Passive Home Heating
Most of passive solar heating principles and techniques are specific to cold and moderate climates.
Homes in hot climates with seasonal cold nights may apply some passive solar heating rules, but mainly passive solar cooling principles. See: Passive Solar Cooling.
Passive Solar Heating Goals
The goal of passive solar heating is to get solar gains without causing overheating; this principle is associated with another principle: to store that solar heat in certain building materials and to release it in a later moment (during the night), in order to keep the whole house comfortable for long periods.
The Elements Of Solar Heating
The goal of passive solar heating is achieved through…
– high thermal construction materials, able to absorb and also to store the sun’s heat and to distribute it in a later moment.
– a smart window-skylight system, associated to the shape of the building and its orientation.
Thermal Storage Materials
The walls, the floor and the sun-exposed parts of the house should use materials with adequate thermal storage, that is, materials able to absorb solar heat without creating overheating, and also able to provide a slow release of the stored heat during the night.
Materials like concrete, tile, brick, stone and masonry have those thermal storage capacities in different degrees.
Thermal Storage Area
It’s common to estimate the area of the house with those thermal storage materials at 30 times the area of the windows in the sunny side of the building, but this is a rather questionable rule. The right thermal storage area depends on climate, and on particulars involving the home, the site or the orientation. In many climates, energy efficiency strategies based on thermal mass are inadequate and collide with other strategies, namely high levels of insulation and sealing.
Materials with moderate-dark or dark colors are the best suited for intense passive solar thermal storage. That means, in cold climates, dark color floors, tiles, walls and roofs. White or close to white colors can be used to produce the opposite goal, in hotter climates.
Orientation, Shape And Occupation Of The House
Also according with passive solar heating principles, the most used rooms should have a southern exposure (in the North hemisphere) or a northern exposure (in the South hemisphere), while the less used areas should be located in the opposite side. Layout should also take into account the rules concerning thermal buffers.
The Windows And Skylights
Windows and skylights (and in some case the doors) are crucial in passive solar heating. They should be designed to reject solar gains in summer and get it in cold weather seasons.
To achieve it, we may use some broad rules, which have to be adapted to the local climate conditions:
– Most – or at least half of the area of the windows – should face the south (in North hemisphere countries) or the north (in South hemisphere countries); this area of windows should involve around 7-10% of the total floor area.
– Overhangs on the sunnier side of the building can be sized to provide shade in the summer, without blocking the sun in the winter (when the sun’s path is low).
– Windows and doors should be energy-efficient ones; they should have the right Solar Heat Gain Coefficient (SHGC) and U-factor
– In Northern hemisphere countries, north-facing windows should involve less than 2% 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.
– The house should have one or more operable window (or 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 hot days.