Its always great to jump on OG and see what you have all been up to.
I have been busy myself setting up my room and have a question on my mind I hope you guys and gals can answer. Currently it is a room that is 3M x 3M. In it I have 2 tents, 4’ x 4’ each, a mother plant chamber which is 2’ x 2’ and a clone/propagation tent. All of them will be drawing air from the room and exhausting the air into the room via filters. The veg tent will have 150 watts of LEDs and and the flower tent a 600 W HPS. The room is air conditioned to keep temps right. Now if I was to keep this room shut up, I am assuming that the plants will eventually use up most of the CO2 and start to suffer as a result. However I have no idea just how quickly the plants can use it up. Would I be fine if I left the door to the room open for a short period each day to let the air get replaced or will I need to have a constant flow of air going into the room to keep the plants happy?
I leave my door open with a fan blowing into the room all day to move air around, but that’s just me. it works well enough for me in a 12’x12’ room
and yes, when I was growing in my basement last summer the plants used all the co2 and started to get big crinkle leaves because of it, had to add co2 to the tent and basement before they started to get better again
One thing to be aware of is that ventilation works in volumes, not areas. If your 3x3m room is 5m tall that’s 45 cubic metres, if it is only 2m tall then that is 18 cubic meters.
For ventilation, you aim to exchange the air in the room every 5 minutes or so. You should see that the first room, at the unrealistic height of 5m would need a fan 2.5 times the capacity of the second room.
You will need to tell us the height of the room and each tent to know how much you would need to air the main room each day.
If you can, it would be best to have a fan equal to or greater than the total of the ones exchanging air from the tents to the room and which is on at the same times or longer.
Also, you are mixing metric and imperial (3m square room, 4ft square tent) which needlessly makes things much harder.
Tell us the three dimensions (width, length, and height) of your two tents and the room in either metres or feet and we can let you know the ideal ventilation/fan size you should be aiming for.
EDIT :
Of course, if it is not an option to ventilate, then as your temperatures are controlled (and I assume your humidity too) then injecting CO2 would also work fine as a solution.
@toastyjakes, ok, thanks for that. I will definitely have to use some sort of CO2 system as having the door open all the time is not preferable. So I guess that opens another question. Are there any decent DIY CO2 producers around that can supply enough CO2 for two 4’ x 4’ tents? The only things I have seen are CO2 cylinders which are not DIY and a yeast method but I think the yeast method only provides minimal CO2 for seedlings and small plants.
@MicroDoser, I had it in my mind that i was providing sizes in metric and imperial but was hoping no one would pull me up on it
Ok, here goes:
Room: 3M x 3M x 2.4M
Tents: 1.2M x 1.2M x 2.2M each
Also a little background as to why. I am in an area where smell is a problem. Venting air outside of the house was something i was trying to avoid but am aware that this is very difficult and likely not possible. I am wanting to have a fresh Carbon filter at all times with the flower tent constantly recycling some of its air to make the carbon filter work harder to take as much of the smell out. So that when i vent as little amount of air out of the room and into the house as possible, while still keeping the plants healthy, it will hopefully have much less scent left in it. So my main goal is: provide the least amount of ventilation while still providing enough CO2. The rest of the conditions I can keep under control.
If smell is a concern then one of the best ways is to ensure your main room is at negative pressure. Smell cannot go upwind so you make sure air is always trying to get into your main room.
One of the best ways of making this happen is to have a fan pulling air out of your main room through a carbon filter.
If you do nothing else, ventilate your main room into the rest of your house. As a plus you get some free heating
If this is difficult, maybe you rent, then you could do worse than take the door off the hinges, replace it with a very cheap door and cut holes into that one which you could disguise somehow. Then put the original door back when you move out (it can also be put back for inspections or nosy guests)
This is what I do. I make sure air is passively pulled through the wall from the entrance hall behind the front door into the room and actively vented into the bathroom. This makes the place inquisitive noses might try to sniff (the front door) somewhere that will never allow out any air from my room. I use a carbon filter for the air coming out of my ‘tent’ then another on the fan pulling air out of the main room. I dehumidify the air where it vents into the main house and cools (which releases moisture anyway) and then use the heat from the air to heat my home. I save almost as much on my heating bill as it costs to run the lights.
I have looked at costs for Co2 many times over the years and still today the best, cheapest, accurate, and reliable is the tank of gas released by solenoid either on a timer or when the CO2 levels are sensed to drop. One of the worst and most expensive is using yeast and sugar.
TL;DR In your situation I would suggest to double filter your air, try to vent it to maintain negative pressure in your room, maybe get a CO2 injector run from a tank if you need to.
