Getting the right airflow in my grow room

[keith1975]

I've tried numerous things and even though I thought what I did was working, I'm starting to think my attempts were just random. Yes, adding a dehumidifier certainly brings down the humidity, but not in the whole room and not as far down as I need it to be. I believe the reason this is happening is:

a) The room has two air vents, but they also allow air to come in (not just go out). This is what the air vent looks like.

b) My extractor fan blows against the air vents from the back and therefore it seems like a lot of the air is still staying in the room.

I believe these two vents are the biggest factors as the room is essentially free to allow any air to come in. And with relative humidity of over 70% outside, this means the air inside quickly becomes replaced with the high humidity outside air.

Below are a few questions, but please keep in mind, these are in the context of the grow ROOM, not the grow TENT. Inside this room will be 3 tents. I am trying to get the room's Relative Humidity to be as low as possible, or for me to have some control over it using the dehumidifier.

1. Is it better to have the whole room sealed as much as possible?

2. If I seal the whole room, what type of vent would be used to make sure:
2.a) bad air goes out
2.b) fresh air comes in from time to time
Is there some specific type of vent used for this? What is generally done to a room that is completely sealed and has no roof, but air needs to go in and out?

3. Is there some sort of breakdown somewhere of "air theory" in a room so I can understand it? How do I get my grow room to be as controlled as a lizard's enclosement at a zoo?

4. Would an air conditioner possibly solve my problem?

5. Is an air conditioner the cheapest solution? Or are there other solutions?

 

[keith1975]

With regards to point 3, what I mean is:

• The room has two vents. Is that perhaps causing "suction" in the room, making more air come in? I.e. Would 1 vent result in less air coming in?
• Is there perhaps some specific type of vent that only allows low humidity air to come in?
• Should vents be a specific width/height depending on the size of the grow room

I believe there is probably a lot of theory you need to understand and probably a bit of building experience to do this. I can't get allow a builder to go into my grow room, so I would need to figure this out myself, or stop my entire grow for a month. Which I am trying to avoid.

 

[TurboBucket]

If you seal the room and fill three tents full of plants you're going to need to supplement co2. And an ac unit. And a couple circuits to handle the load.

Sounds like your equipment can't keep up. Those small vents are probably not your humidity issue.
How big is your current dehumidifier? How much water do all your plants use in a day?

 

[keith1975]

If you seal the room and fill three tents full of plants you're going to need to supplement co2.

Hectic. Was really hoping I didn't have any big expenses left. I'll do some reading about co2 supplements. I know nothing about it.

Sounds like your equipment can't keep up. Those small vents are probably not your humidity issue.

That could be. It could be many thing. But my theory is that:
a) The floor isn't sealed well, allowing moisture to come in.
b) The two vents allow air to come in
c) The door itself, if I put my hand by the keyhole, I can feel air coming in.

So my theory is that the outside air is having the biggest influence. I back that up by saying that on sunny days, when the air is generally less humid outside, it is also less humid inside. It's almost like most of the air I'm getting is the outside air.

How big is your current dehumidifier?

It's this one: Takealot.com: Online Shopping | SA's leading online store
It has an outlet pipe so I hook that up to a huge bucket which I then pump out of the room.

How much water do all your plants use in a day?

I've decreased the amount of water I give as of yesterday. Now I'm giving about 10 liters to 7 plants, but twice per day. I.e. One bucket full of water in the morning between the 7, and another bucket later that day, again spread between the 7. So 20 liters total per day.

 

[TurboBucket]

It's almost like most of the air I'm getting is the outside air.

This is far more likely if you keep that room negatively pressurized it's going to suck air in from anywhere it can.
Are you exhausting air from this room somewhere?

That little portable AC is not a real dehumidifier. It has dehumidifying qualities, but its not designed for that. It's also a self evaporative unit, so it actually puts all the water it removed from the air back into the exhaust if that's not being blown out of the room your just spinning your wheels. If it has a drain outlet on it so you can drain the water out of the room it would help.


