Blower To Hepa Size

Nan's Nook : Archives : Gloveboxes : Flow Hoods
 Posted by: montego Jan 30 03, 11:58 PM GMT Does anybody have a formula to determine minimum blower size for given filter stats? I know the goal is a minimum of 100 cfm delivered, but how do you make sure that's what you're getting?(my hepa is huge!)

 Posted by: Mycota Jan 31 03, 12:45 AM GMT Easier to C&P this than write you a whole ne explanation: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 filterAccording 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 ft22. 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 blowerEvery blower should have a data sheet with a characterisitc curve that shows the air output in dependance of the static pressure.Credit to ANNOMycota (6T)

 Posted by: Alien Jan 31 03, 11:37 AM GMT Nice info

 Posted by: Mycota Jan 31 03, 12:39 PM GMT Sometimes you bump into fans cheap & buy them. Same goes for filters.Then you find they are miss matched. If the fan is will not produce a workable CFM, you need a bigger one.If the fan is an ass kicker, you can add static pressure by increasing the depth and/or type prefilter. I found automotive car engine filters, make great pre/filters. They are cheap & very high quality.Mycota (6T)

 Posted by: montego Jan 31 03, 03:22 PM GMT Thanks for your reply -- I'm sorry I didn't find that when I searched for the Hepa/ Blower info. This will really help me out a lot. I'm trying to just go ahead and do this stuff right the first time, and this site is helping me incredibly.This is a great site, and I'm just blown away by you guys. Thanks again.

 Posted by: slickstk187 Feb 03 03, 01:43 PM GMT i was just reading through this and it's exactly what i needed to see. i don't have a hepa yet but i was wondering what cfm was and how to work that out. nice post. i just thought i'd bring it back to the top for anyone like me who might have missed it the first time.slick

 Posted by: slickstk187 Apr 29 03, 03:33 PM GMT Posted on Feb 03 03, 06:43 PM GMT-------------------------------------------------------------------------------- i was just reading through this and it's exactly what i needed to see. i don't have a hepa yet but i was wondering what cfm was and how to work that out. nice post. i just thought i'd bring it back to the top for anyone like me who might have missed it the first time.slicki just got my hepa filter and was going to try to use a big radial fan that i have for it. it's only about 6"x4". my fan is too big for it but i was thinking about wrapping a 50 gallon trash bag around the frame of my fan and taping it on with duct tape. then cut a whole in the bottom of the bagand tape the cut edges onto the side of the hepa (it's about 3 inches deep.) you said in your post 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) my filter is significantly smaller. it's rated at 99.99% and made by HEPA CORPORATION of Anaheim, CA. i was just wondering why 2x1 ft. would be the smallest reasonably usable filter. is that the smallest it can be to get through enough airflow?thanks myc'slick

Posted by: DirtyWOP Apr 29 03, 07:20 PM GMT
 QUOTE the smallest reasonably usable filter would be 2ft x 1ft

not true.....mine is only 1 ft. by 1 ft.
You need to multiply the dimensions to find the area of the filter.
If you get 100 cfm when you divide the square footage into the CFM of the fan.......

so....in other words.....your fan should be capable of delivering at least 50 CFM, if your dimensions are 6" X 4"

I wish I could find such a small filter for my greenhouse!!!

edited to say that this figure doesn't include a pre-filter

 Posted by: DirtyWOP Apr 29 03, 07:23 PM GMT You might put that tiny filter to better use in a positive pressure glovebox....there is no way you can work in an area less than 1 sq. ft.I can barely work in mine.....

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