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Senior Member
Username: Highflyer
Post Number: 670
Registered: 12-2002
| | Posted on Friday, November 21, 2003 - 05:36 pm: | 
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THIS POST SHOULD BE AT THE BOTTOM OF THE THREAD
I wrote Fungi Perfecti and they told me 2 things of importance...
1.) Use a 480-488 cfm @ 0 stactic pressure blower for a 12" x 24" filter.
2.) If you use a blower with that blows too hard, then you will eventually blow a hole in your filter.
(Message edited by highflyer on November 21, 2003)
"I hold it to be the inalienable right of anybody to go to hell in his own way." - Robert Frost
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Joe Millionaire (Rotterdam_y2k)
Senior Member
Username: Rotterdam_y2k
Post Number: 283
Registered: 07-2003
| | Posted on Tuesday, November 18, 2003 - 01:12 pm: |
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Hey everyone. My friend just got this 800 cfm blower to make a flow hood. She is going to follow the directions provided by Mycotopia's TEK section.
Question: What size filter should she use? They TEK says a 495cfm blower for a 24 X 12 filter.
Can she go bigger???
(Message edited by rotterdam_y2k on November 18, 2003)
"Ekam Sat Vipras Bahudda Vidante"
The One Truth is named by the wise in many ways.
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Highflyer (Highflyer)
Senior Member
Username: Highflyer
Post Number: 632
Registered: 12-2002
| | Posted on Tuesday, November 18, 2003 - 01:24 pm: |
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This may help you:
Every filter has a different "resistance" when air blows through it at a certain speed, this resistance is called the "static pressure".
Press your hand against your mouth. Now try to blow through it. Dependant on how firm you press it against your mouth, you will have some difficulties blowing air out and you will feel some resistance, this is the static pressure.
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.
The static pressure is expressed in inch of water column in the english units, a typical value would be 1", the SI unit for pressure is Pa(Pascal).
1" water column is around 250 Pa. Each filter has a data sheet (consult the manufacturer if this is not the case) where the static pressure at the working point is entered. Before the air enters the blower it is usually pre-filtered by a furnace filter around 1"(2.5cm) thick placed in front of the blower to protect it and the HEPA filter from big paricles like dust and hair. It can be assumed that the static pressure for this prefilter at the working point is around 0.2"(50 Pa)
Matching a blower to the filter
According to Stamets (Paul Stamets and J.S.Chilton: The Mushroom Cultivator p. 347 ff) the air speed of the air flowing from the filter surface should be (at least) 100 feet per minute(fpm).(around 30 meter per minute or 0.5 meter per second).
1. Find out the area of your filter by multiplying the width and the hight in feet (for instance the smallest reasonably usable filter would be 2ft x 1ft)
2ft x 1ft = 2 ft2
2. Multiply the required air speed(the one Stamets specifies) with the area of your filter
100 ft/min x 2 ft2 = 200 ft3/min
So 200 ft3/min(cfm) is the amount of air your blower must deliver at the STATIC PRESSURE of the HEPA filter + prefilter.
NOTE: 1 cfm= 1.7m3/h
So if you use the above filter with 1"(250Pa) static pressure and a furnace prefilter with a static pressure of 0.2"(50Pa) your blower must deliver 200 cfm(340m3/h) of air at a static pressure of 1.2"(300Pa).
Finding the correct blower
Every blower should have a data sheet with a characterisitc curve that shows the air output in dependance of the static pressure.
Credit to ANNO
You can use a larger blower, but the airflow may be to great comming out of the flowhood. You can use a rheostat to control the speed of the blower, or you could add several layers of prefilters which will give more resistance to airflow. You would need to use the math above to figure out what type of prefilters to get.
"I hold it to be the inalienable right of anybody to go to hell in his own way." - Robert Frost
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Highflyer (Highflyer)
Senior Member
Username: Highflyer
Post Number: 633
Registered: 12-2002
| | Posted on Tuesday, November 18, 2003 - 01:41 pm: |
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And its usually easier to fit a blower to your particular filters, rather than the other way around. It can still work though.
"I hold it to be the inalienable right of anybody to go to hell in his own way." - Robert Frost
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rodger rabbit (Skyypilot)
Senior Member
Username: Skyypilot
Post Number: 1162
Registered: 02-2003
| | Posted on Tuesday, November 18, 2003 - 03:46 pm: |
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A couple of points. Paul now recommends a minimum flow rate of 150 feet per minute. That has been increased since TMC was published. I took my flow hood to work and checked it using a digital capture hood http://www.professionalequipment.com/xq/ASP/Produc tID.838/id.9/subID.271/qx/default.htm and the velocity leaving the filter measured 162 feet per minute, with the two speed fan running on high speed. This hood works great. I don't think you can have 'too much' flow from a flow hood. The flow is laminar and away from the filter, so don't get your hands between the filter and your work. Second, you can't use a rheostat to control speed on an AC motor. You can cut a piece of cardboard or aluminum foil to cover part of the intake to reduce airflow. This will also reduce the amount of AC current the motor draws, as less work (airflow) equals less amperage.
