Understanding air intake and exhaust.

[VagPuncher]

Hi,

I have never used intake or exhaust to cool a grow room. I have always used sealed rooms with split system air conditioners.

Now, I will be setting up 2 grows in a part of Canada that gets very, very cold in the winter. -35 degrees and lower.

During these winter months I would like to ditch the AC's for 2 reasons.

1) Save the electrical consumption.

2) The chance of the AC's crapping out during the winter due to very cold winter conditions.

My questions is:

Can I not just hook up some intake fans to a temp controller and have the cold air get pulled in to the grow room to cool it?

AND

If I do use intake fans will I need to also exhaust the same amount of air out?

Will the cold winter air meeting the warm grow room air wreck havoc on humidity? Will the humidity go up or come down?


Thanks.

 

[Guest 150314]

how many lights?

you want more air being exhausted than brought into the room to maintain negative pressure and keep the smell from escaping. if its -35 degrees outside and depending on how many lights your running you could get away with only using an outtake fan and just cut a hole for a passive intake.

it will also help if you have a speed control or dimmer for the outtake so you can dim the fan speed down when the lights are off.

humidity will not be a problem if you have your outtake running 24/7

 

[VagPuncher]

how many lights?

you want more air being exhausted than brought into the room to maintain negative pressure and keep the smell from escaping. if its -35 degrees outside and depending on how many lights your running you could get away with only using an outtake fan and just cut a hole for a passive intake.

it will also help if you have a speed control or dimmer for the outtake so you can dim the fan speed down when the lights are off.

humidity will not be a problem if you have your outtake running 24/7

Smell is not a problem. Both properties are on huge acreage.

 

[VagPuncher]

I think the rooms will be 12 lights each. 2 rooms.

2 12 x 12 flips.

 

[prune]

humidity will not be a problem if you have your outtake running 24/7

...as long as the outtake from the interior runs to the outterior...

 

[Guest 150314]

good point.clearly you dont want to dump your outtake air anywhere but outside..

Vag, a friend has a similar set up and uses 3800 cfm squirrel cage blowers for each room that are dimmed down when lights are off to help keep day and night time temps similar. He has a intake fans on a thermostat that only kick on around 70 degrees. The rooms aren't quite side by side (if they are close enough the lights on room will keep the lights off room warm) so they built ducts with inline fans to dump air from the lights on room into lights off room, this saves a lot on heating costs in the winter.

I think if you just have a intake on thermostat to pull air in you will have some humidity problems.

Dialing in air intake and exhaust to perfect day and night temps and humidity can be a huge pain and you have to constantly adjust to compensate for outside temperature

 

[gloryoskie]

Hey Vag, maybe have a chat with someone who does vent hood installs for commercial kitchens, assuming stealth is no issue, which I know it is not. A reputable company will have good options for your needs.

Keeping your drop even every day will keep them bushy plants of yours happy.

Nice grow, by the way.

 

[resinryder]

Couple of years ago I figured I would use the cold outside air to cool the lights and exhaust it outside again. Came in the room the next morning and it looked like it was raining from my duct work. The cold outside air meeting the warm duct work inside created so much condensation that it was literally dripping water through the ducting insulation all over the floor and wall. Needless to say I reversed the airflow in very short order.

 

[redbudduckfoot]

okay, here is the deal. you wanna have a "lung room" to condition the air before it goes into the flowering room. I'm right on the canadian border, and i know all about cold winter nights.

so all you wanna achieve is lowering the temperature in the lung room to whater temp brings the flower room to your desired temp. So if the lung room needs to be 55 deg to achieve 77 deg in the 12/12 room, thats what you do. intake turns off during lights off, while the 2nd room intake kicks on, and so on and so forth.

the lung room will need a smallish intake fan, in relation to the size of the flower room intakes.

hope this helps.

rbdf

 

[Shafto]

1708cfm 12" Maxfan with passive intake on a Can150 keeps my 12.2K bare bulb room cool during warm summer nights on the island, no need for 3800cfm.

If you're set up to go sealed though with a minisplit and CO2 already, just ditch the minisplit when temps go down and switch to a liquid heat exchanger to keep the room sealed and cool.

Cheap and easy to build from car radiators. One outside, one inside, water pump, fans on both, and a drip tray under the inside radiator to catch the condensation that will form.

 

[faulker]

listen to redbudduckfoot, lung room. i'm in Canada and thats the best way to do it imo. i put my outside intake straight into my room a long time ago. learned from that mistake. in the middle of winter, even with all lights on it still gets too cold. and lights off, forget about it. Condensation problems too. And dimming the exhaust at night just made it cold and humid and ended up with powdery mildew everywhere.

 

[samba]

If you have the cash you could use a heat recovery unit, google it.
This way you cold use co2.

 

[Stonefree69]

Another name for heat recovery unit is an "air to air heat exchanger" I believe.

 

[Shafto]

Another name for heat recovery unit is an "air to air heat exchanger" I believe.

