Summer is coming, and it's the season to eat barbecue and drink beer, and we often see diners blowing air conditioners, drinking beer, and feasting on roadside stalls.
I don't know if you have observed, this kind of air conditioning fan that blows cool air is not the kind of air conditioner installed in our office or home, this air conditioning fan and outdoor spray cooling, and even the ancient "rain pavilion" and "cool hall" have the same principle, they actually use evaporative cooling.
Air-conditioned fan, outdoor spray system and rain pavilion
1. What is evaporative cooling?
Evaporative cooling is a process of cooling air through the evaporation of water, that is, water absorbs the heat of the air and evaporates to cool the air.
The drier the air, the stronger its ability to hold moisture, the greater the reduction in air temperature when spraying air with water, and the cooling effect of the air is better if the tap water or well water with a lower temperature is used.
Therefore, in a high temperature and dry environment, the use of evaporative cooling air conditioning fan to cool the air consumes much less electric energy than the use of air conditioner, so as to have a good energy-saving effect.
However, the amount of moisture that can be accommodated in the air is limited (after reaching the limit, the increase of moisture will flow out of the air in the form of liquid water), so the low temperature air temperature that can be produced by evaporative cooling is limited by this characteristic, and it is impossible to produce very low temperature air.
Second, it turns out that the ancients used evaporative cooling and refrigeration
Thousands of years ago, ancient Egypt and Persia used evaporative cooling air conditioning in the form of rooftop wind shaft "wind catchers". The "wind catcher" is set upwind, and the air flows down the wind well into the fountain in the building, and then sends the cooled air into the room.
Middle Eastern "wind catcher" with wind shield and indoor fountain (fresco from the 2nd century BC)
There are also records of evaporative cooling air conditioners in ancient China, and the Han Dynasty inventor Ding Huan invented the seven-wheel fan, "seven-wheel fan in a row of seven wheels, most of them are all diameters (Xijing Miscellaneous Records, Volume 1)", later generations used water power to drive it and introduce water flow to the position of air flow, not only provided power, but also used evaporative cooling to reduce the air temperature, making people feel "shivering, not silk and bamboo, heavenly sound and distant news (Qianlong's "Forty Scenes of the Old Summer Palace").
Similarly, there are Ziyu Pavilion and Liang Hall, there is a poem Yun "Amber red suspected of leaking rain, crystal curtain is more ventilated (Liu Yuxi "Liu Luma Water Pavilion to escape the summer")", transporting cold water to the top, and then flowing down from around the eaves to form a water curtain, which has the effect of cooling down the heat.
It is estimated that the principle of including the temple of the Old Summer Palace is forty views of Mizuki Mingse
In ancient times, the use of the principle of evaporative cooling to escape the heat and cool down in the summer is often a service that dignitaries can enjoy, and now, with the development of society, the use of electric drive refrigeration air conditioners, multi-connection has "flown into the ordinary people" family, however, evaporative cooling still has an irreplaceable role.
Evaporative cooling has changed from a very simple ventilation cooling method to an energy-saving and green technology that uses renewable energy such as dry air, which will effectively promote the realization of "carbon peaking and carbon neutrality".
Third, green and energy-saving evaporative cooling technology
In arid or semi-arid areas in the west, many industrial buildings use evaporative cooling cooling air systems to completely replace mechanical refrigeration and air conditioning systems, while in humid and semi-humid areas, dew point evaporative cooling can also be used to achieve cooling, thereby improving the working environment of the workshop.
In the era of big data, communication rooms and data centers operate uninterruptedly throughout the year, and energy consumption continues to increase, while the use of evaporative cooling technology in winter or transition season, combined with indirect evaporative cooling pre-cooling in summer, can greatly reduce the energy consumption of annual operation.
Evaporative cooling also plays an irreplaceable role in household air conditioning, in addition to the aforementioned air conditioning fan, evaporative cooling can also be combined with new household air conditioning technology.
In the Global Cooling Technology Innovation Award held in 2021, the Chinese team proposed an air conditioner scheme of "advanced vapor compression refrigeration technology integrating evaporative cooling and solar photovoltaics", which organically combined evaporative cooling, solar photovoltaic and high-efficiency refrigeration systems to achieve high efficiency and energy saving of air conditioners and precise control of indoor temperature and humidity, and won the championship from more than 2,100 teams.
This technology applies evaporative cooling to dry air as a means of regulating the indoor environment, combined with climate-adapted ventilation control technology, realizes the functions of ventilation, cooling and dehumidification, and opens up a new direction for the development of air conditioning technology.
Combining evaporative cooling, a technology with thousands of years of application history, with new technologies, the application value and energy-saving potential of evaporative cooling can be tapped, so as to contribute more wisdom, solutions and forces to global energy conservation, emission reduction and low-carbon transformation, and inject strong momentum into green development.
Global Cooling Technology Innovation Awards Ceremony
Bibliography:
[1] Kheirabadi, Masoud (1991). Iranian cities: formation and development. Austin, TX: University of Texas Press.
[2] Xu Aiqing. What are the tips of the ancients to escape the summer[J]. Science Grand View Park, 2022,No.645(13):72-75.
END
Author: Yang Zixu, postdoctoral fellow in the Department of Building Technology Science, Tsinghua University
Contribution: Beijing Refrigeration Society
(Some illustrations from the Internet)
Editor-in-charge: Gollum
Source: Tadpole staves