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Fresh Air Exchange Calculation-Measurement
    #13135901 -

Premise: To determine the amount of fresh air exchange needed every hour in relation to the cubic feet of the given fruiting chamber to rid it of CO2 build up.


Information needed:
a) FPM (Feet Per Minute) or CFM (Cubic Feet Per Minute) - In rate of air speed
b) Volume of fruiting chamber

Materials Needed: Electronic Anemometer will be needed if you do not already know the FPM or CFM of the method you use to exchange air.


Method:
Example 1) In this example I will be using a 64 quart monotub with 6 holes filled with polyfil (4 around the substrate on the sides and two towards the top on the ends of the tub) and one 120mm computer fan built into the side of the monotub with a CFM rating of 44.73. You will also need a fan as an exhaust fan with the same CFM of 44.73 n order to achieve equilibrium pressure; the amount of air leaving the space and entering the space must be the same.

Now most computer fans & household fans already display the CFM of the fan. If your given fan does not list the CFM then you can purchase an electronic anemometer on eBay for under $15. The anemometer will measure the FPM which you can then convert into CFM with the following equation; Feet Per Minute * Square Feet = Cubic Feet Per Minute

Now that we have our CFM, and volume in cubic feet we have all the needed data. The goal here is to have 1 ACH; eaning that the cubic volume of air in the container has been fully exchanged once every hour.

The equation for ACH is: N = 60*Q / Volume

    N = number of air changes per hour
    Q = Volumetric flow rate of air in cubic feet per minute (CFM)
    Volume = Space volume L × W × H, in cubic feet

The given fan has a CFM rating of 44.73 and the monotub has a volume of 64 quarts which we must convert to cubic feet. If you don't know the volume of your fruiting chamber then multiply  L x W x H. Since 1 US quart = 0.0334201389 cubic feet we then multiple .0334201389 by 64 which equals 2.13888888662875 Cubic Feet.

Our equation thus becomes: 1 = 60*Q / 2.13888888662875

We know our CFM of the fan but we do not plug it into the equation because we want to know the needed CFM to just have 1 ACH (Air Exchange Per Hour).

So to find out our needed CFM to have 1 ACH we simply divide our volume in cubic feet 2.13888888662875 by the minutes in an hour, 60. So 2.13888888662875 / 60 = 0.0356481481104792.

So the needed CFM for a 2.13888888662875 cubic foot chamber is 0.0356481481104792 if the fan was running the full 60 minutes.

Our given fan though has a CFM rating of 44.73 and we only need 0.0356481481104792 CFM.

Thus: 44.73 CFM / 2.13888888662875 Cubic Feet = 20.91272729482551 Seconds

The given fan (and exhaust fan) would need to only be turned on for roughly 21 seconds every 60 minutes.

Now, if we were not to use the fan as the means of air exchange and simply fan with the lid then we would need to determine the average CFM of one pass of the lid; this would require the digital anemometer. Simply measure the single pass of the lid with the anemometer 10 times and then find the average CFM. Then follow as above using the same method and you will be able to find out the amount of fanning you would need to do every hour in order to achieve 1 ACH.

Now I doubt most people won't manually fan every hour so instead of dividing the cubic feet of the fruiting chamber by 60 simply divide it by how ever many hours you want a full exchange. If you are going to fan every two hours then divide by 120; if every 3 hours then 180, so on and so on.


This can be used with all types of fruiting chambers, not just a monotub and all different methods of air exchange.

Conclusion: Knowing this it allows us to exchange the air in the chamber exactly as needed without over doing it and drying out the substrate and having a loss in our relative humidity.


:discorex:


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My Drying Chamber




Edited by Satori23 (09/01/10 10:20 PM)

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Re: Fresh Air Exchange Calculation-Measurement [Re: Satori23]
    #13137169 -

:eek:


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"Yeah well, you know...that's just like...your opinion, man." - The Dude

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Re: Fresh Air Exchange Calculation-Measurement [Re: ph34r]
    #13139843 -

:bump:


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My Drying Chamber




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Re: Fresh Air Exchange Calculation-Measurement [Re: Satori23]
    #13139889 -

Y do you need to fans to equal pressure? one wouldnot work and just and just make a brief over pressure, for 21seconds


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The death of one man is a tragedy. The death of millions is a statistic..  Josef Stalin

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Re: Fresh Air Exchange Calculation-Measurement [Re: idunno]
    #13139966 -

idunno said:
Y do you need to fans to equal pressure? one wouldnot work and just and just make a brief over pressure, for 21seconds



I'm not sure I know what exactly you are asking. But I'm referring to equilibrium pressure, it is not a must, but in order to achieve equilibrium pressure the amount of air leaving the space and entering the space must be the same.