Indeed. Basically the same thing as the car radiator heat exchanger that I described above.

 

[sidekick20]

What's up mag...quick question about carbon scrubbers. My tent is 162 ft sq and I was wondering if I bought a fan that move 190cfm would that pull to much and would it pull the air so fast that the scrubber couldn't clean it?

 

[Stonefree69]

Well VagPuncher, you can exhaust w/temp controller and put in an intake on a damper. Better fan is pulling than pushing.

sidekick20 depends on the duct size. 4", 6" 8"? You'll lost about 20% of that cfm because of added scrubber resistance. But that would exchange air about once every 2 minutes if that the only fan your using. You want every 3 minutes at minimum. Some like to exchange air at even 2x/minute like Heath Robinson does, and I'm not arguing with him!

 

[Stonefree69]

Whoops sidekick20, thought I said about 1x every 1 minute for your case, not every 2 minutes like I just mentioned above. It's 1x/1 minute. Damn typos!

 

[Inspired333]

Hey, I know this is a sorta old thread but kinda relevant so..

I posted a thread asking:

I want to cool my light with a cooltube by exhausting the hot air outside. Instead of drawing air from the entire room I want to draw the air directly from outside via ducting, in a "closed loop", and through the cooltube, then directly back outside via ducting.

My question/concern is; Do I need to worry about moisture passing over the bulb?

I have made an insert (like a window) with two 8" holes which I will mount two 8" flanges onto on the inside of the room. The holes are about 2" apart - one above the other; I want to pull outdoor air in the bottom hole down through ducting, up over the bulb/through the cooltube, then up and out through the top hole. Like a closed loop to cool the bulb without exhausting room or house air.

There is a small 'window sill type ledge'/'recess' on the outside of the window (outside).
I'm worried that maybe if it's rainy/misty that water might "hit/splash/cause mist" whatever, and be drawn into my bottom/intake hole than be pulled though the ducting and pass over the light bulb on it's way through and out... possibly causing the bulb to get..wet? ..and bad things happening to it?

Think I should be worried about this?


Edit:
I see a possible humidity(?) problem with drawing in really cold air to cool a hot 600 or 1000 watt bulb, or with it being just to cold and damaging the bulb when it's off/comes on because it's so cold(?) like in the late fall/winter.
But I'm talking about doing this in the early spring/summer, still, the lows/night temps could as cold as *-10*C (45*-50*F) at first. Then the lows might get warmer later like 15*C / 60*F and up and that's no worry of too cold for the bulb or condensation, right?

What is too cold to draw air over a bulb (on or/and off); freezing point? 40*F? 55*F? Hmm :/

 

[Pangea]

Old thread bump, same questions, same situation as VagP

I think StoneFree is onto the right track, a fresh air intake damper, perhaps with a damper on the exhaust as well. Thinking that the exaust fan would recirc in the room until the temp controller kicks on at high temp, which would control both intake and exhaust dampers. The concern then would be the intake damper freezing up.

I've never used one so not sure how well they work, but perhaps, as suggested, the HRV(air to air exchanger) would work as well, biggest issue with them is the inflated price.

It would be insane to run AC's in the winter here, reg temps are -15c to - 30c and colder.

Anyone have a link, info or insight would be greatly appreciated!

More thoughts(after breakfast joint),

I think I need to understand balancing better, or how its achieved.

Ideally each room would have its own air handler, running 24/7 positive pressure with, filter, 2 coils for cooling/dehumid and (re)heating, the part that I'm not to sure about is the balancing and how to maintain it when bringing in fresh air(cold winter air). I know about balancing dampers but thats about it, I think im on the right track with commercial control balance dampers and commercial volume control dampers.

edit2:
Heres a good break down from this site: http://www.energyvanguard.com/blog-...n-of-Positive-Pressure-Mechanical-Ventilation

Here's a brief rundown on what's going on:

When the heating & cooling system is running, the blower in the AHU pulls air from the house on the return side, conditions it, and puts it back into the living space through the supply vents.
Whenever the electronic damper is open in the ventilation duct, the AHU is also pulling a little bit of air from outside and mixing it with the air from the house. This extra air added to the house is what provides the positive pressure.
The amount of air that comes through the ventilation duct depends on the size (and other characteristics) of the duct and how the mechanical damper is set (and ideally is based on what ASHRAE 62.2 requires).
The electronic damper is wired to a controller that determines when ventilation air is allowed to enter.
The electronic damper can be open or closed when the heating or cooling system is operating.
The electronic damper also can be open when the house doesn't need heating or cooling, in which case it will run the blower in the AHU independently of the furnace, heat pump, or air conditoner.
The controller allows the homeowner to set how much ventilation air the home gets.

 

[Pangea]

For posterity,

Anyone looking into free cooling in northern climates, look into the use of an "Air-side economizer" http://www.peci.org/ftguide/ftg/Sys...apters/Chapter_3_Economizer_and_Mixed_Air.htm

Free cooling for norther growers with cold winters.