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 Stargate
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 Laminar Flow Hood Calculations 
#23018952 - 03/18/16 12:05 AM (7 years, 4 days ago) |
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I'm having a little trouble trying to find the correct cpm I need for this HEPA filter. I just bought a Flanders Alpha 2000 - 24'' x 24'' x 11.5'' - High Capacity HEPA Filter 99.97%.
I'm going through this page, but can't seem to figure it out. I may still be a little fried from vacation.
http://www.fungifun.org/English/Flowhood#match
Anyone willing to help me out? I would appreciate it. I need to find a good blower for this flow hood. Thanks 
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 mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23019437 - 03/18/16 05:35 AM (7 years, 3 days ago) |
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Yea I love flow hoods hehe.
You really shouldn't have bought the 12" deep filter. I know its cheaper than the 6" deep filters, and they *will* work for laminar flow but they are so bulky and heavy.
Is there any chance you can return it? Also check for any damage, bent or crushed metal pins or tears in the paper.
A 6" deep filter will require at least a 6" deep plenum behind the filter. These are the prefered filters for flow hoods. Most of us go bigger than 6" behind the filter, I built my hood with a 12" plenum and its pretty big amd heavy. Seeing as your filter is 12" deep and will require a 12" deep plenum at minimum... but would be better to have 18" plus behind the filter that is going to be a very bulky, very heavy hood.
Your filter is 24 x 24". 24 x 24 =576 576/144 = 4 x 100 = 400.
Your hood will need a blower that pushes at or around 400CFM @ a static pressure of 1.2 (.2 added for the pre filter).
Blowers are usually listed by what they push at free air. My blower pushes 570 something CFM @ free air and a little over 300 CFM at an SP of 1.2.. my filter is 18 x 24 so this is perfect.
So beforr you purchase a squirell cage blower you will have to ask for the blower specs. It will be a graph or a listing of CFM output from free air up at various static pressure figures. Find one that pushes close to 400 @ 1.2 SP
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Supalemonhaze
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23019525 - 03/18/16 06:59 AM (7 years, 3 days ago) |
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His hepa is high capacity, 400cfm @1.2 is probably too much. Not sure but I read that a few times in old threads when I was sorting mine out.
Flanders should have a cfm rating for 100fpm, mine did at least. Yours could be rated for more fpm since it's high capacity and usually used to clean entire rooms at high fpm.
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Supalemonhaze
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Just downloaded their pdf for that hepa. As I suspected it is rated for 500fpm @ 1.35wg. Luckily they have a chart for it's performance.
Now I am assuming that you have the HEPA not the ULPA since you said it's rated for 99.97% efficiency. As you can see, at 125fpm (coming out of the filter) the pressure in WG will be .3 and at the commonly targeted 100fpm I'm aproximating somewhere around 0.2-0.25WG. If adding 0.2 for prefilter it's total SP will be around 0.45WG at 400cfm. This means that your blower should be rated for 400cfm at 0.45wg. Personally I would buy a speed controller and get my blower about 10-15% stronger. Filters will have their sp increase during their lifetime because of trapped particles in the material.
If you are adding 0.2 for the prefilter, I reccomend using a good one that will at least come close to that so you won't miss the mark by much.
I used a very thin stove extractor filter so you can imagine how that threw my calculations out the window. My FH runs at around 200fpm (approximately, my anemometer sucks) but luckily it did not matter all that much. Still works good but you have to remember that the higher the fpm, the less efficient your filter will be and will shorten your filters' working life.
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mushpunx
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The numbers on the filter have no use for us because we are technically re purposing these filters.
The only specs you need to know from the filter itself is the length and width of the filter face, and the depth.
The static pressure we are worrying about is what builds up in the plenum. A 12" filter needs at least a 12" plenum. Even a little 2" deep HEPA can acheive laminar flow, it just has a shorter lifetime. Same as a 6" won't last as long as a 12" (although most peoples hoods outlast the cultivators interest.. many many years).
The static pressure listed on the filters themselves is what they were tested at with a particle counter at the factory, and the CFM is what comes out.
Basically X.X SP will give you X.X CFM
The SP for a Laminar flow is around .8 and 1.2wg. You have to maintain a flow rate of around 100CFM per square foot of filter face area while maintaining the 1"wg plenum pressure.
The flow rate is the difference with thicker filters its a little higher and may have a little less resistance.
But the flow will still be laminar which is our purpose.
This is what confuses most people building hoods.
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Edited by mushpunx (03/18/16 09:09 AM)
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23019955 - 03/18/16 10:34 AM (7 years, 3 days ago) |
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http://www.fungi.com/product-detail/product/universal-blower-1040-cfm-8-sp.html
As for 400CFM @ 1.2 SP thats correct for a 24 x 24. Mine is 18 x 24 and my blower pushes 549CFM @ free air and like around (forgot the specs) 360 CFM @ .8 sp. So at 1.2 SP its * juuuuuust* about perfect for my filter as it needs 300CFM at 1.0 sp for laminar flow.
If you look at this link and see the all purpose blower recommend for 24 x 24, 24 x 36 and even my filter at 18 x 24! It blows 1040CFM at .8SP. I imagine you have to choke the intake to Adjust for different sizes.
So if he finds on close to 400CFM @ 1.2SP he will be golden.
OP go over 400 if you have to, if its too powerfull you can choke it down but too weak and you won't be able to hit Laminar.
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Supalemonhaze
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23019969 - 03/18/16 10:40 AM (7 years, 3 days ago) |
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But if he gets a blower that's 400cfm @1.2 he will get at least 4 times the fpm he wants.
I'm no engineer but the .8-1.2 sp requirement is for filters with a lesser capacity. Their resistance is much higher so you would need a better blower to get the required fpm. As the chart for his hepa says, if the filter has 0.8sp blowing from behind, he will have about 350fpm coming out of the filter.
I did the same mistake myself, I wasn't sure if I should follow their chart or follow my calculations. Since my calculations were higher I decided to go with them. My thinking at the time was that if my blower is too strong, my speed controller can decrease the cfm of the blower until I get 100fpm. But my calculations were so high that I couldn't do that without overheating the blower. Fortunately, 200fpm worked for me.
Here's a quote from a guy that actually worked with and recommends the thicker filters:
Quote:
Sci-Fi said:
The size of the plenum has little to do with the static pressure or back pressure for the fan to work against. The plenum should have as little restriction on the airflow as possible. An 8 to 10 inch plenum would be more than enough. 12 inches won't hurt anything, it will just make your box take up more space in your lab. The HEPA filter will provide 90% of the static pressure which isn't even a good thing. I'll tell you why.
To be clear about static pressure, the less static pressure that is applied or CFMs pushed through it the MORE efficient the HEPA filter becomes.
You should buy a super thick (thicker usually less back pressure) pleated HEPA filter with a low as possible static pressure at the CFM and feet per minute that you need. The more static pressure the HEPA creates the bigger and more expensive fan you're going to have to buy. I recommend 70 to 100 feet per minute. Any less will not provide a fast enough flow to keep contams from possibly drifting into your sterile work space. Any more and you will have dry spores blowing off your foil and your alcohol lamp not work as well and the flame will be burning sideways.
Do NOT order a 95% DOP. You need a Hepa filter for sure. HEPA means it's rated at 99.99% minimum efficiency at 0.3 microns @ "X" inches W.G. It should come with some document of the tested measurements.
ULPA filters will work just fine, but... they are more expensive, unnecessary, typically create more beck pressure (requiring a bigger more expensive fan), and aren't usually rated for the air flow or FPM you're going to want for a biological flow hood.
The W.G on a filter is the amount of back pressure it creates at a specific CFM. The picture below says my filter creates 0.5" W.G. of static pressure when I'm pushing 720 CFMs through it and it will be a minimum of 99.99% efficient down to 0.3 microns. My filter is 8 square feet and I run it at it's maximum CFM which creates is 90 feet per minute through the work space.
The W.G on a fan tells you how much static pressure it can create at a specific CFM. As the CFM it produces is variable depending on the back pressure. Example
The pressure (W.G.) will always increase with the CFM or feet per minute in both cases.
The Fan should be matched as close to the TESTED efficiency of the filter as possible and NEVER exceeding it.
Look at the "Air Performance Data" table on page 4 of this engineering detail this is exactly the data you will need to match your filter and your fan.
You should always build an work space enclosure in front of your filter to create a sterile space and not space where sterile air mixes will all the other air in the room.
Your hood should look like this
NOT THIS
People I know that work in corporate biological labs never use a so called flow hood with no enclosure on the front.
Notice his first couple paragraphs. I'm not sure that with the thicker filters the 0.8 sp is a requirement since they are so high capacity. I think that is quite accurate when it comes to 6" thick hepas with considerably lower capacities and higher static pressure.
It's important to remember that this guy actually built flowhoods with those type of filters, I've read tons of his posts back when I was making mine. Unluckily, he's not active anymore but my guess is that he didn't mention a minimum sp because it's dependent on how much air the filter actually allows to go through it.
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Supalemonhaze
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23020009 - 03/18/16 10:54 AM (7 years, 3 days ago) |
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Quote:
mushpunx said:
http://www.fungi.com/product-detail/product/universal-blower-1040-cfm-8-sp.html
As for 400CFM @ 1.2 SP thats correct for a 24 x 24. Mine is 18 x 24 and my blower pushes 549CFM @ free air and like around (forgot the specs) 360 CFM @ .8 sp. So at 1.2 SP its * juuuuuust* about perfect for my filter as it needs 300CFM at 1.0 sp for laminar flow.
If you look at this link and see the all purpose blower recommend for 24 x 24, 24 x 36 and even my filter at 18 x 24! It blows 1040CFM at .8SP. I imagine you have to choke the intake to Adjust for different sizes.
So if he finds on close to 400CFM @ 1.2SP he will be golden.
OP go over 400 if you have to, if its too powerfull you can choke it down but too weak and you won't be able to hit Laminar.
But you are forgetting that he has a 12" deep filter and you have 6". If he gets that blower his filter will be blowing over 400fpm.
I think the best thing to do is contact flanders and ask them personally. I did that and they responded within a day. Turned out I didn't follow their advise and in the end they were right and the calculations I used ( same as the ones you're reccomending) were wrong. 200fpm takes some getting used to but I'm afraid 400fpm will be too much.
You also cannot reduce that much power from a blower because the way a speed controller works. If the blower is made to get for example 1000rpm and you decrease the speed via speed controller, the motor will get less power but will still try to turn at 1000rpm. I know this first hand because when I tried to calibrate my FH to 100fpm I had to go down to about 30% of the rated power and the blower was humming incredibly loudly. This would in turn overheat the blower and you would have a disaster waiting to happen.
