Green Europe

Passive Solar Energy

Solar energy is a renewable resource that is environmentally friendly. Unlike fossil fuels, solar energy is available just about everywhere on earth. And this source of energy is free, immune to rising energy prices. Solar energy can be used in many ways - to provide heat, lighting, mechanical power and electricity.

Passive solar heating represents an important strategy for displacing traditional energy sources in buildings. Anyone who has sat by a sunny, south-facing window on a winter day has felt the effects of passive solar energy. Passive solar techniques make use of the steady supply of solar energy by means of building designs that carefully balance their energy requirements with the building’s site and window orientation.
The term “passive” indicates that no additional mechanical equipment is used, other than the normal building elements. All solar gains are brought in through windows and minimum use is made of pumps or fans to distribute heat.

All passive techniques use building elements such as walls, windows, floors and roofs, in addition to exterior building elements and landscaping, to control heat generated by solar radiation. Solar heating designs collect and store thermal energy from direct sunlight.

Another solar concept is day lighting design, which optimises the use of natural daylight and contributes greatly to energy efficiency. The benefits of using passive solar techniques include simplicity, price and the design elegance of fulfilling one’s needs with materials at hand.

Passive solar heating of buildings occurs when sunlight passes through a window, hits an object, is absorbed and converted to heat. The most efficient window orientation for heat gain is due south, but any orientation within 30 degrees of due south is acceptable. Once the heat has entered the building, various techniques come into play to keep and distribute it. Prevention of overheating in the sun space presents one of the biggest challenges.

To let the sun in, a ratio of roughly eight per cent window to floor area is recommended for south walls. Although this number may seem small, it is important to remember it comes from the floor area, which is much larger than the wall area. Again, the control of overheating is a significant issue.

Once the heat is in, a well insulated and air-tight building envelope helps prevent heat loss and allows the solar heat to provide more of the heating needed. A crucial component of the energy-efficient building envelope is the window system. Where common double-glazed windows let heat escape, high performance windows, with insulated frames, multiple glazing, low-e coatings, insulating glass spacers and inert gas fills, can reduce heat loss by 50 to 75 per cent.

High efficiency windows, together with R-2000 levels of insulation and air-tight construction allow passive solar heating to cover a large proportion of heating needs in many locations. With the heat contained, often a simple ceiling fan or a forced air furnace fan (furnace burner off, of course) is all that is required for heat distribution. Using building envelope upgrades alone, up to 25 per cent of a building’s heating requirement can be gained with passive solar techniques.

A helpful technique to control overheating and extend warm conditions in the sun space once the sun is down, is to employ the use of heavy mass materials within the construction of walls and floors. Quarry tiles or stone on floors in a mortar bed, and one withe of brick or double layers of gypsum board on walls, will absorb solar radiation, smooth out the peaks of solar gain, and slowly radiate heat back into the room when the sun is gone.

Some solar homes use a centrally located masonry wood heater to store heat. The bricks and stones surrounding the firebox absorb the solar gain or heat from short but intense firings and slowly radiate it into the room.

Obviously, a lot of work and attention to detail has gone into making passive solar heat an optional and cost effective way to heat your home and it has the added bonus of being environmentally beneficial.

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