Everything about Solar Gain totally explained
Solar gain (also known as
solar heat gain or
passive solar gain) refers to the increase in
temperature in a space, object or structure that results from
solar radiation. The amount of solar gain increases with the strength of the sun, and with the ability of any intervening material to
transmit or resist the radiation.
Objects struck by sunlight absorb the short-wave radiation from the
light and re-radiate the heat at longer
infrared wavelengths. Where there's a material or substance between the
sun and the objects struck that's more
transparent to the shorter wavelengths than the longer, then when the sun is shining the net result is an increase in temperature - solar gain. This effect, the
greenhouse effect, so called due to the solar gain that's experienced behind the glass of a greenhouse, has since become well known in the context of
global warming.
Shading coefficients
When discussing the properties of fenestration (for example [window]s and [door]s) and shading devices, shading coefficients are commonly mentioned properties. Shading coefficients measure the solar energy
transmittance through windows. "G-value" is the coefficient commonly used in Europe and "solar heat gain coefficient (SHGC)" is used in the United States. G-values and SHGC values ranges from 0 to 1, a lower value representing less solar gain.
Shading coefficient values are calculated using the sum of the primary solar transmittance (T-value) and the secondary transmittance. Primary transmittance is fraction of
solar radiation that directly enters a building through a window compared to the total solar
insolation, the amount of radiation that the window receives. The secondary transmittance is the fraction of inwardly flowing
solar energy absorbed in the window (or shading device) again compared to the total solar insolation.
Solar gain and building design
In the context of
passive solar building design the aim of the designer is normally to maximise solar gain within the building in the winter (to reduce
space heating demand), and to control it in summer (to minimise cooling requirements).
Thermal mass may be used to even out the fluctuations during the day, and to some extent between days.
In direct solar gain systems, the composition and coating of the building glazing can also be manipulated to optimise the greenhouse effect, while its size, position and shading can be used to optimise solar gain. Solar gain can also be transferred to the building by indirect or isolated solar gain systems. For further details, see
passive solar building design.
Further Information
Get more info on 'Solar Gain'.
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