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Why extract from the top?

extract fans heat airflow with farty bits

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#71 Anonymiss

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Posted 11 August 2016 - 08:46 PM

If i may ask, what would be the benefit of extracting air from bottom, vs the light source.


If the ventilation air enters the chamber from the top and leaves via the bottom then the temperature gradient across the plants (from top to bottom) is smaller than it would be if the air entered from the bottom and left via the top. The same is true of the humidity gradient.

A smaller temperature gradient is preferable because it makes for more-even growth, and it stops the roots and base of the plants being so cold in relation to their tops.

Concerning humidity, in a top-down system the incoming dry air hits the top of the plants and then slowly increases in humidty as it passes downwards. This mimics natural conditions far better than bottom-up, and I imagine that it might well help to prevent or at least reduce the chances of bud rot.

This seems, to me, to be preferable to bringing dry air in and then passing it straight over the wet soil/medium where it immediately picks up moisture, and then having it wend its way up through the tangle of leaves, becoming even more damp along the way, before it finally hits the buds, by which point it's become laden with vapour and is unable to pick up very much more.
 

inefficiences


Yeah, I can see that being an issue, although with good runs of solid duct there would probably be little in the way of extra resistance. In any case, I suspect that a top-down system might still require more air flow overall than a bottom-up one does though.
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#72 Mrs Willy

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Posted 11 August 2016 - 08:59 PM

If the ventilation air enters the chamber from the top and leaves via the bottom then the temperature gradient across the plants (from top to bottom) is smaller than it would be if the air entered from the bottom and left via the top. The same is true of the humidity gradient.

A smaller temperature gradient is preferable because it makes for more-even growth, and it stops the roots and base of the plants being so cold in relation to their tops.

Concerning humidity, in a top-down system the incoming dry air hits the top of the plants and then slowly increases in humidty as it passes downwards. This mimics natural conditions far better than bottom-up, and I imagine that it might well help to prevent or at least reduce the chances of bud rot.

This seems, to me, to be preferable to bringing dry air in and then passing it straight over the wet soil/medium where it immediately picks up moisture, and then having it wend its way up through the tangle of leaves, becoming even more damp along the way, before it finally hits the buds, by which point it's become laden with vapour and is unable to pick up very much more.
 

Yeah, I can see that being an issue, although with good runs of solid duct there would probably be little in the way of extra resistance. In any case, I suspect that a top-down system might still require more air flow overall than a bottom-up one does though.

 

very interesting and makes sense in terms of a more uniform environment. I had missed the intake from top bit as i am most passive intake.. as well as dry air being pulled over medium by default down below,  Similarly i do appreciate warmer root mass and i always water my plants with luke warm water. (having made the mistake of from the cold tap a couple of years ago.) Why are they not growing quick? = cold rootmass.

 

Quite right tho in terms of battling against the natural hot air rising scenario which may require more power than a traditional setup.

 

 


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#73 MDS

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Posted 11 August 2016 - 08:59 PM

interesting MDS. you have just landed some memories.

But you are still blowing through ducting which arguably creates more (but 2 tenths of bugger all) resistance, unless you are blowing through horizontal ducting out the side of a tent.

 

Why do you have to have ducting connecting the fan to the cooltube or hood? A clamp that clamps both together is readily available :)
 

 

And you are then sucking the air from the side of the room, as opposed to a more directly over the plants in my scenario?

 

It'd still be towards the side of the room anyway unless you move the light to one side? Can't see you doing that somehow, so what does it matter?

 

 

I would question whether the heat into the bearings and motor is relevant, as it does heat up anyway with the fan going like the clappers, so they are designed for it anyways? or does it decrese the power when heats up?

 

Of course it's relevant, most hydroponic fans weren't designed for hydroponics but for ventilation systems in buildings. The usual maximum temperature rating that they'll handle inlet wise is 40C... With a grow room in summer & a red hot HPS tube up it's ass it'll likely see way more than that, not a good idea me thinks.. Anything that runs cooler that is electro-mechanical will be better off & last longer the cooler it runs. The power isn't likely to decrease, no...

 

 

Similarly, i suspect that temps would be higher in that scenario than mine, which arguably means that the light cannot be as close to the plants in a 1ft channel of a cooltube.

 

The temps are likely to be lower in my scenario, sorry :) These fans are great for blowing & generating pressure, they aren't so hot at sucking & creating negative pressure. It's why it's best to blow through a CF rather than pulling air through one ;)

 

 

Like you said, 2 tenths of bugger all difference i think, but on paper, it seems to me at least that sucking air through a 10 inch glass tube with an open end, is simply more efficient than pushing or pulling through a tube into ducting out of the other end?

 

So how come it's better to blow through a CF then, make your mind up here :P

 

You're wrong... Best to blow though it... You'll still have ducting the other end even if you're sucking with a fan, you have to connect it to the CF outside the tent, remember ;)


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#74 Anonymiss

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Posted 11 August 2016 - 09:26 PM

very interesting and makes sense in terms of a more uniform environment. I had missed the intake from top bit as i am most passive intake.. as well as dry air being pulled over medium by default down below,  Similarly i do appreciate warmer root mass and i always water my plants with luke warm water. (having made the mistake of from the cold tap a couple of years ago.) Why are they not growing quick? = cold rootmass.
 
