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Offlineouuwee
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Flowhood questions
    #26828466 - 07/17/20 08:57 AM (3 years, 6 months ago)

Using a SAB in this hot weather is killing me so I decided to finally get a flowhood. I've been searching around for a 12x24x6 and I just requested a quote from a popular filter company. They no longer offer wooden frames for their HEPAs. Their only options are plastic frame or metal, so which one should I get for the filter? Also, they are asking me what's the application for the filter and what is the CFM. What should I tell them? Do I tell them I'm using it to build a flowhood? Do I say 100 CFM or do I include the area of the filter (2ft x 1ft = 2ft squared x 100ft/min = 200ft cubed/min) and tell them 200 CFM?

(I'm looking for places that sell cheap filters, so if you have any suggestions please let me know)


Edited by ouuwee (07/17/20 09:04 AM)


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Re: Flowhood questions [Re: ouuwee]
    #26828542 - 07/17/20 09:28 AM (3 years, 6 months ago)

Get a metal frame. Tell them it's for laminar flow, they should know what you're talking about. You need 100ft/min @ at least .5" water guage. They should already know all of this once you tell them what the application is, tell them you're a gourmet mushroom farmer if you like.

The CFM is unknown and can be anything at this point, unless you already have a blower but I'm assuming that you do not. The important part at this point is ensuring the correct flow rate at the correct static pressure. Your CFM should come out between 200 CFM and 240.


Edited by Stipe-n Cap (07/17/20 09:37 AM)


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Offlineouuwee
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26828557 - 07/17/20 09:37 AM (3 years, 6 months ago)

Quote:

p9hu7 said:
Get a metal frame. Tell them it's for laminar flow, they should know what you're talking about. You need 100ft/min @ at least .5" water guage. They should already know all of this once you tell them what the application is, tell them you're a gourmet mushroom farmer if you like.

The CFM is unknown and can be anything at this point, unless you already have a blower but I'm assuming that you do not. The important part at this point is ensuring the correct flow rate at the correct static pressure.




Thank you. They recommended me to purchase the PURACEL metal aluminum separator filters. These are their options. What is the difference between standard and high capacity?



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Re: Flowhood questions [Re: ouuwee]
    #26828562 - 07/17/20 09:40 AM (3 years, 6 months ago)

So the first one looks good. 12x24x6 250CFM@1"SP:thumbup:

Now it should be 100ft/min with those stats, just make sure before pulling the trigger.


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Offlineouuwee
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26828595 - 07/17/20 09:59 AM (3 years, 6 months ago)

Quote:

p9hu7 said:
So the first one looks good. 12x24x6 250CFM@1"SP:thumbup:

Now it should be 100ft/min with those stats, just make sure before pulling the trigger.




Thank you!!! Now on the lookout for a compatible motor...  If I'm only going to tape a pre-filter on the intake (wont be building a small box for it), would that make the static pressure 1.2? So I would need to find a blower that can do at least 250CFM@1.2?


Edited by ouuwee (07/17/20 09:59 AM)


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Re: Flowhood questions [Re: ouuwee]
    #26828600 - 07/17/20 10:03 AM (3 years, 6 months ago)

Click the link in my sig, scroll down to the HVAC video and take a look at how pressure drop varies between different kinds of furnace filters. Your average filter is about .4"W.g if I remember correctly.

As long as there is a seal around the intake so that the flow is only going through the filter material and not running free along the sides you can be sure that the static pressure of the prefilter will remain true, not so if there are leaks from an improper seal. Better to use a box, that way you're not wrapping everything up with an ungodly amount of tape to keep it sealed.


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Offlineouuwee
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26828690 - 07/17/20 10:50 AM (3 years, 6 months ago)

I think I'll pass on the pre filter since it will just make finding a motor more difficult. I'm looking at the 1tdt2 and 1tdt7 dayton. they both have similar CFM @ 1.0

1TDT2


1TDT7


Which one is more appropriate?


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Re: Flowhood questions [Re: ouuwee]
    #26828733 - 07/17/20 11:09 AM (3 years, 6 months ago)

The first one only pushes 210@1" SP, your filter requires 250@1"SP.

The 1tdt7 does 240 max. Both are under powered.

Confirm that the flow rate of that filter is 100ft/min at 250.


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Offlineouuwee
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26829554 - 07/17/20 06:28 PM (3 years, 6 months ago)

So I just heard back from the company and they quoted me $190 before shipping which is out of my budget. I found a different site that is selling a 99.97% wooden frame rating at ~$110 shipped. How much of a difference is 99.97 vs 99.99? Should I pay more for a 99.99% metal frame (about $180 shipped)?

I'm not sure if I could post links to the site I'm looking at.... if it's not too bothersome, can I PM you the links to see if they are good?


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Re: Flowhood questions [Re: ouuwee]
    #26829838 - 07/17/20 09:55 PM (3 years, 6 months ago)

You can PM me if you want, brother, no problem. My recommendation however will always be to get the better quality equipment, you get what you pay for. Although it's $70 more it is worth the investment. You can definitely get by with  the cheaper wooden frame filter, it will work 100% having said that...

