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活性炭真的有效吗?

我发表DIY净化器制作方法的时候,我说在中国最担心的是颗粒污染–PM 2.5。HEPA滤网就能减少颗粒污染,但是颗粒污染不是一切。气体污染(比如VOC)小得都能穿过HEPA。而且VOC(挥发性有机化合物)不友善:能导致癌症、喉咙发炎、头晕和其他的作用

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担心VOC的时候,大的净化器公司说我们应该用活性炭,但是活性炭真的有效吗?

我最发表DIY说明的时候,我不想建议别人用活性炭因为我没测试过,没有数据,而且我不想盲目地相信净化器公司。所以今年我决定测试VOC看看活性炭是不是真的有效。

方法

决定之后,我很快就发现做气体测试不容易。“有害气体”不是一种自然类型。我可以买一个激光测试仪,测到某一个大小以上的所有的颗粒,但是没有一个全能的“有害气体”的测试仪。只能每种气体买一个测试仪,而这并不便宜。

所以我的科学精神让我愿意花$3,542美金买这台Industrial Scientific Ibrid MX6。 它能测到VOC、一氧化碳、二氧化硫、氢化硫和二氧化氮。

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下一步就是找到一个VOC来源。有意思的是,我在我的公寓测不到VOC,而且在我8个北京朋友的公寓里也都测不到VOC(之所以这样做,是因为我想避免让人盲目地害怕VOC)。

因为家里测不到VOC,我就找了一个VOC来源。我选了香烟因为测试证明香烟会发出VOC,比如苯甲醛

每次测试时,我在3.78m2的阳台点燃了3跟万宝路香烟。在5次测试当中,我同时我开了带有复合活性炭滤网大炮

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另外在4个控制条件测试中,我开了一台不带滤网的风扇。这样有风流,但是没有活性炭。过了大概15分钟,香烟自然灭了。灭了之后,我让风扇继续开30分钟。

结果

烟灭之后,VOC降低,比如这次测试:

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不过,真的是因为有活性炭吗?还是VOC会自然下降?

为了回答这个问题,可以比较光有风扇的控制条件测试。算所有测试的平均,大炮带活性炭的时候,VOC最高达到0.9 PPM。不带活性炭的时候,VOC达到1.5 PPM。

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烟灭了之后,大炮最快几分钟内消除了所有的VOC。不同测试平均来说,大炮在5-20分钟内就消除全部的VOC。没有活性炭的时候,30分钟之后,空气当中还有VOC。

平均算所有的测试,当烟灭的时候,活性炭平均消除了38%的VOC。再过5分钟,消除了68%。烟灭之后20分钟,VOC平均到0。

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结论

数据显示活性炭有效地减少VOC。所以我决定在淘宝开始提供这个被验证过的复合活性炭滤网

所有的人都需要活性炭吗?

如果净化器公司能说服人担心VOC而买活性炭滤网,他们赚的钱就多。虽然数据显示活性炭有效,我不想让人盲目地担心VOC而买活性炭。

为什么呢?因为我测试了13个北京的地点,然后我发现只有带有明显VOC来源才能测到VOC,比如新装修、抽烟和烧烤。而且测到VOC的地方我都闻到化学物的味道。这个有道理因为很多VOC有明显的味道,比如甲苯和 甲醛.

我不想说VOC从来不是问题。这台MX6不是世上最灵敏的测试仪。如果用其他的测试方式,结果可能不一样。不过,香港的科学家测试了不同的公寓,发现大多数不抽烟的家里没有超过危险程度的VOC。我们需要更多的这种测试。

目前为止,我在我家里不打算用活性炭,但是有几种情况值得考虑活性炭:

  1. 最近装修
  2. 最近刷墙
  3. 抽烟
  4. 异味
  5. 附近有气体污染来源(比如工厂)
  6. 呼吸道症状(比如哮喘和发炎)

有了活性炭,我还需要HEPA吗?

需要。活性炭是针对有机物,而不是广泛的颗粒物。我本来没打算测试只有活性炭的大炮,但是Anna有一天忘了加HEPA,而做了一个只有活性炭的测试。

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结果不是很漂亮–比带有HEPA的95%效果低多了。所以我不建议只用活性炭。

跟之前一样,为了其他的书呆子同胞们,我在下面发布原始数据和详细的测试方法。

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聪明空气HEPA滤网寿命测试-第130天

聪明空气HEPA滤网能用多长时间?为了回答这个问题,我的合伙人Gus仍然坚持不懈地每天开DIY 1.0,每天用空气测试仪看看净化器能减少屋里百分之多少颗粒。从一月份开始,我们的测试已经完成第130天了!(除去中间去了一趟美国)。

第90天的时候,测试数据显示第1天的效果和第90天的效果是一样的。现在测试已经完成了130天(951个小时)开机时间,HEPA这么黑了:

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结果:在第100天,HEPA的总效降低了4%。不过,HEPA还是能平均减少屋里80%的0.5微米颗粒:

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结论:

