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InvisibleStipe-n CapMDiscord
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26833098 - 07/19/20 07:30 PM (3 years, 6 months ago)

Quote:

mushpunx said:
I don't have the flow chart for his filter so I don't know what that number is going to be except that it should be lower than 1.0", yeah?








This was what he posted as possible filter options. The top filter is the only suitable one so those were the stats we were working with, moot at this point however.


Yes I was responding to you in part.
I may have misunderstood you though, my apologies if so.

I thought that you were recommending the blower that you have for his filter, it was one of the blowers he had shown charts for. The blowers were underpowered at a maximum of 240cfm at the specified SP.

The furnace prefilters are likely almost never .1 or .2" though, they aren't very efficient, more likely to be half inch than anything.

Quote:

You said his filter is 1"SP @ 250CFM.
His filter face is 12 x 24" , wouldn't that mean he needs to know what his filter's static pressure is at 200CFM?




This part kind of confuses me though. His filter is listed at 1"SP at 250CFM so he would have to make sure that this test flow is at 100ft/min and not something too  low or too high, if that had of been the case he would of needed a blower that pushed a min 250CFM @ 1.4, .4 for a standard 1" thick  furnace filter.

But hopefully he gets something different.


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Re: Flowhood questions [Re: ouuwee]
    #26833099 - 07/19/20 07:30 PM (3 years, 6 months ago)

Quote:

ouuwee said:
I've always been a frugal guy. I only buy things that I would make good use of and I don't mind paying the money for it. After hearing about how small 24x12x6, I decided I'll be getting the bigger 24x18x6.




I had an 18 x 24" hood but I actually downsized to a 12 x 24. It's much less bulky and easier to move around. Height is way less important than width to me I found, I've been able to do anything I could in front of the 18" tall hood in front of the 12 x 24" with ease, even tall spawn bags (angle the bag to inooculate or keep the mouth of the bag in the flow and lower the rest under the hood, I stand it up on a stool). That said the 18 x 24 is a nice compromise if you don't mind spending a bit more and don't mind the extra bulk/weight. You'll never need to lift anything very high in the flow though.
When I have a permanent space and it's time to build a larger hood, I'm going to go big and wide.
Just a thought.


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Edited by mushpunx (07/19/20 08:19 PM)


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Offlinemushpunx
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Re: Flowhood questions [Re: mushpunx]
    #26833165 - 07/19/20 08:07 PM (3 years, 6 months ago)

Sorry man I ended up deleting my first  reply because it got too long and complicated haha.

As far as I understand it, because his filter face is 12 x 24", the number we are looking for on the flow chart would be the static pressure his filter develops at 200CFM.
So far we don't have that number, we would need to see the flow chart to get it.
A filter doesn't have a specific Static Pressure. When I say my 12 x 24" filter has a 0.8"SP I mean 0.8" @ 200CFM..
My 18 x 24" HEPA was 0.8" @ 300CFM.

I've been told that SP that is listed on the filters, is just what they are tested at with a particle counter, and the corresponding cfm coming out of the filter.
Meaning that at X.X" sp you get XXX cfm.


How to figure out how much to add on to our static pressure for a furnace filter, I have absolutely no idea. We are only using X amount of the filter face, to cover up a hole with a 5 or 6" diameter , if that makes any difference to it I have no idea. :shrug:


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Offlineouuwee
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Re: Flowhood questions [Re: mushpunx]
    #26833182 - 07/19/20 08:18 PM (3 years, 6 months ago)

I thought about long term, seeing as though this will last me for years, I would like something that I could use comfortably when I decide to scale up to unicorn bags. I'm sure the 12" height will work for bags, but I would have to set the bags lower than the flowhood so that the opening of the bag is in front of the laminar flow. No big deal, the cost difference from 12" height to 18 or even 24 is still under my budget.

I e-mailed several distributors and I should be hearing from them when the week starts. Depending on their quotes, I should be getting either the 18x24x6 or 24x24x6. I will provide an update once order is placed!


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OfflineRoscoeReturnsS
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Re: Flowhood questions [Re: mushpunx]
    #26833189 - 07/19/20 08:20 PM (3 years, 6 months ago)

Here is some info on sp for common pre filters at different flow rates. Listed pressure is through a 24”x24” filter.