"I feel rowdy and I don't know why. . .Excuse me, while I kiss the sky!" jimi hendrix
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Highflyer (Highflyer)
Senior Member
Username: Highflyer
Post Number: 635
Registered: 12-2002
| | Posted on Tuesday, November 18, 2003 - 04:04 pm: |
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In Nan's Hood he says that to use a rheostat then the "motor must be of the split capacitor type". How can you tell if the motor is this type?
"I hold it to be the inalienable right of anybody to go to hell in his own way." - Robert Frost
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Joe Millionaire (Rotterdam_y2k)
Senior Member
Username: Rotterdam_y2k
Post Number: 284
Registered: 07-2003
| | Posted on Tuesday, November 18, 2003 - 06:17 pm: |
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Thanks for the response. I must admit that it is a bit overwhelming.
So here goes a shot at some math.
The filter I am looking at is 2 ft X 1 1/2 ft
OR
3ft2
According to Rodger 150 ft/min is appropriate
150ft/min X 3ft2 = 750 ft3/min (cfm)
So that checks out ok. My gals blower, 800 cfm (1/4 hp), can power the flow hood with a 24" X 18" filter.
She is totally sick of wasting time cooking rye just to lose them to contams. Z strain and petri isolation here we come! It is my opinion that the biggest mistake that a newbie makes is trying to do this thing "ghetto" expecting results like Rodger and philnwierd post. God bless you guys!
"Ekam Sat Vipras Bahudda Vidante"
The One Truth is named by the wise in many ways.
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rodger rabbit (Skyypilot)
Senior Member
Username: Skyypilot
Post Number: 1166
Registered: 02-2003
| | Posted on Tuesday, November 18, 2003 - 07:20 pm: |
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The flow hood will make all the difference.
As for using a rheostat, it doesn't matter if it's a capacitor motor or not. The speed of an AC motor is determined by the frequency of the power supply. In the U.S., it is 60hz. Only a DC motor can be controlled by a rheostat. They do make motor speed controllers that will work, and one would need to get one that would match the amp rating of the motor. An easier way would be to install a baffle on the intake. Just block half or more of the intake and you'll get the same result. Less airflow, and less electricity used. A good rule of thumb for flow hoods is that at 12" away, it should blow the flame from a bic lighter sideways, but not blow it out.
"I feel rowdy and I don't know why. . .Excuse me, while I kiss the sky!" jimi hendrix
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Joe Millionaire (Rotterdam_y2k)
Senior Member
Username: Rotterdam_y2k
Post Number: 290
Registered: 07-2003
| | Posted on Tuesday, November 18, 2003 - 09:58 pm: |
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Anyone know what happened to this site???
filtersrx.com
It is listed in the TEK section as a viable retailer of filters. Any other places to buy them?
"Ekam Sat Vipras Bahudda Vidante"
The One Truth is named by the wise in many ways.
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Hippie3 (Admin)
Board Administrator
Username: Admin
Post Number: 7753
Registered: 02-2001
| | Posted on Wednesday, November 19, 2003 - 12:45 am: |
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archive material.
not sure, joe.
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Highflyer (Highflyer)
Senior Member
Username: Highflyer
Post Number: 651
Registered: 12-2002
| | Posted on Thursday, November 20, 2003 - 08:27 pm: |
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150ft/min X 3ft2 = 750 ft3/min (cfm)
I think you should check your math again. Should be 450. Check to see if the blower is rated at least 450cfm at a static pressure of 1.0.
Fungi Perfecti has the filters as well. They are a little expensive though. $130.
"I hold it to be the inalienable right of anybody to go to hell in his own way." - Robert Frost
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Joe Millionaire (Rotterdam_y2k)
Senior Member
Username: Rotterdam_y2k
Post Number: 313
Registered: 07-2003
| | Posted on Thursday, November 20, 2003 - 09:10 pm: |
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You're right on my poor math skilz. (spelling too) <----- and grammar...
It's rated at 800 cfm. Built the box today. Should be getting the blower in anytime. Will purchase the filter a week or so after the next harvest... I will write up a little tek for the bigger unit. According to my girlfriend, it looks NICE so far. Pics to come...
"Ekam Sat Vipras Bahudda Vidante"
The One Truth is named by the wise in many ways.
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Highflyer (Highflyer)
Senior Member
Username: Highflyer
Post Number: 652
Registered: 12-2002
| | Posted on Thursday, November 20, 2003 - 10:12 pm: |
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I have a question if anyone can answer it.
Is there any way to find the cfm at a given static pressure if its not listed in a manual? Like if you are given the the cfm at static pressures of 0, .2, .4, and .8....is there any way to figure what the cfm would be at 1.0, or 1.2?
