PASSIVE SOLAR DESIGN

Passive solar design refers to using the solar energy to heat the interior spaces of a building without relying on mechanical devices that require additional energy.  Passive solar system rely on the natural heat transfer processes of conduction, convection and radiation for the collection, storage, distribution and control of solar energy. Here, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design or climatic design because, unlike active solar heating systems, it doesn't involve the use of mechanical and electrical devices.

Conduction is the transfer of heat between substances that are in direct contact with each other. The better the conductor the more rapidly the heat will transfer. Good conductor are copper, iron, steel etc. Poor conductors are wood, paper, air etc.

Convection is the primary method by which heat moves through the gases and liquid in up and down movement with the heat transfer. As the gas is heated it warms, expands, rises because it is less dense. When the gas or liquid cools it becomes denser and falls. As the gas or liquids warmer and rise or cools and falls it creates a convection current

Radiation are the electromagnetic waves that travel through the empty space. The sun warms the earth through radiation of electromagnetic waves.

Based on the relationship with sun, the interior space and the heat collection system there are three types of passive solar heating.

1)Direct gain

2)Indirect gain

3)Isolated gain

1) Direct gain

        Direct Gain System is a type of passive solar heating system in which south-facing windows provide heat gain during the daytime and high-mass thermal-storage materials absorb and store that heat. At night, the stored heat radiates back out, warming the space. This is the simplest type of passive solar heating system, but careful design is required to prevent overheating.

         Direct gain attempts to control the amount of direct solar radiation reaching the living space. This direct solar gain is a critical part of passive solar house designation as it imparts to a direct gain. The cost effectiveness of these configurations are currently being investigated in great detail and are demonstrating promising results.

2) Indirect gain

       Indirect gain systems control heat gain at the exterior skin of a building. It is of three types:-

i. Trombe wall

ii.Sun space

iii.Roof pond

i.Trombe Wall

       A Trombe wall is a system which consists of a dark coloured wall of high thermal mass facing the sun, with glazing spaced in front to leave a small air space. The glazing traps solar radiation like a small greenhouse. The solar radiation first strikes the trombe wall located between the sun and the living space. The sun absorbed solar energy moves through the wall by conduction and then to the space by radiation and convection.

ii.Sun space

            A ‘Sun space’ is usually a south-facing glazed area located outside of the main fabric envelope of the building. The space naturally heats and cools allowing daytime temperatures to raise higher and night time temperatures to fall further than the ‘comfort zone’ temperatures of the adjoining living space. This sun space having a floor of a high thermal mass by a thermal storage wall from which the heat is drawn as needed. For cooling the sun space can be vented to the exterior.

   iii.Roof Pond

         This is another form of indirect gain system that serves as a liquid mass for absorbing and storing solar energy and insulation panel is moved over the roof pond at night along the stored heat to radiate downward into the space. At night, the insulation is removed and the water exposed, losing significant amount of heat by radiation to the night sky. Early in the morning, the insulation panels are replaced to protect the water from the heat of the day and solar radiation. The water remains relatively cool throughout the day, cooling the ceiling of the space below. A cool ceiling is particularly effective in rooms where heat is being generated as warm air always rises to the top, to lose its heat almost immediately to the ceiling. The water is typically contained in black bags or dark coloured containers to maximize radiant emissions and minimize evaporation.

3) Isolated gain

      Isolated gain involves utilizing solar energy to passively move heat from or to the living space using a fluid, such as water or air by natural convection or forced convection. Heat gain can occur through a sun space, solarium or solar closet. These areas may also be employed usefully as a greenhouse or drying cabinet. An equator-side sun room may have its exterior windows higher than the windows between the sun room and the interior living space, to allow the low winter sun to penetrate to the cold side of adjacent rooms. Glass placement and overhangs prevent solar gain during the summer. Earth cooling tubes or other passive cooling techniques can keep a solarium cool in the summer.