Passive Solar House Heating

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Passive Solar House Heating

Passive Solar House and Climates

Most of passive solar heating principles and techniques are specific to cold and moderate climates.

Hot climates with seasonal cold nights may apply some passive solar heating principles, but most of them aren’t applicable and involve Passive Solar Cooling. See: Passive Solar House Cooling.

Techniques of Passive Solar House Heating

The big goal of passive solar heating systems is to get the sun's heat within the building and keep it there as much as possible. Absorbing heat for later use, keeping the house comfortable is crucial. But prevent overheat is also important.

To achieve this goal, there are two primary techniques:

- a smart windows system (connected to the shape of the building and its orientation) and
- construction materials (thermal mass) able to absorb and to store and distribute the sun’s heat.

The windows system

Home's windows and skylights (and in some case the doors) can be designed to reject solar heat in the summer and get heat in other seasons.

Most - or at least half of the window area of the house - should face the south (in North hemisphere countries) or the north (in South hemisphere countries); this window area should involve a minimum of 7-9% of the total floor area. Overhangs on that sunnier side can be sized to shade in the summer, without blocking the sun in the winter (when the sun path is low). See Overhangs.

- Windows and doors should be energy-efficient ones; they should have the right Solar Heat Gain Coefficient (SHGC) and U-factor: See Energy efficient window basics

- In Northern hemisphere countries, north-facing windows should involve less than 2 percent of the house’s floor area; in southern hemisphere countries the rule is equivalent, but involving the south-facing windows.

- Skylights shouldn’t occupy more than 1% of roof area, and should have the right SHGC coefficients: see Skylights.

The house should have one or more operable window (or a skylight) in the roof or at the top of walls, to allow natural ventilation. Windows in opposite parts of the house should allow crossed ventilation in the summer and hot days. See House Ventilation Techniques.

Thermal storage of walls, floor…

- The walls, the floor and the more sun-exposed parts of the house should use materials with good thermal storage, that is, with the capacity of quickly absorbing solar heat without overheating, and also with the capacity of providing a slow release of stored heat during the night. Materials as concrete, tile, brick, stone and masonry have those thermal storage capacities…

- It’s common to estimate the surface of the area of the house with those thermal storage materials at 30 times the area of the windows in the sunny side of the house.

- Moderate-dark or dark colors are the best suited for passive solar thermal storage. You should take into account the possible cooling needs of your house (which demand white or close to white colors for best performance) and balance them with the opposite rule: in cold climates, dark color floors, tiles, walls and roofs have clearly advantages in terms of thermal storage capacity.

See also: Thermal materials for cooling

Orientation, shape and occupation of the house

The most used areas of the house should face the south (in Northern hemisphere) or the North (in Southern hemisphere) while the less used areas should be in the opposite position. Layout should also obey to some rules in order to obtain thermal buffers.

See, for more details:
Orientation and shape of the house
Overhangs

Florida Solar Energy Center
www.fsec.ucf.edu