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OfflineMilaweak
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Registered: 05/29/15
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HEPA Filter resistance - flow hood build
    #21788253 - 06/10/15 01:11 PM (8 years, 7 months ago)

Hello everyone, first post here.

So yesterday I was doing some open-air G2G transfers in my backyard and I
figured I needed a flow hood...

I live in Europe and I found this filter.
It looks nice and from what I know (from here and there) it would work.

BUT there is a but : it may have not enough resistance.

Here's why :

The area of the filter is:

  1.5ft x 2ft = 3ft2

We want a flow of 100fpm through all the area so :

  100fpm x 3ft2 = 300cfm


Now, the technical sheet of the filter contains this chart which shows that,
for an air velocity of 100fpm (0.5m/s), it needs 135Pa (0.54 W.G.)
of pressure drop :

look the H14 red curve


But from what RR says in this post :
Quote:


For good laminar flow, look for a filter that size with about that same flow rate, only at .8 to 1.1 W.G.  It's hard to imagine getting laminar flow at less than half an inch of static pressure.
RR




So my question is :

  Do you think this filter would work, or is it just not resistant enough ?


Edited by Milaweak (06/11/15 03:11 AM)


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InvisiblePirateSwazey
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Re: HEPA Filter resistance - flow hood build [Re: Milaweak]
    #21788630 - 06/10/15 02:34 PM (8 years, 7 months ago)

I don't see on the website the filter's resistance, but you need 300CFM @ the filters resistance to make laminar (100CFM) coming out of the front of it. Where did you see the filter's resistance? If you're pulling the .54 from the chart that is irrelevant.


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OfflineMilaweak
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Re: HEPA Filter resistance - flow hood build [Re: PirateSwazey]
    #21788759 - 06/10/15 03:03 PM (8 years, 7 months ago)

Thanks for your answer my friend. I've seen your Flowhood post before :smile:

Is it ? Is it really irrelevant ? It's not what RR seems to say, or am I misssing something ?

They sent me pdf's of the characteristics. The filter I choose is grade H14.
If you can't find the filter resistance then me neither...
On the site it's written :

421m³/hr @ 120Pa

Isn't that the resistance ?


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InvisiblePirateSwazey
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Re: HEPA Filter resistance - flow hood build [Re: Milaweak]
    #21788954 - 06/10/15 03:48 PM (8 years, 7 months ago)

Yes it is important! I converted the 120pa to inches of W.G. and it's .42"

So if RR is saying your filter needs .8 - 1.1" of resistance to make laminar I don't think that one will work.

The site seems to have a lot of options for HEPA filters so maybe you can find something else thru them!


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OfflineMilaweak
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Re: HEPA Filter resistance - flow hood build [Re: PirateSwazey]
    #21789027 - 06/10/15 04:07 PM (8 years, 7 months ago)

It does but they all seem not resistant enough..

Going to need to find another filter making company.
That's too bad, it was almost it.. I'll post my findings.

Thx !


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Offlinekushroom
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Re: HEPA Filter resistance - flow hood build [Re: Milaweak]
    #21789117 - 06/10/15 04:28 PM (8 years, 7 months ago)

Good luck to you with your build im thinking of building one myself.


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InvisiblePirateSwazey
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Re: HEPA Filter resistance - flow hood build [Re: kushroom]
    #21789363 - 06/10/15 05:20 PM (8 years, 7 months ago)

There are a lot of filters available on ebay, the astrocell 24x24 is pretty popular around here & is relatively  inexpensive


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OfflineMilaweak
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Re: HEPA Filter resistance - flow hood build [Re: PirateSwazey]
    #21791632 - 06/11/15 03:27 AM (8 years, 7 months ago)

From what I can tell, this Astrocel I on ebay is not suitable either.

In this 12" thick version at least. In the documentation it says :
1050cfm at 1.0 in. w.g.

But you would want only 400cfm at 0.8 to 1.0 in. w.g.

So I think if this filter worked for some then the first one should too.

I know it's only $75 but with the the shipping and handling to europe it would cost me $200


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InvisiblePirateSwazey
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Re: HEPA Filter resistance - flow hood build [Re: Milaweak]
    #21791927 - 06/11/15 06:44 AM (8 years, 7 months ago)

The 1050 CFM is just what the filter was tested at and is not important.

You need a blower that produces atleast 400 CFM @ 1" W.G. to make laminar flow with that filter.

$200 shipped is pretty expensive though.. Maybe you can find a UK seller on eBay??


--------------------
 

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OfflineMilaweak
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Re: HEPA Filter resistance - flow hood build [Re: PirateSwazey]
    #21796258 - 06/12/15 07:26 AM (8 years, 7 months ago)

Quote:

PirateSwazey said:
Yes it is important!


:biggrin:

I thought it wasn't too but look at this :

Quote:

Quote:

bleedheat said:
    Its probably good to note that i dont have the chart for my filter, only a small label with these stats

    CFM 450
    IN W.G. 1"
    % Pen 0.01



In which case you're screwed.  The curve between static pressure and flow is not linear.  You need that chart.  The label only reflects the test they ran after manufacture to ensure the filter is within the curve.
RR




If someone has that chart for the Astrocel..

