开着小米自动档有用吗?不安全的空气占86%的时间

从我开始测试DIY空气净化器,我一直说安全的空气不需要花很多钱。所以小米出1,000元以下的机器的时候,我假设效果不错。我一直没有来得及测试它;我最近终于做了测试,而结果出乎我的意料。

 

测试

Smart Air联合创始人Anna在北京朝阳门15平米卧室测试了全新的小米2 (Mi2)机器。这个卧室是我们以前测试DIY、IQ Air, Blue Air和飞利浦的房间。Anna分别做了6次自动档测试,和6次最高档测试(小米把最高档叫做“最爱档”)。

 

Minion

 

测试很简单:Anna早上出门的时候开机;回家的时候关机,所以测试的时候,没有开门开窗走来走去的干扰。(测试方法细节和所有原始数据在这儿。)

 

为了算效果,Anna用了一台Dylos Pro激光空气测试仪。这个Dylos测到≥0.5 微米和≥2.5微米颗粒。我做了对比测试发现,  Dylos 0.5微米数据跟美国大使馆PM2.5相关性很高r = .90)。

 

和我之前做的测试一样, 为了算效果,我算了(卧室里开机前的颗粒数)比 (测试最后四个小时的颗粒平均数)。

 

结果

小米的结果算是我测试过最低的之一。平均来说,消除了大概60%的0.5微米颗粒在测试的最后4个小时。

 

Xiaomi effectiveness

下面是小米的和我在同样的房间测试过的其他机器的结果比较。

 

平均消除的颗粒

 

下面是比较正常的测试,我还加上了世界卫生组织的PM2.5 24小时上限(25微克)

 

小米的房间测试

 

小米特入自模式

数据为什么这么低?关键是,就算让小米开最高档,过了三个小时之后,它就自动调成自动模式。为了确认,我们做了过夜测试,开了最高档然后用了噪音仪看看它的“工时”。

 

Room

 

可以看到,前面三个小时一直开着高档,然后可以看到自动档的上下波动:

 

xiaomi 杂音

我在下面的图加上了PM2.5数据(Dylos记录的)。可以看到每次停止运转,PM2.5上升。

 

杂音VSPM 2.5

这些数据显示小米对“安全的空气”的定义有点太宽容。PM2.5降到40微克的时候就关机,而40微克高于WHO的上限。等PM2.5到70微克的时候才开机,70是WHO上限的差不多3倍。

 

真的不能一直开着高档吗?

我觉得不能一直开着高档很奇怪,所以我让Anna问小米客服两次。客服确认了,三个小时之后就自动调成自动档(整个聊天记录在实验详细页面)。

 

Blurred

 

百分之几的时间安全线

小米的自动档经常让室内的空气在安全线的两倍以上。我算了室内空气有百分之几的时间超过安全线,用了这个规则:

 

净化器开机至少一个小时的时候,同时外面的空气不安全(PM2.5 > 25微克),有多少小时室内空气也不安全(> 25微克)?

 

以这个标准,小米开机的时候,室内空气竟然86%的时候不安全。我测试过的其他大小相似的机器,结果它们7-16%的时间超过安全线。

 

%时间不安全的空气

也许小米使用的是中国官方的PM2.5 24小时上限(35微克)。即使如此,在小米启动77%的时间里,室内的空气污染 指数还是是属于不安全的。

 

等一下,你确定确定

得到这个结论我想特别小心。我看到过其他人测试小米第一个版本,然后结果不错,包括美国医生Dr. Saint Cyr的测试。(不过,我也看到报告说小米的机器有问题,比如这个人,滤网还在塑料包装里,让小米开最高档,app还说污染立刻下降。)所以第二次第三次分析了数据(所有的数据也是公开的):

 

  1. 我们用了别的空气测试仪在别的房间做测试。
  1. 我开除了外面AQI有任何比较大的波动的测试天。
  1. 我分析了外面AQI中度或以下的测试天(< 150微克)。
  1. 我比较了这次测试和我最近在这个房间做的测试。

 

这些不同分析的方式结果都差不多(在这儿)。但我必须在此声明,我们只使用了一台小米Mi2。因此,使用另一台机器的结果有可能是不一样的。我也向所有有Mi2的网友们做用这个测试方法做重复试验。

 

那小米怎么办?