  1. 聪明空气的DIY 1.0的HEPA用了100天而没有失去一点儿效果。这100天内开机时间是729个小时,也就是平均每天8个小时(具体算下来是7.29个小时)。
  2. 在第100-第130天之间,效果降低了大约4%。这时候要换HEPA吗?我觉得这个要看个人选择。如果是我,我不会换。
  3. 你可以按每天开机几个小时算你用的HEPA的寿命。比如说,如果你每天开24小时,聪明空气的HEPA可以连续开机大概30天而保持效果不变。

之前说过,我觉得这种数字比有的大的过滤公司给的数字好,因为(1)这个测试是在中国做的,所以是以中国的空气污染程度测试出来的,(2)有具体能用多少个小时,而不是光说几个月。当然,在不同的季节,不同的公寓,不同的城市会有稍微不一样的结果。

缺陷:

  1. 这个数字不一定能用在“大炮”身上。一方面是大炮风量更大,所以HEPA会更快地捕捉颗粒。不过,我们的大炮HEPA有前过滤网。前过滤网让HEPA的寿命更长。我们接下来会做大炮HEPA寿命测试!
  2. Gus在第102天搬家了,所以测试不理想。不过,在他搬家前后,平均效果没有明显的变化(看第100天和第110天的数字)。我们将来还要重复做这个测试,让结果更可靠。

测试仍然继续!如果你想知道测试最后的结果,请加聪明空气官方微信。

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Q&A

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.

joshuaw81 提问: Hi Thomas, just started one of your cannon kits earlier today and it’s already turning gray. Already a fan of your work! Two quick questions for you: 1- I received a foam/fiber square that is white on one side and light green on the other. I’m assuming this is packaging, and not part of the filter? 2- Are these HEPA filters washable? Many thanks!

 

Hi Joshua,

Good questions! We’re actually working on a pamphlet to go along with the cannon that will answer these two questions, so it’ll be clearer in the future! But here are the answers:

  1. What’s the pre-filter for?

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The pre-filter goes behind the HEPA filter, and it catches the larger dust particles so that the HEPA will last longer. We don’t include pre-filters on the Original DIY because the fan isn’t as strong as the Cannon.

  1. Can I wash the HEPA?

Unfortunately, no. HEPAs are not washable. That’s one reason we try to keep our HEPAs as affordable as possible.

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Creative Workarounds

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.

Adam in Suzhou sent me a picture of a creative solution to a filter problem.

The fan he had at his house had an opening that was slightly larger than the HEPA. So Adam cut out a piece of cardboard to close up the edges. Great idea!QQ20160617-0

Adam says, “It’s already turned slightly gray after one night!

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Q&A

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.

passport4adragon 提问: Hi, I’m in Shanghai and recently put together your DIY purifier and bought the same fan and filter you suggested – I think it’s working! A couple of questions – 1. I bought the exact same filter you did on Taobao – how often should it be replaced if I run the purifier every night? 2. The filter came with 3 extra thinner, foamy filter pieces (if you revisit the Taobao page, I think it’s item #1, I don’t know about #3) – should I stick that in between the actual filter and the fan, or not? Thanks!

Great questions!

  1. I don’t have good data on how often the filter should be replaced. I’ve been replacing mine after the filter turns dark, but that’s just based on my intuition, not data. What I need to do is use the particle counter to test effectiveness over time and figure out at which point it starts to lose effectiveness. Hopefully I’ll have more on that later!
  2. You’re right! The filter comes with some “pre-filters.” I don’t use them, but you could use them. On the plus side, they’d probably help your HEPA last longer. On the downside, I’d be worried the pre-filters would cut down on the air flow too much, but I haven’t tested that possibility with the particle counter.
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How to Make a DIY Air Purifier

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.

Based on my research into how different filters work, I concluded that a HEPA filter is all you really need to fight particulate air pollution in China.
Given the fact fancy air purifiers run for 8,000 RMB here in Beijing, and I’m only here for a year, I thought I’d try making my own.
I’ll give details on how well it works later, but here I’ll explain how I made it:

  1. Buy a fan. It’s important that it has a flat front so that you can strap the HEPA filter to it.
    Fans with flat fronts usually have a recessed motor unit, so look for that. Here’s the one I bought for 58 RMB:

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  1. Buy a HEPA filter. I bought this one for 108 RMB, and I’ve tested it with my particle counter, so I know it works:

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  1. Pull the grating off the front of the fan. It helps if you have pliers for this. Then turn the power setting to 3 and pull the knob off.
    The knob gets in the way of the HEPA. Without the knob, I turn the fan on and off by plugging and unplugging it.

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  1. Use string to strap the HEPA filter onto the front of the fan, and you’re done!
    The metal bar in the middle will stick through the filter a little bit. You could saw the metal bar off, but my tests show it doesn’t seem to make a difference.

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Total cost, 166 RMB (US$27). Compare that to 8,000 RMB ($1,300) for the fancy purifiers here in Beijing.Your next question is probably, does it work? See a live test here.