Op, I reccomend you send flanders an email, you can get it from their site and ask what sp you need to operate at to get 100fpm and if said sp is capable of laminar flow. I'm willing to bet money this is the case because Sci-Fi successfully built FH's with those filters that work at 100fpm and there's no way you can get 100fpm on those filters with 1.2sp.
I am by no means a pro but I have gone through this myself and the calculations on fungi fun are definitely not for every type of hepa. Every hepa has a different flow to pressure performance so it's impossible to make a formula that works with everything.
Edit:
Please let us know what you end up doing and the results. Information like this will always stay on the forums for people to find. There is so little information when it comes to 12" filters so this will prevent people from buying way overpowered and way overpriced blowers which will give them way too much fpm to work properly. Any info flanders gives out will also be a goldmine for someone who might go through what yoy are going through atm.
Edited by Supalemonhaze (03/18/16 11:00 AM)
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Stargate
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Well that was a burst of information. I do intend to not only use this HEPA for laminar flow, but will also be using it to clean the air in the lab consistently. After all the chatter, I feel that I did pick the right filter for what I want.
Supalemonhaze, I shot an email off to Flanders, asking them what you instructed me to ask. I definitely don't want to screw this up the first time, so I'll be taking the safe road here. For educational purposes of the future readers, I do plan to document the building of the laminar flow hood and post it.
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23020334 - 03/18/16 12:44 PM (7 years, 3 days ago) |
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Like I said dude we are re purposing these filters for laminar flow hoods. The specs that come with the filter dont mean anything to us, they are just the factory testing them with a particle counter.
We only need to concern ourselves with the static pressure built up in the plenum.
Stargate: dont make this harder than it is. Your filter is 12" deep so you will need at minum a plenum of 12", I recomend 18" or so.
Your blower should blow around 400CFM at 1.2sp
If you get your blower about that power and you use a plenum bigger than 12" you *will* acheive laminar flow.
The only numbers we need are the square footage of the filter face and the depth so se know how big to make the plenum. That is all you need from the filter.
You only need to get specs for the blower. Start looking at squirell cage blowers that push 7 to 900 CFM @ free air and ask for the blower specifications. Find one that pushes just over 400CFM @ 1.2SP, go a little above it
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23020344 - 03/18/16 12:46 PM (7 years, 3 days ago) |
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Very cool of you. People will most definitely be helped with that info.
You're going to buy a new filter? Or did I understand that wrong? As munxpunx was saying, the best filter you can get is a 6" one. That is the longest lasting one but that is not to say thinner ones won't work. I got a 4" one myself and even saw a successful build with a horrible 1" filter used for a vacuum if I remember correctly. The 12" ones are not usually used for hoods because of the high fpm they let through, making them more useful for scrubbing big rooms like operating theatres and such.
That said, if you have an up to spec FH the other filter is totally unnecessary for mycology. We use FH so that we have a sterile space we are able to work in. The rest of the room will not matter with a properly built FH because there is no way the air is able to make it into your work. The most common contamination vector when using a FH is yourself so the other filter still won't be a help with this. Unless you decide to take a 2 hr shower at 15psI that is  .
Whatever you buy, I suggest you stick with good brands like flanders which are actually my favourite. They provide good info, perfect tested products and great after sales service. They also win the cake for me because of the good protection packaging they send the filter in, which was super important for me since I live in the EU. I'm sure there's other companies just as good but if I ever need a new one, they will be my choice.
Before buying anything from flanders make sure you check that model's pdf file, just type in that long product number that has numbers and letters in google. In that file you will have everything that they installed in that filter, just compare the numbers and letters to the description.
Some things that I would recommend is a faceguard, very useful to protect from scratches. Unfortunately mine didn't have one and I didn't realise how good it would be to have one. Size matters when you are buying something which should last the better part of a decade so get the biggest one you can afford. As I said before thickness matters but should not be your no1 priority. A 2.5" filter can still last a decade if installed correctly and the prefilter is changed often. By installed correctly I mean that the pleats should be vertical rather than horizontal. This will keep the filter from tearing from the extra weight the filtered gunk adds. I read that in their pdf file too late unfortunately.
Goodluck, let us know what they say and how it goes.
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Supalemonhaze
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23020353 - 03/18/16 12:49 PM (7 years, 3 days ago) |
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Quote:
mushpunx said:
Like I said dude we are re purposing these filters for laminar flow hoods. The specs that come with the filter dont mean anything to us, they are just the factory testing them with a particle counter.
We only need to concern ourselves with the static pressure built up in the plenum.
Stargate: dont make this harder than it is. Your filter is 12" deep so you will need at minum a plenum of 12", I recomend 18" or so.
Your blower should blow around 400CFM at 1.2sp
If you get your blower about that power and you use a plenum bigger than 12" you *will* acheive laminar flow.
The only numbers we need are the square footage of the filter face and the depth so se know how big to make the plenum. That is all you need from the filter.
You only need to get specs for the blower. Start looking at squirell cage blowers that push 7 to 900 CFM @ free air and ask for the blower specifications. Find one that pushes just over 400CFM @ 1.2SP, go a little above it
But you do know that it will operate at around 400 fpm right? Do you think that is fine? Or maybe you think that at 1.2 sp it will be pushing 100fpm?
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23020364 - 03/18/16 12:54 PM (7 years, 3 days ago) |
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Quote:
Stargate said:
Well that was a burst of information. I do intend to not only use this HEPA for laminar flow, but will also be using it to clean the air in the lab consistently. After all the chatter, I feel that I did pick the right filter for what I want.
Supalemonhaze, I shot an email off to Flanders, asking them what you instructed me to ask. I definitely don't want to screw this up the first time, so I'll be taking the safe road here. For educational purposes of the future readers, I do plan to document the building of the laminar flow hood and post it.
It will work , it will actually last longer than a 6" filter which is good. But it will be very bulky and hard to move which is why most people use 6" deep filter.
As long as you know the dimensions of your Hepa (24 x 24 x 12) you have all the information you need to match a blower to it properly .
The thicker filter will have a higher flow rate and less resistance. This is why you can use the same blower for a 12" filter as a 6", provided you build the correct size plenum.
Goos luck!
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mushpunx
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"But you do know that it will operate at around 400 fpm right? Do you think that is fine? Or maybe you think that at 1.2 sp it will be pushing 100fpm?
It will be pushing 100CFM evenly across the whole hood. Youre forgetting the square footage. And the proper plenum to let the static pressure build up properly for even laminar flow.
Take my hood for example.
Its 18 x 24 x 6. My blower pushes 549 CFM @ free air. To do the calculation, you go.. 18 x 24 = 432 , ÷ 144 = 3.
3 x 100 = 300.
I checked the blower specs before I bought my blower, and saw it pushes a little over 360 (if I remember correctly, might have been higher) at .8 sp. Moving up the graph it blows just over 300CFM
@ 1.2 sp. I used a 10" plenum. I needed a 6" plenum at minimum.
It blows at perfect laminar flow.
His blower is 24 x 24 x 12. His needs to blow at least 400CFM at 1.2 sp and he needs at least a 12" plenum.
Fungi Perfecti sells hoods that push 100cfm@ 1.2 sp, the Stamets recomendation for laminar flow. Thats the formula I used as well
Thats why you need the square footage of the filter face and the proper plenum. So it blows 100CFM *EVENLY ACROSS* the whole filter.
Hence the 3 x 100 in the calculation.
Im not an expert by any means. I dont really understand the ins and out of this, its complicated. But I do know how to match a blower to a filter for a flow hood. To build a simple hood that reaches laminar flow, that I do know how
So how many CFM @ 1.2 SP do YOU think his blower should push then?
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Edited by mushpunx (03/18/16 01:24 PM)
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Stargate
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23020511 - 03/18/16 01:50 PM (7 years, 3 days ago) |
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Not sure if this matters much, but I don't mind having a large plenum. Size isn't an issue for me.
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23020532 - 03/18/16 01:57 PM (7 years, 3 days ago) |
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Quote:
Stargate said:
Not sure if this matters much, but I don't mind having a large plenum. Size isn't an issue for me.
Good then! Id go at least 18". Mines 6" and I either used 10 or 12"
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Supalemonhaze
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23020789 - 03/18/16 03:24 PM (7 years, 3 days ago) |
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Quote:
mushpunx said:
It will be pushing 100CFM evenly across the whole hood. Youre forgetting the square footage. And the proper plenum to let the static pressure build up properly for even laminar flow.
Take my hood for example.
Its 18 x 24 x 6. My blower pushes 549 CFM @ free air. To do the calculation, you go.. 18 x 24 = 432 , ÷ 144 = 3.
3 x 100 = 300.
I checked the blower specs before I bought my blower, and saw it pushes a little over 360 (if I remember correctly, might have been higher) at .8 sp. Moving up the graph it blows just over 300CFM
@ 1.2 sp. I used a 10" plenum. I needed a 6" plenum at minimum.
It blows at perfect laminar flow.
His blower is 24 x 24 x 12. His needs to blow at least 400CFM at 1.2 sp and he needs at least a 12" plenum.
Fungi Perfecti sells hoods that push 100cfm@ 1.2 sp, the Stamets recomendation for laminar flow. Thats the formula I used as well
Thats why you need the square footage of the filter face and the proper plenum. So it blows 100CFM *EVENLY ACROSS* the whole filter.
Hence the 3 x 100 in the calculation.
Im not an expert by any means. I dont really understand the ins and out of this, its complicated. But I do know how to match a blower to a filter for a flow hood. To build a simple hood that reaches laminar flow, that I do know how
So how many CFM @ 1.2 SP do YOU think his blower should push then?
His blower should blow at 400cfm, on that you are correct but at 0.45wg now 1.2wg.
You are thinking about the filters being all the same resistance, they are not.
Imagine we are pushing water in a pipe, yours has a half closed shutvalve due to higher resistance while his has an open one. How can they both have the same amount of water coming out of one end
if they allow 2 different amounts of water through them?
Do you agree that his filter allows more air through it than yours? It's pretty easy to understand that his filter will be blowing a lot more than 100fpm.
Lets take a look again at the chart:
Do you see how much fpm the filter let through during testing? How is he going to use 1.2sp and get a different result than them? I tell you, impossible. Because the only thing the plenum changes is that it allows the pressure to build up evenly but the plenum does not effect the fpm coming out of the filter. The filter's resistance to air is what effects the fpm.
