The bioclimatic architecture enters what is called passive solar energy. This type of architecture uses natural elements of the place (sun, wind, water, soil and vegetation) to achieve thermally efficient buildings capable of satisfying thermal comfort requirements, regardless of the use of air conditioning systems.
The bioclimatic approach is related to the principle of self-sufficiency and the realization that the main phenomena that negatively affect the environment are caused by the consumption of large amounts of non-renewable energy, fossil fuels or nuclear energy. Construction is a highly polluting sector because most of the gas and CO 2 emissions come from the air conditioning and heating systems favoring climate change and the greenhouse effect.
The objective of the bioclimatic architecture is the control of the internal microclimate, with passive design strategies that, by minimizing the use of mechanical systems, maximize the efficiency of the heat exchanges between the building and the environment.
The bioclimatic architecture defines the geometric and structural characteristics of the building, its location and orientation in such a way that it adapts to the different climatic conditions.
In general, in temperate regions there are three thermal phases that correspond to different construction requirements:
- Winter: solar irradiation on walls and windows should be encouraged to heat the interior; The high thermal insulation of the enclosure is also necessary to conserve the accumulated heat.
- Summer: it is necessary to protect the building from solar radiation with shade systems, having high mass covers and, therefore, a high thermal inertia, as well as favoring the natural ventilation of the building.
- Half season: requires the combination of cooling and heating solutions.
Types of energy capture in bioclimatic architecture
In bioclimatic architecture we can distinguish three types of energy capture: direct uptake, indirect uptake and separate uptake.
Passive systems of direct capture are called architectural systems that represent an immediate and easy use, for example, oriented homes capture solar energy from the sun directly; but this is not the only requirement to be able to talk about solar housing. This form of use of solar radiation is a clear example of passive solar energy.
The direct systems must also include components to control the energy losses of winter nights and exaggerated temperature rises in summer. Undoubtedly, the direct passive systems of solar energy are close to the traditional ones.
Passive indirect collection systems are called architectural systems in which, through a sensor, the heat is conducted into the interior of the interior integrated within its structure.
Of the passive systems of indirect capture, the so-called Trombe wall stands out, Invented by Michel Tromble: it is a glass on top of a solid matt black wall that acts as an accumulator and as a diffuser of heat inside the house. This simple device can represent an important energy saving.
In hot climates, however, you must take into account the problems with excess heat energy that are suffered in summer, which can also be solved with the implementation of ailerons or umbrellas that keep the wall in the shade.
Another system consists of replacing a wall or ceiling with black metal drums filled with water or black collectors, respectively. In both cases, the water tanks would heat during the day, and during the night, isolated from the outside, they would release the thermal energy inside the house.
Passive systems of separate collection are called architectural systems that, through a sensor, conduct thermal energy into the interior of the passenger compartment and are separated from the house, but not far away.
If they were far away, they could not be called passive, since forced transport would be needed and we would be talking about solar air heaters. In this system, the solar radiation is collected in a glazed chamber, which can be used as an agricultural greenhouse, separated from the home by a collecting surface.
Integration of renewable energies
Buildings that have been considered a bioclimatic architecture, in addition to the use of passive solar energy are usually installed additional renewable energy systems.
Through the integration of renewable energy sources, it is possible that all energy consumption is self-generated and non-polluting. In this case, the objective is to build buildings or emissions. The buildings plus energy are those buildings generate more energy than consumed.
Method of bioclimatic architecture
The bioclimatic architecture is based on three axes:
- Capture solar radiation and take advantage of it for domestic activities.
- Transmit solar energy and protect it.
- Save the energy or evacuate it according to the needs.
These requirements are essential, especially in warmer regions (such as the Mediterranean), since the capture and conservation of energy in winter seems to contradict protection and evacuation in summer. Resolving this apparent contradiction is the basis of a well understood bioclimatic design.
Capture and protect yourself from the heat
Large areas of glass are often useful in temperate zones.
Revegetation is a technique to limit solar gain in summer and reduce thermal losses in winter.
The Earth is tilted on its axis with respect to the plane of the ecliptic at an angle of 23 ° 27 '. The height of the sun on the horizon and the path that runs through the sky vary during the seasons.
