Ventilation/Cooling Question - T5 Vertical Grow Cab

[timmur]

Hi All,
I'm just finishing up a new cabinet and have realized a bit late that I should have read the Ventilation 101 thread more carefully. I thought that the cab design was fairly well thought, but my problem is that the cooling CFM requirements are much higher than what is necessary for normal air change for healthy plant growth. The picture below shows the basic design of the cabinet. Here's a rundown of the cabinet. It has four 48" T5 HO fixtures @ 54 watts each. The dimensions of the cabinet are 16" x 16" x 65".



In the ventilation thread it was suggested that the air for cooling of the lights should be ideally handled separately from the air exchange required by the plants. According to the calculations in that thread I would need about 140 cfm for cooling. Unfortunately this is about 30x more air than is necessary for the plant and would likely stress it out. Ideally some sort of cool tube design on each light would work, but I can't figure out how to do that easily (I'm not really handy). Would it work to just put an extraction fan on top and cut in some vents on each of the sides at the top as well? This would handle cooling for the lights and then a very small fan at the bottom with a few small vents on the bottom as well could provide regular ventilation.

BTW, light leaks and odor are not an issue. This cab will be kept in a room that can be kept completely dark on any schedule.

I have another thread where I asked about this issue, but I changed the cab design twice in that thread so I thought a new thread was warranted. If not, Mods please LMK.

 

[Nes]

I'd just stick an exhaust in the top with a passive intake at the bottom. Unless its creating wind that whips the plant arround, too much freh air isn't going to stress it out. How are you going to keep the air in the room fresh, - temp build up, co2 and the proper humidity?

 

[timmur]

The room has a heater for winter and a small (5,000 btu/hr?) AC for summer.

 

[Nes]

will you be supplementing co2? seems like you're running a box in a sealed room.

 

[timmur]

Down the road I will. I have a tank and regulator from my beer brewing so it probably won't cost much. I have to learn how to grow first!

 

[Nes]

The problem is, in a sealed room, even with only 1 plant, it will rapidly consume the available co2 and its growth will slow significantly, even halt. with the size of your operation, I'd concider looking into one of the fungal co2 generators. If you like gourmet mushrooms, some of them come in the form of bags of substrate out of which a variety of goumet mushrooms will grow.
Good luck
Nes

 

[SmokinErb22]

Elevate the grow box a few inches and then do as stated above... intake on the bottom, exhaust fan at the top.

As for fresh air, a cheap duct booster fan with a timer can be used to bring in cool air at night. My basement is sealed for the daylight hours and at night a fan comes on bringing in fresh cool air. Doesn't seem to be causing any negative effects compared to 24/7 fresh air. Though... If you have central air, you're already bringing in fresh air, and I do have a AC vent in my grow area, so I guess its not really sealed.

Also, a 4" vortex-type fan should take care of your ventilation.

 

[timmur]

Elevate the grow box a few inches and then do as stated above... intake on the bottom, exhaust fan at the top.

As for fresh air, a cheap duct booster fan with a timer can be used to bring in cool air at night. My basement is sealed for the daylight hours and at night a fan comes on bringing in fresh cool air. Doesn't seem to be causing any negative effects compared to 24/7 fresh air. Though... If you have central air, you're already bringing in fresh air, and I do have a AC vent in my grow area, so I guess its not really sealed.

Also, a 4" vortex-type fan should take care of your ventilation.

Thanks SmokinErb22. I know that I can get a fan that will handle the cooling with ease, but I was concerned about turning over the air in the cabinet 14x per minute instead of the recommended 1 air change per 5 minutes. This concern was voiced in the ventilation 101 thread.

 

[Nes]

Thanks SmokinErb22. I know that I can get a fan that will handle the cooling with ease, but I was concerned about turning over the air in the cabinet 14x per minute instead of the recommended 1 air change per 5 minutes. This concern was voiced in the ventilation 101 thread.

moving all the air out every 5 minutes is a co2 issue. according to my local hydro store guy, and many of my grower friends, this is a bare minimum and hydro said if you can get it to turn over everyminute, even better.
The only reason more airflow would hurt it would be if the force of the wind was actually damaging the plant. If you are going with a vortex fan, use a fan speed controller to dial it down. You can also instal a furnace filter over your intake to keep nasties out, but it'll also diffuse the airflow.

