Thomas Talhelm – Page 16

Is a 30 RMB HEPA Reliable?

2020-07-152015-02-01 by Thomas Talhelm

After I published directions for how to make your own purifier, people asked me: “Which HEPAs should I use? Is this one trustworthy?”

That’s the type of question that makes a nerd like me happy because it means we need to get more data. So I ordered HEPAs from every manufacturer I could find, and I tested them all. After all the testing was done, I found I could ship the HEPAs that worked best for 80 RMB, which was cheaper than the 110 RMB HEPAs I was buying–quality and price!

Can HEPAs be even Cheaper?

Later I found HEPAs for 20 RMB wholesale. I was excited. If HEPAs are that cheap, we can make the DIY even cheaper!

But the test data was terrible. These HEPAs weren’t anywhere close to getting 99% of particles, so I passed on them. If didn’t want to use it in my home, why would I want to ship them to other people?

A 99.97% HEPA for 30 RMB?

Thus I wasn’t surprised a couple weeks ago when I saw a store on Taobao selling HEPAs for 30 RMB and claiming that my HEPAs are 暴利 (aggressively overpriced). They claim that their HEPAs get 99.97% of particles, and if that’s true, maybe these were the holy grail of HEPAs I was looking for all along!

So I ordered two online and put them to the test. The first shock was seeing that it doesn’t have a frame:

That makes it harder retain its shape, but it might still be effective without a frame, so I put it through the tests.

Air Outlet Test

First, I tested it by putting it on the Cannon and testing the air coming out of the HEPA with a Met One Aerocet 531S. (The Met One is useful because it has a pump to regulate airflow. In air outlet tests, the particle counter is sitting in a stream of air, so using a pump maintains constant readings.)

The results weren’t pretty. Smart Air HEPAs got over 99.9% of particles, but the 30 RMB HEPA was below 90%–far below their claim of 99.97%.

Air Speed

But particle effectiveness isn’t everything. A HEPA in the 80% range might work better if it has better air flow. In that case, maybe the HEPA could process the air more times and clean the room air as well as a real HEPA.

To test that possibility, I put each HEPA on the Cannon and used a tool to measure air speed (fancy name “anemometer”). I placed the anemometer on the HEPA at four locations (left, right, top, bottom) and took the average air speed.

Again, the results weren’t pretty. So not only was the 30 RMB HEPA getting far fewer particles, it was letting much less air through.

Conclusion

Quality HEPAs for 30 RMB are still a dream. They’re not useless, but using this 30 RMB HEPA would expose people to significantly more particles.

I still hold out hope that manufacturers will be able to innovate cheaper HEPAs without sacrificing quality, but I haven’t seen those HEPAs yet.

Is the Taobao Store Owner Being Dishonest?

The 30 RMB HEPA store makes claims that their HEPAs get 99.97% of particles, and the data clearly contradicts that, so it’s tempting to think that they’re lying.

But are they? I don’t know what’s in their mind, but my guess is that they simply didn’t go through the hassle of buying a particle counter and testing the HEPAs. I suspect that half of what seems like dishonesty on Taobao is actually just sloppiness.

As usual, I’m posting the raw data below.

Does Adding a Carbon Layer Reduce Particulate Effectiveness?

2020-07-152015-01-13 by Thomas Talhelm

I recently published tests showing that carbon actually removes VOCs. But adding that carbon layer raises a question: adding carbon means the fan has to power through yet another layer of resistance. Does that make purifier less effective at removing particulates?

Test Method

To test this question, I ran 10 room tests with the Cannon and 10 tests with the Original DIY in the same 15m2 Beijing apartment as my earlier tests without a carbon layer.

I measured how much particulate it removed with a Dylos particle counter and compared the particle counts (1) before I turned on the purifier at night and (2) the average of the last four hours before I woke up in the morning.

Carbon vs. HEPA Results

With the additional charcoal layer, the Cannon particulate effectiveness dropped 1-2%. Thus, charcoal has a very minor negative effect on the Cannon.