In the northern hemisphere, in the latitude of Europe (around 45 ° on average), in winter, the sun rises in the southeast and is located to the southwest, staying very low on the horizon (22). ° on the winter solstice). Only the south facade of a building receives adequate sunlight. To capture this solar energy, it is appropriate to place the main glazed openings to the south.
The glass lets in light, but absorbs the infrared re-emitted by the inner walls that receive this solar radiation, which is called the greenhouse effect. Solar radiation is converted into heat by the opaque surfaces of the building (walls, ceilings and floors). It is on this principle that a passive solar building is conceived: solar, because the source of energy is the sun, passive, because the system works alone, without a mechanical system.
Even in the northern hemisphere, in summer, the sun rises in the northeast, is northwest and is high on the horizon at noon (78 ° at the summer solstice). The facades of a building radiated by the Sun are mainly the east and west walls, as well as the roof. The angle of incidence of its rays on glass surfaces facing south is high. It is advisable to protect these glazed surfaces by means of solar protections, sized to block direct solar radiation in summer and to leave the maximum sunlight available in winter.
In the openings of the east and west facades, the horizontal solar protection has a limited effectiveness, because the solar rays have a lower incidence; Opaque sunscreens (shutters), and even more deciduous vegetation, are effective on these facades. Persistent vegetation is also effective to protect cold winds, as long as it does not oppose the winter sun.
In the northern hemisphere, in European latitude, a bioclimatic construction is characterized by:
- Large openings in the south, perfectly protected from the summer sun.
- Very few openings to the north
- Few openings to the east, except for rooms for early use, such as kitchens: morning sun.
- Some openings to the west, especially for the rooms, to protect from the setting sun in the summer.
In a bioclimatic approach, these generalities must adapt naturally according to the environment (climate, environment, ...) and the pace of life of the users of the building.
Transform / diffuse heat
Once sunlight is captured, a bioclimatic building must know how to convert it into thermal energy and distribute it wherever it is useful.
The transformation of sound radiation into heat is carried out through a certain number of principles, so as not to deteriorate the interior comfort:
- Maintain an adequate thermal balance.
- Do not degrade the luminous quality.
- Allows thermal diffusion by the ventilation system and the thermal conductivity of the walls.
In a construction, the heat tends to accumulate upwards of the premises by convection and thermal stratification. The conversion to the heat of the light must be done mainly at ground level. In addition, the absorption of light by a wall makes it dark and limits its ability to diffuse this light. This absorption should not prevent the scattering of light in less illuminated areas, and should not generate contrasts or reflections.
Therefore, it is important to favor very clear ceilings to diffuse the light in the rooms without glare, to darken the floors to favor the capture of energy in this level and to use variable tones in the walls according to the priority that is given to the diffusion of the light or the capture of solar energy, and according to the need for heat or freshness of the premises in question.
The shades that most likely convert light into heat and absorption are dark (ideally black) and rather blue, those that are best able to reflect light and heat are clear (ideally white) and quite red. Thus, one can, through a simple play of colors, direct the light and then the heat to the areas that require it. Matt materials with a granular surface (particularly natural materials) are also better for capturing light and converting it into heat than smooth, shiny surfaces (mirror effect, metallic or lacquered appearance, etc.).
Good heat diffusion (or freshness) can also be achieved by adequate ventilation methods.
Under a temperate climate, a bioclimatic construction designed optimally from a thermal point of view requires few or no heating or air conditioning systems, to maintain an interior temperature of between 20 ° C in winter and 25 ° C in summer, day and night.
Keep the heat / freshness
In winter, once captured and transformed, solar energy must be stored inside the building so that it can be used in a timely manner. In summer, it is the night freshness (which is easily detected with good ventilation) that must be stored in a lasting manner to limit overheating during the day.
The simplest method is to store this energy in heavy construction materials, provided they are accessible and, therefore, are not covered with thermal insulation, hence the importance of insulation. From the outside, or possibly the distributed insulation.
The storage of energy in the materials and the return period uses its specific heat, its total volume, but also other physical characteristics to determine its energy efficiency. Certain techniques allow to dynamically improve the return period.
Valuing the environment
The environment (hills, forests, ...), as well as the vegetation planted around the construction also have a protective role: as windbreaks, we opt for the soft woods in the north and the hardwoods in the south; They protect from solar radiation in summer, but they let light in winter. A water point in front of the building, to the south, will also provide an update of one or two degrees in summer.