Thomas First DIY Air Filter Setup

A New Way to Test Whether the DIY Works

So far, I’ve been testing air purifiers by taking a baseline measurement of particulate pollution in a room, and then turning on the purifier and testing whether the counts drop. I’ve used that method to test the DIY and more expensive machines.

DIY Purifier Test Mongolia PM2.5 Dylos

However, I recently bought a second laser particle counter, so my collaborator Gus suggested another method:

  1. Run one particle counter in the bedroom that has the purifier
  2. Run another particle counter in a different room that does NOT have a purifier.

Two Problems Solved

The benefit of this method is that the control room represents the counterfactual–what would have happened if we hadn’t turned on the air purifier. That can answer two types of “what if’s.”

1. Fluctuations in outdoor air pollution

If a northwest wind hits Beijing and makes the outdoor air a lot cleaner, we can separate the effect of the outdoor air fluctuations from the effect of the purifier. In that situation, my old method would artificially raise our estimates of effectiveness. Changes in outdoor air can also artificially lower our estimates of effectiveness if the outdoor air gets dirtier after we turn on the purifier.

In previous tests, I corrected for this by averaging over multiple tests. I also analyzed the data after removing days in which outdoor air pollution fluctuated a lot (for example, I do that sort of analysis in the extra nerd notes here).

But it’s always nice to use different types of tests to make sure an effect is real, so Gus did this experiment.

2. Particles settling in closed rooms

If you close a room, the particles–even really small particles–will slowly float down and settle out of the air.

 

Particle settling speed velocity

 

Thus, if we’re testing in a closed room at night, how do we know the purifier is causing the reduction, and not particle settling?

The Control Room Purifier Test

Gus set up one particle counter in his room and one in his kitchen: 1

He let the particle counters run for several hours, and then a timer turned on the Original DIY in his room. (The kitchen had no air purifier.) Here’s what happened:

DIY Purifier Test Control Room

The difference between the bedroom and the kitchen air quality can approximate the effect of the air purifier. It looks like Gus would have been breathing 16,000 of these 0.5 micron particles in the air in his bedroom if he hadn’t turned on his DIY purifier.

And it’s pretty clear that the kitchen air quality (where we don’t have a purifier running) is following outdoor air quality:

Indoor Air Pollution PM2.5 Versus Outdoors

(Be aware that I’m overlaying these two lines on the same graph, but the Y-axes are different. This is NOT saying that indoor air is as bad as outdoor air. Indoor air is usually cleaner than outdoor air.)

Conclusion

Similar to earlier tests, the double particle counter test shows that the DIY purifier is removing particulate pollution from the air.

As always, I’m including more details for fellow data nerds below.

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Measuring Air Purifier Noise

The new Cannon kicks butt (scientific definition of kicking butt), but it’s noisier than the Original DIY. How noisy is it? As is my habit, I wanted to answer this question scientifically.

So I bought a decibel meter:

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And I tested the Cannon, Original DIY, Blue Air 203/270E, and IQ Health Pro Plus on their highest settings from 1.95 meters away. That’s the distance between my pillow and where I put the purifiers. Here are the results:

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The cannon is noisier than I’d like, but it’s similar to the Blue Air on the high setting. To give you an idea of how loud that is, this decibel chart says that’s between “conversation at home” and “conversation in restaurant.”

It’s louder than I’d like, but fortunately I’ve found that the Cannon is still very effective on the lower settings:

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So I recommend running the cannon on a lower setting if you find it noisy.

Conclusions: 

  1. Cannon-owners can use the lower settings without sacrificing much performance.
  2. For people who are particularly sensitive to noise, the Original may be a better choice.
  3. For people who are VERY sensitive to noise, the Philips AC4072 is expensive (2,700 RMB), but it’s quite quiet on the low setting.

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

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DIY air purifier effectiveness blueair iqair philipps cheap god air purifier

Directly Comparable Tests: DIY vs Blue Air

I’ve wanted to know for a long time whether DIY air purifiers are as effective as the Ferrari filters.

DIY Air Purifier Cheap

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.

How We Tested The Air Purifiers

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.

DIY Purifier Test Method PM2.5

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 a Dylos DC1700 laser particle counter to take hourly measurements of the air in her 15m2 room.

DIY Air Purifier PM2.5 Test

Anna used the highest setting on each purifier. (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:

DIY Purifier Test BlueAir Philips IQ Air PM2.5

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:

Price versus Effectiveness DIY Air Purifier Philips Blueair

(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 as much particulate as the Blueair, yet costs about 10% 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 Blueair on average, yet the Blue Air costs more than 16 times as much.

Bottom Line: Air Purifier Test

You can remove particulate pollution from the air in your home and pay far less than a Blueair or Philips

What About Gas Pollution?

Now, as I’ve said before, particulates are not everything. There are also gases like ozone and nitrogen dioxide (although I’m less concerned about those). Here’s how to know whether your home has serious gas pollution. If it does, tests show that activated carbon removes gases like formaldehyde and benzene.

Open Data and Methods

As always, I’m posting the original data and detailed methods for fellow nerds. Don’t believe me. Check out the data and decide for yourself.

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DIY Cannon: Better, Faster, Stronger

Ever since I started my DIY filter experiments, I’ve been wondering whether I could create a super DIY by using a stronger fan. In the past three months, my collaborator Anna has helped me test a half dozen different fans. She now has a home full of fans:     … Read more

Comparing Air Purifiers

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

Independent Confirmation

Independent Confirmation. I’ve always suspected that what I’ve “discovered” is so basic that people must’ve known about this before. Lo and behold, doctors at the University of Michigan recommend that people who suffer from allergies make a purifier for $25 with a furnace filter and a box fan.   Getting independent … Read more

DIY Purifier Tests

How do I know if a DIY purifier works? I think you can break this down into two questions: Is the air coming out of the DIY purifier clean? The test results are as clear as can be. The DIY purifier shoots out very clean air. But is that enough to actually … Read more

DIY Air Outlet Tests

I made a video to show if the air coming out of the HEPA filter of my DIY is clean. See the filter in action. This settles that the air is coming out clean. But is that enough to actually clean the room air? See the room test data and how it compares … Read more

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