DIY HEPA Air Purifier (Lasercut + 3D-print)

After having seen IanVanMoruik his Open Source Air purifier I decided to make a similar device. https://www.instructables.com/id/OPEN-SOURCE-AIR-P...

I include some basic steps in order for you to replicate the air-purifier. However, the main goal is not providing a full detailed construction overview, but showing that using some cheap parts together with some Fusion 360 creativity can result in an actual working air purifier.

I've tested the air purfier with a PM sensor and the results are positive (see testing).

Step 1: Acquire a Cylindric HEPA Filter (€9.99)

After hours of searching for a cheap certified HEPA filter I finally came across a German manufacturer Albatros that at that time offered a cylindric model of 22.4 cm in height and 19.2 in diameter. This model is used for industrial vacuum cleaners so it should provide an actual air cleaning effect (tested and confirmed). The inner diameter however within the rubber band is only 15cm. In order for a larger fan to be used together with a higher airflow rate and naturally a higher diameter, a funnel needs to be created.

Specifications:

1. HEPA certified
2. Inner diameter (rubber ring): 15cm
3. Outer diameter (rubber ring border): 19.2cm
4. Height (from bottom to top of rubber ring): 22.4cm

Pros:

1. Certified Hepa filter, you know it will actually filter particles (tested it).
2. Probably cheaper than producing it on your own.
3. High structural quality (strong internal mesh support).
4. I prefer a cylindric HEPA filter as these guys look more space efficient when compared to a flat hepa filter with just a fan strapped onto it.

Cons:

1. "Not fully DIY".

Shop-URL:https://www.albatros-shop.de/waschsauger/hepa-filt...

Step 2: Acquire a Fan With a High Airflowrate (CFM, €21.95)

BitFenix Spectre Pro Led 230mm pc case fan:

For this build I was looking for a relativily quiet fan that still provided above average static pressure and a high airflow rate.

Specifications:

1. Airflow rate: 156 CFM or 4.4m³/min. Thats an impressive 4400 one liter bricks of air passing through the fan every single minute.
2. Static Pressure: (mmH2O)1.81 mm
3. Noise: 25.6 dB(A), relatively low as it has enormous fan blades, for a pc fan.
4. Power consumption: Knowing the estimated Amperage of 0.41A and using it at 12V would give us a an hourly consumption of +- 5Wh.

Pros:

1. High airflow rate & static pressure
2. Pretty silent

Cons:

1. This thing is pretty huge
2. Is more expensive then a normal 120mm pc fan.

Product info: https://www.bitfenix.com/global/en/products/access...
Store-URL:https://www.megekko.nl/product/0/952057/BitFenix-S...

Step 3: Acquire a Simple DC Power Adapter (12V, € 13.85)

To be able to choose the fan-speed I bought a simple Universal DC power adapter on amazon together with some simple female 5.5x2.1 adapters to connect the fan to.

Pros:

1. Voltage can be changed to increase or decrease the RPM of the fan, thus increase its airflow (from 5V to 15V, 2.4A to 1.5A respectively).
2. Fine build quality and a lot of included adapters.

Cons:

1. More expensive then a simple 12V DC adapter.

Shop-URL: https://www.amazon.de/gp/product/B01MFCR6W2/ref=oh...

Step 4: 3D Printed Air Funnel (+- €5).

Finally we can start creating something to connect all our components. I needed some sort of air funnel between the fan and the filter to compensate for the diameter difference (from 15cm to +-19cm). I've created a very simple funnel in Fusion 360. Included the .STL in here. Took +- 4 hours to print.

I attached the funnel to the fan with some simple hot glue.

Step 5: Lasercut Frame (approx. €12)

I've created a simple design in Fusion 360 that relies on 2 rings that are made out of 4mm thick Berk wood, and 50 blade components which are 3mm MDF. The Fusion 360 archive files are included so you can personalize it to your needs. There are many online guides to convert these models to DXF for a laser cutter.

As you can see in one of the first build attempts the blades are supposed to be skewed and rest upon the ring. The assembly process is pretty difficult and I recommend doing it as follows:

1. Assemble 3 blades in 3 parts of the circle without any glue.
2. Iteratively add a blade to each part untill the structure is filled up.
3. Now we take out a blade one by one.
   1. Add some wood glue to the cutouts/slots
   2. Put it back into its position and keep it there for a solid minute.
4. Repeat for all blades.

The hardest part is just fitting them together without glue, once the glue is applied it stands rock solid.

DXF Conversion:https://www.autodesk.com/products/fusion-360/blog/...

Thank you FabLab Brussels for providing a work environment, materials & help for students.

http://www.fablab-brussels.be/fablab/

Step 6: Testing (€ 20)

Once the assembly of the frame is done we simply put in the filter with the assembled fan and funnel and its done. Pretty straightforward. The big question however is; does it actually work?

To answer this question I bought a Plantower PMS7003 sensor from aliexpress. Wrote some code (https://github.com/vandenbroucke/PlantowerCSVLogger) and tested it within a near perfectly sealed closet.

I gather a lot of dust from above my closets and sprayed it within the test cabin together with some aereosols (propane & butane). My goal target was around 100µ/m³ of PM2.5 to start the tests with.

The tests clearly indicate that the filter does in fact work and provides an air cleaning effect. You can also very clearly see when tapping the filter (video) after 3 days of usage that a lot of dust comes loose which indicates that it has actually done something.

After the tests were done inside the chamber the air within the test chamber was "cleaner" or less polluted then the air outside. We can clearly see the difference as we opened our test chamber after testing the filter.

Plantower PMS7003:

• http://aqicn.org/sensor/pms5003-7003/
• http://www.plantower.com/en/content/?110.html