Experiments on a $50 DIY air air purifier you may make in 30s
Bad air is bad for you. The air air purifier market, although, is a large number. Each air purifier makes use of incompatible proprietary filters, presumably to lock you into shopping for replacements. How do we all know these really work? Few appear to publish lab assessments. And why does it value $100-$300 for an enormous plastic field with a fan and a filter inside?
It’s widespread to construct DIY air purifiers by principally strapping a filter to a fan. I like the thought of those, however once more, it’s exhausting to be assured they actually work. There’s a couple of experiments on the market, however not sufficient to make me snug. So I made a decision to do some experimenting of my very own. I made a air purifier, generated smoke, and measured how properly it removes tiny particles.
TL;DR: YES IT WORKS
For those who’re in a rush, this put up says that in the event you strap two HEPA filters to a field fan, it can clear the air of principally all of the particles we will measure, and it’ll do it quicker than a industrial filter that prices twice as a lot.
The experiment
DIY air purifier
My DIY air purifier was very easy. (I don’t need to promote any explicit manufacturers right here. Contact me in order for you the precise merchandise.)
- A typical field fan. (Value: $19)
- Two HEPA air filters, every roughly 32 cm x 22 cm and 5cm thick. (Value: $35 for each)
- A bungie wire. (Value: Free)
Meeting takes about 30s. You set the filters on the consumption facet of the fan and strap them on with the bungie wire. Right here’s an image:
Timeless magnificence and charm, it isn’t. I get the shakes simply that little bit of crinkled filter.
Industrial air purifier
As a comparability, I obtained a $100 air air purifier from a widely known model that’s meant for small rooms. It makes use of makes use of a single HEPA filter that’s about 25cm x 12cm and 4cm thick. Substitute filters presently value round $25.
Smoke
It’s surprisingly exhausting to repeatedly generate a constant quantity of smoke. I attempted burning varied issues (paper, cardboard) and located that the variety of particles generated can fluctuate by an order of magnitude, relying on the burn sample. That is troublesome to regulate and successfully random.
Ideally, I’d have preferred to burn some meals product like oil, for the reason that kitchen is often the largest supply of indoor air air pollution. I couldn’t work out a great way of doing this, both: You’d must have the identical quantity of oil distributed in the identical manner and heated to the identical temperature.
I lastly settled on utilizing incense. I reduce sticks to the size of a typical bank card after which connected the ends horizontal to the bottom. This gave the impression to be fairly constant. Looking back, I wager that burning toast in a toaster would work properly. (I didn’t have one readily available.)
Measurements
I borrowed a cheap-ish ($100) air high quality monitor from a pal. I believe it’s made by some firm in China after which re-sold by varied white-label manufacturers. I can’t work out who the unique producer is. Primarily based on information I’ve seen for the reliability of different air high quality displays, I wouldn’t belief absolutely the numbers, however the I believe the relative measurements ought to nonetheless be OK.
The everyday measurement for particulate air pollution is “PM 2.5” which is in models of μg/m³. That is meant to measure what you’d get in the event you did the next:
- Take a cubic meter of air.
- Filter all of the strong particles out of the air.
- Hold solely the strong particles which might be are 2.5 micrometers (μm) or smaller.
- Weigh all of the particles you saved in micrograms (μg).
Listed here are some methods to interpret these numbers:
- The EPA says yearly averages must be beneath 12 and each day averages beneath 35.
- The common outside degree ranges from 6 in Finland to nearly 100 in Nepal. Wealthy international locations are usually below 15. The best ranges are usually present in Asia and Africa.
- Cooking can simply trigger PM 2.5 measurements to spike into the tons of. I’ve noticed myself that this may occur with solely a small quantity of seen smoke.
Logging
Because the air high quality monitor doesn’t log information, I used an ultra-hacky different: I set the monitor subsequent to a laptop computer working a stopwatch. I then aimed a pill at each of these screens and took a timelapse video. Lastly, I manually transcribed the information by going to every minute marker within the information. (This was much more tedious than it sounds.)
Ends in a Tiny Room
I ran a primary experiment in a tiny room of round 8 ㎥. As a result of worries that wind from the purifiers may change the velocity the incense burned, I positioned it on the other facet of a wall, with a niche of round 20 cm close to the ceiling.
I repeated the experiment as soon as with no filter, as soon as with a industrial filter, and as soon as with the DIY filter. Listed here are the outcomes:
Issues are a bit random across the starting, most likely because of the drifting of the smoke earlier than it’s equalized within the room. With no filter in any respect, this spikes all the way in which to 1000 μg/m³, the utmost the instrument can present.
If we make the y-axis logarithmic, it turns into fairly clear that the DIY filter is cleansing the air at a greater charge. (That is the image from the highest of this web page.)
If we take the EPA’s threshold of 12 μg/m³, the DIY filter will get there in round quarter-hour, whereas the industrial filter take round 25 minutes.
Ends in a Massive Room
Fortunately, I don’t spend most of my time in an 8 ㎥ room. Thus, I repeated the experiment in a big room of round 100 ㎥. Right here there was no wall between incense and air purifier. As a substitute I left round a meter of distance between the incense and air purifier and the air purifier and the monitor.
