Heat Island

Urban issues to be resolved concerning building energy systems involve not only global warming but also the heat island phenomenon, the planning of urban infrastructures for electricity generation and distribution, and water purification.

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.

Our recent study has shown that the acrylic silicon polymer is useful to formulate self-cleaning topcoat which may maintain the thermal insulation effect of cool roof effectively. 
A 2K self-cleaning topcoat was formulated with a water-borne type acrylic silicon polymer. Its effect to maintain high solar reflectance was confirmed by outdoor exposure test in comparison with coatings having no self-cleaning function. The solar reflectance performance was well maintained regardless of installation angle, lightness of colour or pigment type. 

High urban temperatures are observed during the last 100 years due to heat island phenomenon. The effect is intensively pronounced even in small sized cities by temperature differences between rural and urban environment reaching even 6 oC. In order to keep the phenomenon under control, mitigation strategies, especially concerning cool roofs has been established. Under hot and arid climates roof temperatures reach almost 70 oC and about 50% of heat enters into buildings through roof slab.  

The present paper deals with the application of 4500 square meters of reflective pavements in an urban park in the greater Athens area. The aim was to improve thermal comfort conditions, reduce the strength of heat island and improve the global environmental quality in the considered area. It was estimated that the use of cool pavements contributes to decrease the peak ambient temperature during a typical summer day, up to 1.9 C. In parallel, the surface temperature in the park was reduced up to 12 C while comfort conditions have been improved considerably.

Heat island phenomenon rises the temperature of cities, increases the energy demand for cooling and deteriorates comfort conditions in the urban environment. To counterbalance the impact of the phenomenon, important mitigation techniques have been proposed and developed. The use of cool pavements presenting substantially lower surface temperature and reduced sensible heat flux to the atmosphere, appears to be one of the most important proposed mitigation solutions. The present paper investigates and describes the actual state of the art on the field of cool pavements.

Τhe present article deals with the development and testing of photovoltaic pavement for heat island mitigation. The scope of this study is to evaluate its contribution to the balance of the Urban Heat Island phenomenon. For this reason, we made a photovoltaic pavement for purely experimental reasons (dimensions 3.5x1.3m) that consists of two different voltage polycrystalline photovoltaic panels. On top of them, a triplex security glass with a nonslip silk screen, PVB standard 1.14 mm was placed.

An urban heat island results in higher urban temperatures than the surrounding area and is considered as the most documented phenomenon of climate change. This increase in urban temperature has a serious impact on the energy consumption for cooling and also contributes to higher urban pollution levels. Athens suffers from high summer temperatures that affect the quality of life of citizens. In response to the problem, a major rehabilitation plan was designed and applied, based on the use of advanced mitigation techniques.

This research concentrates on evaporative cooling, a sustainable and alternative way to cool a roof surface by taking advantage of the properties of porous materials. During periods of rain or high humidity nights, water sorbents store moisture in their small pores inside their particles. During a warm sunny day, the latent heat released due to evaporation of moisture, maintains the surface temperature at low level. Lower roof temperatures contribute to smaller heat flow inside the building while reducing the cooling load.

For energy conservation and good Indoor Air Quality (IAQ), it is crucial to improve Outdoor Air Quality(OAQ). For achieving good OAQ in urban areas, wind flow patterns among buildings should beimproved as well.In this paper, effects of building layout on outdoor thermal climate and air quality are investigatednumerically. In addition to the environment around pedestrians, enthalpy of outdoor air introduced intobuildings and its air quality are examined from the standpoint of IAQ.