You say that we are re purposing the filters and that the chart is not accurate but can you explain to me how what we do changes the filter's natural resistance? The way we use filters on hoods is basically the same as how they use them in hospitals and such. You cannot get air through a filter if you do not have an air tight container. The only difference with what we do is that we aim for 100fpm. In fact the chart was made by tests identical to what we do. They make an air tight chamber, a blower on one end and filter on the other, how else can they measure fpm under sp? What we are doing is totally the same and you would have to be a fool to not follow their chart. I know I didn't and I have a FH that pushes 200fpm. That's why I know that how the calculations I used were wrong, because I went through them and they didn't add up to what I ended up with. (Same calculations as yours.) Hell if you remember you were the one to help me with it.
You are comparing your 6" FH with fungi Perfecti 6" FH, which more or less have the same resistance but his 12" filter will not be the same. His filter will allow a lot, and I really do mean a lot more air.
The only thing I'm not sure about is if there is a minimum sp for laminar flow, but I know for a fact that 400cfm @1.2 sp will be around 400fpm due to the filters low resitance. It's name shows you even more, high capacity.
Quote:
RogerRabbit said:
It depends on the resistance of the filter, which is selected based on how much air you want to flow. A low-resistance filter needs more static pressure to develop laminar flow, but might blow the petri dishes off the table because of the extra current. A high resistance filter(better for a flowhood) will flow less, and also require less static pressure to achieve laminar flow.
You determine it based on the charts supplied with the filters. Find one which will deliver a velocity of 100 feet per minute at around .8 to 1.1 W.G., and then select a blower to match.
For good laminar flow, look for a filter that size with about that same flow rate, only at .8 to 1.1 W.G. It's hard to imagine getting laminar flow at less than half an inch of static pressure.
Here even RR recognises the fact that on a high capacity filter the high sp will blow plates off the table.
This is why I said I'm not sure about the minimum sp for laminar flow. Sci-Fi positively confirms that he personally built flow hoods with those filters at 100fpm, which would hint that the minimum sp depends on the filter's resistance.
On the other hand RR thinks that half an inch is too low for laminar flow, but he is just guessing.
Almost everyone knows RR is an engineer but you can see how he is just guessing on the unknown. While Sci-Fi claims he has built flowhoodw with high capacity filters and he clearly has some HVAC industry experience. Of course I'm not in both these people's minds but I do understand from both their comments that a high capacity filter will blow a lot more air at high sp than a 6" filter will.
Edit:
Don't get me wrong, your calculations are spot on when it comes to 6" filters because they all have more or less the same resistance since they are made specifically for flowhoods but even when it comes to 4" filters it starts to loose accuracy as it did with mine. Fortunately, with mine it all worked out even with double the normal fpm but with the high capacity filter I'm not so sure it will be possible to work with 400fpm blowing in your face.
Edited by Supalemonhaze (03/18/16 03:42 PM)
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Stargate
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Hmmm, I'm still trying to understand the graphs and all. Do you think this one would work for a blower?:
http://www.ebay.com/itm/PSC-Squirrel-Cage-Blower-Voltage-230-1500-RPM-400-CFM-EE1G-230-180-04-/191792804478?hash=item2ca7bdf27e:g:br0AAOSwpzdWqAQU
PSC Squirrel Cage Blower, Voltage 230, 1500 RPM, 400 CFM - EE1G-230-180-04
http://www.ebmpapst.us/media/content/literature/flyers/web_downloads/EE1G_Centrifugal_Blowers.pdf
If so, I would just have to figure out how the hell to wire it up.
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23021175 - 03/18/16 05:52 PM (7 years, 3 days ago) |
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Wiring is simple its just 3 wires.. 2 wires and a ground wire you just wire it to an extension cord.
Those blowers are way too small. Like Ive been saying, blowers are listed by what they push at free air. Those push 400cfm at free air. You need 400cfm at a static pressure of 1.2
What you need to do is look at blowers, maybe in thr 700 to 1000 CFM range and get the specs from the seller. It will show what they push at .1 .2 .3 .4 .5 sp etc.
Follow the numbers or graph up to 1.2... the blower should push close to 400CFM at 1.2sp
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Supalemonhaze
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23021547 - 03/18/16 08:26 PM (7 years, 3 days ago) |
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Edit:
I mean shit, least you can do is explain to us why both RR ( which is an engineer) and Sci-Fi (who definitely knows his shit) arw wrong in your world. Not trying to be an ass or anything but I give you a good explanation with quotes and shit and you ignore it and keep reccomending the same flawed answer as you did before.
Seriously I'm gonna stop wasting my time but I'm sure op is seeing the holes in your logic if you can't seem to find a good explanation. I dunno how 1+1=5 in your world and you won't even admit it's flawed or at least acknowledge the fact that what I'm saying has merit.
Can't actually believe that you believe a 12" filter has the same resistance as a 6" one. On which planet does that make sense?
2nd Edit:
Even fungufun with the exact same formula as the one you're using says the sp and working point of filters is different between filters.
Here: "Every filter has a different static pressure at the working point. The working point is where the amount of the air flowing through the filter is sufficient to meet the requirement of the laminar flow."
I feel a real explanation is in order, unless we're gonna ignore facts all day.
3rd edit:
Now I'm not saying all this to see who's right or wrong, that doesn't matter but a reasoning should have facts to back it up or else it's just an opinion. That does matter.
How does our "re purposing" actually effect the resistance of the filter and what is the reason it will work at 100fpm when at 1.2sp even though the manufacturers state that it will be pushing close to 400fpm? Simple.
Edited by Supalemonhaze (03/18/16 08:58 PM)
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Supalemonhaze
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That is just around what ypu need. See tje the description. 410cfm .4in sp means it blows 410cfm at .4wg sp.
A little bit more powerful would be on the safe side but im willing to bet it will be enough because the prefilter is almost never 0.2wg
Did flanders confirm that you will be building a jet plane if you go 1.2wg?
And which chart are you not understanding? The blowers? In.sp is the same ad wg. Wg means water gauge and its units is inches so for example 0.4in means 0.4wg sp
OP: seeing as neither of us are engineers I suggest that you do not buy anything until flanders confirms wheter or not it will work at 100fpm at 400cfm @ 1.2wg sp. The question for them is simple, if I use this filter for a flowhood, will it work at 100fpm when it's at 1.2wg or is the chart you supply accurate?
Edit:
I will gladly admit I'm wrong if it turns out that 400cfm@1.2sp is the correct figure, I just don't want anyone to mak costly mistakes. My ego online is not worth people wasting money over. I just hope munxpunx thinks the same.
Edited by Supalemonhaze (03/18/16 09:20 PM)
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As for emailing Flanders, I got forwarded to someone else in their department named Jimmy. I haven't gotten a response back from Jimmy just yet, but I'll update this thread when I do.
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23021943 - 03/18/16 11:24 PM (7 years, 3 days ago) |
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I dunno man, my flow hood works beautifully.
Ill gladly stand corrected if someone else proves me wrong. I wish someone else would chime in.
But I maintain that the match is still the same, if the filter is 24 x 24 x 12 you want a blower that pushes 400CFM @ 1.2 SP AND a plenum of 12" minimum.
The only difference in a hood with a 6" deep filter and a 12" deep filter is the size of the plenum built behind it.
My blower pushes 549CFM at free air... . It blows just over 300CFM at 1.2 SP and I get perfect laminar flow.
He has a bigger filter face than mine, but you are suggesting a blower that is much less powerfull than mine
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23022266 - 03/19/16 02:29 AM (7 years, 3 days ago) |
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Ok I think we are getting somewhere.
You think the only difference between the filters is the needed plenum size. I will confirm that a 12" filter will allow a lot more air to pass through it than a 6" one.
Quote:
RogerRabbit said:
You want about 450 to 500 cfm(cubic feet per minute, a measure of volume) blowing through the filter to get a speed of 100 to 125 fpm(feet per minute, a measure of air speed). I suspect with that filter, you'll achieve the desired flow with a resistance of around .5 or so. Find a 500 cfm blower at .5" to .7" W.G.
This quote is a response from RR regarding the same type of filter. That is thr 12" thick one. Why would he recommend such a low working sp if the filter did not have less resistance than the 6" one?
Next is another shroomerite who bought a 12" thick hepa and was not sure how to calculate his SP at the cfm he needed. The quote is from someone who told this fellow shroomerite how to calculate this.
Quote:
Terry M said:
Quote:
Amanita virosa said:
ut oh! so will the resistance be lower or higher at lower cfm? or is there some kind of conversion factor? now i am really confused
The simplified relationship that, for example, HVAC people use is that for a fixed system, resistance will change with the square of the air velocity. The filter has a resistance of 1.1 inches at 1000 cfm. Its resistance is going to decrease at lower cfm.
The 2x2 filter has an area of 4 square feet. So to achieve the recommended 100 linear fpm, you need 400 cfm.
The square the ratio of air velocities is the conversion factor for the resistance, so
(400/1000)^2 = 0.16
The filter resistance at 400 cfm is 1.1*0.16 = 0.18
Add in the resistance of the prefilter, and you've got the total flow resistance that your blower must support. Of course, as the flow resistance increases, the blower will deliver a lower flow rate. Blower manufacturers should be able to provide this curve. If the blower delivers a high flow rate for the filter resistance, you can always lower it by partly obstructing the intake area.
Regards,
Terry
0.16 w.g sp, that's how much pressure his hepa has when it was going to operate at 100fpm.
Now munx, when you built your flowhood you followed exactly the fungifun reccomendations by getting the 6" thick filter. Because you and the tek you followed had the same filter thickness, the resistance was more or less the same so you got the same result. Now when I built my FH the only variation there was was that I bought a 4" thick filter instead. The difference in resistance is what caused the formula to lose it's accuracy, hence why I have 200fpm.
In your first reply you said to OP that 12" thick hepas are not commonly used yet they have a longer working life. Now imagine that they had the same resistance, wouldn't the first choice for hoods be the 12" thick one since it lasts longer? The only reason why they don't reccomend that filter is because it lets a lot more air through it.
Now next are 2 comparisons between filters like mine and filters like OP'S.
My filter's description:
OP's filter description:
The difference in resistance is easily seen here. While OP's filter achieves 500fpm @1.35wg, mine is able to work at 150fpm at a maximum of 2.0wg. So what causes more airflow to flow through OP'S filter at a lesser static pressure than mine? The filter's resistance to air passing through it.
Here are a number of sizes, depths etc from my modelnumber and OP'S model number.
OP's:
Mine:
The difference between them is pretty much self explanatory but I hope I was able to explain simply enough foe you to understand the differences in resistance between a 6" filter and a 12" one.
You might be wondering, well yours is a 4" filter so why isn't there a drastic difference between 4" and 6" like there is between a 6" and 12"? The answer is because the filters like mine (and yours) are made specifically for flowhoods so a high resistance will both guarantee laminar flow and has a low enough fpm for someone to work in front of it comfortably. In fact you can see in the last pic that this same filter material is used for a number of different thicknesses from 2-6inches. This means that the material is what makes all the difference.
