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HEPA filter question
    #10874875 -

Hello everyone,

Lately I been thinking of building a laminar flow hood and I have a question on the type of filter I should use.

In my area I found a company that sells HEPA Filters and they have two types. One is called a "mini-pleat" type which looks like this:


And the other is called a "separator type" which looks like this:


Both of them offer 99.999% filtration at .3 microns.

Initially I was going to go for the mini-pleat, but then I read a post in another thread where roger rabbit said the filter needs to be at least 5 inches thick.
The dimensions of the minipleat are: 610X610X75 (HxWxD), i'm thinking D means depth which is probably the thickness? if 'D' is indeed thickness, than 75mm would be less than 5 inches.

The separator type comes in various sizes, with various measurements for 'D' as well, ranging from 75mm to 292mm. (Specifically 75mm, 150mm, and 292mm)

So should I go with the separator type? Is that a suitable filter?
Also, am I right in assuming 'D' represents thickness? If so, should I go for 150mm or 292mm, or does it not matter?

Thanks for your help, i'm sure i'll have more flowhood questions later, but for now knowing which filter to buy will be enough.

Extras: Filter Print Post Top
Re: HEPA filter question [Re: phaseflux]
    #10874906 -

You need the resistance figures for both filters to make an informed decision. The reason a thicker filter works better, even though both might have the same efficiency, is the thicker filter has more resistance thus builds static pressure on the back side in the plenum, which in turn ensures laminar flow out the front.
RR


--------------------
Download Let's Grow Mushrooms



semper in excretia sumus solim profundum variat

"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison

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Re: HEPA filter question [Re: RogerRabbit]
    #10874935 -

The website of the company has a lot of information about the filters, but since its not in English, I'm not exactly sure what represents what. There are numbers listed in a column as "CMM" and also a graph showing "CMM" and "MMAQ".

To be honest I'm not sure exactly what those are because the website I was reading on how to make a flowhood doesn't seem to use metric measurements.

is CMM the resistance figure?

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Re: HEPA filter question [Re: phaseflux]
    #10874950 -

You can get information and plans on building a laminar flow hood with metric measurements from Anno's website.
RR


--------------------
Download Let's Grow Mushrooms



semper in excretia sumus solim profundum variat

"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison

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Re: HEPA filter question [Re: RogerRabbit]
    #10881848 -

Ok I feel stupid asking this, but how do I find the resistance figures? Getting all this right has been stressing me out, I must have spent the last couple hours searching about hepa filters both here and in google and still don't know exactly.

I have a chart and a table for the "mini-pleat" filter I posted above. The table looks like this:


You notice the first part is dimensions, the second part is air quantity (I think CCM is cubic meters per minute), and the last two columns under mmAq was listed as "initial", and "final"

Here is the corresponding graph with two lines differentiating between the two available depths for this specific type of hepa filter:


Are the resistance figures able to be figured out by this info? Or is this something i need to contact the company about?



I don't have the graph for the "separator" type I mentioned in the first post, but I have the table, which is why i'm asking about the "mini-pleat" one first.
The table for the "Seperator-type" looks like this:

Edited by phaseflux (08/18/09 10:56 AM)

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Re: HEPA filter question [Re: phaseflux]
    #10884080 -

hmm anyone at all able to point me in the right direction?

Extras: Filter Print Post Top
Re: HEPA filter question [Re: phaseflux]
    #10886618 -

Quote:
You notice the first part is dimensions, the second part is air quantity (I think CCM is cubic meters per minute), and the last two columns under mmAq was listed as "initial", and "final"

Are the resistance figures able to be figured out by this info? Or is this something i need to contact the company about?


Yes. I am going to assume "mmAq" is mm aqua, which would be mm water column. Initial means at the beginning, when the filter i clean, it has a lower resistance, and after a few years, when the filter is getting clogged, it has a higher resistance.
1 mmAq ~ 1 Pa(Pascal)~ 0.039 inch water column

With this info you should be able to match a blower according to http://www.fungifun.org/English/Flowhood#match


--------------------
Grow Mushrooms from Spores - PF-Tek for Simple Minds

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Re: HEPA filter question [Re: Anno]
    #10888147 -

Ok great, thanks for the reply.
I have one question though.
On this conversion site:
http://www.translatorscafe.com/cafe/units-converter/pressure/calculator/microbar-to-millimeter-water-(4-degrees-C)-%5BmmAq%5D/

I noticed there is inch water (4°C)  and also inch water (60°F).

