Evaporative cooling experimentations in urban areas
The global air conditioning market has been growing strongly since the 2000s. Air conditioner sales increased fivefold between 2000 and 2017 in China, for example . A JARN study released early this year indicates that growth is expected to continue, with a 3 % increase forecast in 2019 .
The increase in the number of devices has a double impact:
- Significant energy consumption (9 % of the annual consumption of the city of New York in 2017 ).
- An increase in greenhouse gas emissions.
Current research is moving in two directions: the development of energy-efficient appliances, or the study of alternatives to generate freshness without using any device. Evaporative cooling techniques are therefore studied, especially in cities, to avoid heat islands.
An innovative bitumen has been tested for three years in a few streets of Paris, France. It is lighter than traditional coatings, which increases the effect of albedo: it reflects the rays of the sun better and therefore absorbs less heat. In addition, this coating has good water retention capabilities. By watering it (with non-potable water), the actual temperature drop was estimated at 2 °C, and the decrease in perceived temperature at 3 °C .
A study examining the role of trees in urban climate regulation is currently under way in the United Kingdom. It is funded by the Department of Environment, Food and Rural Affairs. It has already shown that areas with a large number of trees can be 4 °C cooler than areas with no vegetation.
The most efficient trees for freshness have a large leaf area, dense crowns and high transpiration rates. Plant transpiration is the process caused by the evaporation of water from the leaves which cools ambient air. . The plane trees, the sessile oaks and the cherry trees are particularly adapted species for the city of London.
By choosing these trees and planting them near office buildings, 22 million pounds sterling could be saved each year. Energy consumption could fall by 13 % in London thanks to the phenomenon of evapotranspiration.
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