Quite right tho in terms of battling against the natural hot air rising scenario which may require more power than a traditional setup.

 
I reckon that if anyone wanted to try it in a domestic setup then a cooltube/hood system such as yours is the way forwards :)

Create an intake at the top centre of the chamber, above the lamp, either directly or via some ducting from an appropriate opening; run some duct from the inlet side of the tube/hood down to floor level, finishing directly under the lamp; route the tube/hood outlet to the fan/filter as desired.

I think that in such a setup the airflow would look a bit like a ring doughnut or smoke ring, with the cool incoming air flowing down to meet the rising warmer air coming off the reflector housing, causing turbulence and mixing the flows. It would then move up and sideways, and eventually cascade down the walls of the tent, to be drawn back towards the inlet in the middle of the floor.

Or something like that anyway :)
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#75 Anonymiss

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Posted 11 August 2016 - 10:01 PM

It also works well for smells as well I used to test it blowing fag smoke into groom, to monitor airflow

 
Veering completely off-topic for a moment... Given the amount of time you spend in places where you can't smoke but probably want to, have you ever considered getting or making a small, portable carbon filter and fan to take with you?

I reckon that with a decent-ish PC fan, a small, cheap filter, and a short length of duct to act as a collector/inlet to blow into, you could be onto a winner :)
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#76 Dekay

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Posted 11 August 2016 - 10:31 PM

 
Veering completely off-topic for a moment... Given the amount of time you spend in places where you can't smoke but probably want to, have you ever considered getting or making a small, portable carbon filter and fan to take with you?

I reckon that with a decent-ish PC fan, a small, cheap filter, and a short length of duct to act as a collector/inlet to blow into, you could be onto a winner :)

 

OMFG dragons den missy ;)


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#77 captain beefheart

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Posted 12 August 2016 - 04:08 PM

duw duw what a load of bollox ive read here last few days :lol:   jest grow a plant ..........wash it........then toot it ffs........all this air movement malarkey jest aint worth a fook imho.......good luck :lol: :lol: :lol:


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#78 Mrs Willy

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Posted 12 August 2016 - 08:28 PM

 
Veering completely off-topic for a moment... Given the amount of time you spend in places where you can't smoke but probably want to, have you ever considered getting or making a small, portable carbon filter and fan to take with you?

I reckon that with a decent-ish PC fan, a small, cheap filter, and a short length of duct to act as a collector/inlet to blow into, you could be onto a winner :)

 

I havent missy, but i did come up with the concept of carbon filter underpants on tuesday night live and exclusive on the shoutbox.., to solve the problem of smelly farts  for the entire population of the world.

 

In all honesty, i can toot a J in a hotel room bathroom, so the need for such a device is small for me... But i do deliver some stinking farts in some far from ideal circumstances.  Which explains my take on additional uses of carbon filter.

 

Sorry for more off topic.. but Carbon filter underpants are sort of relevant to extraction out of the bottom.


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#79 Dekay

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Posted 12 August 2016 - 10:04 PM

I havent missy, but i did come up with the concept of carbon filter underpants on tuesday night live and exclusive on the shoutbox.., to solve the problem of smelly farts  for the entire population of the world.

 

In all honesty, i can toot a J in a hotel room bathroom, so the need for such a device is small for me... But i do deliver some stinking farts in some far from ideal circumstances.  Which explains my take on additional uses of carbon filter.

 

Sorry for more off topic.. but Carbon filter underpants are sort of relevant to extraction out of the bottom.

 

They been invented swilly, the underpants, she threatened to buy me some :)


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#80 Anonymiss

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Posted 06 July 2018 - 11:05 AM

post-7-0-62475400-1530873937.jpg

So, I was helping someone set up a new (their first) tent yesterday and after some discussion we decided to break with the usual inlet-at-the-bottom/extract-from-the-top tradition.

The tent is 1 m x 0.5 m x 1.8 m, with a double-socked 8" vent on the top, and one on each end for a cool tube.

There are also three fly-screened passive inlets with covers, and two double-socked cable inlets (one at the top and one at the bottom).

The lighting is a 250 Watt HID.

The fan is a Soler and Palau TD-SILENT 350/125 placed outside and on top of the tent, blowing into a 100 mm carbon filter.

The final plan uses split extraction, drawing air from both the top and bottom of the space, with the inlets coming in through the cool tube vents and then some short lengths of duct to direct it into the space between the lamp and plant.

The extraction ducting comes in through the top vent and then splits using a T-piece, with one leg taking air out of the very top of the tent and the other dropping down to floor level.

Will it work? I don't know, but preliminary testing using garden cane and paper plate 'plants' to disrupt the air flow looks good, with decent temperatures throughout and a small (2°C or so) variation between the top and bottom (of the plant-occupied space, not the entire area - it's obviously hotter above the lamp).

I'll report more when things are up and growing :)

I didn't have a camera available so there's no photos, but I'll try to remember next time

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