The cold roofs reduce the heat

Posted on August 11, 2017

It is known that so-called "cool roofs" have life-saving effects during the summer: they give more coolness to the interiors of the buildings while limiting the effect of the thermal urban isle - thus, to a certain extent, combating the tendency of city centers to Show higher temperatures than the surrounding countryside.

Now a study from China first finds out that this action is significantly greater in heatwave periods. This adds another "point" to reflective roofs, which are in the last place on the upward trend in the context of energy saving and the fight against climate change.
"Bounce" of the radiation
Reflective roofs, also known as "cold" or "white" roofs, although extremely ecological, are different from the "green roofs" covered with plants. This is not because they are simply white in color but because they are specially designed and lined with the appropriate materials to reflect part of the solar radiation by sending it back to space. In an urban center where concrete is "boiling" in the summer months, this has been proven to offer multiple beneficial effects.
By absorbing less heat the buildings are cooler both abroad and inside, causing both the temperature in the surrounding area to fall and their residents' air conditioning costs. Some scientists even argue that the adoption of reflective roofs and surfaces on a large scale can change the leucygia (or altitude, the "measure" of reflectivity) of the Earth as an effective geomechanical approach to the fight against the greenhouse effect and its "braking" Climate change.
Despite all these virtues, no one had ever thought of looking at the effect of cold rooftops on the conditions of "normal" summer heat but on those of the heat seasons. This was done by researchers from the Laurens Liebherr National Laboratory (also known as the Berkeley Lab) in Guangdong, China in collaboration with Chinese researchers. As described in their study in Environmental Science and Technology, they saw that during a heat wave the reflective roofs are even more protective, reducing the temperature of the environment and smoothening the thermal urban islet phenomenon significantly more than in Periods of simple heat.
Better in the heat
Using a local climate model coupled with an urban model that allowed them to adjust the reflectivity of the roofs, experts found that the average urban temperature at midday with cold roofs fell by 1.2 ° C in hot conditions, 50% more Than in conditions of normal summer heat. "The more heat it does, the more cool we get with the cold roofs and the difference is important in relation to the margin of error," said Dee Milstain of the Berkeley Lab, head of the study. "We have seen that one of the main factors responsible for this is the suffocating conditions of the heatwave, during which the air" sits "over the city."
As far as the thermal urban islet phenomenon is concerned, the results were also significantly improved in the extreme heat conditions compared to the usual summer temperatures. "Considering the average temperature difference of each square on the map of the city compared to its adjacent rural areas, we saw that cold roofs had a more dramatic effect, keeping the differences in significantly lower levels during the heat wave," he said. Milstein.
As the researchers explain, they chose to study the benefits of cold roofs in heat conditions for the sake of protecting public health and energy "vigor". "In these circumstances, lowering of the higher temperatures can have the greatest health benefits," said Mr Milstein. "Then, too, the grid gets the most pressure, with the air conditioners working in full continually.
So a slight change in the temperature range can have a much greater effect. " The researcher, however, underlined that the study was based on the assumption that - although "aged" and thus less efficient - all the rooftops of a city are cold. And this is still a long way from reality ...

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