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InvisibleStipe-n CapMDiscord
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So you're building a flowhood....easy flowhood math template. * 14
    #26679345 - 05/18/20 05:04 PM (3 years, 8 months ago)

  There seems to be a lot of confusion when it comes to selecting a filter, then matching it to a blower. In this post I'll attempt to make a no-brainer, fill in the blanks Aide-mémoire for people struggling with the math. Each line in this template will inform the next, this is why you need to solve the filter issue before tackling the blower. Choose the filter first, then match the blower.

Not all High Efficiency Particulate Air filters are appropriate for laminar flow applications. HEPAs have a wide range of applications from furnace air filtration to Hospital and laboratory applications.

HEPA filters remove particulate such as micro-organisms, pollen, and mold spores from the air. HEPA filters used in clean benches should have a minimum filtration efficiency of 99.99% against airborne particles 0.3 microns in size. Filtration efficiency will be greater than 99.99% on particles that are larger than 0.3 microns.

My current filter is 99.999% down to .1 micron.



Not all flow regimes are appropriate for laminar flow, laminar flow is not just any ol breeze coming out of any ol filter, as mentioned above. Laminar flow is orderly and parallel, turbulent flow however is chaotic and non linear.

Laminar flow occurs when a fluid (like air, air behaves the same as a fluid) flows in parallel layers, with no disruption between the layers. ... Turbulent flow is a flow regime characterized by chaotic property changes. This includes rapid variation of pressure and flow velocity in space and time.

Don't expect laminar flow just because your fan has a HEPA filter on it, if you don't follow this template you can be assured that you will have turbulent flow.

Turbulence = contamination



This is a great example of what not to do:



The Template


Step 1: The filter

After you've decided which HEPA filter you want you'll need to download the .pdf file for that filter or ask the retailer/manufacturer to supply the spec sheet which will have the velocity/resistance chart:



Here is a sample chart for a 2ft by 4ft HEPA which shows three different filters by thickness represented by the three different coloured lines. On the left you will notice that it's labelled "Resistance [W.g]" W.g stands for Water gauge and it's the unit of measure used to measure your static pressure (SP).

Before you can match any blower to your filter you need to find out how much resistance (Static pressure) your HEPA has at a velocity of 100 feet/min +/- 10 FPM. 100ft/min is the minimum velocity necessary to achieve laminar flow across the surface of your filter.

FPM refers to the "air speed" produced by the filter(at a specific static pressure), as measured in Feet Per Minute. CFM is a measure of the "air flow," stated in Cubic Feet per Minute. In other words, FPM is a measurement of how fast (velocity) the air moves and CFM measures how much air is moved (volume).



The red line show's exactly where the filter (green line) intersects with the W.g on the left and 100 feet/min on the bottom, it's now clear that this filter produces .5 inWG of static pressure at 100 feet per minute. Now it's time to figure out the volume of air we need to move to achieve a velocity of 100ft/min across the surface of the filter.

1. HEPA measurements:
Length___ft x width___ft = ___ft²

2. Flow rate:
100ft/minute x ____ft² =____ft³(CFM)
Maximum CFM for the filter is +20% of minimum CFM.

So let's use this template with the filter represented by that chart above.

1. HEPA measurements:
L_4_ft x W_2_ft = __8_ft²

2. Flow rate:
100ft/minute x __8__ft² =__800__ft³(CFM)
Maximum CFM for the filter is +20% of min CFM.

So this filter requires a blower that blows 800CFM at .5 inWG of static pressure (not including the prefilter).
Any filters that we use as prefilters will also produce static pressure, many standard 1" furnace filters usually have a resistance of around .4 inWG of static pressure, this needs to be added to the static pressure of your HEPA.

Let's add static pressure to the equation:

1. HEPA measurements:
L_4_ft x W_2_ft = __8_ft²

2. Flow rate:
100ft/minute x __8__ft² =__800__ft³(CFM)
Maximum CFM for the filter is +20% of CFM.

3. Static Pressure:
HEPA SP _.5___+ prefilter SP_.4___= .9" W.g (SP)

Using these simple equations we can see that this filter requires a blower that is minimum 800CFM - max 960CFM @ .9 inWG (SP) to achieve 100ft/min.

Step 2: The Blower

Now blowers have charts of their own, here's an example:



As you can see on the left hand side of this chart they've listed the static pressure, on the right in bold they show the CFM at the corresponding SP.
We can see that this particular blower pushes 360CFM @ .8" SP....this blower is not strong enough, keep looking.

Here's an example of another type of blower chart:



This chart shows a blower (top line) that is 911CFM @ .9 inWG, this blower will match the above 2ft x 4ft filter :thumbup:


Step 3: Application

Now do it for your own filter, just plug in your own numbers and you'll be gtg. The combined answers you get from line 2 and line 3 will give you the specs for your blower, as shown below.


