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大炮能够净化多大的房间?

我测试所有能找到平面的风扇之后,

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……当中一台最突出。因为它独特的样子和它非常好的效果,我决定叫它“大炮”。

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在15m2的北京公寓,大炮大量地消除了颗粒,连很小的0.5微米颗粒也降低97%

但是在更大的房间内,效果怎么样?一般大的公司会用风量来算适用面积,但是这种算法会受到房子密封性和外面空气的污染程度的影响。因为中国的空气更脏,我觉得有必要在真实条件下做测试。

方法

幸亏我搬到大的四居室公寓,包括30.5m2的客厅。在这个客厅,我做了6次大炮高档测试。我用了激光测试仪来测试颗粒污染。每次测试持续了至少3个小时。

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我算了大炮从测试开始到最后一个小时消除百分之多少颗粒。

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这次测试跟之前做的测试有比较重要的区别:

  1. 这些测试是白天做的。很多人觉得PM 2.5是晚上最低,因为开车的人少(不过这个想法是错的,数据显示PM 2.5是晚上最高)。
  2. 这些测试是在人走动和开门的时候做的。这个比睡觉的时候的测试更保守,因为大炮要克服开门进来的脏空气。

结果

通过6次测试,即使有人走动和开门,大炮消除了92%的0.5微米颗粒和89%的2.5微米颗粒。

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这次测试有一个小意外:0.5微米的效果稍微比2.5微米效果要高。在之前做的测试,一般0.5微米的效果会低一点。我猜这是因为测试的时候有人走动,而走动对大颗粒的影响更大。

结论

大炮至少净化30.5m2的房间。这个比 3,6000元的Blue Air 203适用面积(22.3m2)要大。

跟之前一样,为了其他书呆子同胞们,我在贴子下面发布原始数据。

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净化器需要全天开着吗

测试:真的必须一整天开净化器?

有的净化器公司建议一整天开净化器,就算不在家里。真的必须一直开吗?这样是不是浪费滤网,浪费电?

测试方法

为了回答这个问题,我买了一个定时器,让我的《聪明空气大炮》每天自动开两个小时:

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为了避免人走动影响数据,我是在去旅行的时候做测试的。

卧室是13.5M²,在北京朝阳门。我设置Dylos空气测试仪每分钟测试空气。

结果

六天之后,我回家看了数据。下面的图是很小的0.5微米的颗粒:

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这6天内,北京的空气越来越差。不过,大炮每天自动开机的时候,颗粒明显下降。下降特别快,意味着大炮工作地很快。

我下面算了6天的平均效果。这样可以看大炮需要多长时间清理空气:

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结论

大炮平均10分钟内减少了50%的颗粒。20分钟内,减少80%了。

建议:像大炮的很强的空气净化器很快就能清理空气,所以我不会不在家的时候开净化器。

睡觉的时候可以关机?

这个数据也可以回答另外一个问题:有几个人问过我《我睡觉的时候不喜欢风扇的声音,所以我能不能先开一会儿,然后睡觉的时候关机?》

大炮自动关机之后,外面脏的空气马上进入房间了(虽然门和窗户一直是关着的)。一两个小时内,房间的空气跟没开净化器一样脏,所以:

建议:我不建议睡觉的时候关机。

公开数据

跟之前一样,我公布了原始数据和测试方法。我还会发布更大的房间(30.5M²)的测试,还有我在家走动的情况下的测试。

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Does Chinese New Year Affect Inside Air?

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

I’ve posted data before showing that outdoor air quality is strongly correlated with indoor particle counts (r = .71), but Chinese New Year gives nerds like me a great chance to see what happens when we get a momentary shock to air quality.

The media made a big deal about people cutting back on fireworks this year out of a concern for air quality, and that may be true, but you can still see a strong spike in PM 2.5 as Beijingers rang in the year of the horse:

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Not all that surprising. But what’s more interesting is that you can see a corresponding increase in the particle counts in my collaborator Gus’s bedroom (blue line):

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These indoor counts are without a purifier running, so they demonstrate how quickly outdoor air pollution can find its way indoors and how variable indoor air quality can be in a single room over time. Simply put: the worse the air is outside, the worse it is inside.

Yet the glass half empty can also be half full. When outdoor particulate goes down, indoor particulate can go down in a hurry. Check out what happened after the firework apocalypse ended:

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A note for fellow nerds: The indoor particle counts are not precisely on the hours, so the apparent time lag between indoor and outdoor counts may be exaggerated.

