Passive solar house cooling

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Houses & Passive Solar Cooling

Though some of the passive solar cooling principles and techniques are common to passive solar heating, there are also some specific passive solar techniques for cooling, specially valid in hot and temperate climates. They include, namely, the right thermal mass for cooling, ventilation and shading…

Shading strategies & Trees

Shading is crucial in any passive cooling strategy. The more shaded a building is - especially the windows and the roof - the better.

The best shading is accomplished outside the building, and trees (deciduous trees in most cases) are usually the best option. See for more details: Shading and trees

The use of trees depends a lot on the particularities of each climate. In cold or temperate climates, do not use evergreen trees too close to the house. Instead, use deciduous trees on west and east side of home to reduce summer heat; and in some cases, use deciduous trees in the sunnier side of the house (south in the northern hemisphere; north in the southern hemisphere).

Other Shading Strategies

Other alternatives on shading include:

- other buildings or parts of the house: one part of the building may shade another part …
- overhangs, arbors, screens, awnings...
- interior shading (of windows) through blinds, drapes and other interior shading devices (Note: interior shading isn’t as effective as exterior shading).

Shading & overhangs

Overhangs are very effective solar passive tools in many climates: properly dimensioned they block the sun during the summer months, when it is higher in the sky.

See, for details: Shading & Overhangs

Thermal mass and cooling

Materials used in walls, floor and other sun-exposed parts of the house should have adequate thermal storage or reflectance, that is, thermal properties able to respond to the needs of the climate where the building is located.

In cold climates the capacity of quickly absorbing solar heat and the capacity of providing a slow release of stored heat during the night, is crucial when choosing materials - masonry and stone for floors, walls, and roofs are materials that have those properties.

Obviously, thermal properties demanded to materials in hot climates - where cooling needs are predominant - are very different from those demanded in colt climates.

Low thermal mass materials

Low thermal mass walls and structures are a very common option in the hot and humid climates with high nighttime temperatures.

Materials like light metal, metal roof, wood frames are very common in passive cooling, since they don’t heat well and cool very quickly when the sun disappears.

Reflective exterior surfaces

The use of highly reflective exterior surfaces is very advantageous in hot climates, due to the large amount of the sun's heat that can be reflected away by reflection. Reflective roofing is particularly effective.

Color and texture are very important in this case. White or close-to-white colors are good options for reflectance. Shinier and smoother materials are also good options, since they are more reflective, which makes the house cooler.

High mass materials

The use of high mass materials - materials that hold heat well and cool slowly, like masonry and stone for roofs, floors or walls - are adequate in hot dry climates, with cold or relatively cold nighttime temperatures.

Recent studies also show that high thermal mass elements can be used with advantage either in temperate climates and some hot climates. Low thermal mass materials aren’t the only solution.

Natural ventilation

In hot and humid tropical climates, with small day/night temperature amplitude, natural ventilation isn’t a good option. But in most other cases natural ventilation is an excellent solar house passive technique.

Obviously it demands a correct location of the windows, and a proper orientation of the building (which in some cases may collide with solar heating or cooling strategies).

Window style (double-hung and casement windows), window placement and the home shape and orientation are crucial for natural ventilation.

See, for details: Natural and mechanical ventilation

National Renewable Energy Laboratory
www.nrel.gov