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Offlinemushpunx
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Re: Flowhood questions [Re: ouuwee]
    #26833198 - 07/19/20 08:23 PM (3 years, 6 months ago)

I'd go with Fungi Perfecti for the 18 x 24 HEPA. Not the blower though.

I do tall bags in front of the 12 x 24 without lowering the bottom below the table though. You just angle the bags. Watch how RR inoculates large spawn bags on letsgrowmushrooms


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InvisibleStipe-n CapMDiscord
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Re: Flowhood questions [Re: mushpunx] * 1
    #26833204 - 07/19/20 08:26 PM (3 years, 6 months ago)

Quote:

mushpunx said:
As far as I understand it, because his filter face is 12 x 24", the number we are looking for on the flow chart would be the static pressure his filter develops at 200CFM.




I'm sorry brother but this is incorrect, you need to know the static pressure at a flow rate of 100ft/min. The CFM is a how many cubic feet of air/min required to achieve the 100ft/min flow across a specific surface area.


Quote:

So far we don't have that number, we would need to see the flow chart to get it.




This was clearly listed on the sheet above.

Quote:

A filter doesn't have a specific Static Pressure. When I say my 12 x 24" filter has a 0.8"SP I mean 0.8" @ 200CFM..
My 18 x 24" HEPA was 0.8" @ 300CFM.




This is also incorrect, static pressure (resistance) increases with airflow. The filter will have a very specific resistance at a very specific air flow measured in feet/min (FPM)

Quote:

I've been told that SP that is listed on the filters, is just what they are tested at with a particle counter, and the corresponding cfm coming out of the filter.
Meaning that at X.X" sp you get XXX cfm.




Whoever told you this is 100% incorrect. In fact it's backwards and the unit of measure is wrong.
@ x CFM FPM* you will have y resistance.

Just take a quick glance at this flow rate chart and it will be obvious.



Note the increase in resistance is correlative to the increase in flow. This is what makes a slightly pressurized plenum possible. The higher the flow rate the higher the resistance. The pressure in the plenum makes laminar flow possible, otherwise you would have chaotic flow. This is also why your choice in HEPA must have a min static pressure of .5 inWG or the filter won't create enough pressure in the plenum to organize the flow into lamina.

Quote:

How to figure out how much to add on to our static pressure for a furnace filter, I have absolutely no idea. We are only using X amount of the filter face, to cover up a hole with a 5 or 6" diameter , if that makes any difference to it I have no idea. :shrug:




Well you can look on the filter itself and sometimes they will list the information, if not you can google it...other than that watch this video for reference.



Edited by Stipe-n Cap (07/19/20 08:58 PM)


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Offlinemushpunx
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26833307 - 07/19/20 09:46 PM (3 years, 6 months ago)

Yeah , you're right man, I butchered that :rofl:

I got FPM and CFM crisscrossed in my head
and it just got alll fucked up from there


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Re: Flowhood questions [Re: mushpunx]
    #26833318 - 07/19/20 09:52 PM (3 years, 6 months ago)

The shit is a bit confusing, but I absolutely love it. Happens to the best of us :thumbup:


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Offlineouuwee
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26836720 - 07/21/20 05:59 PM (3 years, 6 months ago)

Pulled the trigger and ordered a 24x24x6 99.99% glasfloss 1100 series hepa filter.



The specs say the FPM is 175 and the resistance is 0.8 rounded up. So if we want the flow to be 100 FPM, does that mean the resistance of that filter (before adding prefilter) is ~0.45 rounded up to 0.5 wg?

Calculations 175/1.75=100 FPM so 0.8/1.75 = ~0.45wg before prefilter

So I need to find a motor that does 400 CFM at 1wg? (Assuming pre filters are 0.5wg added resistance)

Does anyone have links to where they buy their furnace prefilters? Would like to know the resistance for that so I can find a motor.


Edited by ouuwee (07/21/20 06:04 PM)


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InvisibleStipe-n CapMDiscord
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Re: Flowhood questions [Re: ouuwee]
    #26836723 - 07/21/20 06:01 PM (3 years, 6 months ago)

Minimum 100FPM, no need to nitpick. 175@.8 is perfect:thumbup:

Use the math template to match a blower. No need to go over it again when it's there.