I notice that you are using inch water (60°F), and just wanted to double check to see if this is the correct unit I should be converting too. The site you and RR linked to doesn't seem to say which one to use.

I also find it odd that the initial and final pressures of the "mini-pleat" type is lower with the thicker depth (according to the first table). Is that normal? I would think thicker depth would cause more resistance..

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Re: HEPA filter question [Re: phaseflux]
    #10888429 -

Be sure to get a blower that rated at lest 1,500 CFM.... You can/should (+ adds life to the Hepa filter)add pre-filters to help
reduce air flow...

And get the "separator type" you can spray drown the front of it with rubbing alc..


--------------------
:Awesketch:

:cool: Fair is Fair :devil:

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Re: HEPA filter question [Re: phaseflux]
    #10888495 -
Log in to view attachment

phaseflux said:
I noticed there is inch water (4�C)  and also inch water (60�F).

I notice that you are using inch water (60�F), and just wanted to double check to see if this is the correct unit I should be converting too. The site you and RR linked to doesn't seem to say which one to use.



The viscosity of a fluid such as water changes slightly with temperature.  Use the 60F figure since it's closer to the normal room temperature you'll be working with.  Static pressure is measured in inches of water column or the metric equivalent.

Imagine taking a piece of tubing and bending it into a U shape an filling the bottom of the U with water.  The water would equalize in the bottom and extend the same distance up each side of the U.  If you connected a hose from the plenum of your flowhood to one side of the tube and it pushed the water down 1" while raising it 1" on the other end of the tube, that would be 1" WC static pressure.

Scroll down to the bottom of the attached document and there's a description of manometer operation.
RR


--------------------
Download Let's Grow Mushrooms



semper in excretia sumus solim profundum variat

"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison

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Re: HEPA filter question [Re: phaseflux]
    #10888826 -


if you convert:
1 inch water (4°C) = 1.000960445 inch water (60°F)
so there is about  4/100000 of an inch difference in the two measurements. negligible to say the least.


I am super new to this, but based on the graphs in phasefluxs post

( the chart seems to be titled average decline, so it would be the
deterioration of the filter over time at a specified blower speed

so based on the graph:
we want from stamets a Filter output of

                  100ft/min = 30.48 m/min
                            = .508 m/sec

we can see that that will result in a Static Pressure of about 9 mmAq

                    SP=  9 mmAq =~ 88.25 pA 

if we add 50 pa to this for the prefilter
  we have a total SP of 138.25 pA. this is the resistance of your
entire system with a laminar output

which means we need a blower that delivers about .5 m/sec at 138.25 pA

given our filter size is .61m x .305m we mulitply buy .508 m/sec
and end up with .0930m3/s  and  x 60s/m * 60m/h =  334.89 m3/h  at pressure of 138.25 pA

so  looking at the blower graph from Anno's website
we see this blower is much too strong.

anyway. this is a lot of work for my first post.
if anyone sees anything wrong please point it out. we can only get better together.

my questions:
this static pressure seems low to me. is there a recommended static pressure to have. the higher the static pressure the more resistance, the harder for stuff to get through the filter. right? anyone have a value to shoot for?

brainiac suggested a filter rated for 1500cfm. cubic feet/minute
this seems outrageous.

the reason the thicker pleated filter has a lower Static pressure is the pleats mean the filter surface zigzags back and forth, so there is more actual surface area for the air to go through. think of the surface area of a  Z compared to a [    wind--> Z  and wind--> [ 
also blow through a smaller straw ( less surface area ) and a larger straw ( more surface area). which one has more resistance?

phew

Edited by bluepiss (08/23/09 09:03 AM)

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Re: HEPA filter question [Re: bluepiss]
    #10889077 -

Hmm the way I see it is that it might be easier for me to choose the 610x305x150 "separator" type filter, the dimensions in feet would be almost exactly 2ftx1ft for the length and width.

and since the initial resistance is listed as 25.4 mmAq which equals almost exactly 1" water column, then all the measurements would seem to be almost exactly the same as those listed on the fungifun site.