1. HEPA measurements:
Length___ft x width___ft = ___ft²

2. Flow rate:
100ft/minute x ____ft² =____ft³(CFM)
Maximum CFM for the filter is +20% of minimum CFM.

3. Static Pressure:
HEPA SP ___+ prefilter SP____= ___ "W.g SP


Blower match = 2. ____CFM@ 3.____"SP


A note on "clogging the intake"

Blocking the air intake of your blower excessively will put unnecessary strain on the motor and will likely effect it's lifespan/efficiency. Chocking the intake can be done within reason however I suggest getting as close as possible to the proper output without choking the intake. No need for six prefilters to close the gaps of incomplete planning.


Here's an interesting HVAC video that clearly illustrates pressure drop in filters.
An average 1" pleated furnace filter will produce ~ .4 to .5 inWG in pressure drop.



Thanks to Sandman420 for this laminar flow smoke test video:




I hope this write up clearly illustrates the relationship between filter, blower, and their respective charts.

Happy building.
The above filter and blower match up were used in this build


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OfflinePinkStormtrooper
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Re: So you're building a flowhood? [Re: Stipe-n Cap]
    #26679448 - 05/18/20 05:36 PM (3 years, 8 months ago)

math. brain. mushy. help. what if the motor blower is rated for a high static pressure like it says 1000CFM at 8" pressure. I can't math can you please show how to apply that?


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InvisibleStipe-n CapMDiscord
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Re: So you're building a flowhood? [Re: PinkStormtrooper]
    #26679456 - 05/18/20 05:39 PM (3 years, 8 months ago)

You buy/choose the filter first then match the blower, not the other way around.


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Re: So you're building a flowhood? [Re: Stipe-n Cap] * 3
    #26679547 - 05/18/20 06:18 PM (3 years, 8 months ago)



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Invisiblegizmo1
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Re: So you're building a flowhood? [Re: PinkStormtrooper]
    #26679666 - 05/18/20 07:15 PM (3 years, 8 months ago)

Finally got tired of us noobs asking questions huh p9


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InvisibleStipe-n CapMDiscord
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Re: So you're building a flowhood? [Re: gizmo1]
    #26679675 - 05/18/20 07:21 PM (3 years, 8 months ago)

Lol, not at all. Just thought this would have been helpful to read when I was trying to wrap my head around it for the first time. I find templates helpful, hopefully someone else will as well.


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OfflineMH5109
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Re: So you're building a flowhood? [Re: gizmo1]
    #26679677 - 05/18/20 07:22 PM (3 years, 8 months ago)

Fungi perfecti has a pretty good list with common filter sizes and blower pairs.


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Re: So you're building a flowhood? [Re: MH5109]
    #26679679 - 05/18/20 07:23 PM (3 years, 8 months ago)

Yeah but they don't tell you what the product numbers are or how to match them if you're buying them from another source.
They also don't show you the charts. If you live in a country other than the US and cannot order from them...


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Re: So you're building a flowhood? [Re: Stipe-n Cap]
    #26679704 - 05/18/20 07:41 PM (3 years, 8 months ago)

Quote:

p9hu7 said:
Yeah but they don't tell you what the product numbers are or how to match them if you're buying them from another source.
They also don't show you the charts. If you live in a country other than the US and cannot order from them...



Thats pretty damn foul.


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InvisibleStipe-n CapMDiscord
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Re: So you're building a flowhood? [Re: gizmo1]
    #26679708 - 05/18/20 07:43 PM (3 years, 8 months ago)

Yeah that Stamets character is pretty shifty. They use their own product numbers for the blowers.


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Invisiblegizmo1
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Re: So you're building a flowhood? [Re: Stipe-n Cap]
    #26684310 - 05/20/20 09:01 PM (3 years, 8 months ago)

So p9. You have been helping me alot answering my questions about FH. I get how to pair the blower and HEPA for the most part. The part I really don't understand is choosing the HEPA. What kind and depth is ideal? Wth is a mini pleat? We talked a little about it in cult general discussion the filter I had picked out was 99.99 but at .3 microns. Ideally I would want one that does 99.97 at .1 micron? I believe you said something like that. Is a deeper filter better than a shallow one? Does it matter? Also is the filter material important? Would it be better to have one framed in metal than wood? Where is it ok to skimp out on filter?
There is alot of stuff about pairing filter and blower, not so much about choosing the filter itself.


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Re: So you're building a flowhood? [Re: gizmo1]
    #26684440 - 05/20/20 10:27 PM (3 years, 8 months ago)

Those are great questions that 100% need answering when considering a filter. They've been covered soo many times by people far more expert than myself that I didn't cover it in my post, I haven't come across any kind of math template so I saw a potential niche that I could personally fill that would be somewhat original. Having said that I'm happy to weigh in on what you've mentioned...

