cost-effective

能不能降低安全空气的价格而不牺牲效果?

我开始做DIY空气净化器之后,很快就有人冒出来模仿我的DIY。我不介意,因为我把制作说明发布到网上,所以谁都可以做,并不是一定要用我的。不过,我看到两家价格比我便宜,还说我太贵了!

作为一个书呆子,我第一反应是要研究。所以我订了他们的货,发现他们用的风扇更小,而用的HEPA捕捉颗粒效果特别低。HEPA一般能捕捉99%的0.3微米及以上的颗粒;我发现这个更便宜的HEPA捕捉了85.8%(测试)。

有没有办法让HEPA再便宜?

不过,如果能有同样效果但更便宜的HEPA就更好了。所以我开始测试宽度稍微小一点的HEPA。为什么呢?因为HEPA能便宜6%,但是宽度还足够盖上风扇的出风口。

测试

作为一个书呆子,我还是想先去测试,以确认效果没有降低。所以我用DIY 1.0 + 29mm HEPA做了10次过夜房间测试,然后跟我之前发布30mm HEPA的测试比较了

测试是在北京的15㎡卧室里做的。空气测试仪是一台Dylos DC1700,能测到0.5微米颗粒(手提空气测试仪跟大使馆官方测试仪相比,准不准?)。

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为了算效果,我算了起床之前最后4个小时的颗粒污染浓度,然后跟没开净化器的时候比较。同时我记录了外面的PM 2.5数据。以下是其中一天测试:

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结果

10次测试,DIY 1.0 + 29mm HEPA平均减少了86%的0.5微米颗粒和91%的2.5微米颗粒。

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这个测试结果是说明29mm的HEPA效果跟30mm HEPA没有区别。所以我把HEPA的价格降低6%,从80元到75元。书呆子这回高兴了!

HEPA价格对比

从性价比看,淘宝上Blue Air HEPA要359元,IQ Air要2,150元(还有长期使用成本对比)。

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书呆子注释:实验重做

做实验的时候,科学家注重replication(重做)。如果一个现象是真的,应该能在不同的实验当中重做而得到类似的结果。虽然做这次测试的时候,重做不是主要的目标,这系列的测试是我测试DIY 1.0的第三个系列的测试 (包括早期测试200天长期寿命测试)。再加上美国医生Dr. Saint Cyr的测试,被重做的次数已经足够。

公开数据

跟之前一样,为了其他学霸同胞们,我发在下面布了原始数据和测试方法细节。

原始数据

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户外PM 2.5的波动

我觉得这种几个小时的测试比常见的20分钟测试(比如CADR测试)更好,因为这是我们用空气净化器的更常见的方式。不过,八个小时测试的短处是,做测试的时候,外面的PM 2.5有可能会上升或者下降。如果外面PM 2.5下降,会夸大净化器的效果。如果外面PM 2.5上升,会低估净化器的效果。

如果算10次测试的平均值,这些波动应该会互相取消,但是还是值得分析数据,确定外面PM 2.5的波动没有影响结果。这10次测试当中,两天(9/25和11/10)的PM 2.5数据有比较大的波动。我去掉这两天的数据之后,平均消除的颗粒数据基本没变:84%的0.5微米颗粒和91%的2.5微米颗粒。

测试中户外PM 2.5

也值得看看测试的那10天,外面PM 2.5是不是跟北京平常PM 2.5水平一样。这10次测试的时候,外面PM 2.5平均值是116微克。这个比北京近5年的平均PM 2.5高差不多20微克(以我分析的美国大使馆PM 2.5数据为准)。所以这些测试能够代表北京常见的PM 2.5水平或者甚至更高的水平。

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新的测试!450元DIY大炮和8千元IQ Air直接对比

去年北京空气超标的时候,我掏出信用卡,准备把8千块给IQ Air公司。不过,这个价格让我怀疑。净化器是必须那么贵吗?

我开始研究,然后发现其实净化器捕捉颗粒污染最重要的配件是HEPA滤网,而HEPA是美国20世纪40年代的发明。所以我DIY了自己的净化器并开始做测试

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后来我就很好奇:我DIY的净化器能像8千块的IQ Air一样捕捉颗粒?IQ Air是市场上最贵的净化器之一,而他们的广告说《保证:最干净的空气》。再加上,IQ Air的耗电有DIY大炮的两倍,所以IQ Air应该能捕捉更多的颗粒:

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测试方法

有一位好人借给我借他的IQ Air Health Pro (8,000元),而我做了11次测试。然后我比较了Blue Air 203/270E (3,600元), Philips AC4072 (3,000元), DIY 1.0 (200元)和大炮 (450元)。

所有的测试是开净化器的最高档,在同样的15㎡的北京公寓,同一个激光测试仪和同样的测试时间范围(过夜)。我为了算效果,我算了房间没开净化器和开净化器之后的颗粒。测试仪能测两种颗粒大小:0.5微米和以上的颗粒和2.5微米和以上。(详细测试方法

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结果

IQ Air平均消除91%的0.5微米颗粒和95%的2.5微米颗粒。这个效果不错,但是没有比大炮高:

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这个结果出乎我的意料,尤其是因为IQ Air的噪音感觉明显比大炮大:

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因为我之前的测试条件都是一样的,我们可以比较我之前测试的品牌:

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结论

所有的净化器都减少了我的卧室里的颗粒污染,但是450元的大炮消除的颗粒跟名牌净化器一样多。连200元的DIY 1.0效果跟Blue Air只差6%的0.5微米颗粒和4%的2.5微米颗粒。

价格越高 = 效果越高?