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My Drying Chamber




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Re: Fresh Air Exchange Calculation-Measurement [Re: Satori23]
    #13140290 -

Makes sense.  In a monotub, would one use the volume of the tub minus the level of the substrate?  Say the sub and trash bag occupy the bottom 4", that would change the volume of the tub.  Shouldn't that be a factor?

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Re: Fresh Air Exchange Calculation-Measurement [Re: abltsandwich]
    #13140570 -

abltsandwich said:
Makes sense.  In a monotub, would one use the volume of the tub minus the level of the substrate?  Say the sub and trash bag occupy the bottom 4", that would change the volume of the tub.  Shouldn't that be a factor?



The ideal answer would be yes, to factor it in; but it won't be an outrageous amount to really off throw the equation by that much.


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My Drying Chamber




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Re: Fresh Air Exchange Calculation-Measurement [Re: Satori23]
    #13141977 -

How does one set up a computer fan system to be automated with this setup?  I'd like to try this.  I'd assume that one doesn't need any additional air circulation in the room as well since the computer fans take care of all of the FAE needed.  I want to go this route to save on energy consumption since having a small fan running 24/7 in the room is hurting my electricity bill.  ~20 seconds a day vs. all day will make a difference AND be more efficient.  Win-win.

Secondly, will it make a difference where the fans are located on the monotub walls?  Like do you want one up high and the other near substrate level?  Both in the middle or at same height?  I'd think if one was up top and the other was near substrate level that would most-efficiently move the air out vs. being level with one another.

Edited by abltsandwich (09/03/10 10:33 AM)

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Re: Fresh Air Exchange Calculation-Measurement [Re: abltsandwich]
    #13141983 -

Why do you run a fan 24/7? And why such a big one?


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You make it all possible. Doesn't it feel good?

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Re: Fresh Air Exchange Calculation-Measurement [Re: Doc_T]
    #13141990 -

It's not that big, little $6 fan from Wal-Mart like 4 or 5" across.  I have the fan running in the room 24/7 pointed away from the monotubs for air circulation when I move to fruiting conditions and begin the 12/12 light cycles.  Is that not correct?

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Re: Fresh Air Exchange Calculation-Measurement [Re: abltsandwich]
    #13142001 -

:shrug: It's not what the tek calls for, but if it works for you, then w/e. But it runs up the power bill?


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You make it all possible. Doesn't it feel good?

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Re: Fresh Air Exchange Calculation-Measurement [Re: Doc_T]
    #13142010 -

Not as much as the light itself.  The teks I've read (don't have them bookmarked on this computer) I thought I recall having a fan running in the room for fruiting conditions.  How do you do it?  I've been having humidity problems, great pinset but mostly aborts, and all of my fruits are toward the edge of the tub with nothing but aborts in the middle.  My last pinset gave me a hardon and I'd say a good 80+% of them aborted so I know I'm having humidity issues and maybe that fan is the problem.

EDIT:  Doc_T I know you've been touting the monoshotgun hybrid, but in a traditional monotub is what I'm asking about here.  The monoshotgun I plan to try at some point when I get the rest of this down pat.

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Re: Fresh Air Exchange Calculation-Measurement [Re: abltsandwich]
    #13142019 -

:yesnod: I'm talking about the traditional Ohmatic monotub tek. Review what it says about fans.

(I use a greenhouse, so not relevant to this discussion.)


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You make it all possible. Doesn't it feel good?

