你的空气净化器有自动模式吗?数据警告别用。

我们生活里的很多东西都越来越智能化,从手机到汽车,连空气净化器也加入了智能化大军。不过实验数据却显示智能空气净化器错误频出,经常把用户置于危险的空气中。

 

 

净化器自动模式的理想

 

空气净化器自动模式想法很简单:只有在空气不好的时候运转。这么做的好处显而易见,可以节约能源,减少噪音。

 

 

自动模式实地测试

Smart Air的共同创始人Anna测了两款流行空气净化器的自动模式:小米2和飞利浦AC4072 。

 

 

测试方法就像大多数人怎么用。在北京一个普通的15平米的卧室,Anna用13天时间每天睡觉或者白天把小米或者飞利浦净化器调到自动模式开了8-13个小时。

 

 

她用了Dylos Pro镭射颗粒物测试仪来追踪测试0.5微米和2.5微米的颗粒物。(Dylos跟官方PM2.5数据的相关性很高123)。为了算效果,我比较了开机前和醒来以前的四个小时里的平均颗粒物数据,比如12月7日的测试:

结果不健康

下面的照片是小米测试刚开始和结束的空气质量。虽然小米在密闭的房间内运转了整个晚上,空气还是在不安全的范围内。

 

 

平均来说,小米减少62%的0.5微米颗粒,飞利浦59%的0.5微米颗粒。

 

 

对比来看,这组数据还是比只单纯用个带子把过滤网绑在风扇上效果差了20%。

 

 

那机器有问题吧?

不过,会不会只是飞利浦或者小米的净化器不够好?也许他们用了不合格的过滤网,也许他们的风扇不够强力?

 

我们其他的测试表明情况并非如此。在之前的高转速测试中,飞利浦净化器的得分一直名列前茅。

 

 

小米2在高转速测试中也表现很好,但不能维持在高档的状态。真的不能维持在高档的状态吗?3个小时以后,无论用户选择与否,机器都会自己转到自动模式。

 

 

自动模式真的不安全吗?

存疑的读者可能会说:“颗粒物减少60%也并不坏啊。这还不够好吗?”

 

60%肯定比0%好,可是如果看空气污染对身体健康的影响的研究,这些水平明确对人有害。室内空气平均达到世卫组织公布的24小时PM2.5上限两倍 (这个上限还是世卫组织的宽松上限!)。

 

 

为什么自动模式这么烂?

高速运转测试表明这不是风扇或者滤网的问题。那怎么解释自动模式的问题呢?

 

原因1:内置空气质量测试仪不准的离谱

一个原因是自动模式是由内置空气质量测试仪控制的,而且测试发现小米测的跟实际PM2.5差异达到218毫克!绿色AQI和黄色AQI之间的差异才12微克

 

 

所以这些机器有时候会在空气“有毒”的时候判定空气是安全的。

 

原因2:小米对“安全空气”的定义太宽松

也有可能这些净化器只是对“安全空气”的定义过于宽松。中国设定的PM2.5上限是35微克,世卫组织的年平均上限是10微克。然而研究表明即便是20微克的差距也会对健康造成严重的影响

 

自动档须知

自动模式经常会让室内空气停留在一个远超过健康空气底线的状态。我不推荐使用自动模式 (而且因为Mi2过三个小时就强迫用户开自动档,除非改比较复杂的地理围栏设置,我不建议用Mi2。以前的Mi1没有这个问题。)

 

公开数据

跟每次一样,我把原始数据和更多测试方法细节贴出来和书呆子们分享。

 

The Sqair air purifier Kickstarter

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Cecilia

I have my Xaoimi in my bedroom with all doors and windows closed. If I open the ensuite bathroom door for just a few minutes the reading on my Xaoimi will change. Doesn’t this mean that it is detecting the bad hair from the bathroom? Which would indicate that it’s working well and doing it’s job?

Hi Cecilia! You’re right that the Xiaomi may well be detecting that the air quality has got worse since opening your bathroom door. But what we would class as ‘working well’ would be ‘providing accurate results’. We’ve found that the Xiaomi sensor isn’t accurate, so whilst it may be able to detect the trends in air pollution (like the levels increasing when you open your bathroom door), it may not be giving the actual correct reading. That’s dangerous if the purifier under-estimates the indoor air pollution (and turns itself off as a result).

David Tise

You say that the Xiaomi works fine on high setting. How then is it possible that being used in a clo… Read more »

Great question David! The answer lies in the fact that no room is ever truly ‘sealed’. Ever room will have small gaps between windows or doors, which will let in outdoor air pollution. If the clean air the purifier is pushing out isn’t enough to overcome the dirty air coming in (as is the most often case when purifiers are in auto mode) then the purifiers will never get the air in the room clean.

David Tise

Thanks for your response. As it happens, a few Xiaomi Pros became available yesterday and I went for… Read more »

Fe Ev

Hi David, I’m in your same situation in Bangkok. Would love to hear what results you are getting with fhs xiaomis. And do they also turn auto after 3 hours?

Book

Won’t the technique of putting a fan with a strapped on filter cause the fan the break? I’m pretty sure normal household fan aren’t optimised for that much pressure as the filter requires a lot of pressure to push through. Wouldn’t it just break the fan after a period of time?

You’re spot on that most household fans aren’t designed to also push air through a HEPA filter. However we’ve been shocked to find out that after shipping over 30,000 of these simple DIY filters, they work surprisingly well! I’ve heard of reports of people using their simple DIYs for over 4 years with no issues, so the answer is likely that the fan and motor are still powerful enough to push the air through, or that the air resistance of the HEPA filter isn’t so high that it damages the fan.

Luciano

Hi! So this tests applies to the Xiaomi Mi Air Purifier PRO version? This one have a Laser sensor, and I’ve been reading is really accurate… Haven’t tried max setting much… I always use it on Auto Mode and always shows less than 20 or even 10 on the screen, I live in Coslada, Madrid, Spain.

Hi Luciano! This test applies mainly to the Xiaomi 2 air purifier, however we did test the Pro Air Purifier sensor. Check out the data in our previous report explaining the accuracy the Xiaomi’s air quality sensor.

Paul The Rock

I think that there is a problem with China limits… If you look to auto mode for Xiaomi it thin… Read more »