Home | Community | Message Board

Magic-Mushrooms-Shop.com
This site includes paid links. Please support our sponsors.


Welcome to the Shroomery Message Board! You are experiencing a small sample of what the site has to offer. Please login or register to post messages and view our exclusive members-only content. You'll gain access to additional forums, file attachments, board customizations, encrypted private messages, and much more!

Shop: MagicBag.co All-In-One Bags That Don't Suck   Left Coast Kratom Buy Kratom Extract   North Spore North Spore Mushroom Grow Kits & Cultivation Supplies   PhytoExtractum Maeng Da Thai Kratom Leaf Powder   Kraken Kratom Red Vein Kratom

Jump to first unread post Pages: 1
Some of these posts are very old and might contain outdated information. You may wish to search for newer posts instead.
Invisiblepsyke101
Test Subject


Registered: 04/30/11
Posts: 748
Understanding static pressure - building a flow hood.
    #20192547 - 06/27/14 03:21 AM (9 years, 8 months ago)

Ive been researching how to build a flow hood using some of the resources on the forum and linked to offsite.

Im mainly using the method outlined on the Fungi Fun site:
http://www.fungifun.org/English/Flowhood

In the Fungi Fun example, the author uses the example of a HEPA filter that has a static pressure of 1" WC (250Pa).

After doing a bunch of research and looking at a variety of HEPA filters, I am yet to find one that has a static pressure of anything other than 1"WC (250Pa).

Is it safe to say that all HEPA filters of the type commonly used for flow hoods have a static pressure of 1"WC?


--------------------
Useful bulk substrate calculator

Extras: Filter Print Post Top
OfflineRogerRabbitM
Bans for Pleasure
Male User Gallery


Registered: 03/26/03
Posts: 42,214
Loc: Seattle
Last seen: 1 year, 1 month
Trusted Cultivator
OG Cultivator
Re: Understanding static pressure - building a flow hood. [Re: psyke101]
    #20193303 - 06/27/14 09:02 AM (9 years, 8 months ago)

Filters don't 'have' static pressure.  They apply a resistance across the airflow which causes the static pressure.

Filters are usually rated by how much flow will pass through the filter at a given static pressure. (resistance)
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
Invisiblepsyke101
Test Subject


Registered: 04/30/11
Posts: 748
Re: Understanding static pressure - building a flow hood. [Re: RogerRabbit]
    #20195265 - 06/27/14 05:45 PM (9 years, 8 months ago)

Ok thanks for the clarification RR.

Im finding it confusing. Some HEPA manufacturers use a measurement called pressure drop rather than static pressure. From what I can tell the terms are related but slightly different..

For my purposes, ie determining the resistance of a filter for use in a flow hood, can I assume pressure drop and static pressure ratings are interchangeable?


--------------------
Useful bulk substrate calculator

Extras: Filter Print Post Top
OfflineRogerRabbitM
Bans for Pleasure
Male User Gallery


Registered: 03/26/03
Posts: 42,214
Loc: Seattle
Last seen: 1 year, 1 month
Trusted Cultivator
OG Cultivator
Re: Understanding static pressure - building a flow hood. [Re: psyke101]
    #20195417 - 06/27/14 06:16 PM (9 years, 8 months ago)

Yes.  If your blower develops .9" of water column between itself and the filter, it's said the pressure drop is .9" because that's the difference you would read between the plenum and the outside air.

You shouldn't have to calculate anything.  Your filter should come with a chart.  Simply match the desired flow to the pressure drop(static pressure) and then then select a blower which will deliver that flow at that static pressure.
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
Invisiblepsyke101
Test Subject


Registered: 04/30/11
Posts: 748
Re: Understanding static pressure - building a flow hood. [Re: RogerRabbit]
    #20196654 - 06/27/14 10:47 PM (9 years, 8 months ago)

Ok great, thanks again RR.. I think I have my numbers worked out. I ended up using the flow hood construction guide on the Lotte and Thomas orchid site here

The filter I am considering buying (from here) has the following specs:

Size: 0.305m x 0.61m (by coincidence its the same size as in the example linked above)
The airflow capacity = 350CFM @ 250Pa Initial Pressure Drop (which I interpret as being equivalent to 250Pa Static Pressure)

So my required airflow (from the blower) is:
0.305m x 0.61m x 0.5s/m = 0.09303
0.09303 x 3600 = 335m3/h (=197CFM)

197CFM is about 56% the nominal capacity of my filter: (197/350)x100=56%.
And the static pressure at that % capacity is approx 145Pa (according to the filter's data sheet).

So I need a blower that can deliver air at 335m3/h (197CFM) @ 145Pa.