But anyway, if it gives 1000cfm @ 1.0" , I assume it will deliver the 400cfm we need at less than 0.5"
Don't you think ?

I found several sources of HEPA filters that mention a quasi-laminar outflow :
http://en.fulfilter.hu/
www.viledon-filter.hu and others..
Don't know if we want a quasi-flowhood though

As a mather of fact, nearly all the most resistant H14 HEPA filters I've seen so far
need only 0.5" of pressure to deliver 100fpm

Well except this one, with a 30mm frame.
The same Lotte & Thomas except they used a 78mm frame and run it at 150pa (0.6" W.G.)
And they do in vitro orchids and stuff


The real question is : Why is it hard to achieve laminar flow at less than half an inch of pressure ?


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Invisiblemaddchef
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Re: HEPA Filter resistance - flow hood build [Re: Milaweak]
    #21796267 - 06/12/15 07:33 AM (8 years, 7 months ago)

Because if you don't have a good deal of resistance at the filter then air comes out at different speeds/times relative to when you pump it in the plenum.


--------------------
In the land of the blind, the one eyed man is king.

All mushrooms are edible, but some only once.....                     

                                        Easier than cakes

I do science and shit.

:havesomescience:


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OfflineMilaweak
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Re: HEPA Filter resistance - flow hood build [Re: maddchef]
    #21796312 - 06/12/15 07:55 AM (8 years, 7 months ago)

Yes, the air will be blown more on some areas of the filter and less or none on others.
(edit: or is it just a speed issue ?)

Right, thank you !

So what would you think of the Astrocel maddchef ?


Edited by Milaweak (06/12/15 07:57 AM)


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Invisiblemaddchef
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Re: HEPA Filter resistance - flow hood build [Re: Milaweak]
    #21796364 - 06/12/15 08:19 AM (8 years, 7 months ago)

Link the particular one


--------------------
In the land of the blind, the one eyed man is king.

All mushrooms are edible, but some only once.....                     

                                        Easier than cakes

I do science and shit.

:havesomescience:


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OfflineMilaweak
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Re: HEPA Filter resistance - flow hood build [Re: maddchef]
    #21796420 - 06/12/15 08:36 AM (8 years, 7 months ago)



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InvisiblePirateSwazey
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Re: HEPA Filter resistance - flow hood build [Re: maddchef]
    #21796424 - 06/12/15 08:37 AM (8 years, 7 months ago)

I have used blindingleafs flowhood & we both built ours without a spec sheet.. The filters are tested at whatever CFM the manufacturer chooses @ the filter's resistance. All that is important is the W.G.

This is all the info that came with mine:



I have not had any problems with it after consistent use for over a year. Leaf's flowhood is used to feed an entire mushroom farm! His unit actually has 2 blowers on it and I have seen where RR has posted to NEVER DO THAT because it won't work lol.

I promise building a flowhood is one of those once you get it you get it kind of things.. It's really not that complicated, it's just confusing because you're unfamiliar with the terminology & keep getting your ideas muddled up by reading too many posts about it!

The thing I would listen to RR in your situation is the filter resistance being high enough, .8-1.1" or whatever he said. That makes sense because if the filter doesn't have enough resistance you won't get even flow coming out of the front.

Later on I will double check in my Stamets books for you on that! :grin:


edit: woop! I thought that was blindingleaf not bleedheat in your quote!! lol


--------------------
 

BULK RYE PREP  -  MY FAVORITE THREADS  -  BUILD A FLOWHOOD



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OfflineMilaweak
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Re: HEPA Filter resistance - flow hood build [Re: PirateSwazey]
    #21817825 - 06/17/15 05:52 AM (8 years, 7 months ago)

I've phone filter companies and there is no problem with the filter resistance.
Today filters for laminar flow hoods are made to give about 90fpm @ 120Pa (0.5 w.g.)
Some flow hoods even blow at 50fpm for some applications.

The guy told me that what makes a great deal is also how the air is blown into the filter.
But as Sci-Fi said :
Quote:

Building a laminar flow hood where the air being pushed out of the fan makes one 90 degree turn in a plenum the width of the filter to enter the filter would be more than enough to create a almost perfectly even static pressure. Even with a filter at 0.3" W.G.



Like this (almost):


Also enclosure is really good.
The guy told me that it would be even better if the walls of the enclosure were perfectly aligned with the filter but if you look at flow hoods pictures you can always see the frame of the filter so it must be ok as long as the frame is not too wide.

The above quote comes from THIS POST, Sci-Fi gives really good infos.

Not sure though about the part where he says to buy a filter with the LESS resistance possible, because what RR says about that makes sense to me..
It would be hard to have a homogeneous air flow if the filter had NO resistance at all right ? Maybe its thickness would compensate.

Also have a look at the pictures of this home-made flow hood. Damn' !


Edited by Milaweak (06/17/15 06:07 AM)


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