Tutorial Air scrubber for microgrowing. An Idea that works.

[StrangeVisitor]

So here is a well working tested technology effective and 100% DIY. I’m happy to share it, as most of ideas I’ve picked up on the forums and icmag particularly. I wish this humble contribution will help those who desire to grow on their own and get off the nasty dependance. Peace.

In the photos below you can see the filter inside a growbox (on the right side) and after assembly ready to be put into operation.

The key element of the scrubber is a radial fan (blower, turbine). These types of fans are capable of moving air well enough through a filter (air resistance). The pressure that a radial fan develops is approx. 10 times greater than a comparable axial fan (regular pc fan) does.
The filter contains about 1l (1/4 gal) of charcoal, 34mm (1.3”) thick. That's enough for several cycles with smelly strains.

 

[StrangeVisitor]

The description and a short guide below.

Structurally, the filter is a 2-level box glued onto the base (which is one of the growbox’s inner walls, made of 4mm plywood).

The filter framework is made of 2 separate rectangular bars and 2 plywood parts that are improvised gaskets. The bottom compartment has positive pressure in it and holds the fan. The upper compartment is a filtering unit filled with charcoal.
The so called “gaskets” help to hold a fine metal net that is used to separate the positive pressure chamber with the fan inside from the charcoal in the other part. They also serve to make the pressure++ part of the construction airtight. The charcoal is covered with another layer of net and the second gasket. This one is a bit different from the first one (further on).
The pressure++ chamber is glued onto the base and is thoroughly greased with silicone both inside and outside. The fan is silicone glued onto the plywood “wall” with it central part sitting on the air intake opening cut in the wall. It is good to use more flexible material to fix the turbine, so that this material will prevent the vibrations and noise.
The upper part of the framework is bolted (screwed? )) ) to the lower part, so that when you need to change the charcoal you only need to remove the upper gasket with the net.
The parts of the framework have to be made very accurately and be plane in surface.

 

[StrangeVisitor]

Now about the difference between the two gaskets.
As this scrubber is positioned vertically and the box is being moved every other day, the charcoal tends to move downwards creating an airgap in the top. To prevent this, 2 things were done.
The first one – the upper gasket has a larger surface in the upper part which closes this gap.
The second one – the filtering chamber has a bar in the framework which helps to hold the charcoal from moving down + the gasket has a lamella in the same place.
These actions did help and there were no incidents with odor after the upgrade.

Here's few pics of the first version that had an air-gap issue.

Photos of the fixed version that work as it should.

 

[StrangeVisitor]

The fan is 12V 3,6W radial ball bearing fan. I won’t speculate about the numbers of rotation speed and pressure it creates because of two reasons:
- the fan is running seriously underpowered (~6V, does anybody know, how to find it’s true power without measuring the actual current draw?);
- I don’t remember the declared spec. on this noname fan; one thing I’m sure of – it did less than half of the promised lifetime before starting to make noise of a wear out bearing ((.
Before it started to produce faulty noise, it was running less than 25dB measured with a smartphone from a 1m distance in a very quite room (<21dB). Not very good result, I'd like to have it quiter.

Still this exhaust fan is more powerful than it is really needed. It is possible to smell some minor odor if you snuff the outtake air just after the scrubber (when a plant is in a most smelly period of the cycle). However, nobody ever noticed any odor in the room (with no ventilation) the growbox is running in. If the speed of airflow going through the scrubber is reduced, there should be no odor at all.

I am quite sure that a less powerful fan of higher quality will do the job producing less noise. We keep in mind, that a smaller fan moves less volume of air through, and we want it to be within certain levels (changing the air in the grow chamber at least 1 time per minute (desirable change ratio is about 3 times per minute)).
However, I didn’t manage to measure the airflow accurately yet.

This kind of scrubber isn’t as easy to make as some others, though it works very well and could be scaled and used in different micro setups. Anyway growing for one’s demand leads to carpentry as someone here has said )).

 

[Mr. Sparkle]

Yeah basic scrubber, the trick is to have air going slow enough to be caught in the carbon particles but still enough to cool your box and provide air exchanges.


different take but heres my scrubbers made of ducting tin and riveted and glued together to creat a scrubber that just fits over a 120mm fan by magnets in the fans stock location for a pc case

 

[Soulrebel239]

This is the the carbon scrubber that I need to build for my set up.

 

[Imsurethiswillwork2022]

Can this be stickied? I believe this is probably one of the best contributions to micro grows? I'm sure it can be implemented into other larger builds, based on the premise.

 

[Gunter]

I have my doubts that these PC fans can run against negative pressure needed for the filtration. I could be wrong of course because it is also not a lot of active coal they have to work against.

 

[Ca++]

PC fans of the axial type may struggle. You can stack them to add to the pressure available, but the blower the OP shows is the right thing. These can shift air through a filter without any worries.
You don't want one too big, as spinning these by hand, you can usually feel the cogging. It kinda moves past the magnets in a lumpy fashion. These lumps, need to be overcome. So the big lumps of a bigger motor, mean your minimum rotation effort has to be higher. So a greater noise floor.
It would be interesting to break up the old one, and see if it is actually an EC motor like most PC fans, or if it's brushed.
It's interesting that 3.6w was too much. I recently got a 9730 iirc, rated more like 30w. It's a beast. I don't want it. It's like a hair drier. It won't go low enough to be useful. I think I should of avoided 2 wire fans, and gone for a 4 wire. To know it's the real deal.
Filters are typically 50mm deep, or 30mm for hobby. You shouldn't have the air speed too low, at any depth. So a massive filter in tiny fan, isn't good. The air speed needs to cause turbulence, or some air will just slip through.

I did actually make a filter, with an axial PC fan, though an unusual one. It was just a 50mm fan, but was about 30mm deep. Fully overlapping blades. I filled a mug sized gravy granule container with pellets, after chopping it to 50mm deep. Holes here in there, bit of glue gun action. It stopped a shoe cupboard from smelling. The draft was little more than breathing though. The fan wasn't really enough. It's been working a few years though. I reckon a paint can might help some of us. fill to 50mm. Then drop in something perforated over the carbon. Bit of glue. Bobs your uncle.


I know people like papst make little EC fans, that would rock this project. We might be stuck with cheap DC (perhaps brushed) fans though. Few of us will buy a world class fan, for a micro-grow. Which then brings methods of control into question.

 

[plutiot]

I have my doubts that these PC fans can run against negative pressure needed for the filtration. I could be wrong of course because it is also not a lot of active coal they have to work against.

more fans!, for real, had problems extracting hot air out , added just a tiny pc fan in the other end, its not the size that matters its how you use it, someone gave me a small round flat carbon-filter for a oven-extractor fan, only a inch or so wider than my duct, i cannot really say how well it works yet, i have a proper carbon filter, but to insert it i have to re-do the whole fucking duckting, short on space 4 it