Ecotect allows you to calculate absorbed and transmitted solar radiation. These values give the designer more detail on how much of the incident solar radiation will actually penetrate the building through the walls and windows. These calculations do take into account material properties. To get accurate results, you need to ensure these properties are correct.

For walls and roofs, the properties taken into account are the “solar absorption” of a material absorbs (Fabs) and the material’s transparency value (Ftrans). For windows, the transparency value (Ftrans), shading coefficient (SC), effects of refraction (Frefract) are considered. For more detail on these parameters and the underlying equations, see the Ecotect help files.

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Absorbed Solar Radiation – In Ecotect, this is determined by Fabs, a value from 0 to 1 that is based on the color of the material (1 = high absorption). However, a solar reflectance index (SRI) is more common in practice (see Direct Gain). SRI is based on both reflectance and emissivity and is given as a value between 0 and 100 (100 = low absorption). Also, the heat capacity (specific heat) of the material helps calculate how much of that absorbed radiation can be usefully stored (see Thermal Mass).

Solar Radiation Transmitted – Ecotect uses a transparency value for both walls and windows. And for windows, the transmitted radiation depends on the input values for a shading coefficient and a refraction index. In industry, these glazing properties are often based on solar heat gain coefficients (SHGC – a number between 0 and 1, 1=high transmittance). See NFRC. The SHGC of a window is effectively equal to: (Ftrans)*(SC)*(Frefract).

It is often good practice to control the scales of your solar radiation results to clearly isolate values that are “too much” or “too little.” If the scale only ranges between a desired maximum and minimum value, you can clearly see areas you need to focus on.