Sunlight ‘yes’, heat ‘no’
In climatology, heat and light are intrinsically linked. Blind belief in looks and sometimes in light has led people to have big windows, resulting in heated-up interiors. Incidentally, one major shift in Indian buildings has been from small wooden windows to large sheet glass windows, without considering why small openings were provided for centuries, nearly all over India.
In south India, light invariably brings in heat, due to its geographical location on the surface of Earth. The reference to region is very important, for it also dictates lifestyle, as in Europe requiring more indoor warmth than south India. Here sun moves along lower altitudes in winter, penetrating deeper into the buildings through the windows, letting in more direct light. The indoor temperature also rises which is welcome during winters. In contrast, during summer, we need to keep indoors cooler, and ensure that least direct light penetration happens into the indoors. The fact that sun moves at higher altitudes during summer helps in this direction. Incidentally, there are locations when sunlight and heat are undesirable round the year, for the winters are also pretty hot.
On an average, from 10 a.m. to 3 p.m., there is maximum heat gain through roof conduction and oblique light penetration through the windows. During other times, light and heat enter through wall openings more directly. Appropriate shading of openings using chajjas , staggered walls, fins, roof overhangs and such others need to be employed. On a daily calculation, maximum heat gain comes from the roof; hence it should be properly designed and treated.
Northern light is both minimum and least heat, hence an ideal direction for openings. The eastern wall is comparatively safe though as day advances, light and heat may build up, but this heat dissipates during the day time. Properly designed sunshades can resolve majority of solar heat problems. The south orientation faces much of solar radiation; hence simple window top chajjas may not be sufficient.
Verandahs, vegetation, designed roof overhangs and such others are necessary. Among the problem fronts is the western façade, which receives solar energy during afternoon hours, heats up, conducts it inside and makes the indoor warm during the evening and night, just when we need to use them most.
There are many ideas like tilting the building to best orientation, using materials with thermal mass or designing the type of opening which help in mitigating heat due to solar radiation.
In urban contexts, it may be easier to employ skylights with adequate hot air vents. However, among the best to get light without heat is the idea of internal courtyard with minimal openings to outside – no glare, equal distribution of light and cross ventilation, all together. No wonder, our forefathers realised this and lived in courtyard houses. We need to modernise this concept for application today.