Listed here are the outcomes:
There’s much more randomness across the starting, most likely simply as a result of how the smoke drifts round. Primarily based on the room quantity we’d anticipate a peak focus with no filter of round 80 μg/m³ = 1000 μg/m³ * (8/100). Reassuringly, that is fairly near what we see.
The DIY air purifier seems to be a bit higher. If we plot in log house, it’s extra clear that it’s certainly filtering at a greater charge:
Taping
It’s widespread recommendation for DIY purifiers like this to seal across the edges of the filter so that each one air should move by way of it. I share the instinct that this might assist, nevertheless it’s exhausting to make sure: For those who block airflow, you decelerate the fan. This could possibly be counterproductive.
On this case a minimum of, experiment is less complicated than principle. I took packing tape and thoroughly sealed across the consumption facet.
And the outcomes are…
…nothing!?
This was sudden. I believed the tape would assist, however I wouldn’t have been shocked if it harm as a substitute. As a substitute, there’s principally no distinction in any respect. I don’t know sufficient about fluid dynamics to even speculate about what’s taking place right here, so I gained’t strive.
There could possibly be some bizarre quirk in how I ran this experiment. This doesn’t essentially imply that each one the recommendation to tape across the filter is improper. Nonetheless, I’ve by no means seen any experiments that present taping helps both.
Ideas
Value. The DIY air purifier isn’t dramatically cheaper than the industrial one, however I anticipate the filters would have to be changed a lot much less typically. The industrial air purifier makes use of a single filter with an space of 300 cm², whereas the DIY air purifier makes use of two filters with a complete space of round 1400 cm², and likewise barely thicker. It’s cheap to imagine the DIY filters may take away ~4 occasions as many particles earlier than alternative.
Sturdiness. One concern is that field followers aren’t meant for use with filters connected and will put on out. That is cheap. Nonetheless, field followers are less expensive than industrial purifiers, and I’ve been utilizing this explicit fan with varied filters connected for a number of years now with out challenge. The larger concern right here might be that warmth build-up may in precept trigger a hearth, which could possibly be harmful. Additionally, there are some ideas that warmth buildup on {the electrical} parts may create poisonous particles, which is likely to be harmful for birds. I don’t know the way severe this hazard is.
Electrical energy. The price of electrical energy is one other issue. Typical field followers appear to make use of round 55W, whereas industrial purifiers usually use 30-45W. If electrical energy prices $0.13 / kWh, the field fan would value round $62 to function 24 hours a day for a 12 months, whereas a 30-watt air purifier would value round $34. Clearly, these numbers lower in the event you run the air purifier much less. Some (dearer) industrial purifiers have air high quality sensors in-built and robotically activate solely when wanted.
MERV or HEPA? Most individuals who construct box-fan purifiers use MERV-rated filters meant for furnaces. Industrial air purifiers use HEPA-rated filters. Roughly talking, HEPA filters are “higher” in that they’re rated to take away a better proportion of particles in a single move. It’s not clear that HEPA filter will precise carry out higher when connected to a fan, although: A filter that catches fewer particles in a single move may nonetheless be higher if it permits for quicker airflow.
That one video. For those who’re studying this text after it was linked from some discussion board, I’d wager you that somebody within the feedback hyperlinks to this video from the Michigan Sinus Middle. I discovered this inspirational, however observe a few issues: First, whereas the outline says they use HEPA filter, the video clearly signifies a MERV filter. Once more, that’s not essentially unhealthy! They declare that round 90% of particles sized 0.3 microns are bigger are eradicated in a single move. That’s good, however not completely reassuring. The query is, does it take away 99% in two passes? If 90% of the particles within the ambient air had been massive and the filter solely catches massive particles, then extra passes would by no means eliminate essentially the most harmful small particles. That is why I belief HEPA filters a bit extra: since they take away nearly all particles in a single move, I’m assured they need to take away nearly all particles ultimately. That is additionally why I strongly want experiments that truly measure particles faraway from the air in a room, relatively than simply the air popping out of the air purifier.
Additional questions. There’s a number of issues that additional experiments may have a look at:
- Does the fan velocity make an enormous distinction?
- How does the air purifier examine to bigger industrial purifiers?
- How do MERV-rated furnace-type filters examine below the identical situations?
- How can it not matter if there’s tape across the filters!?
- Does fan velocity matter? (I all the time ran the field fan at most velocity.)
- Is it higher to place the filters on the consumption or outtake facet of the fan? Instinct suggests the consumption facet, however as we’ve seen, surprises occur.
On purifiers and well being. If the surface air is clear the place you reside, your first precedence most likely shouldn’t be to get an air air purifier. As a substitute, I’d suggest you watch out when cooking. Having an air high quality monitor round actually drives dwelling how even small quantities of cooking smoke may cause gigantic spikes in particulate ranges. For most individuals, not creating these particles within the first place is one of the best technique. Attempt to not create any smoke in any respect. When you’ve got a variety hood that vents exterior, use it! For those who do create smoke, open home windows instantly. One problem is that it’s really fairly exhausting to guess what number of particulates you’ve created. There’s an inexpensive case that you must spend your cash on an air-quality monitor earlier than a air purifier.
Incense. It’s most likely unhealthy for you. I’d keep away from it.