**4. Conclusions**

438 Solar Radiation

had a mean maximum temperature of 39.7 oC (Tair + 5 oC) and a mean temperature of 32.6 oC (Tair + 1.4 oC), while the brown-coloured one has mean maximum temperature of 48.9 oC (Tair + 14.2 oC) and a mean temperature of 37 oC (Tair + 5.8 oC). Compared to the temperatures, which were measured when the samples were facing west, the above-

The surface temperatures of the composite wood panels with southern orientation were not very high. The light-coloured and the intermediate sample reached a maximum temperature of about 42.3 oC, while the dark-coloured one had a mean maximum temperature of 47.6 oC, which was 12.9 oC higher than the mean maximum air temperature. Concerning the mean surface temperatures, the samples were warmer than the air by 2.6 oC to 5.1 oC. A quick comparison with the temperatures measured for the western orientation reveals that the mean maximum temperature of the light-coloured sample is lower by about 10 oC, while that of the dark-coloured one by about 12 oC. Concerning the mean surface temperatures, the differences between the "western" and the "southern" surface temperatures range between 2.4 oC for the light-coloured sample and 4.3 oC for the dark-coloured one. Again,

When facing towards the south, light-coloured composite aluminium panels (white colour) recorded low surface temperatures, but higher than the corresponding air temperature by only 2.6 oC. For the range of colours, mean maximum temperatures ranged from 2.6 oC (for white colour) to 16.5 oC (for black colour) higher than the mean maximum air temperature. The differences with the measured mean maximum temperatures of the western orientation are impressive and range from 7.4 oC, for the white colour, to 15.3 oC, for black colour. Mean surface temperatures ranged from 31.5 oC for white to 38.7 oC for black panels, and are thus 0 oC to 7 oC higher than the mean air temperature. The differences between the "western" and the "southern" mean surface temperatures of the two extreme colours (white and black) are 2.7 oC and 4.1 oC, respectively. Finally, the surface temperatures at 20:00 (after the

> *Mean maximum Τ [oC]*

Air 34.7 28.3 31.2 **Composite aluminium panels 20 x 30 cm facing South** White colour 37.3 (+2.6) 22.5 (-5.8) 31.5 (-0.3) Yellow colour 41.6 (+6.9) 23.8 (-4.5) 33.6 (+2.4) Red colour 42.5 (+7.8) 24.3 (-4) 34.4 (+3.2) Silver colour 44.3 (+9.6) 23.6 (-4.7) 34.8 (+3.6) Green colour 46.4 (+11.7) 24.5 (-3.8) 35.8 (+4.6) Blue colour 47.2 (+12.5) 24.5 (-3.8) 36.8 (+5.6) Black colour 51.2 (+16.5) 25.1 (-3.2) 38.2 (+7) **Composite wooden panels 20 x 30 cm facing South**  Light-coloured 42.3 (+7.6) 24.1 (-4.2) 33.8 (+2.6) Intermediate 43.3 (+8.6) 24.2 (-4.1) 34.1 (+2.9) Dark-coloured 47.6 (+12.9) 24.8 (-3.5) 36.3 (+5.1)

*Mean minimum Τ [oC]* 

*Mean mean Τ [oC]* 

mentioned surface temperatures are considerably lower.

the observed differences due to the change of orientation are significant.

sunset) are below 5 oC than that of the air temperature at that time.

**3.3.2.c Wooden products** 

**3.3.2.d Metal products** 

### **4.1 The effect of orientation**

For paving materials, the horizontal placement, in combination with the high sun altitude angles during the summer period and the large amounts of solar radiation result in maximum absorption of solar radiation and the overheating of the materials, depending on their colour and thermo physical properties. For facade materials, the orientation determines the angle of incidence of the solar rays, the duration of insolation, as well as the hours of the day when it occurs.

In the case of northern facades, the solar radiation, which is received throughout the summer period, is limited. Consequently, the surface temperatures of north-facing materials, as the in-situ measurements show, are lower than or equal to the air temperatures throughout the summer days.

The insolation of southern facades is largely affected by the high sun altitude angles (74,4o for Athens, at noon on June the 21st). As a result, most south-facing materials do not record very high absolute maximum surface temperatures in summer.

Eastern and western facades receive large sums of solar radiation at angles which are nearly normal to their surfaces. Western facades may record higher surface temperatures than eastern ones due to the fact that during the afternoon, the large sum of solar radiation, which impinge on western facades, coincide with the highest daily air temperatures.