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Re: Fresh Air Exchange Calculation-Measurement [Re: Doc_T]
    #13142068 -

With a search, I'm finding lots of people have a small fan in the room when in fruiting conditions to circulate air to prevent it from becoming stagnant.  Couldn't find anything in the original Ohmatic tek.  There are even a few links in Ohmatic's original tek that recommend using a fan in the room:

http://www.shroomery.org/forums/showflat.php/Cat/0/Number/7780127/an/0/page/0
"35) with an osciallating fan in the room, this can help with your fae. you can also get a hairdryer or cpu fan to use for air exchange if you need it. it isn't necessary but it never hurts to do it once a week or even once a day."

http://www.shroomery.org/forums/showflat.php/Cat/0/Number/7893964/an/0/page/0
"The bin is done. I put it in a room much like this one with a fan on 24/7 about 1.5 feet above the bins and a couple of floro lights that are on about 12 hours a day.. I do this right away I don't use any kind of incubator  or put additional coverage on the top of the substrate.. I'm looking for knotting just about the time that the entire bin is colonized... the sooner the better.. give that fucker light right away."

http://www.shroomery.org/forums/showflat.php/Cat/0/Number/7946219/page/0/fpart/1/vc/1
"Used some rye>HMC. Monotub obvioulsy and you can see the fan and heater being used. Sub depth is about 5" and there are nots everywhere."

And those links are directly from Ohmatic's original tek.  Didn't see anything in his tek about fans though.  I did notice that his tek calls for a frosting layer, so maybe if he doesn't recommend using a fan it's because it may be outdated slightly.  I don't know...

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Re: Fresh Air Exchange Calculation-Measurement [Re: abltsandwich]
    #13142095 -

Quote:
"35) with an osciallating fan in the room, this can help with your fae. you can also get a hairdryer or cpu fan to use for air exchange if you need it. it isn't necessary but it never hurts to do it once a week or even once a day."


Once a day. Oscillating. You said you're drying out your tubs- for what?


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You make it all possible. Doesn't it feel good?

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Re: Fresh Air Exchange Calculation-Measurement [Re: Doc_T]
    #13142125 -

I think it was referring to the hair dryer or computer fan thing once a day, not the oscillating fan.  It's a little ambiguous but that's what I gathered from that sentence and its phrasing.  Either way, I'm seeing lots of people with fans in their fruiting conditions to circulate air.  It makes sense to me, since stale air = contams and FAE is good.  How else is a monotub going to get FAE?  I don't want to fan and mist or anything, because if I'm going to do that I'd use trays and a greenhouse.  I like monotubs because they're largely set it and forget it.  I work a lot and I just can't fan enough times per day.

As for my sub drying out, I don't know that that's the case; it doesn't shrink at an abnormal rate and if I do lift the lid (I've tried the fanning thing before) I get a blast of warm, very humid air as I lift the lid.  My understanding is that this is a sign of proper humidity.  I'm at a loss as to how to fix my humidity issues.  What I really need is a hygrometer I just haven't gotten one yet.

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Re: Fresh Air Exchange Calculation-Measurement [Re: Satori23]
    #13142156 -

What mushroom  mycelium wants at fruiting time is fresh air, and a CO2 level less than about 800 ppm.  It's really irrelevant how many air exchanges per hour they receive, since the ultimate goal is to reduce the CO2 concentration in the air.

The best method I've found if you have no CO2 meter is to make sure that if you mist well, the water is gone off the fruits in about fifteen minutes.  This ensures enough fresh air to take away the excess moisture, and by default, one could assume the CO2 is being scrubbed away too.

There's a few CO2 monitors on the market for under $300, so you might want to look into one of these.
RR


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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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Re: Fresh Air Exchange Calculation-Measurement [Re: RogerRabbit]
    #13149325 -

I suppose my goal was a mathematical outlook on keeping the substrate from drying out yet keeping a consistent rate of air exchange.


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My Drying Chamber




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Re: Fresh Air Exchange Calculation-Measurement [Re: Satori23]
    #13149432 -

I like it. Have you calculated the ACH for the monotub alone with no fan? What's the pressure differential across the polyfill?


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The above post is fictional, hypothetical, or downright nonsensical.


:moon:  :moon:  :moon:  :moon:    :moon:

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Re: Fresh Air Exchange Calculation-Measurement [Re: anonjon]
    #13153536 -

I have yet to calculate the standing ACH in a monotub, this would obviously turn up different results for each individual seeing as people have different amounts of airflow through their house.


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My Drying Chamber




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