However, the Original DIY had a harder time powering through the extra layer. Its 0.5 micron effectiveness dropped 19%, and 2.5 micron effectiveness dropped 15%.

Conclusion: Carbon Tips

For people who need carbon (and that may not be everyone), I would recommend adding the carbon to the Cannon, but I would think twice about adding carbon to the Original. One workaround is to have one Original fan running with a HEPA and another running with a carbon filter.

As always, I’m posting the raw data and more details on the test for fellow nerds below.

Can DIY Air Purifiers Clean Large Rooms?

2020-09-252014-12-31 by Thomas Talhelm

Can DIY air purifiers clean large rooms? Hundreds of hours of Smart Air tests have found that DIY air purifiers cut fine particulate, reduce smoke, remain effective over 200 days, and even capture chemicals like formaldehyde. But an important practical question is whether DIY purifiers are effective enough to purify large rooms.

DIY Air Purifier Search

To answer this question, I tested every fan I could find, as long as it had a flat front. I was looking for a fan that put out a lot of air.

After getting all the data, of one fan stood out above the rest. I called it “the Cannon.”

In Anna’s 15m2 Beijing bedroom, it crushed particulates. It removed 97% of the small .5 microns particles.

But how well can it do in larger rooms? Most companies estimate this using flow rate, but those calculations depend on how well houses are sealed and how dirty the air outside is. I wanted to know how well a DIY air purifier can clean under real-world conditions.

DIY Air Purifiers Clean Large Rooms: The Test

I tested the Cannon on its high setting six times in a 30.5m2 living room–a large, open space. To track pollution, I measured 0.5 and 2.5 micron particles using a Dylos laser particle counter. Each test lasted at least three hours.

I calculated the percentage reduction in particles from the first hour to the last hour.

Besides testing in a big space, this experiment extends the findings of the earlier room tests because:

1. These tests were run in the daytime. Several people have the intuition that pollution goes down at night because people are less active and fewer cars are on the road (but the data shows that intuition is false–PM2.5 pollution is worst in the middle of the night in Beijing).

2. These tests were run while people were moving around in the room and opening the door to the outside. This is more conservative than the nighttime tests because the Cannon has to fight influxes of outdoor air.

DIY Air Purifiers Clean Large Rooms Effectively

Over six tests, the Cannon removed 92% of .5 micron particles and 89% of 2.5 micron particles even with people moving around and opening doors.

In previous tests, 2.5 micron reductions were usually slightly larger than .5 micron reductions, so it’s a little surprising that the 2.5 micron reduction was 3% lower than the .5 micron reduction. My guess is that this is because people were moving in the room, and human movement affects the 2.5 micron readings much more than the .5 micron readings.

Bottom Line

Bottom Line:

With a fan as strong as the Cannon, DIY air purifiers clean large rooms effectively, reducing 0.5 micron particles 92% on average.

Smart Air

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

Is Guangzhou’s Air Safe?

2020-07-152014-09-27 by Thomas Talhelm

Beijing’s air pollution is the most famous in China, but that can make people in some other cities think their air is good–at least, not as bad as Beijing’s. But is the air in other cities safe? In 2013, Shanghai had newsworthy air pollution that convinced many people in Shanghai …

HEPA Longevity Test: 170 Days

2024-05-062014-09-06 by Thomas Talhelm

When I started Smart Air, a lot of people asked me how long the HEPAs last. Several people criticized the DIY on Zhihu because they said you’d probably have to change the HEPA so often that it’d end up being more expensive than the expensive brands. At the time, I …

Who’s Breathing Smart Air?

2020-07-152014-08-18 by Thomas Talhelm

Destination of orders shipped from Taobao 9/2013 through 7/2014.