My propagation tent is 2'x4'x5', I have 4 shelves, each with 2 - 4' 54watt t5s. 8 total. a 4in duct booster moves enough through there to keep is cool enough.

 

[timmur]

moving all the air out every 5 minutes is a co2 issue. according to my local hydro store guy, and many of my grower friends, this is a bare minimum and hydro said if you can get it to turn over everyminute, even better.

Nes, thanks and I get what you're saying. I was just going by the info presented in the ventilation thread. The author seemed sure that more than one air change per minute was problematic. That's the only reason I started this thread was to get some feedback regarding this issue and potential solutions if it really is that big of a deal. Sounds like it's not.

Just to be clear though, my cabinet has about 9.5 cubic feet of volume so a fan that is supposed to adequately cool the cabinet will require about 140 cfm to keep it within 5 degrees of ambient. If I get a fan that will do that, it will mean about 14 air changes per minute which is quite a bit more than the 1 air change per minute that you mentioned.

From the ventilation thread regarding 3 ACpM:

For you hydro guys, this means more rez changes and nute swings because the plants will be drinking alot to keep
up with the dehydration caused by living in a wind tunnel.

 

[Nes]

I hear you, I could see it causing more slightly more transpiration. Why do you think you need to move that much air to keep your temps down?
It seems high.
Have you thought of the fan speed controller connected to a thermostat?

 

[steadydets]

Hi All,
I'm just finishing up a new cabinet and have realized a bit late that I should have read the Ventilation 101 thread more carefully. I thought that the cab design was fairly well thought, but my problem is that the cooling CFM requirements are much higher than what is necessary for normal air change for healthy plant growth. The picture below shows the basic design of the cabinet. Here's a rundown of the cabinet. It has four 48" T5 HO fixtures @ 54 watts each. The dimensions of the cabinet are 16" x 16" x 65".

[URL=https://www.icmag.com/ic/picture.php?albumid=55514&pictureid=1296574&thumb=1]View Image[/url]

In the ventilation thread it was suggested that the air for cooling of the lights should be ideally handled separately from the air exchange required by the plants. According to the calculations in that thread I would need about 140 cfm for cooling. Unfortunately this is about 30x more air than is necessary for the plant and would likely stress it out. Ideally some sort of cool tube design on each light would work, but I can't figure out how to do that easily (I'm not really handy). Would it work to just put an extraction fan on top and cut in some vents on each of the sides at the top as well? This would handle cooling for the lights and then a very small fan at the bottom with a few small vents on the bottom as well could provide regular ventilation.

I wouldn't worry so much about over exchanging air, I think it's a bit exaggerated in terms of aspiration and evaporation.

Try this.

Get a fan controller on your top vent and adjust the velocity according to the temp you need. You'll find that you can find a balance between the heat the bulbs produce and the optimal temperature in your grow room.

Keep an eye on water levels and adjust accordingly. The box, is still in a room, which also has a volume of air and a temperature separate from your grow box. The fan controller will allow you to adjust accordingly.

http://www.amazon.com/Hydrofarm-ACS...3551&sr=8-1&keywords=fan+controller+hydrofarm

 

[timmur]

Steadydets, thanks for the suggestion. The consensus seems to be not to worry about too many air changes so I won't! I have a fan selected that should move the necessary amount of air for cooling so that will be my next project.

 

[timmur]

I hear you, I could see it causing more slightly more transpiration. Why do you think you need to move that much air to keep your temps down?
It seems high.
Have you thought of the fan speed controller connected to a thermostat?

I just used the calculator on the ventilation 101 thread. Its high because I assumed cabinet temperature to stay within 5 degrees of ambient.

 

[timmur]

Just a quick update. I ordered a fan/carbon filter combo and some darkroom vents. The only thing left is the electrical. Should be ready for the maiden voyage right after vacation!

 

[timmur]

Oops. I forgot to mention that I tested the temperatures with the fan at 100%. The ambient temperature in my garage was 82 degrees and the cabinet got up to 87 degrees which is what the calculations predicted! Since the cabinet will be in a temperature controlled room, I figure I'll be able to run the fan at less than 100% and time it to run with the lights.