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The Really Small Stuff

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

To test how effective the DIY filter is, I’ve been posting lots of data on 2.5 micron particles. But my particle counter also measures smaller 0.5 micron particles, and I’ve been looking closely at that lately.

Remember that the “PM 2.5” you hear in the news is different from the numbers on most particle counters. Laser particle counters count X particle size and above. Government machines estimate the weight (mass) of particles of X particle size and below. 

0.5 micron particles are tougher to get rid of, so how well does the DIY filter do? To answer that question, my collaborator Anna tested the DIY filter we’re shipping from Smart Air on three different nights in her home. Here’s the average amount of 0.5 micron particles the DIY filter removed, with 2.5 micron particles as a comparison:

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As with my most recent test, I calculated percent reduction compared to the room air before turning on the filter, rather than compared to outside air. This is a more rigorous and conservative way to calculate effectiveness than comparing reductions versus outside air.

Conclusion: On average, the DIY filter got 92% of the 2.5 micron particles and 84% of the 0.5 micron particles. Although 0.5 micron particles are smaller and harder to catch, the DIY filter is still getting 84% of them.

(Update from the future! Want more data? I do! These results are replicated in 200 glorious days of a longevity test here.)

As always, I’m detailing my methods for data nerds here:

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Methods: For the DIY tests, we used the same HEPA and Meidi fan we’re shipping from Smart Air. As in the tests I reported earlier, my Smart Air collaborator Anna took a baseline measurement of her bedroom air with the Dylos “beast” particle counter, then she turned on the DIY filter and switched the particle counter to take hourly measurements.

Anna took the baseline measurement before she went to bed, and she set the particle counter to take hourly measurements until she woke up in the morning. To calculate effectiveness, we averaged the 0.5 micron readings for the four hours prior to waking up, and calculated the percentage reduction from the baseline reading (before the DIY filter was turned on). As I’ve said before, I think this method of calculating effectiveness is more rigorous than calculating as reduction from outside because indoor air is cleaner than outdoor air.

As always, the DIY filter and particle counter were on opposite sides of the room. The filter was against the west wall. The particle counter was close to the east wall, on top of a sofa, like this:

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Anna’s room is 15 meters squared. The windows were closed at all times, and the bedroom door was mostly closed before Anna went to bed, and it was always closed during sleeping hours.

The raw data is here:

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If you look at the outside AQI, you’ll see that the first test (9/9) has the most stable outside AQI counts. Thus, that number is probably the most reliable. It also happens to be the average of the three numbers.

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How Safe is Indoor Air?

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

I recently had a conversation in Beijing that went something like this:

Friend: I’m not sure if I can make badminton tomorrow. I have a basketball game in the day.

Me: Oh man, do you play outside?

Friend: Nah, it’s inside.

Me: Oh, phew. Good.

Friend: Wait, why do you say that?

Me: Oh, the air is way worse outside. I used to feel like I had asthma after playing basketball outside.

Friend: Really? No, they’re not that much different. I saw it’s just 20% different.

Seeing as how nerds cannot let matters of fact go, I started using my particle counter to take measurements of inside and outside air at different locations around Beijing. This answer is important: it tells you if it’s any safer to exercise indoors and how much damage you’re doing to your lungs by choosing that seat outdoors at your favorite cafe or restaurant.

So I took measurements in six locations around Beijing, in apartments, cafes, and my gym. I only chose bad days (pollution concentration above the WHO standard of 25), and I avoided days where it rained (because rain can cause quick changes in air quality). Here’s what I found:

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On average, indoor air had only 36% of the pollution outdoors.

Things were a little worse for the smaller .5 micron particles, but still much better than outside:

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On average, indoor air had only 51% of the .5 micron particulates of outside air. My guess is that the .5 micron data was worse than 2.5 micron data because it’s easier for smaller particles to get into your home and stay suspended in the air.

There is a lot of variation between places. For the 2.5 micron particles, the locations varied from 14% to 58%. Dr. Saint Cyr also found significant variation between two apartments he lived in, 50% to 70%.

Conclusion: In terms of particulate pollution, you’re safer snagging an indoor seat and working out indoors, particularly on bad days (I’ve seen some argue that we are particularly vulnerable when we work out because we breathe more deeply than normal).

But remember that doesn’t mean indoor air is safe, just better than outside. For example, if your air at home had 40% of Beijing’s concentration last night at 11pm (8/15), you would’ve had 64 g/m3 in your home, which is more than twice the WHO standard of 25.

As usual, I’m posting more on my methods and raw data below.

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