How Long Do Smart Air HEPAs Last? Longevity Test Day 130

2020-07-152014-07-11 by Thomas Talhelm

How long do Smart Air HEPAs last? My quest to give a solid empirical answer has now completed 130 days! Gus is still dutifully tracking the effectiveness of the HEPA he’s been using in his bedroom since January (with a trip to the US in the middle), calculating the percent …

Are All DIYs the Same? Poor Results from Huanwo Lantian

2020-07-272014-06-06 by Thomas Talhelm

When I did my first experiments, several people told me not to publish the data. “Don’t give it away for free,” they told me. “Use it to make money!” I decided then that my main goal wasn’t to make money. I almost got tricked into paying $1,000 for clean air, and I wanted to help people avoid getting tricked too, so I published the data anyway.

Of course, publishing the instructions online has made it easy for people to copy the idea. The Huanwo Lantian (还我蓝天) was one of the first to follow in our footsteps, selling a DIY filter a few months back. They even use a screen capture of Smart Air co-founder Gus’s appearance on Chinese TV on their shop:

I was curious to see how their filter works, so I decided to order one off of Taobao and put it to the test.

Now I’m in an awkward position because I found that their HEPA was not working nearly as well as my Smart Air HEPAs. It’s awkward because, if I publish the data, will people think I’m just trying to attack a competitor?

In the end, I think it’s better to publish the results and be honest about my conflict of interest. At the very least, I think people have an interest in knowing how well other DIYs work–especially when some of those websites use graphs that are lifted from my site, which can mislead people into thinking the test results are from their machines.

And as always, I’m publishing my raw data and testing methods at the end of this post, so fellow nerds can replicate my studies.

DIY Purifier Test Method

My collaborator Anna used the same methods as our earlier tests in her 15m2 room. Anna did five overnight tests with the same Dylos Pro particle counter, and I calculated effectiveness as the percent reduction of particles in the room air, averaging the last three hours (more info). Then I compared the results to my earlier tests in the same room.

Imitation DIY Purifier Results

The Huanwo Lantian DIY removed 21% fewer particles 0.5 microns and above and 11% less 2.5 micron particles than the Original DIY.

Is It The Fan?

The Huanwo Lantian fan is slightly smaller than the Smart Air Original, so one explanation could be that the fan is just moving less air. Anna tested that by strapping the Huanwo Lantian HEPA onto our Original fan.

Here’s what that test showed.

There wasn’t much difference. With the new fan, it was getting 4% more 0.5 micron particles and 2% less 2.5 micron particles. Thus, the fan doesn’t seem to be the reason.

Is It The HEPA Filter?

The second possibility is that the Huanwo Lantian HEPA isn’t as good. Anna tested the HEPA by doing air outlet tests with a Met One GT-521, which measures down to 0.3 microns. Anna tested the air coming out of the HEPA for 10 seconds, and I averaged the results from three tests. (More details at the end of the post.)

The Huanwo Lantian HEPA captured 7% fewer particles that the Smart Air HEPA. Thus, the major source of the poor performance of the Huanwo Lantian seems to be the quality of the filter.

Bottom Line

Bottom Line:

In room tests, the Huanwo Lantian DIY removes 21% less particulate than the Original DIY, and the data suggests that the reason is that it uses a lower quality HEPA filter.

Smart Air

Now, don’t get me wrong. The Huanwo Lantian DIY purifier is making the room air cleaner. It demonstrates yet again that DIY air purifiers work. I’d rather have a Huanwo Lantian than nothing. But the results show that this DIY copycat is cutting corners by using cheap HEPAs.

As always, I’m posting the raw data and more detail on the methods for fellow nerds.

Smart Air on PRI/NPR

2020-07-152014-06-03 by Thomas Talhelm

As a nerd who grew up listening to NPR, I was psyched to see Smart Air on NPR/PRI’s The World today! PRI journalist Rebecca Kanthor visited our Shanghai workshop and took audio with Henry and Gus.

How Long Do Smart Air HEPAs Last? At Least 90 Days

2024-04-082014-05-20 by Thomas Talhelm

The most frequent question people ask me these days is: how long does the HEPA last? This question is important because replacement HEPAs are the biggest long-term cost of clean air. IQ Air charges $370 for its filters. So if you have to replace the HEPA every two weeks, the DIY might …