Using these numbers your main room is 21.67M3
your tents are 3.2M3
This means you need a fan that can pull a minimum of 3.2M3 every 5 minutes. Fans are rated in volume per hour so that is 12x3.2 which is 38.4M3 per hour so each room would need a 40M3 per hour ventilation fan for each tent (this is not much at all, you could do this with a single fan and a duct splitter). If you had an 80-100M3 ventilation fan pulling air from the main room that would keep your plants happy. An RVK150 would do this with spare capacity to allow you to have a fan controller slowing it down to keep it quiet.
So the minimum I would suggest to keep your plants in their happy place is a 40M3 fan on each tent, or a single 80M3 fan for both, and a main fan slightly larger than that for the main room.
These are really small numbers for fans, which means the smallest fan you can buy would probably be a bit big and would allow you to quieten them down a LOT with a decent variac fan controller (or one of the fancier new digital ones)
EDIT :
If you decided to just run a grow in all of your main room, you would need a 250M3 fan which would exchange the air every 5 minutes in that size room.
@MicroDoser , that’s great. You got me thinking the last couple of days and i will bite the bullet and put in a 250mm exhaust fan (low flow) will do 150M3 easy. i have a large fan coming soon for the flower. That will exhaust out via a large carbon filter on its end with the fan. I will place the exhaust fan in the corner above the carbon filter. I have a 150 mm fan for the LED Veg tent. Both tents have digital fan controllers on their fans to control the temperature. I dont know if i can get away with it but thinking about having the exhaust fan cycle on for about 5 minutes then stop for a period of time. It is hot here in summer (up to 45 degrees C) so will rely on the air conditioner but it will use a lot of electricity if i have the exhaust fan constantly pulling all the air out.
PS: I should add, I am trying to avoid anything obvious in my roof space.
Do urself a favor and overspec ur fan. U can always use a controller and slow it down. Digital fans are more silent when running on a controller
@MicroDoser is correct, modify a cheap door to put ur fan or filter in if ur trying to be discreet.
Ideally, u would exhaust outside or into a pre-existing vent. This draws air from outside replacing ur co2 depleted air. Also, smell will not be a problem when attached to a properly sized carbon scrubber. Good luck bro
Gday @BudSy I’m running co2 at moment. I have a tank hooked up to gas line through a preset regulator and flow meter with delivery controlled by a solenoid valve. I flow 10 litres a minute into my room and although I don’t have a ppm meter for co2 in the room I can tell it has made a difference, if you’d like I’ll message the details of set up and where I sourced parts to make it. The ones for the shop are a rip off. I have some pictures of it in my grow diary. Cheers
I now have 2 x 360 M3/hour exhaust fans. One will pull from the room and the other will push into the room. They will be on opposite corners of the room and mounted in the ceiling. Pulling and pushing air to/from the roof space which is well ventilated to the outside air. I intend to have them cycle at about 15 minutes on and 45 minutes off. The air conditioner will keep the room cooler during the 45 minutes off period. The veg tent has LEDs and 150mm fan that is speed controlled based on temperature in the tent. The flower tent has a 600w HPS with a 250mm fan that is speed controlled based on temp in the tent and blows the exhaust through a large carbon filter standing on its end beside the tent.
I am thinking about using 4 of these CO2 canisters in the flower tent over the flower period:
They are cheap and should hopefully make a small difference. I have read reviews from people using them in ventilated rooms and they believe they still make a difference.
@ozzie, I was looking at CO2 cylinders and regulators etc but they definitely are very expensive. I will check out your grow diary for sure. Thanks.
My main concern is that if I have the exhaust fans from the main room running at 15 minutes on and 45 minutes off with CO2 canisters in the room, will that be close to enough ventilation for the plants? Keeping in mind the tents are constantly circulating their air and the air conditioner will keep temps in check.
Yeah I think there’s a bit involved in getting the most out of co2. I’ve experimented this grow with it and I’m pretty sure it makes a difference in the recovery time after trimming and tying the plant etc. But light and nutrient levels have to be elevated aswell. I will be getting an accurate co2 meter that logs the ppm so I can understand how much and how quickly the plant uses the co2 and what the level in the room is. A total of 1500ppm is a good level to aim for in the room, during daylight hours. One thing to think about is the humidity in a closed room fan off environment skyrockets really quickly and has been an issue for me.
Yes, I have been curious too about the rates at which a plant in full flower can use the CO2 in a room. Humidity all under control for me as I have an Air Conditioner with climate control and dehumidify functions
There is some debate about incremental benefits from running more than 800ppm; I ran co2 years ago and figured out that the greatest cost-benefit was getting up to about 700-800ppm. Higher co2 will allow you to run much higher canopy temps though, and thus much higher humidity lights-on, so there may be some benefit there. But in terms of yield and quality, as I mentioned, 800ppm was the sweet spot for me, YMMW. And gas lasted way longer than running at 1200 or 1500.
