Additional Activated Carbon for Air Purifier

Update: I updated the compartment and offer two version of that – see below for the differences.

If you use a Levoit Core 300/300s Filter (replacement), you can add with this model an additional compartment to fill with activated carbon. Why? Please see below for my motivation.

The model consists of three parts: The “Stand” to lift the compartment up to the top, the compartment, that contains the activated carbon and a lid to close the compartment.

Take care, the grid structure necessary to let air through the compartment and lid is not part of the model itself, but achieved by using a honeycomb infill without top and bottom layer settings. The reason is that is easier to make directly in the slicer on the one hand, but also more flexible, as you can adjust the grid size depending on the activated carbon and on your experience with air flow. 

For instructions see “print settings”. 

Attention: I use it in my own home-made air purifier, and the headspace after adding this compartment is 5mm which is enough for my use case. I do not know how those commercial purifiers look inside and if they would need more headspace, but I doubt so. But please double check before printing if you want to use it in one of those. 

Filling the compartment

The compartment is probably bigger than necessary, and I did not figure it out myself yet, but I suppose you should not fill it too much, to still let air flow through. If too full air my find other ways eliminating the effect of the filter, or your throughput may decrease too much. 

Motivation

I used those Levoit Core 300/300s compatible replacement filters to build an homemade Air Purifier – I first used this model  https://www.printables.com/model/1067067-air-purifier  and than made a remix of that https://www.printables.com/model/1072116-air-purifier-with-single-filter-and-a-120mm-fan.

I suppose there are more home-made air purifier models out there, but I just know of those two that use that specific replacement filter. 

Nevertheless, when looking into that filter it consists of 3 Layers (outside in): 

• Mesh for filtering out big particles
• Hepa Filter
• Activated Carbon

The Activated carbon is a single layer around the circumference and for the whole height of the cylinder. But this still does not look much for me. Additionally the activated carbon will eventually not work anymore if it is kind of used – even if the Hepa filter would be fine, you would need to exchange the whole thing. It could be of advantage to be able to change the activated carbon only – which is basically what this model allows. 

Print Settings 

First of all please orient all the stl in your slicer for favorable print position. 

For the “Stand” there are no special print settings necessary.

For the “Compartment”, orient it, such that the floor is on the print bed. The Floor of the compartment is 3mm of height, to get a grid into it, use a “height range modifier” for 3mm height or achieve something similar with a modifier cube  – depends on your slicer.

The modified settings should eliminate all top and bottom layers (0) and set the infill to “honeycomb” to get a nice structure. The infill percentage now determines the size of the grid – I am using (“24%”) –> "20%" infill now, and the size of the holes seems appropriate for my activated carbon – but you may experiment with that value on your own. I also changed the number of perimeters or walls for that region, but that is not that important and perhaps in this use case not really necessary.  See below for a screenshot of these settings in Bambu Studio, other slicers should have similar settings available:

For the “lid” use the same idea of honeycomb infill and to remove top and bottom layers, but you can do it for the complete model, and do not need a “modifier”. 

Updated compartment:

I resized the compartment a bit, such that together with original lid and the original stand it will be the same level as the top side of the filter. As you see, I put it inside upside down: 

The reason is, that with this version and an updated version of the middle plate of my air purifier model (https://www.printables.com/model/1072116-air-purifier-with-single-filter-and-a-120mm-fan) it will be fixed in place (no side-to-side wobbling, and no jumping of the compartment), and there will be no free airway around the compartment – see the following photos: 

Big thanks to https://www.printables.com/@itsblxnk_618549  for the comments and the discussion!

Effectiveness

It is really hard to (correctly) measure air quality / pollution and even harder to measure the effect of an air purifier in a non-laboratory situation. I do have an air quality sensor in a living room which is connected to a kitchen/eating room. I do collect the data in a “Home Assistant” dashboard using a esp32 with esphome. The VOC sensor I use is a Bosch bme688 and it is (yet) really hard to make sense of the VOC data – some events I can relate to sensor value changes, some have no effect, but other times values increase without  obvious reason (no people in room etc). I suspect that humidity and temperature levels in the room influence the measurement.

In general I tested up to now the air purifiers without this additional activated carbon (the filters are new, and it should not be necessary to add activated carbon yet). But while I guess their influence cannot be seen on the data clearly, on a subjective level I have the impression that smells (cooking) are not directly reduced, but will vanish sooner than before without the filters. I am still thinking about doing a special test (like spraying perfume into the room or smth. like that) – if this leads to something, I will report it back here.  

If someone uses this, and has some additional experience on the effectiveness, I would really be glad to hear about them in the comments. Thanks!