The increase in temperature of an object, space or structure due to solar radiation is termed as Passive Solar Gain or Solar Heat Gain or simply, Solar Gain. It is directly proportional to the strength of the sunlight and is achieved with the help of such materials that are capable to resist or transmit radiation.
The objects on our Earth have the capability to both absorb and radiate sun’s energy. The short-wave radiation of the sunlight is absorbed by objects, which then radiate it in the form of heat, which has longer wavelength. The long wavelength radiation of heat is called infrared radiation. When materials that are more transparent to short-wave radiations than long-wave radiations are placed around regular object, they let sunlight pass but obstruct capture of heat radiation due to its longer waves. This phenomenon is known as passive solar gain, which was first implemented in colder countries for Greenhouses and so the effect is most commonly referred to as Greenhouse Effect.
Requirement & Concerns
When structures are to be constructed to facilitate passive solar gain, shading co-efficient of doors, windows and other shading equipment is the main property to be considered. Shading co-efficient of a shading equipment is the measurement of transmittance of solar energy through it.
Buildings that incorporate passive solar gain technique are designed to maximize the energy of sunlight and consequently reduce the requirement of electricity. In solar gain designs, doors, windows, walls and floor are made of such material that can capture and distribute energy of sunlight inside the building during summer and vice versa during winters. In this system, climatic condition of the place is targeted rather than electrical or mechanical devices.
Alignment of the building according to the motion of the sun, placement of doors and windows, shading material, thermal insulation and thermal mass are the major concerns in passive solar gain. Designing a new structure based on this concept is easier than modification of an existing one for the same purpose, though the latter is possible too. Besides, following have to be determined and considered as well:
- Position of the sun during different seasons of the year
- Range of seasonal and daily temperature
- Direction of prevailing wind
- Characteristics of different seasons
- Topography of the area and its related features
Orientation & Design
The structure should be designed with lowest possible ratio of surface area to volume. The ideal orientation of the house is at 30° to the South in the Northern hemisphere and to the North in the Southern hemisphere. Besides, the position of the structure against tree-belt or plantation of tree near the house should be at a distance that does not obstruct sunlight during peak hours (9am – 3pm). Interestingly, detailed discussion on passive solar gain designs can be found on the internet. Moreover, numerous construction projects on this concept are under progress in various parts of the World.