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Offlineouuwee
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26836750 - 07/21/20 06:14 PM (3 years, 6 months ago)

I saw your updated math template thread but i'm confused on what static pressure I should be using before adding the prefilter. Is it 0.8 wg or 0.45wg? Because if I start at 0.8wg and add ~0.4wg from the prefilter, I get 1.2wg and most motors I've looked at doesn't have the required CFM at 1.2wg

Also, can you tell me what furnace filters u use for prefilter?


Edited by ouuwee (07/21/20 06:16 PM)


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Re: Flowhood questions [Re: ouuwee]
    #26836770 - 07/21/20 06:27 PM (3 years, 6 months ago)

I honestly have no idea where you're getting those numbers from. Just grab a 1" filtrete furnace filter.


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Offlineouuwee
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26836815 - 07/21/20 06:45 PM (3 years, 6 months ago)

Maybe i'm not understanding it correctly but isnt 175 FPM "overpowered" since we need a minimum of 100FPM? So the static pressure/resistance should actually be lower than 0.8wg?

Also, what dimensions filtrete furnace filters? What MERV? Don't know the general size of a motor.


Edited by ouuwee (07/21/20 07:38 PM)


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Re: Flowhood questions [Re: ouuwee]
    #26836983 - 07/21/20 07:57 PM (3 years, 6 months ago)

You're definitely over thinking things.

All you have to do is ask the supplier what static pressure the filter is at 100ft/min. That's it. You can have laminar flow at higher velocities but it's so fast that shit starts getting blown around.
It really seems like you are continously trying to fit square pegs into round holes.



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Offlineverytastycheese
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Re: Flowhood questions [Re: Eclipse3130]
    #26837009 - 07/21/20 08:07 PM (3 years, 6 months ago)

Quote:

Eclipse3130 said:
Just grab a pre built one, you can find 12x24s for fairly cheap I got mine for $600 Envirco model. Cuts out the time and hassle of building your own of course unless that's what you want to do, it will probably end up costing more and time




Did you order direct from them or used? Just asking because their prices aren't listed.


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Offlineouuwee
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Re: Flowhood questions [Re: verytastycheese]
    #26837039 - 07/21/20 08:24 PM (3 years, 6 months ago)

I just emailed the supplier. And I'm just trying to better understand the math and the meaning behind the numbers rather than just following a template. That way I can build another laminar flow hood by myself if I decide to upgrade/buy another one.


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Re: Flowhood questions [Re: ouuwee]
    #26837742 - 07/22/20 09:02 AM (3 years, 6 months ago)

So the reason why the template is set up that way is because laminar flow happens at 90 FPM+/- 10FPM. This is the industry standard test velocity for laminar flow benches intended for laboratory use.

If your velocity is insufficient then you will have chaotic flow, if there is too much then the same is also true. That knowledge informs your choice of blower because you need to move a certain volume of air to achieve that velocity at whatever static pressure is achieved at that velocity, that's why you always choose the filter first.

So basically:

Volumeteic Flow rate: v = CA
where V = Volume , A = Surface Area, C = velocity.

Super mega simple.

The velocity never changes it's always 90FPM +/- 10 FPM (use 100FPM for simplicity) multiplied by your filters surface area = the CFM needed for your blower.


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Re: Flowhood questions [Re: Stipe-n Cap]
    #26837751 - 07/22/20 09:06 AM (3 years, 6 months ago)

I've always wondered... is the upper limit of the fpm flow capped because eventually at higher flow velocities there is no longer laminar flow? Or is it just because at high velocities it will blow shit around and make it a pain in the ass to work unless you nailed everything down?


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Re: Flowhood questions [Re: Gan]
    #26837841 - 07/22/20 09:50 AM (3 years, 6 months ago)

There's a transition region between laminar flow and turbulent flow. Engineers characterize it with a dimensionless constant called the Reynolds number, but you don't need to know about that unless you work in some field that requires it.

Basically for a given geometry, e.g. a rectangular cross-sectional duct like a flow hood (another common use is in pipe flow), and a given fluid, you can calculate the Reynolds number using the velocity of the flow, the density and viscosity of the fluid, and the shape of the flow channel. There's a sweet spot where your Reynolds number will be sufficiently far below the transition region where things start to look turbulent, but your velocity will be high enough to stop back flow from bulk air movement outside the hood, moving your hands around, etc. At higher (but still laminar) flows, you can start inducing more turbulence downstream of items which is also undesirable.


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