The depth of the filter isn't really important in terms of what is better versus worse. Thickness plays a role in the amount of static pressure produced by the filter and that will have an impact on what blower you choose in the end. What I believe is important however is the efficiency of the filter, for example 99.95 versus 99.99 etc. I think that it comes down to availability of resources. The higher the efficiency the better obviously, .1 as apposed to .3, steel frame is preferred to cork for durability but cork will work and has worked for people in the past. Cork framed filters are always the cheaper option and the price will reflect upon it's efficiency.

Ultimately The question comes down to what can you afford and what is available where you live. A 99.95 cork framed 12" thick HEPA will definitely work(also whether the HEPA is pleated or metal fin) and can make for an affordable build for those who don't have a ton of disposable income for mycology.
My recommendation however, should you have the available funds and resources would be to invest in a metal framed HEPA with a slim build. Metal for the previously mentioned reasons and slim due to the fact that all of the newer high efficiency filters just come that way but also because of the reduced static pressure.

These are questions you'll have to ask yourself, do you have the money to invest in a Cadillac or do you want to be conservative and go with the Prius? Both will get you from A to B but with some obvious differences.

Now I'm by no means an HVAC professional, so should anything I've said be inaccurate I hope someone will step in and set it straight. Hopefully that's at least slightly helpful.


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Re: So you're building a flowhood? [Re: Stipe-n Cap]
    #26684489 - 05/20/20 10:59 PM (3 years, 8 months ago)

Appreciate you p9 always answering my noob ass FH questions. I'm definitely a Cadillac guy. More of a 1987 Cadillac with a flat tire kinda guy though. :howyoudoing:


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Edited by gizmo1 (05/20/20 11:04 PM)


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Re: So you're building a flowhood? [Re: gizmo1]
    #26684498 - 05/20/20 11:02 PM (3 years, 8 months ago)

Lol, but it's still a Caddy ; )


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Re: So you're building a flowhood? [Re: Stipe-n Cap]
    #26684502 - 05/20/20 11:05 PM (3 years, 8 months ago)

In all of its glory my friend.


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Offlinemushpunx
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Re: So you're building a flowhood? [Re: Stipe-n Cap] * 1
    #26684534 - 05/20/20 11:19 PM (3 years, 8 months ago)

Nice write-up!

Quote:

p9hu7 said:
Yeah that Stamets character is pretty shifty. They use their own product numbers for the blowers.




Yeah so people don't go out and buy them for a fraction of their price :lol:
I think I paid $80 + free shipping for mine brand new.

In case anyone is wondering the 549CFM (@ free air) blower Fungi Perfecti sells is the 1tdt2. It pushes 360CFM @ .8sp , *240CFM @ 1.0sp (*as far as I can tell reading the pixilated graph).

It works well with a 12 x 24" filter with an SP of 0.8 .
It is the blower they use in their Series 1 FH , I used it on my new 12 x 24" hood.


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Re: So you're building a flowhood? [Re: mushpunx]
    #26684554 - 05/20/20 11:28 PM (3 years, 8 months ago)

Yes indeed, it's on my series 1.
Yeah, FP intentionally obfuscates any identifying model numbers so that people don't know how to find the simplest of items from their site...like that fuckin scalpel, I want one but I'm definitely not buying one from them. Can't use "Paul's favorite scalpel" as search criterion.


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Offlinemushpunx
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Re: So you're building a flowhood? [Re: Stipe-n Cap]
    #26684607 - 05/21/20 12:01 AM (3 years, 8 months ago)

Quote:

p9hu7 said:
Yes indeed, it's on my series 1.
Yeah, FP intentionally obfuscates any identifying model numbers so that people don't know how to find the simplest of items from their site...like that fuckin scalpel, I want one but I'm definitely not buying one from them. Can't use "Paul's favorite scalpel" as search criterion.




I hear that man! I buy from them sometimes for things that I think are priced fair enough. Small stuff. I did get a HEPA from them before

I actually like the other scalpel they have, it's not Stamet's favorite I guess :lol: but you never have to change the blade and it's easy to clean. If you find the other one tho let me know!


Hey I don't want to derail you but what do you use for a prefilter on your Series 1?
According to the chart adding more than 0.2 SP will drop the flow below 200cfm


Edited by mushpunx (05/21/20 10:42 AM)


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Re: So you're building a flowhood? [Re: mushpunx]
    #26685102 - 05/21/20 08:09 AM (3 years, 8 months ago)

I don't use a prefilter on it.


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Offlinemushpunx
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Re: So you're building a flowhood? [Re: Stipe-n Cap]
    #26685386 - 05/21/20 10:37 AM (3 years, 8 months ago)

Quote:

p9hu7 said:
I don't use a prefilter on it.




Word. Thanks! It should be 360 CFM without one and it's a strong flow. Right now I put one on when I'm scrubbing the room.


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