"I hold it to be the inalienable right of anybody to go to hell in his own way." - Robert Frost
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I_am_me (I_am_me)
Senior Member
Username: I_am_me
Post Number: 138
Registered: 10-2003
| | Posted on Thursday, November 20, 2003 - 10:25 pm: |
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Well just on the basis of math you should be able to compare the info for .2, .4 and .8 If there is a pattern you should be able to just do a simple equasion.
Maybe this would work.
.2 x A = cfm
.4 x A = cfm
.8 x A = cfm
1.2 x A = cfm
Solve for A in the first three equations. If A is the same thing in all 3....then use the value of A to find the cfm for 1.2 This could be totally wrong....but it makes some sense. Could you please post the cfm for .2, .4 and .8?
Microscopes are my hobby. I do not cultivate anything.
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Highflyer (Highflyer)
Senior Member
Username: Highflyer
Post Number: 653
Registered: 12-2002
| | Posted on Friday, November 21, 2003 - 07:48 am: |
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Its a dual speed blower.
CFM @ 0.000 Inch Static Pressure:
760 545
CFM @ 0.100 Inch Static Pressure:
750 530
CFM @ 0.200 Inch Static Pressure:
735 525
CFM @ 0.300 Inch Static Pressure:
710 505
CFM @ 0.400 Inch Static Pressure:
675 495
CFM @ 0.500 Inch Static Pressure:
640 480
CFM @ 0.600 Inch Static Pressure:
610 460
CFM @ 0.700 Inch Static Pressure:
565 420
CFM @ 0.800 Inch Static Pressure:
520 380
Your method doesnt appear to work I Am Me. Ive been looking some more, and several blowers give the cfm as a graph of static pressure vs. cfm. Here is what the graph for this blower would look like.
Its a curved graph, so thats why IAmMe's method didnt work. Anyone know if making a graph would be the way to find it, or would there be another method?
"I hold it to be the inalienable right of anybody to go to hell in his own way." - Robert Frost
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I_am_me (I_am_me)
Senior Member
Username: I_am_me
Post Number: 143
Registered: 10-2003
| | Posted on Friday, November 21, 2003 - 08:03 am: |
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Yeah I didn't expect my method to work....just an outline of an idea. You have to find the relation of the numbers....which I didn't know. After looking at the numbers I realize I'm not sure. When I asked my girl about this (shes was a math major) she started talkin about graphs...so I'll show her this and see if she can figure out anything.
(Message edited by I_am_me on November 21, 2003)
Microscopes are my hobby. I do not cultivate anything.
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Highflyer (Highflyer)
Senior Member
Username: Highflyer
Post Number: 654
Registered: 12-2002
| | Posted on Friday, November 21, 2003 - 10:29 am: |
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I don't think you can have 'too much' flow from a flow hood.
The filter I have says max 273 @ 1.0. I am assuming that means do not get a blower that does over that. It may just mean 1.0 max SP, but i'm not really sure.
(Message edited by highflyer on November 21, 2003)
"I hold it to be the inalienable right of anybody to go to hell in his own way." - Robert Frost
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jimmy jublanski (Zoomerhead)
Senior Member
Username: Zoomerhead
Post Number: 209
Registered: 05-2003
| | Posted on Friday, November 21, 2003 - 05:59 pm: |
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you arn't getting the right numbers because the graph is not linear so then you can't predict a simple pattern like you tried to do. if i remember right there are ways to do it but they involve calculus style math..boooo.
and to be a further picky bastard..you can have a flow hood and it not be a laminar flow hood. laminar flow refers to a nice even steady flow with a reynolds number between a ceratin set of numbers (reynolds number is like a measure of the smoothness of flow). other flows out side of this number are called turbid flows. and there are things one can do to make the flow laminar..like baffles that will smooth out the flow. and there are calculations to figure this all out. wow who would have though my fluid dynamics class would pay off!! all this is just for shits and giggles and probably isn't needed to know but wtf i am bored |
Joe Millionaire (Rotterdam_y2k)
Senior Member
Username: Rotterdam_y2k
Post Number: 326
Registered: 07-2003
| | Posted on Friday, November 21, 2003 - 07:43 pm: |
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you info helped me jim. i didn't know the difference between a laminar flow and a regular flow.
"Ekam Sat Vipras Bahudda Vidante"
The One Truth is named by the wise in many ways.
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Rasilon (Rasilon)
New member
Username: Rasilon
Post Number: 4
Registered: 10-2003
| | Posted on Sunday, November 23, 2003 - 03:07 am: |
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Highflyer,
Print that graph out, then trace the line and extend it out as you need, approximating the line past your last data point. It won't be hard to extrapolate the data you need from the data you have. Looks to me to be [email protected]" SP.
Rasilon |
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