Following on from the previous post I did a quick search for an easy way to understand the energy balance of the Earth’s surface and found the following diagram “Breakdown of the incoming solar energy” by Frank van Mierlo at http://en.wikipedia.org/wiki/File:Breakdown_of_the_incoming_solar_energy.svg
All the radiant energy coming down to the ground from the sun will eventually head back up from the ground in one form or another. Houses in warm climates are often designed to prevent direct solar radiation from entering windows but little is done to prevent the entry of indirect energy coming back up from the ground. Averaged over the Earth’s surface a fair amount of that energy is in the form of latent heat in water vapour but if a house is surrounded by hard surfaces then the energy heading up will be mostly radiation.
The reflectance of various hard surfaces can be found in the table “Solar Albedo of Concrete and Select Other Materials” at
http://www.lehighcement.com/Education/Lehigh-Education-Strange-but-true.htm. If the hard surfaces are a light colour to prevent the heat island effect then they can reflect and scatter up to 80% of visible light and short-wave infra-red into windows. This is a much greater reflectance than that of the average Earth surface which is about 5%. A dark coloured surface will get hot, heat the air in contact with it and radiate long-wave infra-red.
On the shaded side of a house it might be a good idea to have window glass which allows transmission of visible light but blocks infra-red, keeping a lot of indirect radiation out during summer and keeping heat in during winter. Keeping the ground around the house shaded during summer is probably a good idea too. That’s cool shade rather than the hot shade I alluded to in the previous post.
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