The case has been solved! It turns out that the big ball spinning on the roof is for this purpose...

On the roofs of many buildings, we often see some metal balls, which shine in the sun and seem to be out of tune with the surrounding environment. These metal balls are actually part of the unpowered hood, also known as wind balls or ventilation balls.

Today, let me tell you about the past and present of this little thing.

The function of non-powered hood

The unpowered hood is a ventilation device installed on the roof of a building , mainly used in places that require ventilation, such as residences, factories, warehouses, etc.

The ventilation ball on the roof. The picture is copyrighted by the library. Reproduction and use may cause copyright disputes.

Their main functions include:

1

Improve indoor air quality

Through natural ventilation, indoor heat, moisture, smoke and harmful gases are discharged to improve indoor air quality;

2

Lower the indoor temperature

Promote the rising and exhaust of hot air, reduce indoor temperature in summer, reduce the use of air conditioning, and save energy;

3

Preventing mold growth

Reduce indoor humidity, prevent dampness in walls and roofs, and prevent mold growth;

4

Extending the life of buildings

By reducing the erosion of building materials by moisture and harmful gases, the service life of the building can be extended.

Structure of non-powered hood

Unpowered hoods usually consist of the following parts: fan blades, wind necks, internal brackets and bearings .

The circle of arc-shaped blades we see is the result of careful scientific calculations based on the principles of aerodynamics. It not only prevents the hood from being invaded by rainwater when working, but also greatly improves the exhaust efficiency.

It can be said that the fan blade is the most important component of the entire hood.

Source of the internal structure of the hood | An e-commerce platform

The wind neck refers to the part that connects the fan blade to the base fixed on the roof of the building. The function of the wind neck is to support the fan blade and ensure that it can flexibly rotate with the change of wind direction, so as to achieve effective air flow and ventilation.

The internal bracket is the part that fixes the fan blades and the wind neck. It is usually made of aluminum alloy or nylon and can support the weight and rotation of the wind hood.

The bearing is the part that connects the hood to the roof. It is usually made of steel or copper and can ensure the stability and flexibility of the hood.

Working principle of non-powered hood

The reason why unpowered hoods are called "unpowered" is not because they do not need any power at all, but because they do not need additional electricity and are driven by natural wind . Their working principles are similar to those of range hoods and chimneys. They essentially achieve the exchange of internal and external gases through the pressure difference between indoor and outdoor gases.

Source: Internet

1

Relying on natural wind power

When the natural wind outside blows the hood, the centrifugal force of the fan blades during rotation can reduce the air pressure around it, forming a negative pressure area, that is, the air pressure inside the hood is lower than the indoor air pressure. Due to the pressure difference , part of the air flowing in the parallel direction of the room will be transformed into air flowing vertically from bottom to top, thereby pumping the stale air in the house to the outside.

2

Relying on thermal pressure difference

When the indoor temperature is higher than the outdoor temperature, the indoor high temperature gas rises and flows out, which drives the fan blades to rotate. The air velocity around the fan blades increases, the air pressure decreases, and the air in the flue rises under the pressure difference, which can also achieve the effect of extracting indoor gas.

Advantages and disadvantages of non-powered hoods

From the perspective of energy conservation and environmental protection , the unpowered hood uses natural wind for ventilation, does not require electricity, operates continuously with high efficiency and energy saving, is noiseless, spark-free, and explosion-proof; from the perspective of cost-effectiveness, the installation cost is low, maintenance is simple, and the economic benefits are significant in the long run because it reduces dependence on electricity.

Furthermore, the hood has various designs, which can increase the aesthetics of the building . Some designs, such as the spherical lotus shape, have a good decorative effect.

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

From a safety perspective , the hood can also protect the user's personal safety in special circumstances. If a fire occurs in the corridor or public area, this ventilation device can speed up the discharge of internal smoke and dust, thereby providing more escape space for those in distress and reducing the losses caused by the accident.

Of course, there are some disadvantages of non-powered hoods. For example, in areas with low wind, non-powered hoods may not operate normally, resulting in poor smoke exhaust effect; in areas with poor air quality, hoods may draw polluted outdoor air into the room, causing secondary pollution.

From this point of view, as a simple and efficient natural ventilation equipment, the unpowered hood plays an important role in improving indoor air quality, energy saving and environmental protection. Through clever design and reasonable application, it has not only achieved remarkable results in past buildings, but will also play a more important role in future green buildings.

References

[1] Li Xiajie. Optimization design of indoor natural ventilation in pit courtyards in western Henan Province[D]. Xi'an University of Architecture and Technology, 2021.

[2]https://mp.weixin.qq.com/s/MFom3jroYBb7PkPgae7D7Q

[3]https://mp.weixin.qq.com/s/8J-InLFF_BHTWaK9SghQ2Q

[4]https://mp.weixin.qq.com/s/Oagf6kTPL98B6YOduASaiw

Planning and production

Source丨Like Popular Science (id:lxkp_cstam)

Editor: Wang Mengru

Proofread by Xu Lailinlin