When the heat hits is when those of us who live in historically cool latitudes seriously consider installing large-scale air conditioners and if not, ask France, in whose capital its underground system It seems not to be enough for what is coming our way. But there are entire cities and countries that are ahead of us in that “historically cool Europe” in terms of air conditioning.
This is the case of China: there the air conditioning of their buildings goes beyond the simple air conditioner or passive architecture: there are communities that are already cooling their shared outdoor spaces by spraying mist water from the roofs.
The rain in Seville Shanxi it’s a wonder. As explains Mao Ning, spokesperson for the Chinese Ministry of Foreign Affairs, in Yuncheng, a city in central China’s Shanxi province, there is a residential area where roofs rain: a water spray cooling system capable of reducing surface temperatures by 5 to 8 ° C in a matter of minutes. This other similar spray system called HY-WSWD report drops of up to 10°C in roof temperature and savings of 20-30% in air conditioning consumption.
Although it is a political official who shares the system, it does not seem that it is a state air conditioning policy (for the moment), but rather a solution adopted individually by several sprinkler irrigation communities, as they explain in Sina. The principle of operation is essentially the same as a evaporative air conditioner XXL, so it is neither technically revolutionary nor new. In fact, that HY-WSWD is a product that has been on sale since at least 2025.
Why is it important. To begin with, because China is the largest consumer of electricity for air conditioning on the planet and its peaks in electricity demand in summer are directly related to the use of air conditioning, as documented by the International Energy Agencywhich also warns that it will get worse: in Asia the demand for refrigeration in Asia will triple before 2050.
Any technology that reduces the temperature of the building before using the air conditioning is good news for the grid. As quantifies scienceevaporative cooling systems reduce energy consumption by 30-40% compared to conventional air conditioning systems.
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Context. We said that the system is not new, it is actually very old (for this type of technology). In the United States there are a patent from the 70s designed for industrial warehouses and discarded for residential use for aesthetic and another from the late 80’s more discreet that contemplates its application in residential, commercial and industrial buildings. Furthermore, this evaporative misting in urban areas already applied in hot and dry cities like Phoenix or Tempe (Arizona).
Although we are mentioning several American initiatives, the paradoxical reality is that China has its own architectural precedent and it is much older: more than a thousand years ago, the Hanliang Hall of Daming Palace from the Tang dynasty used a circulating cooling system: hydraulic wheels propelled cold water to the roof, letting it fall from the four eaves in the form of a curtain of water that cooled the outer perimeter of the room.
In detail. What is striking about the case is not so much the technology, but the scale: covering complete roofs of entire residential blocks to cool the building as a whole and the surrounding areas instead of concentrating the misting in specific points of outdoor comfort, as happens in so many bar terraces in the West or does the Madrid City Council itself, which has installed nebulizers in squares and streets of the city.
In this sense, it represents a paradigm shift compared to traditional split when it comes to understanding air conditioning: conventional air conditioning units do not eliminate heat, they move it from the inside to the outside through the compressor, and that residual heat is expelled by thousands of individual units. contributes to intensifying the nocturnal urban heat island. This system that is becoming fashionable in China, on the other hand, intervenes in the building’s own thermal environment (the roof exposed to the sun) before that heat generates a load that the compressor has to expel outwards again. Thus, the thermal difference between inside and outside is reduced at the source: the microdroplets expose a lot of surface area to the air, accelerating evaporation, which extracts latent heat from the roof and the surrounding air without the need for refrigerants.
Yes, but. The kryptonite of evaporative air conditioners is the humidityor in other words, this system is only effective in locations with dry climates such as Shanxi, which has a semi-arid continental climate. Of course, in cities in humid southern China like Shenzhen it would be much less effective.
In humid and hot environments, high temperatures become a real nightmare and evaporative air conditioners do not work: they raise the relative humidity, worsening thermal comfort. On the other hand, this is a system that continuously consumes water, a precious commodity that is scarce in some places, which poses a dilemma between energy savings and water stress.
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