original method to predict the temperature of both facades and local air mass on urban scenarios. The effect of changes on coatings may also be estimated.  

Natural ventilation driven by the combined forces of wind and buoyancy has been studiedexperimentally for a building flanked by others forming urban canyons. The steady ventilationestablished in an isolated building was observed to change dramatically, both in terms of the thermalstratification and airflow rate, when placed in the confines of an urban canyon environment. Theresulting ventilation flows and internal stratifications are presented for different combinations of windspeed, opening area and location, and canyon width (building density).

In urban canyons reflected sunlight can play an important role in the illumination of buildings, particularly in orientations and during times of the day where sunlight is not incident on the windows. Facing buildings provide considerable obstruction to daylight by reducing the skylight contribution and sometimes blocking the access to sunlight. However, reflected sunlight is an important contribution to the internal illuminance of a room and should not be underestimated.

As streets usually cover more than a quarter of the urban area, canyon street morphology plays an important role in creating the urban climate. It directly influences the air temperature, moisture and wind flow within the streets as well as the urban surrounding area and has been the topic in several urban climatology studies. Recently, studies based on the street Cluster Thermal Time Constant (CTTC) model have been carried out by the authors with a view to assessing the thermal effects of alternative architectural designs of the flanking buildings and inner courtyards.

Gives an overview of a computational approach to the so-called street canyon phenomenon, whereby microclimate influence on thermal loads of buildings and local contribution to temperature rise from air conditioning unit heat emission can affect the heating balance of buildings. Also discusses the influence of flow and temperature fields on the dynamic thermal balance of the building.

The paper presents further then an integrated model the supporting methodology that allowsto assess natural urban ventilation conditions both outside and inside constructions.Though some particular aspects arid procedures can be complex and time consuming thegeneral structure is quite simple:1. to establish wind regimes as a boundary condition - information can come from windmeasurements at undisturbed areas Like airports;2. to integrate these regimes within the site - using numerical models to transfer information tothe site;3.