“A green awning on the terrace is like having a radiator over the window”
With the arrival of the hot months, the facades of the buildings display their particular summer armor: the awnings. In Spain the scene is quite characteristic when you are walking down the street and, curiously, the color that triumphs in our country It’s green. And although it seems like the perfect shield against heatstroke, a recent technical warning has shaken what we thought we knew about the protective effect it has. Voices against him. One of the most important It’s Jordi Martí’stechnical architect who posed a rather important analogy that has collected Decosfera: having a dark green awning is “like having a radiator in front of the window.” And its premise is based on an undeniable principle of materials physics, since the absorption of social radiation is very different depending on the color. This is something that happens in the world of fashion and is in the mentality of society, since in summer normally choose to wear light colored clothing by better reflecting heat. But wearing dark clothes in the middle of summer is actually a bad idea, since sweat is guaranteed. It happens on awnings exactly the same, since while light colors (such as pure white) reflect most of the light radiation and heat up less, dark colors are true thermal sinks. This means that a dark green awning can absorb between 80% and 90% of solar radiation, a figure that in the case of black tarps is close to 98%. According to Martí, the fabric heats up drastically and generates a stagnant “heat pocket” under the awning. And this is a problem because under the awning is our house, which begins to accumulate all the energy and results in an increase in heat, when we want to have the opposite effect. It is studied. To support the scientific basis of this position, the work of Hubertus Pöppinghaus, a German architect who is a reference in the study of shadows and radiation, is often used. In this case, through the use of thermal imaging cameras, Pöppinghaus analyzed the behavior of different materials, evidencing the temperature peaks that dark fabrics reach. And among his conclusions he makes it clear what the tarps we use should be: The outer face must be reflective with a light color so that visible solar radiation bounces and does not accumulate heat. The inner side should be dark, since this drastically reduces the reflection of shortwave solar radiation bouncing off the street and sidewalks, decreasing the total heat flow. The industry does not agree. Here the Spanish Association of Shading and Dynamic Solar Control wants to deny this statement relying on the wavelength of the radiation. And the energy that the sun sends to the Earth arrives in the form of direct solar radiation, mainly short wave, penetrating through the window panes and heating the interior of the houses. But when an awning, whatever its color, intercepts that exterior radiation, it stops the blow and, indeed, heats up. By doing so, the energy that the canvas re-emits to the environment is no longer short-wave, but long-wave infrared radiation, and here is the fundamental detail that dismantles the “radiator effect”: standard window glass is opaque to long-wave radiation. In other words. For the industry, it is physically inaccurate to state that the dark awning transfers heat from the outside to the inside through the glass, since the thermal radiation emitted by the hot canvas hits the glass and does not penetrate the home. According to AESSO, what is truly lethal for energy efficiency is letting the sun hit the glass directly and, therefore, any system that provides shade is positive. Images | Elisabeth Fossum In Xataka | Popular wisdom is not always right: the great heat myths that we should avoid in summer