450元的大炮捕捉的颗粒最多,但是就算只看大牌子,好像价格和效果没有关系。最便宜的牌子是飞利浦,但是飞利浦消除的颗粒最多:

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这个结论跟美国医生Dr. Saint Cyr的口罩密封测试数据一样:

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按他的数据,6元的3M口罩(像我现在用的)效果比我之前用的349元Respro口罩好。而且,以Respro的价格,我可以买58个3M 9501口罩,而挡住更多的颗粒:

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总的来说,干净的空气不需要花几千块,不管是在你的卧室里还是你的脸上。

跟我之前的测试一样,为了书呆子同胞们,我在帖子结尾处发布原始数据和测试方法。还有,我在其它的帖子会讨论净化器其它的方面:换滤网的长期费用,气体效果和功能。

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Finally! Directly comparable tests: DIY versus Blue 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 wanted to know for a long time whether the DIY filter is as effective as the Ferrari filters. In an earlier post, I compared my data to the tests of Dr. Saint Cyr (whose excellent posts inspired me to look into filters in the first place). But I noted that the comparisons were far from perfect because:

  1. The rooms were different.
  2. The Cyr post did not specify how long the tests were (and that can make a big difference if you’re looking at times under an hour–see this time comparison).
  3. The Cyr post did not describe the particle counter or particle size.

But now I finally have directly comparable data! That’s because two kind souls donated a Blue Air 203/270E (3,600 RMB) and a Philips AC4072 (3, 000 RMB). That means I could finally test the DIY against expensive brands in the same room, for the same amount of time, with the same particle counter.

To do that, Anna ran 11 overnight tests with the Blue Air and 9 tests with the Philips. As always, I calculated effectiveness as percent reduction in particulates from the room air. Anna tested the air before she turned on the air filter, and then set the particle counter to take hourly measurements of the air in her 15 m2 room. Anna used the highest setting on each filter. (As always, I’m putting the original data and more details about the methods for fellow nerds at the end of this post.)

And (drumroll!) here are the results:

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The Cannon removed as much particulate as the expensive machines. Not bad for 450 RMB!

Yet all four filters were making the room air significantly cleaner. For particles 2.5 microns and above, all four removed over 90%. For particles 0.5 microns and bigger, all four removed over 80%. I’m not the first person to say: All you need to significantly reduce the particulate pollution in your home is a simple HEPA filter.

Based on the data, here’s how much you’re paying for each percentage reduction in 0.5 micron particles:

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(And that’s not counting the cost of the exorbitantly priced replacement filters.)

Recently, a Chinese news article claimed air filter companies are making “falsely inflated profits.” That fits with this data showing that the cannon removes more particulates than the Blue Air, yet costs 1/10th per percentage of 0.5 micron reduction. Similarly, the original DIY removes 4% less 2.5 micron particulate and 6% less 0.5 micron particulate than the Blue Air on average, yet the Blue Air costs more than 16 times as much.

Conclusion: You can remove particulate pollution from the air in your home and pay far less than a Blue Air or Philips.

Now, as I’ve said before, particulates are not everything. There are also gases like radon and carbon monoxide (although I’m less concerned about those). People who suspect that their homes may have harmful gases (particularly people whose homes are being remodeled) can get home tests done for gases from Pure Living China. It’s not cheap, but I’d consider it if I had a baby at home.

As always, I’m posting the original data and detailed methods for fellow nerds.

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More Comparisons

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.

Dr. Saint Cyr recently pointed me to great tests of air purifiers from the Shanghai Consumer Protection Bureau:

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The reason this type of research is so badly needed is that Western research (like this report from Consumer Reports) focuses on allergens, not general industrial air pollution. Allergens are probably more relevant for most Americans, but for those of us living in China, particulate air pollution is the real problem. And a lot of smog is smaller than pollen:

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Thus, I was excited to see research that focused on PM 2.5 here in China (results here, in Chinese). In removing PM 2.5, 17 out of 22 models removed more than 90% of PM 2.5 in just 20 minutes in a 30-square-meter room. Pretty good!

Yet even the cheapest of the “non-famous” brands cost about 1,500 RMB. For that price, you could make 9 of my DIY filters, and that’s before eating the cost of proprietary replacement filters (US$200 a piece at IQ Air). Even with these cheaper brands, I still think consumers lack a truly affordable way to get clean air. Using the consumer bureau’s results, I calculated how much you’re paying for each percent reduction in PM 2.5.

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Now, their tests weren’t perfect. The biggest downside I see is that they used cigarette smoke as the PM 2.5 source, rather than outside air. It’s not clear to me if cigarette smoke behaves the same as smog in filters. Also, many filters were less effective at removing the formaldehyde that they released in the room. That said, I don’t know how much formaldehyde is in the air normally.

But these results from Dr. Saint Cyr do use ambient air pollution in China (as do mine 1, 2). In tests with doors closed and the filters at their highest settings, Dr. Saint Cyr’s two Alen Air filters, Blueair, and IQ Air all got rid of at least 95% of PM .3. But the Alen Air A375 will set you back US$500 or RMB 5,000 imported in China. Here’s how to get the same results for 166 RMB.