Save for the extra month or however long that it takes, you have already invested this much time and effort into this hobby, don't cut corners.

That will always be my recommendation.


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Re: Flowhood questions [Re: Stipe-n Cap]
    #26830047 - 07/18/20 01:00 AM (3 years, 6 months ago)

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


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Re: Flowhood questions [Re: ouuwee]
    #26830052 - 07/18/20 01:10 AM (3 years, 6 months ago)

Quote:

ouuwee said:
I think I'll pass on the pre filter since it will just make finding a motor more difficult.





Do not pass on the prefilter if you want your flowhood to be effective for a long time.

Mine has been in daily use for almost 1.5 years with no noticeable changes in flow. The prefilters have to be replaced once a month because they start to hinder flow and they are really dusty and full of different particulate material. If I had just let that junk in I bet I would have had to replace that flowhood months ago.

Edit: my flowhood is a 24x36x6. a smaller one would have accumulated more filth much faster.


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Edited by southbounpachyderm (07/18/20 01:13 AM)


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Offlinew00tmycelium
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Re: Flowhood questions [Re: southbounpachyderm]
    #26830193 - 07/18/20 05:11 AM (3 years, 6 months ago)

When you say prefilter, is that charcoal or HEPA or both?


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Re: Flowhood questions [Re: w00tmycelium]
    #26830336 - 07/18/20 08:28 AM (3 years, 6 months ago)

Quote:

w00tmycelium said:
When you say prefilter, is that charcoal or HEPA or both?



Simple furnace filter. I opt to use merv 13 filters because my blower is overpowered for my filter and it can handle the extra pull.


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Re: Flowhood questions [Re: southbounpachyderm]
    #26832668 - 07/19/20 02:51 PM (3 years, 6 months ago)

Sounds like a good setup, MERV 13 should be plenty for a prefilter by far (to me at least.)


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Re: Flowhood questions [Re: ouuwee]
    #26832753 - 07/19/20 03:35 PM (3 years, 6 months ago)

You are going to want to use a prefilter. It will add years to a HEPA. I just use simple Filtrete furnace filters, doesn't have to be anything fancy.


First check your HEPA specs and see what the WG is at 200CFM, that will be your static pressure.

Then look at the blower specs for your prospective blower and see what it pushes at your HEPA's SP (plus estimate 0.2SP for a prefilter).

On my 12 x 24" Flow Hood I am using the Dayton 1tDT2. Seems to be a good blower for these. My HEPA has an SP of 0.8" @ 200CFM. My blower pushes 360CFM @ 0.8"SP and either 220 or 240CFM @ 1.0SP (adding 0.2" for the prefilter.) It's really hard to read that graph.


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Edited by mushpunx (07/19/20 07:24 PM)


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Offlineouuwee
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Re: Flowhood questions [Re: mushpunx]
    #26832770 - 07/19/20 03:49 PM (3 years, 6 months ago)

So I'm thinking about purchasing the Glasfloss 1100 Series 99.99% HEPA FILTER METAL FRAME 24 X 18 X 5 7/8 for about $216 shipped. Good price or are there better deals? Looking for recommendations!!! I looked up the specs and I'm not really sure what these numbers mean.



Edited by ouuwee (07/19/20 04:08 PM)


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Re: Flowhood questions [Re: mushpunx]
    #26832776 - 07/19/20 03:52 PM (3 years, 6 months ago)

I'm not sure why everyone thinks that 1" furnace filters are only .2 inWG, each filter will be different but you're more than likely adding .4 to .5 inches of static pressure. Half an inch is pretty significant.

Also, not all 12x24 filters are the same either, eash one will generate a different amount of resistance. If he has 100ft/min at 250CFM with 1"SP then both of those listed blowers are under powered even without a prefilter. My point is that you can't recommend the same blower for every filter that has a similar surface area.

Ouwee

My recommendation is to stop trying to sort through the bargain bin for filters. Flowhoods are a somewhat significant investment, expect to spend money. The reason I'm saying that is because you're going to drive yourself crazy trying to read information that doesn't make any sense to you, buy a filter meant for a laminar flow application and drop the dead weight of uncertainty. All HEPA are not created equal.

My recommendation is to grab a FFU from myers mushrooms:

https://myersmushrooms.com/

Grab a filter and blower from FP:

https://fungi.com/apps/omega-search/?type=product&q=Hepa*

Or ask one of the nice chaps around the forum with a baller hood to shoot you a link.


Edited by Stipe-n Cap (07/19/20 04:12 PM)


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Offlineouuwee
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Re: Flowhood questions [Re: Stipe-n Cap]
    #26832809 - 07/19/20 04:12 PM (3 years, 6 months ago)

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.


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Re: Flowhood questions [Re: ouuwee]
    #26832820 - 07/19/20 04:15 PM (3 years, 6 months ago)

Think of it like this, you're not just investing in a laminar flow unit but also all of the time, effort, and materials that you place in front of it over time. You are relying on your equipment to be functional and reliable. If you make a poor investment now by either purchasing incorrectly, purchasing too small or whatever the case is, it will have consequences down the line. Spend big once and have the peace of mind that comes with it.


