2. Climate and air as planning factors
Radiation


Global radiation is a meteorological parameter which indicates the total short wave radiation flow from the sun against a horizontal surface. It consists of the sum of direct solar radiation and the diffuse part of sunlight coming from the blue sky and the clouds.

Various climate stations constantly register global radiation (in W/m²). This data is assembled e.g. in an atlas about solar radiation in Europe (Atlas über die Sonnenstrahlung Europas, 1984). Radiation data for Germany is listed below.

Maximum radiated power on a vertically irradiated surface: 1,000 W/m²

Radiated power under very thick clouds: about 20 W/m²

Annual irradiation on a horizontal surface/a surface inclined by 45° to the South: 900-1,200 kWh/m²

Maximum value of daily irradiation (very clear summer weather): about 8 kWh/m²

Minimum value of daily irradiation (very gloomy winter weather): about 0.1 kWh/m²

Annual hours of sunshine: 1,300-1,900 h

Hours of sunshine (April-September): 1,000-1,400 h

Hours of sunshine (October-March): 300-500 h


It is necessary to apply a building geometry considering the exposure to the sun and shadowing conditions in order to achieve optimum solar radiation and the corresponding energy gain.

Besides global radiation, atmospheric counter radiation also plays an important role. Counter radiation is long wave thermal radiation from the atmosphere hitting the earth. It is strongly influenced by the degree of air pollution. Heavy air pollution leads to a high proportion of counter radiation. 70 % of the counter radiation is produced in the first 100 m of the atmosphere and counter radiation delivers about as much energy as solar radiation on a clear day.

© City of Stuttgart, Office for Environmental Protection, Section of Urban Climatology

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