Passive Solar Energy
Solar energy can be utilized in various ways – to provide electricity, mechanical power, heat and lighting. Passive solar heating and cooling can save substantial electricity bills. Design of a building is very important for tapping passive solar energy. The building and windows are designed in such a way that they carefully balance their energy requirements without additional mechanical equipment. Solar benefits are utilized through windows and pumps, and fans are used minimally.
Passive solar energy utilizes building constituents such as walls, floors, roofs, windows, exterior building elements and landscaping to control heat generated by sun. Solar heating designs try to trap and store thermal energy from sunlight directly. Passive cooling minimizes the effects of solar radiation through shading or generating air flows with convection ventilation.
Daylighting, passive heating and cooling are the main solar concepts.
A commercial building can reduce its electricity bill by using the overall light of the surrounding sky and not just the daylight. It will create a pleasant environment and reduce air-conditioning costs too because a considerable amount of heat is generated by the light bulbs or ballasts.
A good daylighting system takes myriad factors into account such as
- The general orientation and planning of places to be lit.
- The location, form and dimensions of the apertures and openings through which the daylight will pass.
- The strategic placement and orientation of internal surfaces which may be able to reflect the daylight.
- The location of movable or permanent objects which provide protection from excessive light or glare.
Passive Solar Heating:
Passive solar heating happens when sunlight strikes an object and that object absorbs the heat. It can occur in a building effectively if windows are oriented correctly. The most powerful window orientation is south but any orientation within 30 degrees of due south is adequate. Once the heat is inside the building various techniques can be adopted to keep and spread it. For passive solar heating approximately eight percent window to floor area is required for south walls. Once the heat is trapped inside a building and that structure is air tight, heat loss can be avoided effectively. Double-glazed windows are not very effective in trapping the heat. We should install high performance windows, with insulated frames, multiple glazing, low-e coatings, insulating glass spacers and inert gas fills. All these elements can reduce heat loss by 50 to 75 per cent.
Techniques opposite to passive solar heating is applied. Here buildings are designed to keep the solar and air heat away. Internal heating from animate and inanimate objects is minimized and dissipated in the environment through ventilation.
Shading devices fixed or adjustable reduce solar radiation. We can shade a building by natural vegetation and using special glazing in windows. External shading devices can reduce solar gains by up to 90 per cent, while still admitting a significant amount of indirect light.
External heat gain can also be minimized by good insulation, reduced window size and by the use of reflective materials in the walls and roof. At the building design stage, attention should also be paid to cross-ventilation and the direction of prevailing winds, the source of cooling nighttime breezes.