At the end of 2019, people were caught off guard by a sudden epidemic, and many people had to stay at home to avoid the epidemic. The same is true for the editor. After arriving in Beijing early on January 31, I stayed in a rental house and waited for work to resume. I just came back to Beijing and slept all night, and my nose started to become allergic. It was so clogged and uncomfortable that I planned to buy an air purifier for my rental room.

What is an air purifier?

Air purifiers emerged when smog prevailed. In the impression of many people, air purifiers have become synonymous with “smog suction”, but in fact, the function of air purifiers is not limited to smog, it can also solve the problem of smog. Many friends have allergy problems, purify indoor air, reduce dust, reduce pet odor, and even absorb TVOC pollution such as formaldehyde and benzene in the home, making the new home faster.

The cost is less than 150 yuan!Homemade air purifier measured surprise

Why are air purifiers useful?

As a physical purification device, the principle of the air purifier is actually very simple. One motor and one filter element can be combined. When working, the motor sucks in the dirty air, makes the air pass through the filter element to be purified, and then blows the purified air out. In principle, the key to whether the air purifier is clean or not lies in the filter element and the motor.

Motor: The motor determines the amount of circulating air. The greater the motor power, the faster the speed, and the more gas that can be circulated per unit time. To a certain extent, it can be said that the purification efficiency will be faster. In air purifiers, this parameter is called “CADR clean air volume”.

Filter element: If the operation of the purifier is a chemical reaction, then the motor can be said to be the catalyst for the entire reaction, and the filter element is the reactant involved in the reaction. The quality of the filter element will directly affect the air purification effect. At present, the filter elements in the air purifiers on the market are classified according to European standards. , The common household purifiers in my country are H11~H13.

The filter element determines the purification effect: according to the material of the filter element, the filter element can also realize the purification function. If activated carbon is added to the filter element, the porous structure of activated carbon can deodorize and absorb certain harmful gases such as TVOC. However, for the filter element without activated carbon, it can only filter particulate matter, that is, small particles in the air, which are powerless against gaseous pollutants.

The filter element determines the use time: CCM is a parameter of the filter element in the purifier. It is called the cumulative purification capacity. The higher the CCM value, the more dust the purifier can inhale, and the longer the use time. The grade is P4 and the CCM value is 12000 mg.

Hot Topic: Do air purifiers work against the new coronavirus? it works.

To understand why air purifiers are effective, we must first understand why masks can effectively protect against viruses. Whether it is the national standard or the mask standard of other countries, the test of the protective effect of the mask is reflected in the filtration of PM0.3 particles by the mask. Among them, N95 and KN95 refer to the protection degree of PM0.3 particles reaching 95%, and N90 and KN90 refer to the protection degree of PM0.3 particles reaching 90%.

HEPA filter

One of the core components of the air purifier is the HEPA filter. The material of the HEPA filter (meltblown cloth) is also the key component of the protective effect of the mask. The popular air purifiers on the market have a good effect on PM0.3 particulate matter purification. At 99.97%, compared to masks, the effect of air purifiers will theoretically be better.

DIY original intention

After shopping online for several days, I still feel that it is too expensive to buy an air purifier. The price of air purifiers with slightly better parameters is 500 yuan +, which is far beyond the budget. At the same time, I also feel that it is unnecessary, so A DIY air purifier comes to mind. Speaking of which, the working principle of the purifier is actually very simple, so what about the feasibility of a DIY purifier? As long as the fan and filter element are fixed, and the airtightness is ensured, the same purification effect of the purifier can theoretically be achieved.

Purifier DIY

First of all, the DIY purifier needs to solve two key components – filter element and fan. Because most fans are prototypes, if a square filter element is selected, there will definitely be a gap that is not easy to seal between the filter element and the fan.

I took a trick and directly referred to a certain scheme and chose the more convenient Mijia cylindrical filter element. The size of the Mijia filter element is very standard, with a diameter of 200mm. You only need to buy a cylindrical fan and set it on the top, seal and fix it, and you can complete the production of a simple air purifier.

family portrait

Close-up of fan

Cost table:

150mm diameter fan (including metal cover) 55 yuan: 6-inch air volume 320m3/h

Filter element 60 yuan: imitation millet air purifier filter element H12 grade diameter 200mm

PVC variable diameter conversion head 20 yuan: 200mm to 150mm

Speed ​​regulation power cord 10 yuan

Total: 145 yuan

There is nothing to say about the DIY process, almost all of them are finished products. Even the size of the filter element is very standard. The fan directly finds the metal cover installed by the boss. After that, connect the fan and the filter element of the reducing conversion head in turn and you are done. If the connection between the reducing pipe and the filter element is not tight enough, you can wrap it with transparent tape.

Measured effect

Test environment: During the test, the outdoor PM2.5 concentration was 74 μm/m3, the indoor space size was 9 square meters, and the windows were opened for ventilation for 5 minutes. The indoor PM2.5 concentration was 66 μm/m3, the PM10 concentration was 72 μm/m3, and the PM1.0 concentration was measured. For 41μm/m3, the formaldehyde concentration has been reduced to zero due to the ventilation of the windows.

Close the window, open the DIY air purifier maximum air volume, the indoor concentration changes as follows. In nine minutes, the PM2.5 concentration was reduced to 3μm/m3, and the purification effect was quite satisfactory. However, because the filter element I purchased did not contain activated carbon, the formaldehyde concentration actually increased slightly after closing the window.

PM2.5 concentration dropped to 3μm/m3 after nine minutes

Indoor particulate matter concentrations dropped significantly after nine minutes

Noise test: The noise of the DIY purifier was tested under the ambient noise of 34dBA. The noise measured at the maximum wind speed was 49dBA. Compared with the regular air purifier with an improved air duct, the noise of the DIY purifier is louder under the same air volume. Many, although the noise at the maximum wind speed is acceptable, it is not suitable for long-term use. In daily use, it is better to open the wind speed to about half, of course, the purification efficiency will be much slower.

Noise at maximum wind speed is 49dBA

Daily use in half gear is better


The DIY purifier is quite a sense of accomplishment, and the purification effect is not bad. After using it for a few days, the allergic rhinitis has obviously improved. The key is that the price of DIY is very approachable. For my small living space, the budget is limited. friends are very suitable. But are DIY purifiers really worth it? I have another bill.

If the filter element of the DIY purifier is changed to the original Xiaomi filter element (price is 149 yuan), the cost will rise to 230 yuan.

Compared with the Mijia purifier 2s of the car price, the DIY purifier with the original filter element may have similar purification effect, but the noise control is definitely incomparable. After PM2.5 detects castration, it cannot be seen in real time after purification. In addition, the most important filter life Display cannot be checked, the filter cannot be replaced in time, and it is easy to cause secondary pollution. The price difference between the two is only 320 yuan. Isn’t it good to have so many functions?

For ordinary families, I still recommend buying a normal air purifier, which not only has a better user experience, but also looks better when placed at home, as well as a one-year warranty and so on. Of course, if you’re on a budget like me, DIY isn’t a viable option.

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