The 12" ones however, are used to clean say, a really big hospital operating theatre. The filter will probably be installed on the cieling or over doors because it's job is to clean the room in the least time possible. Obviously a 500fpm filter is more practical than a 100fpm one for this use so since laminar flow is not a priority, they reduce the filters resistance so the air can pass more freely.
Now, there have been people who managed to get laminar flow out of these filters so even though it is not a priority for the manufacturer that doesn't mean it's not possible, this is also why they reccomend a bigger plenum since the bigger it is the higher the chances of laminar flow. My guess is that it will also have to operate at more than 100fpm for the sp to be enough to create laminar flow but this is where I stop knowing and start guessing. That's why OP should ask the manufacturer because on the shroomery there is so little information on FHs built with low resitance filters. We know it has been done, yet no one has ever documented it which is a total shame. If they did document it people would probably spend like half the amount they actually spend by buying a lesser resistance filter and a lesser powerful blower.
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23022280 - 03/19/16 02:34 AM (7 years, 3 days ago) |
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Quote:
mushpunx said:
He has a bigger filter face than mine, but you are suggesting a blower that is much less powerfull than mine
This is because your filter material is comparable to mine while OP'S isn't.
Imagine that we have a 6" thick filter and a 12" thick one but they both have the same face size.
The essential difference between the two filter's materials is that the 12" thick filter will have say, 10,000 0.3micron pores while the 6" thick one has 5,000 0.3um pores.
Which of these filters will have a lesser resistance? And which will let more air through it if they operated at the same sp? I'll let you answer this one.
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mushpunx
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Ive already explained this in this thread Ive thought ;
The static pressure we are concerned with * is in the plenum*. 1"wg can be hit with just about any filter if you use the correct blower.
The static pressure required for laminar flow is usually around .8 and 1.2" wg. The key is to provide a flow rate of 100cfm per ft2 of the filter face area while maintaining the 1"wg plenum pressure.
The flow rate is the difference with thicker filters. They usually have less resistance so the flow rate is slightly higher.
BUT the flow will still be laminar and thats whats important for our purposes. You just need to match the blower to the filter dimensions, and build your hood with a plenum equal to or greater than the depth of the filter.
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Edited by mushpunx (03/19/16 08:23 AM)
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23024417 - 03/19/16 07:38 PM (7 years, 2 days ago) |
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Slightly? Sure if 5 times the normal amount of air is a slight difference. There is also 0 information about what the minimum sp is for laminar flow. Also different resistances mean that the minimum sp for laminar flow will be different for every filter. Just like fungifun says:
"Every filter has a different static pressure at the working point. The working point is where the amount of the air flowing through the filter is sufficient to meet the requirement of the laminar flow."
You keep saying its 0.8wg because that's what you probably heard from god knows who and it's accurate for your filter but that's not to say it's accurate for a filter that is very different like the 12". There definitely is a minimum sp but if it was 0.8 no one would be able to work in front of it without having all his work blown away.
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23024441 - 03/19/16 07:45 PM (7 years, 2 days ago) |
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Quote:
mushpunx said:
The static pressure we are concerned with * is in the plenum*. 1"wg can be hit with just about any filter if you use the correct blower.
It's always in the plenum but it's not the plenum that makes the sp go up, it's the filter's resistance. 1"wg on your filter means 100fpm while on OP's its closer to 400. As the description said, 1.35"w.g sp= 500fpm. The size of the plenum doesn't change this, the only difference the size of the plenum does is that the bigger it is, the more it aids in laminar flow hence why they reccomend a big plenum for big filters.
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Heya guys, I found a fan that may work well, but I would like to get some second opinions:
Found it here:
http://www.amazon.com/Vortex-Powerfans-VTX1200-1140-Powerfan/dp/B003AK1NB2/
But elsewhere, I found the graph for it here. Would this be too powerful? Should I just get it, and attach a speed controller to it?
This one is supposed to do well in hydroponic grow houses with high humidity. Its also been said to be very quiet and powerful relative to a lot of other blowers.
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mushpunx
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Dude the sp that is listed on them, is 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
The numbers that are listed on the filters are meaningless for us, like I said we are technically repurposing these filters.. I gaurentee, If he uses a filter that blows 400CFM @ 1- 1.2 SP with a 12" plenum minimum he will get perfect laminar flow.
I would put money on it
Edited by mushpunx (03/20/16 01:38 AM)
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23025467 - 03/20/16 06:29 AM (7 years, 1 day ago) |
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Would you also bet that he would have 100fpm?
Now you are twisting words, I never said laminar flow will be a problem at that sp. I said that he will have over 400fpm, which I'm willing to bet a kidney on.
"Meaning that at X.X" sp you get XXX cfm "
That is it exactly, if he follows your advice hes gonna get the rated 500fpm at 1.35wg.
"The numbers that are listed on the filters are meaningless for us, like I said we are technically repurposing these filters."
This I'm afraid, is a load of hpoo. We use these filters exactly how we are supposed to use them. Repurposing means using an air filter for water. Using an air filter for air is just using it how you're supposed to. What do we do different that we somehow re purpose these filters? Everyone uses them by making an airtight chamber/plenum/duct and a blower on the other side. Exactly what we do.
Quote:
Stargate said:
Heya guys, I found a fan that may work well, but I would like to get some second opinions:
Found it here:
http://www.amazon.com/Vortex-Powerfans-VTX1200-1140-Powerfan/dp/B003AK1NB2/
But elsewhere, I found the graph for it here. Would this be too powerful? Should I just get it, and attach a speed controller to it?
This one is supposed to do well in hydroponic grow houses with high humidity. Its also been said to be very quiet and powerful relative to a lot of other blowers.
That is way too powerful IMO. A speed controller is always a good idea though.
Myself, I followed munxpunx formula to a Tee and I got 200fpm. I had already hooked up a speed controller and when I went to calibrate my hood to 100fpm the motor started humming loudly. These blowers aren't really supposed to be hooked up to a speed controller but if one only needs to adjust the speed just a bit, they won't hurt.
I needed 25% of what the blower actually pushes so if I left my speed controller on the 25% mark my blower would have heated up.
I've said my piece OP, I'm gonna step out of this thread now. People only hear what they want to hear. Ego bruising is a big deal for some so it's better this way.
You should wait until flanders emails you back to see what you should do(kinda strange they haven't already emailed you back). If you need any help feel free to PM me I will be happy to help. If you want I can check what email I used to contact them if they won't send back.
I'll definitely be more help without word twisting and selective hearing pushing my psi guage to the red.
Goodluck.
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Stargate
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I'm sure Flanders will reply in a day or so from now. Chances are, they just aren't responding due to business hours (weekend).
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23027374 - 03/20/16 06:13 PM (7 years, 1 day ago) |
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http://www.fungi.com/product-detail/product/universal-blower-1040-cfm-8-sp.html
When I say "re purposing" Im saying that most of these filters, especially the 12" deep filters, are *usually* meant to be used as scrubbers to clean room air.
I like you Haze, I really dont care who's advice works its up to Stargate to choose a blower. Ill be happy if his hood works and has laminar flow.
Its not my formula, its just the formula I used to match a blower to my filter. I didnt have to block the intake or use a speed controller, I got perfect laminar flow the way it was built.
So Im still gunna tell Stargate the same thing.
My filter was 18 x 24 x 6. From the filter face area it needed 300CFM at 1.2 SP and a 6" plenum at least behind the filter.
Blowers are usually listed by CFM @ free air. Mine was 549 CFM @ free air and it pushes 360CFM at .8SP . If you continue up the spec chart its just around 300CFM @ 1.2 sp which was perfect.
Your filter is 24 x 24 x 12. You need a blower that pushes at least 400CFM @ 1.2SP and a 12" plenum at least. It wont be listed at 400CFM though because thats what it pushes at 1.2 SP. Since its listed by free air, it will probably be listed as around 750-800 CFM. You will then have to ask for the blower specs chart and check to see what it pushes at 1.2SP to be sure, but 750-800CFM range is a good place to start looking.
If you look at the blower I linked you to, it pushes 1040 CFM @ .8SP . Its listed as a universal blower because it pushes more than enough for 18 x 24, 24 x 24, all the way up to 24 x 36" filter faces that is is sold to be matched to.. It just needs to be powered down to fit the smaller filters.
But you can see even a blower that pushes twice the CFM @ .1SP I am sugguesting isn't too big to be made to work for your hood.
If you find one close enough to 400CFM @ 1.2 however you can use it as is and not need to power it down.
The only thing different you would need to do is build a deeper plenum than 12" to accommodate a 12" deep filter.
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Edited by mushpunx (03/20/16 06:28 PM)
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23045881 - 03/25/16 07:42 PM (6 years, 11 months ago) |
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Is it possible to figure out the SP that a centrifugal fan will put out, by knowing the CFM and amperage?
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23046341 - 03/25/16 10:07 PM (6 years, 11 months ago) |
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Quote:
Stargate said:
Is it possible to figure out the SP that a centrifugal fan will put out, by knowing the CFM and amperage?
What you want to figure out is what CFM a blower would put out at a specific static pressure value.
Like my blower was sold as "dayton blower 549 CFM" or something like that, I got it on ebay.
549CFM is at free air, at no static pressure.
I contacted the seller and asked for the blower specs, it usually has either a list or a graph.
Mine had a chart that went up to .8 SP, it showed my blower pushes 360CFM @ .8SP
My seller was able to look at the blower and check the graph it came with. If your seller doesn't have it or wont do that then you probably need to get the model number and ask the company for the blowrr specs.
Whats the brand name/model of the blower you are looking at and what CFM is it listed at (free air)?
Off topic whats the pile of stuff in your sig?
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23046506 - 03/25/16 10:48 PM (6 years, 11 months ago) |
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Quote:
mushpunx said:
Quote:
Stargate said:
Is it possible to figure out the SP that a centrifugal fan will put out, by knowing the CFM and amperage?
What you want to figure out is what CFM a blower would put out at a specific static pressure value.
Like my blower was sold as "dayton blower 549 CFM" or something like that, I got it on ebay.
549CFM is at free air, at no static pressure.
I contacted the seller and asked for the blower specs, it usually has either a list or a graph.
Mine had a chart that went up to .8 SP, it showed my blower pushes 360CFM @ .8SP
My seller was able to look at the blower and check the graph it came with. If your seller doesn't have it or wont do that then you probably need to get the model number and ask the company for the blowrr specs.
Whats the brand name/model of the blower you are looking at and what CFM is it listed at (free air)?
Off topic whats the pile of stuff in your sig?
