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Offlinefractaldill
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Registered: 08/31/13
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Re: Final LFH questions [Re: Kalypto]
    #19283448 - 12/16/13 11:43 AM (10 years, 2 months ago)

Quote:

Kalypto said:
No I was going to do 2x4 feet cause the only blowers I could find at the right SP put out around 800 cfm




get a variable speed controller and lower the cfms


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OfflineKalypto
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Re: Final LFH questions [Re: fractaldill]
    #19283673 - 12/16/13 12:32 PM (10 years, 2 months ago)

Thats what I now plan to do , I had asked to forums numerous times if it would maintain static pressure when using this but never got an answer


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Offlinefractaldill
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Re: Final LFH questions [Re: Kalypto]
    #19284071 - 12/16/13 02:00 PM (10 years, 2 months ago)

the static pressure isnt changing, its the cfms


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OfflineKalypto
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Re: Final LFH questions [Re: fractaldill]
    #19284102 - 12/16/13 02:07 PM (10 years, 2 months ago)

I now know but I needed to be sure before I spent a shit ton of money on a blower


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Offlinefractaldill
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Re: Final LFH questions [Re: Kalypto]
    #19284253 - 12/16/13 02:35 PM (10 years, 2 months ago)

i hear that...


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OfflineRogerRabbitM
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Re: Final LFH questions [Re: fractaldill]
    #19285603 - 12/16/13 07:35 PM (10 years, 2 months ago)

Quote:

fractaldill said:
the static pressure isnt changing, its the cfms




The static pressure changes as you speed the motor up.  As the static pressure increases, the flow increases.

You can also slow down a flowhood by blocking part of the intake filter or stacking several pre filters.
RR


--------------------
Download Let's Grow Mushrooms



semper in excretia sumus solim profundum variat

"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison


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Offlinefractaldill
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Re: Final LFH questions [Re: RogerRabbit]
    #19285654 - 12/16/13 07:47 PM (10 years, 2 months ago)

Quote:

RogerRabbit said:
Quote:

fractaldill said:
the static pressure isnt changing, its the cfms




The static pressure changes as you speed the motor up.  As the static pressure increases, the flow increases.

You can also slow down a flowhood by blocking part of the intake filter or stacking several pre filters.
RR




Now im confused. So if im trying to build a 2x1.5 flowhood, and the filter has a sp of .8, i need a blower that can push 300cfm at around .9,1" right? where in that is the static pressure changing? i can see the output decreasing with a higher SP, but i cant see the SP changing with different fan speeds.


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OfflineRogerRabbitM
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Re: Final LFH questions [Re: fractaldill]
    #19285769 - 12/16/13 08:11 PM (10 years, 2 months ago)

Not exactly.

Filters don't have a 'static pressure' of .8

They might have tested the filter at xyz flow, and found the resistance to be .8" W.C.  If that xyz flow is what you want, then get a blower which can handle that cfm at .8" of water column.

As the blower speeds up, it will try to push more air.  This by definition will increase static pressure in the plenum. This increased static pressure behind the filter will result in more flow out the front.
RR


--------------------
Download Let's Grow Mushrooms



semper in excretia sumus solim profundum variat

"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison


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OfflineKalypto
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Re: Final LFH questions [Re: RogerRabbit]
    #19285899 - 12/16/13 08:40 PM (10 years, 2 months ago)

Does this mean If I have a blower that is rated for 800 cfm at 1.2 SP and I turn it down to 400 cfm It wont be 1.2 SP?

Or will it maintain 1.2 and just slow down then stop ?


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Offlinet3chnobily
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Re: Final LFH questions [Re: Kalypto]
    #19287430 - 12/17/13 07:19 AM (10 years, 2 months ago)

Dude your over thinking this whole thing. 

1. Pick a filter

2  buy a fan rated 20-30% stronger than your going to need

3  build your hood

4  keep adding prefilters/block intake till you achieve laminar flow.

When you really dig into physics behind blower performance and fluid dynamics it gets so complicated and there are so many variables that it quickly boggles the mind.  You don't need an engineering degree to build a flow hood.  As my favorite coworker used to say  " Less jaw'en and more Saw'en"


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OfflineKalypto
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Re: Final LFH questions [Re: t3chnobily]
    #19287439 - 12/17/13 07:26 AM (10 years, 2 months ago)

Quote:

t3chnobily said:
Dude your over thinking this whole thing. 

