Cool roofs reduce the heat

It is known that the so-called “cold roofs (cool roofs) have been life-saving action… the summer season: give more freshness to the interiors of the buildings while at the same time reducing the phenomenon of heat urban island – fight so to a degree the tendency of inner cities to show higher temperatures than the countryside that surrounds it. Now a study from China finds for the first time that this effect is significantly greater during periods of heat wave. That comes to add yet another “point” in favour of a reflective roof, which anyway are last in upward trend in the context of energy saving and combating climate change.
“Repulse” of radiation
The reflective roofs, also known as “cold” or “white” roofs, though highly eco-friendly vary from covered with plants “green roofs”. This is not because they have just white color but why is it specially designed and coated with appropriate materials so as to reflect part of the solar radiation, sending it back into Space. In an urban center where the concrete is boiling” in the summer months this has proven that it offers multiple beneficial effects.
Absorbing less heat in the buildings is more cool on the outside but on the inside, with the result that “falling” so the temperature in the surrounding area as well as the costs of their residents for air conditioning.
Some scientists even argue that the adoption of reflective roofs and surfaces on a large scale can change the albedo (or άλβεδο, the “measure of reflectivity) of the Earth being an effective geoengineering approach to combating the greenhouse effect and the “braking” of climate change.
In spite of all these virtues, no one had thought to consider what effect the cold roofs not on the conditions in the “normal” summer heat, but in those periods of heat. This made researchers from the annex of the National Laboratory Lawrence Livermore of the united states (also known as Berkeley Lab) in Guangzhou, China in collaboration with chinese researchers. As they describe in their study in the journal “Environmental Science and Technology”, they saw that during a heat wave reflective roofs act even more protective, reducing the temperature of the environment and smoothing out the phenomenon of the heat urban island effect significantly longer than the periods of the simple heat.
Best in the heat
Using a model of local climate in conjunction with an urban model that they allow you to adjust the reflectivity of the roof, the experts found that the average urban temperature at noon with the cold roofs fell by 1.2 degree Celsius in conditions of heat, i.e. 50% more than normal summer heat.
“The more heat it makes, the more cooling we take the cold roofs, and the difference is significant in comparison with the margin of error,” said in a Press release Dev Μίλσταϊν from the Berkeley Lab, head of the study. “We saw that one of the main factors responsible for this are the suffocating conditions of the heat wave, during which the air is “sitting” over the city”.
With regard to the phenomenon of the heat urban island effect, the results were also significantly improved in conditions of extreme heat, compared with the usual summer temperatures. “Looking at the average temperature difference of each “square” on the map of the city in connection with the παρακείμενές of the rural areas we saw that the cool roofs were more dramatic effect, while maintaining the differences in significantly lower levels during the heat wave,” said mr Μίλσταϊν.
As explained by the researchers, have chosen to study the benefits of the cold roof in conditions of a heat wave, for reasons of protection of public health and energy “soundness”. “In these circumstances, the reduction to higher temperatures may have the greatest benefits for health,” mr Μίλσταϊν. “Then also the electric network receives the greatest pressure, with air conditioners operating at full blast incessantly.
Therefore a small change in the range of temperature can have a much greater effect”. The researcher emphasized, however, that the study was based on the assumption that – although “old” and therefore less efficient – all the roofs of a city are cold. And that is still far from reality…