The seller and company both have been days with no response now.
I would be buying from:
http://www.ebay.com/itm/Hurricane-Inline-Duct-Blower-Fan-Inch-4-6-8-10-12-CFM-In-line-Active-/121163698153
They posted this:
CFM/AMP Information:
Inline Fan 4" - 171 CFM / 1 AMP
Inline Fan 6" - 435 CFM / 1 AMP
Inline Fan 8" - 745 CFM / 1.7 AMPS
Inline Fan 10" - 780 CFM / 2.1 AMPS
Inline Fan 12" - 1060 CFM / 2.5 AMPS
Company site area for this product:
http://www.hurricane-fans.com/shop/bybrand/hurricane/hurricane-centrifugal-inline-fans
As you can see in the specs pdf, there is no graph.
As for the pile of stuff in my sig, I assume you mean the brown looking stuff on a piece of paper. That would be my attempt at extracting psilocybin from shrooms.
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Edited by Stargate (03/25/16 10:51 PM)
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23046651 - 03/25/16 11:28 PM (6 years, 11 months ago) |
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Oh well dude you dont want an in line blower anyways. People *have* built hoods with them but they suck and are hard to mount.
Look for squirrel cage style blowers.. like they sell on fungi perfecti
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23046799 - 03/26/16 12:17 AM (6 years, 11 months ago) |
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Hmmm, alright, but what makes them suck other than mounting? I don't see mounting as a real issue for me, so is there something else?
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23046862 - 03/26/16 12:55 AM (6 years, 11 months ago) |
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Theyre could be but I either dont know or cant remember. Ive discouraged folks from them but more because theyre hard to mount.
Every thread Ive seen about them though I see folks discourage against in line fans and Im pretty sure Ive seen other reasons too
Since you haven't bought one already I really sugguest looking for a squirrel cage blower 
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23047074 - 03/26/16 04:09 AM (6 years, 11 months ago) |
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Well, a tip for anyone that is listening, the blower that everyone seems to link to on fungi.com $319 + shipping can actually be found on many other sites for $281.16 and free shipping. Thats likely a savings of $50+. Its the same exact blower.
Google Search: dayton 12g810
I'll pick one of those up.
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Supalemonhaze
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23047397 - 03/26/16 08:23 AM (6 years, 11 months ago) |
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I use an inline fan, perfectly good blower as long as it's rated for the cfm at the sp you need.
Fungifun hood tek also uses inline fan. They are widely used I flowhoods since they are much cheaper, even more so in europe since you barely find a squirrel cage fan anywhere.
Only difference between them is the sp to cfm curve, squirrel cage fans normally do better under pressure than the inlines.
Some old members used to say that the way the air leaves the inline makes it unsuitable for a flowhood but that is outdated by hundreds of flowhood builds using them.
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23047406 - 03/26/16 08:28 AM (6 years, 11 months ago) |
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Quote:
Stargate said:
Well, a tip for anyone that is listening, the blower that everyone seems to link to on fungi.com $319 + shipping can actually be found on many other sites for $281.16 and free shipping. Thats likely a savings of $50+. Its the same exact blower.
Google Search: dayton 12g810
I'll pick one of those up.
Yeah Fungi Perfecti's stuff is overpriced for the most part. People buy from them because of who they're doing business with not because they will be striking any deals.
I don't see why people use them so much, must have a lotta extra cash to burn. For the rest of us who live paycheck to paycheck, it's kinda a no brainer.
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Stargate
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Alright, I've ordered the Dayton 12g810 blower that fungi.com sells. Any idea if I need to throttle this thing?
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23057753 - 03/29/16 05:24 AM (6 years, 11 months ago) |
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[quoti]Stargate said:
Well, a tip for anyone that is listening, the blower that everyone seems to link to on fungi.com $319 + shipping can actually be found on many other sites for $281.16 and free shipping. Thats likely a savings of $50+. Its the same exact blower.
Google Search: dayton 12g810
I'll pick one of those up.
Yea dude the blowers on Fungi Perfecti are a bit overpriced. I was only linking you to them as an example to what I sugguest you look for. I bought my filter off FP though, a little expensive but fair since it was brand new and shipped very safe
281$ is still pretty expensive dude try Ebay or something. I bought my Dayton blower new in box off ebay for 90$ free shipping.
And if you look around try asking some furnace repair guys they usually have used blowers for 40-59$
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23061515 - 03/29/16 11:34 PM (6 years, 11 months ago) |
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Too late, already got the thing. But still, any idea if I need to throttle it?
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23062484 - 03/30/16 08:49 AM (6 years, 11 months ago) |
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Quote:
Stargate said:
Too late, already got the thing. But still, any idea if I need to throttle it?
Whats the specs? CFM @ free air and CFM @ .8 or 1.0 SP?
If you got it from fungi link me to which one it is
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23062585 - 03/30/16 09:31 AM (6 years, 11 months ago) |
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Quote:
mushpunx said:
Quote:
Stargate said:
Too late, already got the thing. But still, any idea if I need to throttle it?
Whats the specs? CFM @ free air and CFM @ .8 or 1.0 SP?
If you got it from fungi link me to which one it is
Its this one:
http://www.fungi.com/product-detail/product/universal-blower-1040-cfm-8-sp.html
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23062640 - 03/30/16 09:55 AM (6 years, 11 months ago) |
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Yea you will have to power that down.
You need 400CFM @ 1.2 SP for your 24 x 24 " filter. That blower pushes 1040CFM at .8 static pressure so its 600CFM too high.
FP lists it as a universal blower for several different filter sizes so at least we know it is able to be powered down.
Im not really sure how you do that, I matched my blower close enough that I didnt need to change anything.
Theyre A/C blowers so I dunno if a speed controller would work. As far as I know though you can block off part of the air intake with cardboard to bring it down some.
So if I were you Id go ahead and build the hood. Remember to build AT LEAST a 12" deep plenum
Then you can fidget with the blower intake or a controller untill you have laminar flow.
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23065837 - 03/31/16 01:55 AM (6 years, 11 months ago) |
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Just want to make sure the setup is correct. This is a side view of the box I plan to build. Its in a 3D modeling program, but I color coded the side so you can see where everything is. Those extra colors behind the box are a horizon in the 3D landscape, and some directional lines.
Left side: Entrance. I will be putting a border around the outside, and extending a platform forward to work on. This is so there is no drop below the laminar flow.
Purple: 1" thick outer case.
Grey: The grey on the left side is 11.5" in diameter, and 24" tall. This is where the HEPA will be.
Orange: This is the pre-filter. I plan to place a slot on the top of the frame to easily swap out the pre-filters. They are 1" thick.
Green: Wooden braces that keep the pre-filter from falling into the rest of the plenum.
Blue: The plenum. Its 12.5" deep.
I just want to make sure that this will be enough. Am I cutting it too close, or should I give an extra bit of room in the plenum? Any extra suggestions?
This 3D model (that you are only seeing the side of) was made so that I could figure out what size wood to buy for the frame, and to try to think of any extra pieces I may need.
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23065883 - 03/31/16 02:37 AM (6 years, 11 months ago) |
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The prefilter is usually attached at the blowers intake, I think that will defeat the plenum's purpose like that but I'm not entirely sure. Prefilter would also have to be as big as the hepa itself, which is totally unnecessary if you mount it at the intake.
Here's how I did mine.
Whole thing.
Prefilter
Speed controller.
The table's surface is a few cm's above where the filter starts so I don't have to elevate my plates, much more comfortable this way.
The stud you see in the prefilter's pic is what is holding the blower. Mine is an inline fan so the intake is round. Instead of building supports on the inside, which would take plenum space as well as potentially disturb the airflow I made a couple of holes in the lip of the filter's intake and passed the stud through them. Snug and very strong, the filter has no play if I shake or flip the hood on it's side.
For the actual prefilter I used a metal grate which was previously used to house a round filter for the air intake of a large generator or something of the like. I then took the filter material which is a filter for a stove extractor hood and wrapped it around the metal grate and then attached the grate with screws, locking the filter's edges between the grate and the wood. I also put a thai clip around to hold it tight to the grate so it will be more aesthetically pleasing.
The wire you see coming out was a total oversight and a silly mistake on my part, I should have thought out that the speed controller would look better on the side rather than on top but by the time I changed my mind about that I had already assembled all the wood together with screws and silicone. For a leakproof seal around the wire I used an electrical grommet, which IMO looks better than a blob of silicone and definitely stronger.
If you're using a rectangular prefilter like what's commonly found in the US, you can just thai clip it to the intake but I needed something to keep the blower from swallowing the flexible filter I was using.
Post the end result when it's done, I'm curious if you'll be able to work in front of that hood without physically attaching yourself to the table with that much airflow.
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https://www.shroomery.org/forums/showflat.php/Number/21482484#21482484
Here is the thread where I built my hood,
I built a housing around my blower with a pre filter on top, not everyone does that a lot of people just attAch a pre filter to the blower intake.
I dont understand where you are putting your pre filter. The purpose of the pre filter is simply to filter out larger particles to extend the life of your HEPA, you dont really need one but they are a good idea.
Pre filter should be outside of the blower... the blower intake PULLS air through the pre filter and PUSHES air down into the plenum behind the blower.
12.5... is the very bare minimum for the plenum with a 12" deep filter. Mine is a 6" deep filter and I went with a 12" plenum.
In my opinion, you should go with at least an 18" plenum in yours.
Make sure you silicone the inside the box!
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23066758 - 03/31/16 10:53 AM (6 years, 11 months ago) |
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Ah, alright. In my design, the pre-filter was sitting against the HEPA, so that the air would go through that just barely before hitting the HEPA.
So, I need to have the pre-filter in front of the HEPA. Got it.
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23066823 - 03/31/16 11:18 AM (6 years, 11 months ago) |
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No, the prefilter will be behind it, in an airflow sense.
--airflow-->--prefilter-->--blower-->--plenum-->--hepa-->--workflow.
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23066964 - 03/31/16 11:50 AM (6 years, 11 months ago) |
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Quote:
Stargate said:
Ah, alright. In my design, the pre-filter was sitting againstf2f the HEPA, so that the air would go through that just barely before hitting the HEPA.
So, I need to have the pre-filter in front of the HEPA. Got it.
No dude. The blower pulls air thru the pre filter and pushes it down into the plenum and through the HEPA
Did you look at the photos / build log I dug out for you? Have you looked at any other flow hood builds?