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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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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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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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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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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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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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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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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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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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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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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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InvisibleStipe-n CapMDiscord
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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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InvisibleStipe-n CapMDiscord
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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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OfflineGan
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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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Invisibledfwerydfhg
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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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Invisibledfwerydfhg
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Re: Flowhood questions [Re: dfwerydfhg]
    #26837854 - 07/22/20 09:55 AM (3 years, 6 months ago)

Oh and in theory, there's no minimum velocity for laminar flow. Obviously at a certain point air will only be coming from some parts of the filter, which is not good for maintaining an even flow profile. But as long as every part of your filter is working evenly, it'll be laminar. But as I say above super low velocities are not desirable because air movement in the room, your movements, etc. will then have an easier time getting into your laminar zone and fucking things up.


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Invisiblesandman420
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Re: Flowhood questions [Re: ouuwee]
    #26837858 - 07/22/20 09:56 AM (3 years, 6 months ago)

Quote:

ouuwee said:
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?



its around 0.45....you need to calculate the SP at 100 fpm you had the right idea. Most filters have a rated SP not at 100 fpm and it gets all these people tripped up buying too much fan.


--------------------
- Sandbag Tek - How To Sterilize Spawn Bags - All About Static Pressure / Pressure Drop for DIY Flow Hoods - Sandman's LC Tek-

Marijuanaut escapes earth to cultivate - Grow-room is church temple of the new stoner breed


Edited by sandman420 (07/22/20 10:06 AM)


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Invisiblesandman420
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Re: Flowhood questions [Re: Gan]
    #26837861 - 07/22/20 09:57 AM (3 years, 6 months ago)

Quote:

Gan said:
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?




Laminar air flow can only exist at air speeds of around 90-120 FPM, anything more is not physically possible to be laminar.


--------------------
- Sandbag Tek - How To Sterilize Spawn Bags - All About Static Pressure / Pressure Drop for DIY Flow Hoods - Sandman's LC Tek-

Marijuanaut escapes earth to cultivate - Grow-room is church temple of the new stoner breed


Edited by sandman420 (07/22/20 10:06 AM)


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Invisibledfwerydfhg
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Re: Flowhood questions [Re: sandman420]
    #26837923 - 07/22/20 10:21 AM (3 years, 6 months ago)

Out of interest I just ran the numbers- for room temp air in a 24" x 24" channel, at ~0.5 m/s (~100 FPM), the Reynolds number is actually firmly in the turbulent regime.

But what is actually happening, is that because the filter is pleated so deeply, the actual flow area of the air through the filter is some multiple of the channel area. So as it passes through and exits the filter, the air is still in the laminar regime. Then, as it exits it will begin to transition to turbulent flow. But this takes some time to develop (usually 10+ channel diameters), so for the distances involved in flow hoods it's irrelevant.


Edited by dfwerydfhg (07/22/20 10:22 AM)


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OfflineRoscoeReturnsS
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Re: Flowhood questions [Re: dfwerydfhg]
    #26838169 - 07/22/20 12:10 PM (3 years, 6 months ago)

Another thing to consider is that the filter efficiency drops at increasing airflow. Even in HVAC hepa filter banks, where laminar flow was not a consideration, we routinely kept airflow at or below 150fpm. Anything above that, and we would see “leaks” during integrity testing. No leaks were present, and once velocities were reduced the filters passed testing.


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Invisiblesandman420
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Re: Flowhood questions [Re: RoscoeReturns]
    #26838187 - 07/22/20 12:17 PM (3 years, 6 months ago)

you my old homie roscoe?


--------------------
- Sandbag Tek - How To Sterilize Spawn Bags - All About Static Pressure / Pressure Drop for DIY Flow Hoods - Sandman's LC Tek-

Marijuanaut escapes earth to cultivate - Grow-room is church temple of the new stoner breed


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Offlineouuwee
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Re: Flowhood questions [Re: sandman420]
    #26838335 - 07/22/20 01:29 PM (3 years, 6 months ago)

Quote:

sandman420 said:
Quote:

ouuwee said:
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?



its around 0.45....you need to calculate the SP at 100 fpm you had the right idea. Most filters have a rated SP not at 100 fpm and it gets all these people tripped up buying too much fan.




Thank you for clearing up the confusion I had. I've looked at some filtrete prefilters and they supposedly have a 0.2 wg resistance. What MPR/MERV should I get? With that said, and rounding up to 0.8 wg, it seems like the dayton 1TDT8 matches well with the 24x24 HEPA filter. At 0.8wg, I get 520 CFM. I'll be getting a replacement 1TDT8 to save some money. Can someone else confirm that this blower will work before I go ahead and purchase it?



I was able to find someone locally selling brand new 3-pack filtrete furnace filters 16x25x1 for $10.....
https://www.amazon.com/Filtrete-Allergen-Reduction-Delivers-Throughout/dp/B07GFSKDKM
Would these work as prefilters? MERV rating is 13/Filtration level 2200 and has a pressure drop of 0.21


Edited by ouuwee (07/22/20 05:58 PM)


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