Wouldn't that mean that the example calculations listed on fungifun would also apply to me?

Area
610mm x 305mm = 2ft x 1ft
2ft * 1ft = 2 ft²

so wouldn't this result in the example from the fungifun site:

"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)."

also be applicable to me since the filter would be the same dimensions, and have the same resistance? (well initial resistance anyway. does final resistance matter?).

Or is it not that easy? Am i missing something?

Should I be also paying attention to the air capacity number listed under CMM in the table i posted (which i think means 8 cubic meters per minute)?

Edited by phaseflux (08/19/09 11:50 AM)

Extras: Filter Print Post Top
Re: HEPA filter question [Re: bluepiss]
    #10895883 -

sorry if it seems like I'm asking too many questions, but I'm just curious about a couple of more things.

First off, on the fungifun site, the pictures of the laminar flow hood seem to have no plenum, is this correct? But isn't a plenum necessary to achieve laminar flow, or am i viewing the picture wrong?

and i was wondering about this also:
bluepiss said:
my questions:
this static pressure seems low to me. is there a recommended static pressure to have. the higher the static pressure the more resistance, the harder for stuff to get through the filter. right? anyone have a value to shoot for?



And finally, does the number for air capacity i mentioned earlier (under CMM) matter?

I think thats about all i need to know to feel confident in purchasing the filter and starting construction.

Thanks for the help so far everyone :grin:

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Re: HEPA filter question [Re: phaseflux]
    #10901588 -

ok here we go.

your 610x305 separator was tested with a 8cmm blower
if we multiply 8 m3min x  1/(.61mx.305m)
we get approx  43m/min  so we know the output of the motor
with no resistance and we know the static pressure of the filter 24.4mmAq

Unfortunately we dont know the output of the blower after going thru
the filter, which is the ever so important part.  there is no equation or way to figure out this except by the graph for the filter
we need to know that this output is 100ft/min = 30.48 m/min
                                              = .508 m/sec

i agree the separator filter seems to be the way to go.
but i still wonder about a workable static pressure to go for??
any input??

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Re: HEPA filter question [Re: bluepiss]
    #10903095 -

Well no one seemed to answer the above questions, so i took the plunge and ordered the 610x305x150 seperator type hepa.

SO before i let this thread die, is there anyone that can answer my, or bluepiss's questions above which were left unanswered? Bluepiss is actually a buddy of mine who is aiding in the actual construction

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Re: HEPA filter question [Re: phaseflux]
    #10903318 -

I only have about ten minutes each morning to log in and answer questions, so I don't have time to convert this to metric for you. Sorry.  If you're using a 12" X 24" hepa filter, you need a blower that will deliver an AIR SPEED leaving the filter of roughly 100 linear feet per minute.  Since a 12 X 24 has two square feet, you would want a motor that could deliver 200 cubic feet per minute at rated static pressure IN a perfect world.  Since we don't live in a perfect world, and there's friction losses between the blower and the filter, add about 20% or so to the blower output requirements to make up for these losses.

By the above, if you were using a 24" X 24" filter, you would have 4 square feet of surface, so you would want a 400 cubic feet per minute blower at the rated static pressure IN a perfect world.  Adding 20% to that figure, you'd want a blower that could give you about 480 to 500 cfm.  If your blower is too strong, you can always block off part of the intake to cut down on flow.  This is commonly used in commercial and industrial facilities and won't harm the blower.

The important thing is to make sure the blower you order is rated at the required static pressure.  Many cheap blowers might be rated at 'such and such' a flow rate, but at pressure it drops to near zero because they simply cavitate.
RR


--------------------
Download Let's Grow Mushrooms



semper in excretia sumus solim profundum variat

"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison

Extras: Filter Print Post Top
Re: HEPA filter question [Re: phaseflux]
    #17917030 -

It depends upon u application. Both type of HEPA Filters are used for similar applications. The only difference is you get higher airflow rates in mini pleat HEPA Filter.

Extras: Filter Print Post Top
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