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

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Harland

So which air cleaner out there has a functioning auto mode?

Right now, none that we’ve tested. We wrote a follow up article to this one explaining why a purifier’s auto mode isn’t reliable. In recent years sole purifiers have been released that case work with standalone particle counters. These might be more reliable, but we don’t have any data on it yet.

Harland

So it’s either run full time with all the noise, or buy a separate particle monitor and manually turn it on and off?

My problem is that I can clean the air in the room, and then the air conditioner/heater just pulls in more dirty air from outside. What we really need is a filter in the AC vent. Anything like this out there?

We’ve tested some of the 3M filter paper you can put over air conditioners. We’ve found it works fairly well (but it’s no replacement for an air purifier). You could look into getting that.

Having said that, we’ve tested whether Aircon actually brings in dirty air and it doesn’t. Although it sounds like you have a central air system which could well be bringing in dirty air

Harland

Huh, really? I thought it pulled in dirty air from outside. It doesn’t? Well that’s good… Read more »

Here’s a link to the 3M AC filter we’ve tested, although the page is only in Chinese. If you search for ‘3M Air Conditioning filter’ you should be able to find some more results!

Your observations of the Xiaomi sensor seems to be in line with what we found. We wrote up a separate article on how well the Xiaomi’s sensor performs

Harland

That writeup is for the sensor for the Xiaomi 2. This is the Xiaomi 2S, which has a different sensor.

Harland

Thanks for the link, I bought the filter paper.

The Xiaomi 2S appears to be doing okay. You can’t use the auto mode as the onboard sensor records values much too low and the auto mode’s thresholds are too high. What you can do is go to ‘automation’ and set your own thresholds. I set it to go to ‘favorites’ i.e. high when PM25 reaches 10, and turn back to ‘auto’ at 3. This appears to work.

Fe Ev

Does the automation work with an iphone or only android?

Fe Ev

Does this trick work? At what speed do you have it turn on when pm2.5 gets to 10? And it stays at that speed or goes into auto?

Ray

Hi Thomas, It was a really thorough and detail test. It’s really insightful. I couldn’t … Read more »

Hi Ray, great feedback and thoughts! We have tested the 2S built in particle counter, you can read about the Xiaomi Mi 2 air quality monitor tests we did here. What we haven’t tested is the Mi 2S particle counter. We want to get round to testing that soon, so stay tuned!

Supun

the model 2 Has poor particle measure sensor. Could you please test again with xiaomi pm2.5 Air detector and use this detector to control the mi air purifier 2 In automatiom mode. Is it will be better or not?

Apiwat

It is not designed to run at full power mode all the time. It will break your machine. The actual problem is that it has insufficient air cleaning power for your environment. You should make your room more air-tight by adding rubber seals on your windows and doors.

My room is 30m^3 in Bangkok. And it is more than sufficient for me. The PM2.5 value always below 10 μg/m^3. Sometimes it is even as low as 1 μg/m^3.

Toby

Hi all. I currently have a Cannon, a DIY , a Xiaomi 2S , and I just got a Xiaomi Pro. I never had an… Read more »

Danny

Only the 2S does not switch back to auto. The PRO always switches back to auto. Don’t get the PRO, get the 2S.

Dom

I just bought a pro. No issues with it switching back to auto mode, maybe they’ve fixed this i… Read more »

Joe

Xiaomi air purifier works well at a low cost. The new ones 2S and Pro do not have issue with automat… Read more »

Great writeup Joe, you’ve hit a lot of the main points! The biggest concerns we (Smart Air) ha… Read more »

Bor

Hi guys,

Does anyone have information if Xiaomi have plans to change the Chinese standard for clean air to European standard? Changing the location to Europe in the Mi Home app did not affect the criteria when the fan speed should be increased. I am aware that I can automate the process by setting “Switch to My Favorite mode” when the PM2.5 quantity is >25mg/m3 but I was wondering if this is going to be somehow automated by the purifier itself.

Paul The Rock

Maybe not until these units will be officially sold in Europe… Now they are sold only in China, so they are settled to their standard…

dale

what blue air models were used in these tests?

Hi Dale, good question! The Blue Air we used in our tests was the Blue Air 203/270E. You can find more details specific to the efficiency tests we did on the Blue Air and the other models in this post.

Vladimir Angelov

Can I turn off the wifi somehow?

Not that I know of, I think the WiFi on the Xiaomi is programmed ‘on’. In fact, it’s impossible to control the purifier fully without the WiFi turned on and the app installed. Without WiFi you’d only be able to toggle between the three modes: ‘favorite mode’, ‘auto mode’ and ‘sleep mode’.

Hardik

After testing the mi2 purifiers (2 of them) this is the conclusion.
The device will work all night long as long as you set the speed no higher than (22).
If you increase speed above 22, then the 3 hour cut off kicks in, but 22 or lower seems to be working all night.
You can test it out and share the results.
also this is running on the current firmware, maybe that makes a difference.

Umesh

What about decibel levels, can one sleep on 22 speed setting?