This is a powerfull air purifier which use G4 and F7 filter. The HEPA F7 filter is sufficient to stop pollens. This air purifier is intended to clean the air of a big room during allergic periods.
Step 1: Hardware
The fan as been chosen from the requisites of the filters. The filters are rated for a amount of air flow and oppose some resistance. When they get dirty, the resistance increase as well. The fan is powerfull enough to deliver air pressure up to the max rated by the filters.
I made a mistake when buying the fan. It is no dimable. It's either full power (and noisy) or off.
The fan is inside a crate, creating a depression behind the filters and the exhaust is located one one side.
Step 2: Building the Crate
The fan is fixed inside a crate. It's made with laser cut 5mm plywood. Because the fan is quite heavy, and a rest for the filters is needed, the bottom of the crate is reinforced with wood pieces. Carrefully cuted with the same length, it wasn't correctly pushed to the maximum. I used wood paste to fill the gape and avoid any air leaking possibility.
Step 3: Exhaust
Since I used some foam to try to reduce vibrations and noise, it wasn't very easy to cut the exhaust a the rigth place with the laser cutting machine. I did it with a drill. Not very clean but it won't be visible.
Step 4: Fixing the Fan
Every contact surface of the fan is using foam in a desperate attempt to lower the noise. Because the fan is quite heavy, it was necessary to have two points of contact. A laser cutted piece of wood is used for the exhaust. The bolds are pointing outside, I kept them like this because I will build a silencer for the exhaust and th bolds are very usefull to fix this extension later.
Step 5: Sealing the Crate
To ensure that the low pressure chamber gets air through the filter, I used some putty. The electric cord is also a weak point. I drilled a hole smaller than the diameter of the cord and slightly enlarge it with a file. It fits perfectly.
Step 6: Electric Box
The electric box is glued on the back of the crate. Since the fan is not dimable, I used a simple on/off switch. Some velcro band are used ton fix the electric cord. I drilled some holes in case of heating issues but I did it on the sides of the box which is not the best choice .
Step 7: Inserting the Filter
The H7 filter is seated on a wooden square which is seated on the wooden pieces that also give more strength to the crate. Some ruber band sold to seal windows or doors is used to seal the sides of the H7 filter.
The last filter is just pushed inside the crate. The size is the same. Friction easily keep the filter in place.
To close the crate a more or less pretty grid has been laser cutted. It offers too much air resistance and needs a real fixing system.