Here is a very crude pencil sketch of *my* hood. I use a housing around the blower for the pre filter but you dont need that; you can just stick the pre filter against the intake on the side of the blower
Edited by mushpunx (03/31/16 12:00 PM)
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23067041 - 03/31/16 12:09 PM (6 years, 11 months ago) |
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What I was saying, was that my previous design I drew up had the pre-filter in front of the filter. I was trying to say that I now understand that it needs to be before the blower. I get what you guys are saying. Just trying to think of how I'm going to adjust the design to fit that, and hopefully keep it aesthetically pleasing.
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23067764 - 03/31/16 03:33 PM (6 years, 11 months ago) |
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Quote:
Stargate said:
What I was saying, was that my previous design I drew up had the pre-filter in front of the filter. I was trying to say that I now understand that it needs to be before the blower. I get what you guys are saying. Just trying to think of how I'm going to adjust the design to fit that, and hopefully keep it aesthetically pleasing.
Well a 24 x 24" hood is usually a big rectangle. With youre filter Id probably build it approx 24 x 24 x 30. Furing strips around the inside right behind where the filter sits.
Above the plenum behind the filter I would cut a rectangular hole out of the top where the mouth of the blower is going to get bolted above.
You want to build the hood frame *around* the filter so that it will fit perfectly snug. Its a little tricky but you want the filter to kind of sit tightly inside.
My filter holds tight in my hood but I still ran molding around the front that keeps the filter in place just to be safe/make sure all the air is blowing thru the filter.
Inside the hood you want to seal up all the cracks and behind the furing strips with the proper silicone.
As for the pre filter, you have a choice there. I built a housing around my blower and I have a good Filtrete pre filter held in place by coping... I just undo the top boards to change the filter/access tge blower.
But if you dont want to do all that you can simply hook a filter to the blower, covering the intake.
I think that is how RR has his pre filter on his hood.
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23069570 - 03/31/16 11:58 PM (6 years, 11 months ago) |
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Alright, here is the redesign.
So, this is how it works. There is a top area where with an open top. The blower goes in here in order to pull air down, and shove it through a hole into the plenum. Above where the blower sits, see that bump out? I have 24"x24" pre-filters that will drop right onto there to be suspended above the blower. This would make monitoring and replacing the pre-filter (I have 12 of em) to be easy. It just sits on the top.
See the bump out in the plenum area? Well, the HEPA would slide in from the front to meet those pieces of wood, than the face of the flow hood would be screwed onto the face around the HEPA, not into it. Think this would work?
Sadly, I accidentally didn't save the file when I closed out the 3D modeling program, so these screen shot pics are all I have of what I designed.
Transparent view:
Solid main view:
Top View:
Front View:
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Stargate
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23077579 - 04/02/16 11:52 PM (6 years, 11 months ago) |
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Sooo, can anyone confirm if this design would be good or not?
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Supalemonhaze
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23077832 - 04/03/16 02:36 AM (6 years, 11 months ago) |
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Mine ain't like that so I dunno how that type is supposed to look. If you have enough space for your blower in that top box, it's good I reckon.
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blindingleaf
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yea, that will work. i would get rid of that work area outshoot. keep those filter stops instead of using silicone to adhere the filter. the frame will push up against the weather proofing and hold the HEPA in place without air escaping unnecessarily
 
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23079337 - 04/03/16 02:30 PM (6 years, 11 months ago) |
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That's some nice wood leaf. I used scraps from my garage some got resin stains on them. Ugly as fuck but hey, at least it works just as good.
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blindingleaf
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Thanks dude! I worked my ass off for that hood last summer cause I wantwanted it to b last one I ever build so i did it up. The back peice is scrap wood.
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23081435 - 04/04/16 05:36 AM (6 years, 11 months ago) |
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Quote:
Supalemonhaze said:
Mine ain't like that so I dunno how that type is supposed to look. If you have enough space for your blower in that top box, it's good I reckon.
Well, that's a 3D model I made so that I can more easily convey my ideas. It should fit the blower perfectly. Good to know that it should be a workable setup.[
Quote:
blindingleaf said:
yea, that will work. i would get rid of that work area outshoot. keep those filter stops instead of using silicone to adhere the filter. the frame will push up against the weather proofing and hold the HEPA in place without air escaping unnecessarily.
Thanks for the tip about the filter stops. But I'm wondering, why take off the work area outshoot? You don't think a 1.2 inch drop below the laminar flow will matter?
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Edited by Stargate (04/04/16 05:36 AM)
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blindingleaf
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23081488 - 04/04/16 06:28 AM (6 years, 11 months ago) |
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i think u should be fine. i do elevate my plates now with the larger hood, but with the old one i would pour right onto the table.
the main reason I suggest omitting it is because it will be a PITA to move like that. so if u want to keep it, just don't attach it to the hood itself
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23082064 - 04/04/16 11:10 AM (6 years, 11 months ago) |
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Quote:
mushpunx said:
Yea I love flow hoods hehe.
You really shouldn't have bought the 12" deep filter. I know its cheaper than the 6" deep filters, and they *will* work for laminar flow but they are so bulky and heavy.
we seem to be confusing opinion with fact.
ANY HEPA will generate laminar flow.
each sq in of filter media will flow a certain cfm at a given pressure. greater area of 12" unit means more flow at less pressure, a cheaper blower, catching more crap before replacement.
Edited by Jack Why (04/04/16 11:40 AM)
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23082302 - 04/04/16 12:29 PM (6 years, 11 months ago) |
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Quote:
mushpunx said:
Your filter is 24 x 24". 24 x 24 =576 576/144 = 4 x 100 = 400.
Your hood will need a blower that pushes at or around 400CFM @ a static pressure of 1.2 (.2 added for the pre filter).
the first step in any design project is to properly and precisely define your performance target metrics.
look at the fh as a tunnel with
a prefilter on one end
then blower
then hepa
then the boundry between your virgin air and smegma dripping hell...the outflow of fh.
you want 100 fpm not at the filter face but at the opening.
that's one reason you won't see a fh in a pharm lab w/o a hood. a design with a box for workspace helps prevent contam of the filter as well as allowing cutting blower req to a fraction and lowering air velocity over your work.
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Edited by Jack Why (04/04/16 03:32 PM)
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23082649 - 04/04/16 02:08 PM (6 years, 11 months ago) |
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Quote:
blindingleaf said:
yea, that will work. i would get rid of that work area outshoot. keep those filter stops instead of using silicone to adhere the filter. the frame will push up against the weather proofing and hold the HEPA in place without air escaping unnecessarily
I agree with Blinding leaf!
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23082685 - 04/04/16 02:23 PM (6 years, 11 months ago) |
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Quote:
Jack Why said:
Quote:
mushpunx said:
Yea I love flow hoods hehe.
You really shouldn't have bought the 12" deep filter. I know its cheaper than the 6" deep filters, and they *will* work for laminar flow but they are so bulky and heavy.
we seem to be confusing opinion with fact.
ANY HEPA will generate laminar flow.
each sq in of filter media will flow a certain cfm at a given pressure. greater area of 12" unit means more flow at less pressure, a cheaper blower, catching more crap before replacement.
Like I said.. I even put it between two asterixes.... a 12" filter *will* work for laminar flow... nothing to debate there.
A bigger, heavier filter and the larger plenum required behind it makes for a bulkier, heavier hood than a hood with the same size filter face built with a 6" deep filter. This is fact
That he shouldn't have bought a 12" deep filter because of that... thats my opinion.
I dont see how the two are being confused at all dude
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23082813 - 04/04/16 03:04 PM (6 years, 11 months ago) |
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kool
"You really shouldn't have bought the 12" deep filter"
didn't read like opinion...just sayin'.
since he isn't concerned with size can you see how this filter is perfect FOR HIM?
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23082895 - 04/04/16 03:25 PM (6 years, 11 months ago) |
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Chill dude. Lets not have another thread devolve into semantic blockage
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23083212 - 04/04/16 04:39 PM (6 years, 11 months ago) |
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Quote:
blindingleaf said:
i think u should be fine. i do elevate my plates now with the larger hood, but with the old one i would pour right onto the table.
the main reason I suggest omitting it is because it will be a PITA to move like that. so if u want to keep it, just don't attach it to the hood itself
I use a baking rack when I do transfers and innoculations but since I put a sheet of glass down on my table Ive started pouring down to the table and I haven't had any problems yet
I think it was you Leaf that sugguested giving a cardboard hood a try before actually building one out of wood/plexiglass
I think that would be good advice here too. Try one made of cardboard see if he can move around comfortably and if he likes it build a detachable hood
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23083497 - 04/04/16 05:41 PM (6 years, 11 months ago) |
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I would definitely have a covered ws. every commercial fh I've ever seen has this feature. that's the hood. I designed 1 lam station w/o hood it was installed in a class 10 cleanroom for a particularly sensitive silicon process.
the first step in any design project is to properly and precisely define your performance target metrics.
look at the fh as a tunnel with
a prefilter on one end
then blower
then hepa
then the boundry between your virgin air and smegma dripping hell...the outflow of fh.
you want 100 fpm not at the filter face but at the opening.
that's one reason you won't see a fh in a pharm lab w/o a hood. a design with a box for workspace helps prevent contam of the filter as well as allowing cutting blower requirements to a fraction and lowering air velocity over your work. cover the top half of the opening w/ plexi cuts you flow requirement in half. ergo better and cheaper.
--------------------
until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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Stargate
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23084719 - 04/05/16 12:38 AM (6 years, 11 months ago) |
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Building it out of cardboard the first time sounds like a great idea! Conveniently, I've got a ton of boxes right now due to moving into a new house. I'm going to be using the garage in this house to grow oyster mushrooms. Because of this, I'm thinking of using the fh for both laminar flow, as well as to actually keep the air clean. I'll have to use a variable speed controller for that, or what ever they are called in this situation.
Jack Why, about that hood. Does it need to shoot strait out from the HEPA, or can I taper it a bit outward to make my work space larger?
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From before I started growing gourmet mushrooms:
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Supalemonhaze
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23084844 - 04/05/16 02:12 AM (6 years, 11 months ago) |
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Tapering the enclosure won't give you airflow at the extra space you created. Laminar flow is a body of air that moves straight so unless the air is redirected it will keep going straight, no matter how much extra space there is on the sides.
That said an enclosure is not necessary for our purposes. But yes I agree with jack that an enclosure is extra protection for the sterility of the air and laminar flow as well as the fact that it can be run at lower fpm safely. Some commercial hoods have a low option that operates at 60fpm, this would probably not be possible without an enclosure.
But IMO an enclosure will restrict your movements to a box the size of your filter. A hood is comfortable because unlike a SAB, you are nothing but restricted. An enclosure changes this.
If I were to build and enclosure for the advantages mentioned above, I would only make it a few inches out, maybe 6-10" so I can still put stuff on the table outside of the flow without having to pull my hands back out of the enclosure. You need things like your alcohol bottle and torch to be easily reached but I prefer to leave them outside the flow, an enclosure would make this difficult.