Ive located a 225CFM blower that matches pretty closely...
So my numbers seem to match up pretty well with flow hood guide on the Lotte and Thomas Orchids page.

What Im confused about now is
.. how come all the threads I read on the shroomery talk about needing 465CFM blowers? According to the numbers Ive laid out above a 465CFM blower would way too powerful... I must have stuffed something up?? Or is it that my filter has a low resistance... Is the Lotte and Thomas flow hood guide known to be good? Or is it a bad method? It doesnt seem to match the example provided by FungiFun...


--------------------
Useful bulk substrate calculator

Edited by psyke101 (06/28/14 06:08 AM)

Extras: Filter Print Post Top
OfflineRogerRabbitM
Bans for Pleasure
Male User Gallery


Registered: 03/26/03
Posts: 42,214
Loc: Seattle
Last seen: 1 year, 1 month
Trusted Cultivator
OG Cultivator
Re: Understanding static pressure - building a flow hood. [Re: psyke101]
    #20199628 - 06/28/14 04:37 PM (9 years, 8 months ago)

I don't have time to look it all up right now, but check your English to metric conversions for any mistakes.  If your filter is low resistance, that's the reason for getting away with a smaller blower, but you may not have laminar flow.

Make sure when figuring flow you use cubic feet per minute, not feet per minute, or the metric equivalent.  One is a measure of volume, the other a measure of speed.
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
Invisiblepsyke101
Test Subject


Registered: 04/30/11
Posts: 748
Re: Understanding static pressure - building a flow hood. [Re: RogerRabbit]
    #20200177 - 06/28/14 06:37 PM (9 years, 8 months ago)

Quote:

RogerRabbit said:
I don't have time to look it all up right now, but check your English to metric conversions for any mistakes.  If your filter is low resistance, that's the reason for getting away with a smaller blower, but you may not have laminar flow.

Make sure when figuring flow you use cubic feet per minute, not feet per minute, or the metric equivalent.  One is a measure of volume, the other a measure of speed.
RR





I feel confident Im using the correct units. Ive checked and rechecked my numbers, comparing it to both the fungifun and the Lotte and Thomas examples (however I am totally open to correction, in fact I am expecting it at some stage).

As you say RR, I understand the difference between m/s , fpm (measurements of speed) and m3/H , CFM (measurements of volume). And I think I have used the correct conversions.. again my references are the fungifun and Lotte and Thomas examples.

I think... what I have discovered, and where a lot of confusion on the forums derives from, is the fungifun example (which most people use when making their flow hoods) misses a step. The author doesn't state the nominal airflow capacity of his example filter (for the static pressure of 250Pa), and he doesn't go on to figure out what % capacity his estimated required flowspeed (from the blower) represents for his filter... Instead he just assumes he wants a static pressure of 250Pa and uses that value to match a blower up... but thats wrong. The Lotte and Thomas example shows that.. they state that their required flow speed represents 60% the capacity of their chosen filter, and when operated at that % capacity the static pressure would be 150Pa... they then use that pressure to choose a blower... which results in them choosing a much less powerful blower than what the fungifun example advocates...

In summary I think the fungifun example is wrong... and its taken me 3 days and about a ream of A4 paper to figure it out! :mad2:

However I am 100% open to correction. Im just trying to get my head around this so I can make the right choices for my parts... So if anyone can come long and point to where I'm making mistakes I am totally listening.


--------------------
Useful bulk substrate calculator

Extras: Filter Print Post Top
Invisibleamp244
Sporocarp Stretching

Registered: 08/05/08
Posts: 1,336
Re: Understanding static pressure - building a flow hood. [Re: psyke101] * 1
    #21273530 - 02/14/15 02:35 PM (9 years, 1 month ago)

I know this thread is 8 months old, but I would like to clarify things for those studying on the forums.

“Static Pressure” and “Pressure Drop” in this circumstance are synonymous and can be measured using both standard and metric units ie:

SI measurement:      Pascal (Pa),
Non SI/Standard:      Inches of Water Column (Wc),

The optimum air VELOCITY in laminar flow systems is 100 feet per minute*.
The equation to calculate the correct fan/filter combination can be defined as:
                                                        X=D*Y
where:
X= the optimal net cfm of a fan @ a certain static pressure
D = desired air VELOCITY (coming off the HEPA filter) in FEET PER MINUTE(fpm)
Y = Square feet of filter face

In other words, this is the volume of air, X, that needs to be pushed through an orifice of a specific size, Y, to produce a channel of air at a particular velocity, D, set in this case at 100fpm.