Not that I can measure it at the moment but based on the flow of gas into the room it would be up around 1500ppm initially, which as you say allows higher temp and humidity…possibly saved me this cycle as humidity has been an issue. Although without the gas less transpiration, less humidity. Catch 22 isn’t it. I’ll aim for 800-1000ppm when I get a meter, Thanks for the advice.
A synchronized 1200ppm (co²/nutes) was what worked the most for me in the past in term of yield/quality.
But the need to grow literally 100% optimal the plants to ROI plainly the use of CO² pushed me away from it.
So in the vein of the thread topic I’m looking for some advice specific to my issue and hope I’ve covered the basics before ask for experience in solving it.
I’m testing - not yet got plants inside - a new grow cabinet.
Internal dimensions 0.57x0.56x0.75m = 0.23m3
Surface area is 0.3192 sqm / 3.45 sqf
Light power 123W wall draw (~36W/sqf) solstrip LED with heatsinks running at 43% of rated operating wattage
Intake vents 5 x 20mm holes with 90* bend PVC joints to obscure light backed by 12V 25mm fans
Exhaust vent 1 x 100mm duct over 3m length to 85m3/hr Manrose 100T fan with carbon filter pad (Ikea Nyttig)
Exhaust fan should yield complete air exchange every 10 seconds. Considering most advice is to multiply internal volume by 60 and adjust for ducting then required exhaust should only be 18.4m3/hr meaning installed exhaust fan is almost 5x requirement.
On testing with a known volume plastic bag, it is clear the carbon filter and ducting is causing a massive under performance. While I am still able to exhaust twice the air that the fan assisted intakes are adding the exhaust fan is seemingly only managing to operate at 10m3/hr.
With this arrangement, running the sealed cabinet empty sees my sonoff temp and humidity gauge reading 29-30C at 30-33% RH.
Basis charts for Temp/RH on this forum and general advice that is seriously “no bueno!”.
Working through the FAQ page on OG then basis 16C (winter, no AC and no radiator heating) basement at 45-50% RH, in order to hit 25C with lights at 123W would probably require 0.0112-0.0144m3/s in ventilation or 40-52m3/hr (23.7-30.5cfm). So well we’ll higher higher than the initial estimate from growell website of only 18.4m3/hr.
So… ducting cut away. Manrose fan disabled. Nocturnal NF-P12 120mm 120m3/hr 12V fan attached without ducting or carbon filter.
But all I can get the temperatures down to is 27C with 40% RH with the fan assisted fan intakes running. With no impediments the Noctua should be sucking and exhausting are at it’s rated capacity. Even if it’s only managing 75% it should be able to maintain a temperature difference of 9C to hit 25C even with about 275W of light.
This is in the dead of winter with a pretty chilly basement. What is going on?!
Clearly a ventilation issue.
Do I just need to bang some plants in there and see what happens? Seems to me like I’m just heading for the rocks like a ship in the night if I don’t fix this first.
I have a second Noctua fan. Do I install them back to back to increase the static pressure?
Any advice? I’m I getting the calculations all wrong? Is the issue insufficient in take ventilation?
From your pic the room doesn’t look completely air tight ie the pic of your fan in the cabinet! If that’s the problem area and can’t get negative air pressure then I’d say isn’t big a enough fan for the space or cabinet has leaks also that length of hose you could be loosing some flow.Those small intake elbow with the right fan you should be able to make that room whistle
Thanks mate. I’ll look again at that. The gap in the backplate to the cabinet wall is covered with light blocking film which in turn is duct taped around the fan and to the cabinet. The horizontal gap at the top is closed off also, I used draft excluders on all joints before screwing together the plates.
I can get a piece of paper to easily stick to the outside of the PVC bends when everything is running so air is being sucked in for sure. But yeah. It isn’t quite whistling.
Can anyone comment if the calculations are about right? Using the FAQ forum suggested ball park formula of
Q = V x P x C x dT
where:
Q = Amount of lighting (kW)
V = Volume of air being ventilated (m3/s)
P = Density of air (assume 1.2 kg/m3)
C = Specific heat capacity of air (assume 1.02 kJ/kgK)
dT = Temperature difference between ambient and growspace air in degC
Then using 123W and assuming all is airtight the 120m3/hr fan (even at 75% efficiency) should achieve a dT of 4C. So with the basement / cabinet external ambient temp at 16C the cabinet should be at 20*C.
