**5.3 Conclusion**

442 Solar Radiation

were bound to overheat during the summer, comprise of height-to-width (referred to from now on as H/W) ratios from 0 to 0.5 (or 1). For canyons with NE-to-SW direction, including narrower canyons, have H/W ratio of 1 (or 1.5). Finally, the horizontal surfaces of urban configurations, whose main axis runs East-to-West are prone to overheating in the summer,

In all the above cases, the negative contribution to the urban microclimate and to thermal

Materials which will measure low surface temperatures, compared to the air

Materials shaded by permanent or temporary shading structures and/or vegetation

Porous materials combined with an appropriate system of periodic water-sprinkling

 Materials with low heat capacity and diffusivity, such as dry soil, light-weight concrete, ceramic blocks and wooden boards, which overheat during noon, but cool down

The application of one or more of the above solutions depends on the character and the use of the urban space, as well as on its design principles. Issues of visual comfort should also be taken into consideration, as the choice of certain materials (i.e. materials with light colours

Finally, the materials for urban space should be chosen according to its peculiarities, its character and its patterns of use. During summer days, there should be shaded areas, where the solar radiation is blocked and the surface temperatures of the materials remain low (Khandaker Shabir, 2000). Similarly, during winter and the intermediate seasons (spring and

The overheating of facade materials facing East and West mainly occurs in buildings, which form part of wide urban canyons with H/W ratios smaller than 0.5. (Bougiatioti, 2006) In more narrow canyons, the overshadowing of the facades by the opposite buildings prevents

In general, the materials, which form the outer layer of eastern and western facades, may heat up to very high surface temperatures. For the above-mentioned reasons, the choice of

 Materials, which record low surface temperatures compared to the air temperature, namely light-coloured materials or materials painted with "cool paints" (Pomerantz, et

al., 1998; Heat Island Group, 2005; Synnefa, et al., 2006; Synnefa, et al., 2007). Materials, irrespective of their surface temperatures, shaded by permanent or

temporary shading structures and/or vegetation (trees or climbing plants).

autumn), there should be areas with no obstruction for solar radiation access.

comfort is important, and material selection should, thus, aim for:

temperature, namely light-coloured materials

(trees or climbing plants) (Bougiatioti, 2005)

even in the case of a H/W ratio of 2.

(Bougiatioti, 2005)

Water surfaces

Vegetative cover (e.g. grass, shrubs)

quickly during the afternoon.

and/or glossy surfaces) can cause glare.

**5.2 Selection of facade materials** 

the materials from heating to high surface temperatures.

materials for eastern and western facades should aim for:

Vegetative cover with climbing plants).

It should be noted that the application of one or more of the afore-mentioned proposals to urban open spaces and buildings facades mainly depends on their use and design. For instance, for building facades, it is important to examine the aesthetic result of the application of one or more solutions to street frontages with a certain orientation at the scale of one or more building blocks. A good example is the redesign of the southern facades of city streets with shading devices and solar systems (e.g. PV panels for wall cladding or for shading). Such an intervention could help not only to improve the urban microclimate and the interior climate of buildings, but also to educate the public on issues of sustainability and energy conservation.

Finally, it should be noted that the choice of surfacing materials for both horizontal and vertical city surfaces affects visual comfort conditions in the urban open spaces, as well as the possibility of taking advantage of daylight for the illumination of the interior spaces of buildings (Givoni, 1993). Consequently, for narrow urban streets, where solar radiation penetrates for a limited period during the day, the use of light-coloured materials can help improve visual comfort conditions in the interior spaces of the buildings. (Yannas, 2001) On the contrary, in wide urban canyons with a small height-to-width (H/W) ratio, the use of light-coloured materials can cause glare and degrade visual comfort conditions at the level of pedestrian circulation.
