Knowledge
Knowledge

Air purifiers clean your air of harmful allergens and impurities so you can breathe healthier. Browse our top air purifiers, buying guides, and videos below and learn what to look for when you shop for an air purifier. The air purifier, also known as "air cleaner", it refers to household appliances that can absorb, decompose or transform various air pollutants (generally including PM2.5, dust, pollen, odor, formaldehyde and other decoration pollution, bacteria, allergens, etc.) and effectively improve the air cleanliness. The study also confirmed the impact of kitchen air pollution on human health.



Chinese and American scientists who took part in the study surveyed more than 20,000 farmers in Yunnan Province of China and found that the probability of lung cancer among farmers with no ventilation in their stoves was about that of those with additional chimneys or ventilation in their homes twice as much as farmers. Using an unventilated stove is similar to smoking in terms of lung cancer, the researchers said. Therefore, the market development prospect is very promising.



What is a HEPA filter?The introduction of function and principle of HEPA filter

The main purpose of the HEPA is to remove fine particles from the air, including PM2.5 (fine particles with a diameter of less than 2.5 microns). Any HEPA filter is based on a 0.5 to 5 micron thick cross fiber. The distance between fibers is about 5 to 50 microns. So how can a screen with such a large gap block particles of 0.01-0.3 microns?
When it comes to the principle of the filter, we would think of a funnel: when the diameter of the particles is larger than the gap between the fibers, the particles would be stopped by the filter. But this principle is only effective in the lower grade filter. The principle of HEPA filter is more complicated because the gap between the fibers of HEPA filter is 100 times larger than the trapped particles. If you look at the following photos, you can imagine the proportion of PM2.5 to the gap between the filter fibers:



In fact, HEPA filter "sticks" PM2.5 dust by fiber adsorption. The diameter of the fiber is about the same as that of the dust, and the "mesh" gap between the fibers is even larger. The "wide" space between the fibers allows the air flow to pass smoothly. However, due to the layer by layer arrangement, the fine particles would inevitably bump into a disorderly interweaved fiber and be absorbed. At this micro scale, the intermolecular van der Waals force between fiber and dust is enough to overcome the influence of air flow and "adhere" them together. And the particles in HEPA filter would be effectively stopped if they contact the fiber and would never leave the surface of the fiber. This is called "interception." In addition, the particles that are constantly entering the screen would be attached to the existing particles as long as they contact the particles that have been stopped. So for a long time, the fiber of the screen would accumulate one layer by one layer of particles:



After a long time, the gap between the fibers of HEPA filter would become smaller and smaller, and some gaps would disappear completely. In this way, the filtration efficiency of the filter screen would not decrease, but the air resistance of the filter screen would increase. As a result, the air volume of the air purifier or fresh air system would decrease, and the noise would increase. Therefore, the HEPA filter screen must be replaced regularly. In the picture below, we can see the particulate matter on the filter screen which has been used for several months. The higher the filter grade, the finer the fiber, and the smaller the gap between the fibers. Therefore, the higher grade filter screen is easier to be blocked, because the gap between the fibers will shrink rapidly.



The effect of HEPA filter depends on many elements: fiber diameter, fiber density and fiber material. If the fiber is very thin and dense, the particles are easier to contact the fiber. And the interception effect of different materials is not the same. In addition, the dust capacity of the filter is also very important: a good filter should effectively block PM2.5 for several months before it needs to be replaced.



Therefore, we need to pay attention to the following problems when purchasing Air Purifiers:


First: PM2.5 Filtration Efficiency ( Grade of HEPA Filter)
In order to effectively filter the PM2.5, the air purifier manufacturer usually uses H11, H12 or H13 filter. H11 filter could filter 95% of the most penetrating particles (0.1-0.3 microns), while other particles have filtration efficiency of close to 100%. H12 screen would block more than 99% of the most penetrating particles, but it would also have a greater resistance. Although H13 filter could filter 99.97% PM2.5, it would increase the wind resistance of the whole system, so it is unnecessary to use this filter in the household air purifier.

Second: Air Resistance of HEPA Filter
The higher the filtration grade of the filter, the greater the resistance. Therefore, in the air purifier, there is no need to use H13 level or above filter: such a filter has too much wind resistance, and the filtering effect is superfluous for ordinary families. The use of this filter is limited to operating room, electronic parts manufacturing, dust-free workshop and so on.

Third: Dust Capacity of HEPA Filter Screen
The PM2.5 value of air outlet tested for the first time is the most superficial data. What many users won't notice is the size of the filter. The larger and thicker filter screen generally has a large opening area, so the dust capacity will be larger, the service life would be longer, and it does not need to be replaced frequently.


Fourth: Replacement cost of HEPA filter screen
Some air purifier manufacturers would deliberately raise the price of consumables and lower the price of equipment, hoping to make more money after selling the equipment. However, the general manufacturers would tell users the replacement frequency and price of each filter, so that users could judge the replacement cost of one year. If the equipment has a washable primary filter screen, the cost of replacing the filter screen would be lower.

After understanding the principle and function of HEPA filter screen, it would be easier to choose an air purifier suitable for you.

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