cost-effective

Is it possible to lower the cost of clean air without sacrificing effectiveness?

A few months after I published my DIY tests, there were already Taobao stores up and running, selling DIYs even cheaper than my 200 RMB. I was intrigued. If we could really lower the cost of clean air, that’s a win!

But we have to be sure these cheaper machines are as effective. So I ordered the cheaper machines, tested them systematically, and found they performed much worse (2).

A New Way to Lower the Cost of Clean Air

But that doesn’t mean there aren’t ways to make HEPAs even more affordable. Recently I tested one way to do that: if we can shave 1 millimeter from the size of the HEPA, we can save 6% on the price. This new size still covers the fan opening, but does it still work as well?

Method

To test this question, my collaborator Anna ran 10 overnight room tests with the 29 mm in her Beijing apartment and compared it to my earlier tests of the 30 mm HEPA in the same 15m2 room.

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Like in my earlier tests, I calculated effectiveness as the percent reduction in particulate from the start of the test to the average of the last four hours. Here’s what one of those tests looks like with the reduction calculation laid out. The blue line is indoor 0.5 micron particles; the red line is outdoor PM 2.5

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Results

On average, the new 29mm HEPA reduced 0.5 micron particle levels in the room by 86% and 2.5 micron levels by 91%. These results were almost identical to my prior results with the 30mm HEPA.

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Conclusion

This new HEPA lets us lower the cost of clean air without sacrificing any effectiveness. Win! We just lowered the price of Smart Air HEPAs from 80 RMB to 75 RMB.

HEPA Cost Comparison

Next I took that price and compared it to the two biggest brands out there, Blue Air and IQ Air. (Also check out the long-run cost comparison .)

Nerd Note on Replication

As a side note, this test is now the third series of room tests I’ve published with the Original DIY (early tests; 200-day longevity test). Add that to Dr. Saint Cyr’s tests, and I’d say that’s a satisfying amount of reproducibility.

For fellow data nerds, I’m posting the original data and more details about the test below.

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Outdoor PM 2.5 Fluctuations

I like these long tests more than the common 20-minute tests (such as CADR tests) because this mimics how most people use purifiers. However, one drawback of these long tests is that outdoor PM 2.5 levels sometimes change over the course of 8 hours. If outdoor PM 2.5 drops, that can artificially inflate effectiveness. If outdoor PM 2.5 rises, that can artificially decrease effectiveness.

These changes should cancel out over 10 tests, but it’s worthwhile to re-run the analysis while excluding days with large outdoor changes. Among these 10 tests, two days (9/25 and 11/10) had large outdoor PM 2.5 changes. Without those two days, the averages were almost identical: 84% on 0.5 micron particles and 91% on 2.5 micron particles.

Average Outdoor PM 2.5 During Tests

It’s also worthwhile to check out bad outdoor PM 2.5 was during the tests to see if these days were representative of normal Beijing air. The average outdoor PM 2.5 was 116 micrograms. That’s about 20 micrograms higher than Beijing’s average PM 2.5 over the last five years (according to my analysis of the US Embassy’s PM 2.5 data). Thus, if anything, these tests are tougher than the Beijing average.

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New Tests! Can a 450 RMB DIY remove as much particulate as a $1,000 IQ Air?

When the “airpocalypse” struck Beijing, I got out my credit card to give $1,000 to IQ Air. But the price just didn’t seem right, and I soon learned that HEPA filters are what capture particulates (even in the expensive machines), and they were invented way back in the 1940s. So I made my own and started doing tests.

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Could a fan and a HEPA remove as much particulate as an IQ Air? The IQ Air is one of the most expensive purifiers on the market, and it advertises “the cleanest air guaranteed.” On top of that, it uses more than twice as much energy as the DIY Cannon, so surely it can capture more particles?

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Methods:

Thankfully, a kind soul donated his IQ Air Health Pro (8,000 RMB), and I ran 11 room tests on the highest setting. Then I compared it to a Blue Air 203/270E (3,600 RMB), Philips AC4072 (3,000 RMB), Original DIY (200 RMB), and Cannon (450 RMB).

I tested all of the purifiers in the same 15m2 bedroom in Beijing, with the same particle counter, for the same amount of time (overnight). To calculate effectiveness, I compared the number of .5 micron and 2.5 micron particles before turning on the purifier (baseline) to the average of the last four hours before I woke up. (More methodological details here.)

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Results: 

Over 11 tests, the IQ Air removed 91% of the .5 micron particles and 95% of the 2.5 micron particles. That’s good, but not any better than the Cannon:

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I was particularly surprised because the IQ Air was noticeably louder than the Cannon:

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With this new data, we can use my earlier tests in the same room to compare the DIY to the three major brands:

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Conclusion:

All of the filters significantly reduced particulates, but the 450 RMB Cannon removed as many particles as the highest-performing big brand. Even the 200 RMB Original was only 6% behind the Blue Air on the .5 micron particles and 4% behind on the 2.5 micron particles.

More money = more effectiveness?

Among the different brands, there seems to be no relationship between price and particulate removal. The cheapest name-brand purifier was the Philips, and it removed the most particulates:

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That’s exactly what Dr. Saint Cyr found in his fit tests of pollution masks:

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According to his data, 6 RMB 3M masks like the kind I use now outperform the 349 RMB Respro masks I used to use. With the 3M 9501, I can buy 58 masks for the price of one Respro AND block a higher percentage of particles:

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Bottom line: clean air doesn’t have to cost an arm and a leg, whether it’s in your home or strapped to your face.

As always, I’m posting the raw data and more details on the testing methods below for fellow nerds. And in a follow-up post, I’ll talk about the other important ways to compare purifiers: HEPA replacement costs, gas removal, and extra features.

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Finally! Directly comparable tests: DIY versus Blue Air

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

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.