Quote:

Matching a blower to the filter
According to Stamets (Paul Stamets and J.S.Chilton: The Mushroom Cultivator p. 347 ff) the air speed of the air flowing from the filter surface should be (at least) 100 feet per minute(fpm).(around 30 meter per minute or 0.5 meter per second). Determining the correct blower for a filter consists of several steps:

1. Find out the area of your filter by multiplying the width and the hight in feet (for instance the smallest reasonably usable filter would be 2ft x 1ft)

    2ft x 1ft = 2 ft2

2. Multiply the required air speed(the one Stamets specifies, 100 ft/min) with the area of your filter

    100 ft/min x 2 ft2 = 200 ft3/min

So 200 ft3/min(= cfm = "cubic feet per minute") is the amount of air your blower must deliver at the sum of the STATIC PRESSURE of the HEPA filter + prefilter.

NOTE: 1 cfm= 1.7m3/h

So if you use the above filter with 1"(250Pa) static pressure and a furnace prefilter with a static pressure of 0.2"(50Pa) your blower must deliver 200 cfm(340m3/h) of air at a static pressure of 1.2"(300Pa).

Finding the correct blower
Every blower should have a data sheet with a characterisitc curve that shows the air output in dependance of the static pressure. Every blower has a data sheet (consult the manufacturer if this is not the case with your blower) where the correlation between the flow and the static pressure is represented by a graph or table.

Here is such a set of curves for 4 blowers(numbered 1-4).
NOTE: Each model of a blower has his own characteristical curve. This chart shows the curvers for 4 different particular models of axial duct blowers.
What you can clearly see is that the bigger the static pressure the less air the blower delivers, up to the maximum static pressure where the air output is zero.

Sometimes these data are presented in form of a table

By now you know how much your blower must deliver and at which static pressure. In our example it was 340m3/h at 300Pa.
So what we do now is to go in this chart and find the value of 300Pa(=1.2") at the vertical axis. Then you move to the right until you reach 340m3/h.(=200cfm)
Now, ideally there should be a curve of a blower going exactly trough this point, but this is not allways the case.
So we have to choose a blower that best approximates our requirements.
In most cases we should choose a stronger blower, if it's not too strong.
How strong is too strong? I?d say the blower shouldn?t deliver more that 20% more air than we calculated, so in our case the strongest acceptable blower would be around 400m3/h.
In this example we have a blower that delivers 300m3/h(according to our calculation it should deliver 340m3/h though). This is a difference of mere 10%. The next stronger blower in this chart delivers 530m3/h at 300Pa, which is way too much.

In this case we go for the smaller(and cheaper) blower(Nr.4) instead of the much bigger one(Nr.1, which delivers 530m3/h at 300Pa), despite the fact that it?s generally recomended to take a stronger one.

NOTE: This chart is only an example for a set of 4 particular blowers. The curves of the blowers available to you may look a bit different, but similar.
Usually, if you search long enough, you will be able to find a blower that exactly matches your HEPA.

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peace ohm