1. Pick a filter

2  buy a fan rated 20-30% stronger than your going to need

3  build your hood

4  keep adding prefilters/block intake till you achieve laminar flow.

When you really dig into physics behind blower performance and fluid dynamics it gets so complicated and there are so many variables that it quickly boggles the mind.  You don't need an engineering degree to build a flow hood.  As my favorite coworker used to say  " Less jaw'en and more Saw'en"




I dont know about you , but I like to know how stuff works .
Again as I have said I wanted to make sure it would work before I spend 300$ on a blower


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Offlinedrake89
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Re: Final LFH questions [Re: Kalypto]
    #19287728 - 12/17/13 09:32 AM (10 years, 2 months ago)

if you're gonna spend $300 on a blower, get the biggest one you can so you'll know it will work.  then there's nothing to think about.


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OfflineKalypto
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Re: Final LFH questions [Re: drake89]
    #19287935 - 12/17/13 10:34 AM (10 years, 2 months ago)

Quote:

drake89 said:
if you're gonna spend $300 on a blower, get the biggest one you can so you'll know it will work.  then there's nothing to think about.





How about getting a blower thats not bigger than I need to save money .


Im not a person that just does stuff I think things through .


This hobby can be viewed scientifically and thats how I do it.

I actually want to go to school for mycology so this whole just do it things isnt gonna fly for me , I think things through .


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Offlinefractaldill
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Re: Final LFH questions [Re: Kalypto]
    #19287983 - 12/17/13 10:49 AM (10 years, 2 months ago)

If youre looking into a 24x24 flowhood youre really going to need to get something like the dayton 1tdu2. Ive yet to see a blower that will push 400cfm at 1-1.2". that being said youre going to need to amp it down a bit, as that pushes around 1040 cfm @ .8...


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OfflineKalypto
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Re: Final LFH questions [Re: fractaldill]
    #19287989 - 12/17/13 10:51 AM (10 years, 2 months ago)

I know , Ive said Ive spent hours looking for blower I have multiple alternatives all I needed help with was the Questions at the beginning of the thread


also I am looking for something that does 1.2 ,1.1 minimum


Edited by Kalypto (12/17/13 10:54 AM)


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Offlinet3chnobily
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Re: Final LFH questions [Re: Kalypto]
    #19290008 - 12/17/13 06:36 PM (10 years, 2 months ago)

I looked into all this shit thoroughly and the only people who can give you in exact information you want are the engineers who designed your specific blower.  The variables I  mentioned have to do with the exact configuration of cowl, blade shape of your blower, speed and torque of your motor.  They dramatically affect performance.  Also the exact specifics of your hood design especially the plenum and fan box.  More than likely RH, air temperature and elevation all have effects also.  Even engineers have a imperfect understanding of fluid dynamics.  That is why things are built with safety factors.  Simply make a reasonable estimate of the needed power then make it 20-30% bigger.  Once its put together use the lighter test to dial it in.  This is how things get done in the real world.

If you want to save money score a filter off ebay,  scrounge a blower at an HVAC shop, use Melanie from depot.  My 2 x 4 hood cost about $250  I'm going to stop procrastinating now and go push some blocks through it.


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Offlinefractaldill
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Re: Final LFH questions [Re: t3chnobily]
    #19290070 - 12/17/13 06:49 PM (10 years, 2 months ago)

250 for a 2x4 lfh? God damn here I am about for fork out 400 for an 18x24


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OfflineKalypto
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Re: Final LFH questions [Re: fractaldill]
    #19290200 - 12/17/13 07:21 PM (10 years, 2 months ago)

for sure 70$ filter from ebay and another 30-50 in prefilters maybe a speed contoller will be all i pay


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InvisibleinskiM
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Re: Final LFH questions [Re: Kalypto]
    #19290942 - 12/17/13 10:39 PM (10 years, 2 months ago)

Those speed controllers can be expensive, mine was just over $100 here in New Zealand.

You also need to be sure that your blower is designed to be fitted with one, if it isn't it will most likely burn out!


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OfflineKalypto
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Re: Final LFH questions [Re: inski]
    #19292185 - 12/18/13 07:54 AM (10 years, 2 months ago)

My dad does HVAC so it shouldnt be a problem , now that I know more about the physics of it im pretty sure My dad can do it all pretty easily


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