我看到这些数据只能得到一个结论:风扇和滤网好像没有问题,但是小米的设计有问题。就算我用最高档,睡呼吸不安全的空气。这是一个很重要的问题。

 

只是小米的问题吗

其实我不能建议任何测试过的自动档。我也测试过飞利浦AC4072的自动档,而它平均消除的0.5微米颗粒是59%,跟小米差不多。所以我觉得问题是广泛的自动档的问题,而不仅是小米的问题。

 

不过,我还能推荐飞利浦。为什么呢?因为飞利浦可以一直开着中档或高档,而我测试数据显示高档的效果不错

 

我相信小米可以解决这个问题,只要允许我们一直开高档,而不用强迫我们用自动模式。但是小米解决这个问题之前,我不能建议用小米。

 

公开数据

跟之前一样,为了其他书呆子同胞们,我发布了原始数据和测试方法的细节

 

The Sqair air purifier Kickstarter

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Ian

Hi,
thank you for your work!

I was thinking of buying Xiaomi Air Purifier 2S, but before I decide to buy it I would like to measure air quality in our flat.

Just checked ebay offer and found couple of devices, but I am not sure are they ok or just a waste of money and would like to hear your opinion. Professional devices are just to expensive for me.

https://www.ebay.co.uk/itm/Air-Quality-Monitor-PM2-5-PM10-Formaldehyde-HCHO-TVOC-LCD-Digital-Detector-8In1/123783741639

https://www.ebay.co.uk/itm/LED-Display-Air-Quality-Tester-Monitor-Detector-PM1-0-PM2-5-PM10-TVOC-HCHO-Test/273738083034

https://www.ebay.co.uk/itm/8In1-Air-Quality-Monitor-PM2-5-PM10-Formaldehyde-HCHO-TVOC-LCD-Digital-Detector/382825587642

I hope I didn’t break any rule by posting ebay links.

Do you have any advice regarding Air Quality Tester?

Thanks!

ryan

Hi Alex- would be great if you could test the dyson TP04 and see what results an independent test gives

Thanks for the very informative article! Was thinking of buying a Xiaomi, but I guess I’ll have a look at other brands with different specs.

Alex

The old problem of reverting to auto mode was solved in newer firmware, so the purifier can keep running 24/7 at the level you set it to. So this whole conclusion that it doesnt clean is not valid anymore. The new versions run well, very good bang for buck. I bought 4 meanwhile, one for each room, after being very satisfied with the results, I also always double check with two different PM2.5 meters, which confirm the speed of cleaning the air.

Patrick

That seams true. However the auto mode seems to treat the sensor number as AQI, while it is in fact ug/m3. A huge bug. Also the app seems ‘region locked’. I had to choose location China to be able to even seen my air purifier. Also more favorites would be very useful. Not just for simple button control, but also for more useful automation. I want to set the fan speed easily. Now that’s not possible: only options are sleep, auto and favorite…

Hey Alex! Your comment got me thinking about this, so we checked out the Xiaomi 2 we have in the Smart Air testing lab for a firmware upgrade. Sure enough, there was an upgrade available (see this pic!):
Xiaomi 2S Air purifier firmware update

However, after upgrading the firmware we found that the Xiaomi 2 still reverted to auto-mode after 3 ours. We made a video about this here

Perhaps you’ve got the newer Xiaomi 2S, which Xiaomi may well have updated. However it looks like the Xiaomi 2 is still exhibiting this problem. We’ll have to get ourselves a 2S to check it out!

Turbo

One more interesting thing what I found while using the 2s, which no one seems to have mentioned: Us… Read more »

It is the humidifier adding particles to the air and that will make the air purifier work even harder, therefore, rest assured you have excellent air when the humidifier is on as you have tricked the air purifier to work harder.

Great point Paul! We’ve tested laser particle counters, and we’ve seen that in more humid environments the pollution levels measured are higher than the real pollution levels. This could be the case for your Xiaomi!