I was going to build it to be honest. Was gonna have it made of thick see through plastic sheets but by the time I was going to order them, I realised that I will be restricted and that it is not necessary as I was already having wonderful results with it like it was.
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: Stargate]
#23085443 - 04/05/16 09:33 AM (6 years, 11 months ago) |
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cardboard is a great idea. variable speed and any affordable adjustability goes into all my designs. laminar air can live with 10 degree taper at this speed, no quick changes in cross section. the only place really critical is at the hole that you work through. a sealed box needs no air flow to keep "dust" out. when we put a hole in the box, we need to pressurize the box, making it "uphill" for room air to get into our box. smaller hole =slower air across work= smaller blower = <$$. the flow before this point is totally irrelevant. the air flows out because it's a downhill slide to a lower energy level. vortices or turbulence can give "dust" a higher energy level and a nonzero probability of crossing this barrier, here laminar is good, elsewhere not as much. bottom line... at 100fpm even salmon-ella can't swim upstream. get some smokesticks (cigarettes) they can show u air flow patterns. go spearmint and have fun.
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until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23085525 - 04/05/16 10:03 AM (6 years, 11 months ago) |
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I like using incense sticks to show air flow, that and a flame test
Jack - are you an engineer? You design flow benchs
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Jack Why
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Tapering the enclosure won't give you airflow at the extra space you created.
ya know how boyle's law says when pressure drops, the molecules spread out? the cross section increases, pressure drops,it's like boyle's molecules except the flow lines spread. the books say 7-10 deg no prob.
Laminar flow is a body of air that moves straight so unless the air is redirected it will keep going straight, no matter how much extra space there is on the sides.
not quite or airplanes couldn't fly. a wing cuts air into 2 chunks, 1 under the wing has a shorter curve. assuming both surfaces are going about the same speed, both chunks have to arrive at the trailing edge together, the air has to flow faster across the upper curve. bernouli does the rest. when flow isn't smooth it stalls and falls. laminar means flow lines are basically parallel.
But IMO an enclosure will restrict your movements to a box the size of your filter.
this is counterintuitive but wrap your head around this design: build an airtight box the size of texas ( i'll wait). cut 2 holes, 1 for 1sq ft filter in dallas,1 for 1/2 sq ft access in austin. blow 50 fpm thru filter bring the box up to pressure before opening access hole...this will take a minute. open access you have 100fpm (we're ignoring weather conditions in the box).
exhaust V = filter area*V/exhaust area...this is the key to allowing a small blower.
the box can be any size, by making the access as small as possible vel across work is reduced
laminar flow is not the holy grail.
it's a pressure thing
I prefer to leave them outside the flow, an enclosure would make this difficult.
why that? I wasn't planning that.
thanx
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until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
Edited by Jack Why (04/24/16 06:37 PM)
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23086170 - 04/05/16 01:50 PM (6 years, 11 months ago) |
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Quote:
mushpunx said:
I like using incense sticks to show air flow, that and a flame test
Jack - are you an engineer? You design flow benchs
better yet, keeps your hand out of the flow.
yes,40+ years ago I started designing machines i'm addicted. my last couple jobs were designing custom automated industrial stuff. whatever they wanted I designed.
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until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23087645 - 04/05/16 07:36 PM (6 years, 11 months ago) |
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Quote:
blindingleaf said:
Chill dude. Lets not have another thread devolve into semantic blockage
in reference to what exactly?
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until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23143620 - 04/22/16 08:34 AM (6 years, 10 months ago) |
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Quote:
mushpunx said:
I like using incense sticks to show air flow, that and a flame test
Jack - are you an engineer? You design flow benchs
yes I've designed hoods ,cleanrooms, etc, etc professionally.
there is NO relationship b/t filter thickness and plenum volume.
there is NO minimum static pressure required for laminar flow.
.000001 in h2o static pressure will give laminar flow out of ANY HEPA.
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until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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blindingleaf
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23143727 - 04/22/16 09:22 AM (6 years, 10 months ago) |
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So in ur opinion, it would be impossible for filter media to be damaged from a plenum too small and blower too powerful?
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23144414 - 04/22/16 01:59 PM (6 years, 10 months ago) |
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I dunno man for the home cultivator building thier own hood I think its a pretty good rule of thumb to build a plenum at least as deep as the filter is
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23149407 - 04/24/16 06:52 AM (6 years, 10 months ago) |
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Quote:
blindingleaf said:
So in ur opinion, it would be impossible for filter media to be damaged from a plenum too small and blower too powerful?
the only real aerodynamic function of a plenum is to minimize the kinetic energy of the flow. the manufacturer specs tell u the maximum pressure/flow, don't exceed those and don't point the blower at the filter. the filter will be fine.
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until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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blindingleaf
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23149424 - 04/24/16 07:11 AM (6 years, 10 months ago) |
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so lets say u have two identical filters, and two identical blowers that are matched to spec.
u make two hoods. one hood has a 6" plenum, the other has a 12"plenum, otherwise the hoods are identical.
would you anticipate differences between the two in terms of flow rate across the filter face?
--------------------
A few thoughts on cultivation
MICROBIAL HUSBANDRY!!!!
The whole is greater than the sum of its parts
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blindingleaf
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23149428 - 04/24/16 07:16 AM (6 years, 10 months ago) |
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in my experience, this is what happens when ur plenum is not large enough, even when urblower is matched to the filter size, so i don't agree that plenum size is not important
 
there is much more turbulence at the bottom of the box when ur plenum is too shallow, and can blow out the filter media over time
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A few thoughts on cultivation
MICROBIAL HUSBANDRY!!!!
The whole is greater than the sum of its parts
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23149573 - 04/24/16 08:33 AM (6 years, 10 months ago) |
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Quote:
mushpunx said:
I dunno man for the home cultivator building thier own hood I think its a pretty good rule of thumb to build a plenum at least as deep as the filter is
filter thickness has absolutely no relationship to the distance required from the filter to the rear of the plenum or anything else.
why are you making up a rule of thumb for a relationship that doesn't exist? that's how myth and superstition come into being. I know you try to help others learn (that's what i'm trying to do as well),imo you just need to be a little more skeptical about what you accept as fact before sharing it with others.
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until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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blindingleaf
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23149610 - 04/24/16 08:52 AM (6 years, 10 months ago) |
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well thats why its called a "rule of thumb" because all of us un educated lowly mushroom growers don't have anywhere near the wisdom that engineers do
Quote:
"Rule of Thumb"
noun
1. a general or approximate principle, procedure, or rule based on experience or practice, as opposed to a specific, scientific calculation or estimate.
2. a rough, practical method of procedure.
so we have to rely on and draw from the vast amount of experience from cultivators that have come before, and in this case, their experiences showed that, in general, it is a good idea to build a plenum that is equal to or greater than the depth of the filter itself. over time, a "rule of thumb" was born.
--------------------
A few thoughts on cultivation
MICROBIAL HUSBANDRY!!!!
The whole is greater than the sum of its parts
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23149616 - 04/24/16 08:56 AM (6 years, 10 months ago) |
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the blowers were on top blowing down, right?
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until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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blindingleaf
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23149695 - 04/24/16 09:36 AM (6 years, 10 months ago) |
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yes
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A few thoughts on cultivation
MICROBIAL HUSBANDRY!!!!
The whole is greater than the sum of its parts
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23149760 - 04/24/16 10:13 AM (6 years, 10 months ago) |
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Quote:
blindingleaf said:
well thats why its called a "rule of thumb" because all of us un educated lowly mushroom growers don't have anywhere near the wisdom that engineers do
Quote:
"Rule of Thumb"
noun
1. a general or approximate principle, procedure, or rule based on experience or practice, as opposed to a specific, scientific calculation or estimate.
2. a rough, practical method of procedure.
so we have to rely on and draw from the vast amount of experience from cultivators that have come before, and in this case, their experiences showed that, in general, it is a good idea to build a plenum that is equal to or greater than the depth of the filter itself. over time, a "rule of thumb" was born.
Hah yea that's what Im saying Leaf. And if you are mounting a squirrel cage blower on top and behind a filter you're gunna need about 6" to fit the mouth of the blower anyways.
Most of us probably arent gunna cut it as engineers but we can do simple math to match a blowrr to a filter, and build a rectangular box. If you can do those two things, you can build a flow hood that works well for mycology
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23149790 - 04/24/16 10:22 AM (6 years, 10 months ago) |
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Quote:
blindingleaf said:
in my experience, this is what happens when ur plenum is not large enough, even when urblower is matched to the filter size, so i don't agree that plenum size is not important
there is much more turbulence at the bottom of the box when ur plenum is too shallow, and can blow out the filter media over time
that was caused by the kinetic energy of blower air discharge. when the air hits a dead end, 2 high pressure areas are created. this pressure was added to the static pressure and blew the filter. you could prevent that by making an 8' cube plenum, i'd like to see the rule of thumb for that. or you could kill the kinetic energy with baffles, screens, fiberfill, etc. its like misting your fruiting chamber with a fire hose, u shoot over their heads but the kinetic energy hits the side and makes mushed mushies.
as I said before;
"the only real aerodynamic function of a plenum is to minimize the kinetic energy of the flow. the manufacturer specs tell u the maximum pressure/flow, don't exceed those and don't point the blower at the filter. the filter will be fine. "
--------------------
until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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Supalemonhaze
Spore syringe hater.
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23149837 - 04/24/16 10:44 AM (6 years, 10 months ago) |
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You know when I was showing my build to my brother in law he asked if I used anything to diffuse the airflow, like you said. I looked at him like
and he looked back like
Guess that is what he was trying to say to me. He is an electrical engineer and by no means an expert on fluid dynamics but he sees similar stuff in his profession.
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23150030 - 04/24/16 12:11 PM (6 years, 10 months ago) |
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Quote:
blindingleaf said:
well thats why its called a "rule of thumb" because all of us un educated lowly mushroom growers don't have anywhere near the wisdom that engineers do
Quote:
"Rule of Thumb"
noun
1. a general or approximate principle, procedure, or rule based on experience or practice, as opposed to a specific, scientific calculation or estimate.
2. a rough, practical method of procedure.
so we have to rely on and draw from the vast amount of experience from cultivators that have come before, and in this case, their experiences showed that, in general, it is a good idea to build a plenum that is equal to or greater than the depth of the filter itself. over time, a "rule of thumb" was born.
you missed a critical aspect.
a "Rule of Thumb" is derived by someone who KNOWS the subject.
otherwise what u have is a "rule of thumb up your azz."
false modesty, sarcasm, condescendence, arrogance, and ignorance wow you're the full package. gloating about your ignorance is really attractive.
