What if your roof saves you energy?

Maintain a pleasant temperature inside a house, in summer and in winter, it is energy intensive. A situation that is increasingly difficult to sustain in the context of global warming. This is why researchers are working to develop innovative solutions that would help limit the energy consumption of the sector. And today a team Berkeley Lab (United States), in fact, presents an intelligent roof covering that switches itself from heating mode to cooling mode depending on the outside temperature.

It should be remembered that there are already systems such as reflective coatings or roof tiles on the market. color clear which help to cool the houses by returning the light from Sun in the tunes. They also emit part of the heat absorbed as thermal infrared radiation. In a process that physicists known as radiative cooling. The trouble is, this cooling doesn’t stop in winter. Driving up the heating bill.

The coating developed by researchers at Berkeley Lab has the difference that its radiative cooling capacities are quite simply deactivated in winter. Researchers talk about temperature adaptive radiative coating or Tarc – for temperature-adaptive radiative coating.

A funny metal

At the base of their Tarc, dioxide of vanadium (VO₂). Because in 2017, the team had an amazing feature of this material. It is indeed a conductor of electricity, but thermal insulator. Understand that it does not conduct heat. Furthermore, below 67 ° C, the VO₂ is transparent in the light infrared. But above this temperature, he begins to absorb it. Vanadium dioxide therefore exhibits the typical behavior of a so-called phase change material.

Researchers from Berkeley Lab first tested their coating – a mine layer device “Which looks like scotch tape and can be easily affixed to a roof” – in a real environment. On the roof of one of the physicists. They measured the reactions to changes in brightness and outdoor temperature for a sample of roof covered with Tarc, for a dark roof sample and for a light roof sample.

Incredibly efficient coating

From the data collected and more than 100,000 energy simulations previously performed to assess the performance of solutions already on the market, the researchers simulated the performance of their coating over one year, in cities representing 15 different climate zones on the American continent. . The result is confirmed by spectroscopy experiments. Tarc outperforms existing coatings by matter ofenergy saving in 12 of the 15 climatic zones tested. It is particularly effective in areas with large variations in temperature, whether from day to night or from summer to winter. On average, the researchers estimate that their coating could saveenergy by 10%.

According to their measurements, the Tarc reflects about 75% of sunlight. Its thermal emittance – understand, its ability to release heat by infrared radiation – is 90% when the outside temperature is high – that is, more than 25 ° C. This promotes the elimination of heat in summer. But in winter, this emittance decreases. And the roof can then retain heat.

” The physical predicted the Tarc would work, but we didn’t think it could work as well “, comments Junqiao Wu, researchers in materials science, in a communicated. All the same, it remains to validate these performances on a full-scale prototype. If the results are as good, the Tarc could even serve as thermal protection for the batteries, for the satellites or for the cars. Even to make tents, greenhouse coverings or, why not, clothes.