You say that 100% airflow capacity of your filter is 350cfm@ 250Pa (1”wc). You also say that your filter is roughly 2’x1’. This would produce an air velocity after being pushed through the HEPA filter of 175 feet per minute, which is not optimal for laminar flow*.   
X = 350cfm and Y = 2ft^2; therefore D = 175 fpm

By fixing the desired air velocity at 100fpm and multiplying this by 2ft^2, the optimal net cfm from the fan would be 200 cfm.
D = 100 fpm and Y = 2ft^, 2; therefore X = 200 cfm

Filters will produce a measurable resistance when being operated at any given airflow, and typically come with a chart detailing the resistance at various levels of supportable airflow. HEPA filters have a linear resistance x airflow characteristic, thus when the airflow is lowered there is a commensurate reduction in resistance to airflow. At 200 cfm, this resistance would be around 145Pa (.58”). Laminar flow hood construction is designed for the air stream to hit the filter at a perpendicular angle, allowing the force of the impact to aid in trapping particles into the filter*, so I would think the static pressure is a pertinent variable in achieving efficiency. Stamets illustrates an example where a filter is selected that produces 1” of pressure when the desired air velocity of 100fpm is maintained. I’m not sure if there is an optimal/desirable static pressure for efficiency but I still think your set-up would work for this application.

The reason you only need a fan capable of moving 200cfm through the filter is because your filter face is only 2ft^2, whereas those using a 2’x2’ filter would need a fan with twice the capacity to achieve the 100 fpm “desired velocity”. Obviously, the higher the static pressure from the filter, the more power the fan must exert to supply the desired “net cfm”. Generally, a fan running at 100% capacity @ no resistance will move more air than that same fan running at 100% capacity at 1” of resistance. The higher the static pressure @ a given airflow, the more power the fan must produce to sustain that airflow. Considerations should be made accordingly in selecting the right fan to achieve the desired net cfm.

You need to select a filter/blower combination based on the design of the flow hood, in addition to airflow and resistance requirements. The filter needs to be able to handle the volume of air moved by the fan, and the fan needs to be capable of supplying the right amount of air while handling the static pressure produced by the filter. Remember the equation: X(the fan) = 100*Y(the filter face). The optimal air velocity is fixed at 100fpm, so determining the amount of air that needs to be moved is a matter of deciding the dimensions of your filter. Selecting a filter is based on these dimensions and required air flow. Selecting a fan is based on the required air flow, and filter resistance @ that airflow.

Hope that helps.


*Stamets, P., & Chilton, J. (1983). The mushroom cultivator: A practical guide to growing mushrooms at home (pp. 149-150). Olympia, Wash.: Agarikon Press


--------------------
How to Convert a Normal 24-hour Light Timer into a Short Cycle Repeating Timer


"Monopoly, besides, is a great enemy to good management, which can never be universally established but in consequence of that free and universal competition which forces everybody to have recourse in it for the sake of self-defense." -Adam Smith

Extras: Filter Print Post Top
Jump to top Pages: 1

Shop: MagicBag.co All-In-One Bags That Don't Suck   Left Coast Kratom Buy Kratom Extract   North Spore North Spore Mushroom Grow Kits & Cultivation Supplies   PhytoExtractum Maeng Da Thai Kratom Leaf Powder   Kraken Kratom Red Vein Kratom


Similar ThreadsPosterViewsRepliesLast post
* 24''x24'' Flow Hood Questions
( 1 2 all )
Cow Shit Collector 11,653 26 02/07/05 11:27 AM
by Arp
* flow hood ast 2,324 11 07/16/02 04:41 AM
by Una
* Flow Hood
( 1 2 all )
Shpongloid 7,347 33 08/20/04 10:22 AM
by hyphae
* Blowers, CFM's & flow hoods greenshaman 2,036 5 03/13/03 10:00 PM
by Anno
* Huge Laminar Flow Hood? Pugslee_Atoms420 2,641 8 04/12/03 10:17 AM
by debianlinux
* Tons of contaminations WITH Flow Hood!!! mobyd 3,157 5 05/20/03 07:31 PM
by cyankid
* Poor Man's Flow Hood Cow Shit Collector 3,694 9 09/01/03 05:55 AM
by Cow Shit Collector
* Flow Hood Blower Source altarego 1,211 5 10/29/01 03:32 PM
by un0r

Extra information
You cannot start new topics / You cannot reply to topics
HTML is disabled / BBCode is enabled
Moderator: RogerRabbit, Pastywhyte, bodhisatta
3,180 topic views. 0 members, 4 guests and 5 web crawlers are browsing this forum.
[ Show Images Only | Sort by Score | Print Topic ]
Search this thread:

Copyright 1997-2024 Mind Media. Some rights reserved.

Generated in 0.02 seconds spending 0.004 seconds on 12 queries.