BEFORE YOU TRY TO EDUCATE OTHERS,EDUCATE YOURSELF!
u could start by losing the attitude and asking a civil question. i will explain the physics.
new "Rule of Thumb"= there is ABOLUTELY NO CORELATION BETWEEN THE THICKNESS OF THE FILTER AND THE DISTANCE FROM THE FILTER TO THE PLENUM WALL. but you can use the phase of the moon plus 1' if you like, it will work as well as yours.
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spacechildo
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23150033 - 04/24/16 12:12 PM (6 years, 10 months ago) |
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yeah leaf was truly showing his arrogance there, wow..
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blindingleaf
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Re: Laminar Flow Hood Calculations [Re: spacechildo]
#23150116 - 04/24/16 12:49 PM (6 years, 10 months ago) |
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I'm the worst ain't I?
--------------------
A few thoughts on cultivation
MICROBIAL HUSBANDRY!!!!
The whole is greater than the sum of its parts
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spacechildo
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23150130 - 04/24/16 12:56 PM (6 years, 10 months ago) |
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20k posts of arrogance and snide remarks hidden behind a wall of friendliness and helpful advice,
good thing we have well balanced members, and also our first ever engineer here, like jack showing us what you're really like leaf!
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23150137 - 04/24/16 12:58 PM (6 years, 10 months ago) |
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Quote:
blindingleaf said:
so lets say u have two identical filters, and two identical blowers that are matched to spec.
u make two hoods. one hood has a 6" plenum, the other has a 12"plenum, otherwise the hoods are identical.
would you anticipate differences between the two in terms of flow rate across the filter face?
as long as both keep the kinetic energy to reasonable levels, they would perform the same.
--------------------
until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
Edited by Jack Why (04/24/16 04:18 PM)
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Jack Why
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Quote:
Supalemonhaze said:
You know when I was showing my build to my brother in law he asked if I used anything to diffuse the airflow, like you said. I looked at him like
and he looked back like
Guess that is what he was trying to say to me. He is an electrical engineer and by no means an expert on fluid dynamics but he sees similar stuff in his profession.
yup, for the same reason we don't point the blower discharge at the filter. even if the velocity is low enough to not damage the filter
the kinetic energy will cause "hot spots", areas of higher velocity out of the filter. you can use sheet metal baffles, screens, egg crate anything to break up that column of moving air.
--------------------
until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23150263 - 04/24/16 02:00 PM (6 years, 10 months ago) |
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Jack Why I have an idea. .
Maybe donate a little bit of your time to a written up guide for the layman.
Many of us have managed to build working laminar flow cabinets worthy enough to hold thier own in small spawn labs, without the benifit of experience or an engineering degree with the few guides we have available to us. I know that's all I was really after..
If you think you can present a write up guide to improve our builds in layman terms then by all means please do. It would certainly be quite welcome on this forum.
I mean if these were *that* hard to design in the first place most of our hoods wouldn't work for mycology.
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23150789 - 04/24/16 05:10 PM (6 years, 10 months ago) |
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Quote:
mushpunx said:
Jack Why I have an idea. .
Maybe donate a little bit of your time to a written up guide for the layman.
Many of us have managed to build working laminar flow cabinets worthy enough to hold thier own in small spawn labs, without the benifit of experience or an engineering degree with the few guides we have available to us. I know that's all I was really after..
If you think you can present a write up guide to improve our builds in layman terms then by all means please do. It would certainly be quite welcome on this forum.
I mean if these were *that* hard to design in the first place most of our hoods wouldn't work for mycology.
kool, I was trying to draft one here;
https://www.shroomery.org/forums/showflat.php/Number/23089477
is this the wrong place for such a thing?
you guys can help by telling me what needs further explanation, questions, topics, etc.
I've learned tons about mycology from you guys and would like to return the favor.
--------------------
until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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Jack Why
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23150880 - 04/24/16 05:39 PM (6 years, 10 months ago) |
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Quote:
blindingleaf said:
I'm the worst ain't I?
nah, I've seen MUCH worse, of course they're dead now 
bob
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until u know why, you don't know jack.
Grant me the strength to change the things i can,
the serenity to endure those i can not,
and the wisdom to hide well the bodies
of those who try to tell me the difference.
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blindingleaf
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Re: Laminar Flow Hood Calculations [Re: Jack Why]
#23151041 - 04/24/16 06:22 PM (6 years, 10 months ago) |
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--------------------
A few thoughts on cultivation
MICROBIAL HUSBANDRY!!!!
The whole is greater than the sum of its parts
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bodhisatta  
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Re: Laminar Flow Hood Calculations [Re: blindingleaf]
#23151061 - 04/24/16 06:28 PM (6 years, 10 months ago) |
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Quote:
blindingleaf said:
in my experience, this is what happens when ur plenum is not large enough, even when urblower is matched to the filter size, so i don't agree that plenum size is not important
there is much more turbulence at the bottom of the box when ur plenum is too shallow, and can blow out the filter media over time
quit confusing me with facts and pictures to back up your experiences. and rules of thumbs made up by actual engineers
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dlynn
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23343682 - 06/14/16 02:42 PM (6 years, 9 months ago) |
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So for a 24x24x12 99.99% hepa filter would a 969 cfm fan be too much? Sounds like it will blow things off my table, blow spores away, blow my hair back according to this equation.
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mushpunx
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Re: Laminar Flow Hood Calculations [Re: dlynn]
#23343763 - 06/14/16 03:09 PM (6 years, 9 months ago) |
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Quote:
dlynn said:
So for a 24x24x12 99.99% hepa filter would a 969 cfm fan be too much? Sounds like it will blow things offitmy table, blow spores away, blow my hair back according to this equation.
Well that's 969 CFM @ free air. You would need to contact the seller and get the blower specs, and simply follow up the chart to see what it blows at 1. SP
You'll want about 400CFM @ 1 sp (1.2 actually add .2sp for the pre filter).
My blower is 549CFM @ free air and it pushes 360cfm @ .8sp ... that was as high as the chart went but I drew it out and its just about 300CFM @ 1.2 so it was perfect for my 18 x 24" filter face
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RolledUhhp
Amateur Cultivator
Registered: 08/10/16
Posts: 246
Last seen: 2 years, 7 months
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 Re: Laminar Flow Hood Calculations [Re: mushpunx]
#23604192 - 09/02/16 10:16 AM (6 years, 6 months ago) |
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Quote:
It will be pushing 100CFM evenly across the whole hood. Youre forgetting the square footage. And the proper plenum to let the static pressure build up properly for even laminar flow.
Take my hood for example.
Its 18 x 24 x 6. My blower pushes 549 CFM @ free air. To do the calculation, you go.. 18 x 24 = 432 , ÷ 144 = 3.
3 x 100 = 300.
I checked the blower specs before I bought my blower, and saw it pushes a little over 360 (if I remember correctly, might have been higher) at .8 sp. Moving up the graph it blows just over 300CFM
@ 1.2 sp. I used a 10" plenum. I needed a 6" plenum at minimum.
It blows at perfect laminar flow.
We're dividing 4322 by 144 (or 122) because we're working in ft2, correct?
From your last post in this thread:
Quote:
My blower is 549CFM @ free air and it pushes 360cfm @ .8sp ... that was as high as the chart went but I drew it out and its just about 300CFM @ 1.2 so it was perfect for my 18 x 24" filter face
When you say you drew it out from .8"sp to reach your figure at 1.2"sp was this just a rough estimate, or is there a formula I can follow to calculate what my blower would push at 1.2"sp? The listed specs only show up to 0.8"sp.
Edited by RolledUhhp (09/02/16 11:00 AM)
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Spaghettio73
Instigator
Registered: 03/13/20
Posts: 166
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Re: Laminar Flow Hood Calculations [Re: mushpunx]
#26777944 - 06/23/20 09:50 PM (2 years, 8 months ago) |
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Not to bump an old post but...
While researching build designs with the hope of adapting a thin form factor I found this diagram. There are several plenums but what is most interesting is the blower sitting right on top of the filter. Unless I’m seeing things the design engineers used no rule of thumb in doubling filter depth of plenum space.
Anyway
I too am interested in a design with the inline blower mounted in the plenum. I’ve run across a few diy designed in this manner and several commercial applications where plenum size seemed to completely disregard filter depth.
🤷🏻♂️🤘🏼
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Spaghettio73
Instigator
Registered: 03/13/20
Posts: 166
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Re: Laminar Flow Hood Calculations [Re: Spaghettio73]
#26801436 - 07/03/20 01:10 PM (2 years, 8 months ago) |
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For the record I bit the bullet and bought a prefab FH online. After hours and days of research and collecting info I had my list of parts. I was ready to starting buying the parts but for a bit more money I could have a working hood delivered at the same time to parts would show so I gave in and went the lazy route.
Also- For you stubborn folks like me please know a positive pressure modified SAB will With HEPA and prefiters only creates a turbulent contamination hurricane. You will waste time, effort, plates, and cultures. Don’t do it.
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Rumpleforeskin
Scientist new to mycology
Registered: 07/05/20
Posts: 82
Loc: Canada 
Last seen: 2 years, 3 months
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Re: Laminar Flow Hood Calculations [Re: Spaghettio73]
#26809373 - 07/07/20 04:05 PM (2 years, 8 months ago) |
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Just commenting to track... Lots of great info!
Just to confirm, are there differences in the 99.7% vs 99.9% filters in terms of resistance and if so, are the headaches in calculations worth the extra .2% filtration?
Found a filter source in Canada and am confirming specifications.
Also - Why is everyone using squirrel cages as opposed to a newer centrifugal fan? Just a cost thing? I don't think my grow store sells squirrel cages anymore.
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Spaghettio73
Instigator
Registered: 03/13/20
Posts: 166
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Quote:
Rumpleforeskin said:
Just commenting to track... Lots of great info!
Just to confirm, are there differences in the 99.7% vs 99.9% filters in terms of resistance and if so, are the headaches in calculations worth the extra .2% filtration?
Found a filter source in Canada and am confirming specifications.
Also - Why is everyone using squirrel cages as opposed to a newer centrifugal fan? Just a cost thing? I don't think my grow store sells squirrel cages anymore.
From what I gathered the squirrel cage provides a steady flow and pressure but I asked the same question since both blowers use the same physics to create flow. In my search I did read data sheets for inline blower designs. These blowers when not of the centrifugal design create turbulence. I found designs and claims of success using centrifugal inline blowers. The builds are IMO more visually appealing with the blower mounted inside the plenum. I stopped researching and just bought one online. Building one sounds fun and all but I’m prone to project overload. If you decide to pursue a build with an inline centrifugal please share the results here.
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