Reply by clin

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798 posts in 904 days

#1 posted 07-15-2017 10:08 PM

You want as fine a particle filter as the blower can handle. For a given particle size, the more surface area of the filter, the less back pressure it will create for the blower. Less back pressure means more air movement.

In order to engineer this, you would need the pressure and flow rate curve of the blower. Filter materials have a similar rating. So for a given filter and size, you would know its back pressure per flow like PSI/CFM. Where this intersects the blower curve is where it will operate.

But I’m going to guess you don’t have that info for the blower. In that case, you want the filter surface area as large as you can make it. Then I would start with a HEPA equivalent filter and see how it works. If the blower moves a lot less are with the filter(s) installed, then you need a filter that allows more airflow and that will also mean larger particles will get through.

Or you can go the other way and start with a course filter and work up to a finer filter.

Also, best to go two stage. First filter is course, like common furnace filter, and will trap all the big stuff you can see. This will need to be cleaned and changed often. Have another filter after this for the really fine stuff (HEPA filter or similar). It will not need to be changed that often.

Also, think outside the box. There is no reason the unit has to be a cube or box shape. So instead of have just one filter flat on one side, use two filters, joined on one edge, folded to form a shape like a pup tent. You can double the surface area of the filter. Yes it means twice as many filters, but also, they will clog or fill twice as slow.

But you will have much freer airflow for longer this way.

You could even create more than two surfaces for the inlet side. For example, make a box with 5 sides that hold filters on each side (5 filters), Butt the open side of box this up to the intake side of the blower box. Then the blower will be drawing air through 5 filter surfaces giving you much, much more surface area than just the size of the blower inlet.

You can extend this concept as much as you want.

Hope that made some sense.

-- Clin

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