BY MARCO TORTORICI
Hints of bioclimatics
If we were to ask an architect why a colleague of his (even one as illustrious as F.Ll.Wright) placed a lime tree in front of the openings of one of his architectures, we would hear him answer that the reasons are to be found in a sort of naturalistic vedutism, or even in the search for the so-called “organic” style. Such answers would fade into the background if we looked at the problem from a bio-climatic point of view.
In fact, a tree is also a perfect natural machine that filters the light and heat of the sun in spring and summer and lets them pass through in the winter months, optimizing the performance of an opening. Using sunlight successfully and without contraindications requires a study of the general climatic situations, from latitude and longitude to exposure to the winds, and of the specific conditions of the microclimate with which the building will have to interact. For example, Le Corbusier in his book “Towards an architecture” recommends taking care of the exposure of the building; but the ribbon window (which he made an invariant paradigm of contemporary architecture) seems tied to the context of France and therefore unsuitable in different situations such as Algeria, where Le Corbusier himself built a lot without using this linguistic element. Some data are fundamental to begin designing by making the best use of solar energy: they are the data of the so-called solar geometry and in particular the variation of the position of the earth with respect to the sun and its rays.
The rotation of our planet implies that in the northern hemisphere the sun rises in the south-east and sets in the north-west, and consequently the parts of a building exposed to the north will almost never be directly reached by the sun’s rays, while those exposed to the south will receive them directly and for most of the day. As the seasons change, the inclination of the earth with respect to the sun means that for each latitude the angle of incidence of the sun on the earth’s surface changes; therefore, knowing the latitude you also know the angle of incidence of the sun’s rays for all periods of the year (data tabulated and easy to find). From a generalized analysis of this information comes the conviction that each situation will be different and that it is necessary to foresee the adaptations of the bioclimatic machine so that it is able to accommodate the sun’s rays at any time of the day throughout the year, in order to optimize its performance. One of the corollaries of architectural research in the bioclimatic field follows, that is, the prediction of the operator’s interaction with the space he inhabits, which must be simplified and logical to learn. Furthermore, the problem of energy saving also requires studies on how to allow sunlight to illuminate internal spaces in a widespread manner and for a long period of the day;
The elementary resolution factors are given by:
Size of the windows
Reflectivity and color of floors and ceilings
Shape of reflective surfaces
As can be imagined, the light will reach further into the room the more reflective the floors and ceiling are: light colors are more reflective than dark ones and faceted surfaces are more reflective than smooth ones. So a white wall treated with an orange peel effect will reflect, for example, more light than a smooth wall of the same color. In the case of opaque surfaces, the reflection coefficient, also linked to the color of the material, can be very high (tending to one), in the case of white surfaces, or very low (tending to zero), in the case of black surfaces. The energy that is not reflected is absorbed by the material and converted into thermal energy. At certain latitudes and with Nordic macroclimates, it is often appropriate to store this energy in thermal masses and manage it to heat the environment; however, this energy in temperate or hot areas can produce overheating and lack of internal comfort in the living space. Curvilinear elements in the section will tend to concentrate the reflected rays in a particular area depending on the curvature, easily identifiable by knowing the reflection coefficients since the reflected ray has the same angle as the incident ray.
Similar considerations can be made in the case in which the light comes from above. Knowledge of the angle of incidence and reflection always allows us to predict the behavior of light and design its effects.
In the first and third cases, sunlight is diverted so as to concentrate it on the side walls, a solution that is perfectly suited to the display needs of a painting or sculpture exhibition, as the light is partially diffused and reaches the works on display in a soft manner from above, avoiding annoying reflections. In the second case, a system of sunshades fragments and uniformly diffuses sunlight, creating lighting conditions suitable for reading rooms and offices. Since the angle of incidence varies from season to season, a static solution optimizes performance only in a particular period of the year. Due to the principle of interaction, solutions and mechanisms must be found that allow the operator to adapt the bioclimatic machine to all possible needs. A singular example of a bioclimatic device could be a highly reflective white telescopic windowsill: depending on the length of the room and the height of the opening: as the angle of incidence of the sun’s rays varies, the windowsill changes its length to reflect the desired amount of light into the living space. The main technical-design problem is being able to exploit the potential of sunlight without suffering its thermal contraindications. A typical example of the Mediterranean tradition, from Greece to Italy to Tunisia, is the expedient of painting houses white and light blue and building them with thick load-bearing walls that constitute an excellent thermal mass. In fact, there are two main passive principles for controlling the accumulation of thermal energy: thermal mass and shielding. The first conserves energy to exploit it later and consists of using large masses of poor heat conductors to accumulate it and prevent it from reaching the interior during periods of maximum radiation. This is the case of buildings embedded in rock walls or built underground or that exploit the thermal mass of heavy masonry walls.
Shielding, on the other hand, protects surfaces with a covering that reflects or absorbs thermal energy depending on the needs. For example, a second covering that shades a flat roof would prevent overheating and the spaces below would enjoy thermal comfort even in the hottest periods. Furthermore, if this screening is done by means of solar panels, the energy is not lost but stored and used. The double covering expedient can also be used to force the wind into narrow spaces and create air currents to be exploited for the natural ventilation of the building.
