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Calculating the right blower/filter specs


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#1 Guest_cap_*

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Posted 10 May 2006 - 07:10 PM

high there

few (URGENT!) questions thanks so much for taking the time to view this thread,


- Is a 465 cfm blower OK? most are 465 not 495 as the tek calls for

- What is the largest motor one could use in coincidence with a 24x24" HEPA & 12x24" HEPA,respectively?
ie: would 600cfm be too large for a 12x24 HEPA? I think it would. need some opinions.

- What is the smallest size motor one could use?

Thanks so much:hippie:


#2 Hippie3

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Posted 10 May 2006 - 07:25 PM

Every filter has a different "resistance" when air blows through it at a certain speed, this resistance is called the "static pressure".

Press your hand against your mouth. Now try to blow through it. Dependant on how firm you press it against your mouth, you will have some difficulties blowing air out and you will feel some resistance, this is the static pressure.

Every filter has a different static pressure at the working point. The working point is where the amount of the air flowing through the filter is sufficient to meet the requirement of the laminar flow.

The static pressure is expressed in inch of water column in the english units, a typical value would be 1", the SI unit for pressure is Pa(Pascal).

1" water column is around 250 Pa. Each filter has a data sheet (consult the manufacturer if this is not the case) where the static pressure at the working point is entered. Before the air enters the blower it is usually pre-filtered by a furnace filter around 1"(2.5cm) thick placed in front of the blower to protect it and the HEPA filter from big paricles like dust and hair. It can be assumed that the static pressure for this prefilter at the working point is around 0.2"(50 Pa)

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).

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) with the area of your filter

100 ft/min x 2 ft2 = 200 ft3/min

So 200 ft3/min(cfm) is the amount of air your blower must deliver at 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.


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see http://mycotopia.net...html?1069556827

#3 Guest_cap_*

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Posted 10 May 2006 - 07:38 PM

thx h3 i just read that again and it didnt really help me :(
http://archives.myco...html?1069556827

thx tho, ill continue to look, maybe after supper ill have a clearer head :)

i think it has to do with the thickness of the filter, but, i think where the specs call for a 495, the 465 will work just fine.

thanks for takin the time to help hip, greatly appreciated.

#4 Hippie3

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Posted 10 November 2006 - 07:39 AM

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.

Attached Thumbnails

  • curves.gif





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