If the rest of the house is climate controlled I would positively pressurize your grow room with that air by pushing more air in than can be allowed to escape out.



Edit: I missed the drain into a huge bucket bit. How much water are you taking out per day? If your taking significantly more water out than you give your plants then you do indeed have an infiltration problem as you suspect.

 

[keith1975]

This is far more likely if you keep that room negatively pressurized it's going to suck air in from anywhere it can. Are you exhausting air from this room somewhere?

Yes, through the little window. But as I mentioned, the grid is in the way, so not everything is going out. That is why the room needs a proper vent or extractor fan. Which is why I started this thread.

That little portable AC is not a real dehumidifier. It has dehumidifying qualities, but its not designed for that. It's also a self evaporative unit, so it actually puts all the water it removed from the air back into the exhaust if that's not being blown out of the room your just spinning your wheels. If it has a drain outlet on it so you can drain the water out of the room it would help.

The dehumidifier I bought has a little pipe that allows the water to be drained which I use to drain the water to a larger container. It's 100% a dehumidifier. It's not an AC. I can see why you think so. Because it says so on the box. But it's actually a dehumidifier and a air purifier, more than it is an AC. See here: GMC - Dehumidifier - Low Energy - 26L - Lowest Prices & Specials Online | Makro

If the rest of the house is climate controlled I would positively pressurize your grow room with that air by pushing more air in than can be allowed to escape out.

How does one positively pressurise a room? This sounds like it could make a huge difference. If I open the window even the slightest, its like a fan is blowing air through the window. So there is definitely a lot of air coming in. Which is problem 1. And problem 2 is that the air in the room isn't going out.

That is why I need to know:
a) Should i seal the room as much as possible?
b) And then add a vent?
c) What type of vent should I add? (Must it have an extractor fan, is an Aircon a better idea etc...)

Edit: I missed the drain into a huge bucket bit. How much water are you taking out per day? If your taking significantly more water out than you give your plants then you do indeed have an infiltration problem as you suspect.

What do you mean "infiltration problem"? I think I am giving them too much water in general, which I am backtracking on and trying to make it less. I am already taking out less and less water. In fact, if I water less, but twice a day, then the plant gets most of the water and hardly any ends up in the collection bucket. So there is a good chance I was overwatering.

 

[TurboBucket]

So there is definitely a lot of air coming in. Which is problem 1. And problem 2 is that the air in the room isn't going out.

Air can't come in without going somewhere. Moving air is all about pressure differential. Your room is a lower pressure than the air surrounding it.

Because it says so on the box. But it's actually a dehumidifier and a air purifier, more than it is an AC

A dehumidifier uses a different evaporator coil and operating pressures than an ac unit does. Dehumidifying is all about getting the evaporator coil below the dew point to condense moisture out of the air so it can be drained away. (Basically the same thing as AC)This is best accomplished with a refrigeration system not thermo-electric units that some company's are selling in bedroom sized units.

You've now posted two drastically different items. The latter which states it's removal capacity as 26l which is just a little less than what I use in my basement. (33l)

I would positively pressurize your grow room with that air by pushing more air in than can be allowed to escape out.

The easiest way to pressurize a space is to blow more air into it than is going out of it. Negative pressure is caused by taking out air more quickly than it can be replaced. That's why I was trying to find out how much air your taking out of the space./Where the negative pressure is being created.

Blowing air from the rest of the house into there will help the pressure issue but you still have to cope with all the moisture/heat that may come in with that air %70 Rh is pretty wet

 

[keith1975]

You've now posted two drastically different items. The latter which states it's removal capacity as 26l which is just a little less than what I use in my basement. (33l)

Yes, I think the first link's info was wrong. This one is 26 liter, but you can attach a pipe to it, so it can essentially drain endlessly. I've attached it to a +- 200 liter bucket.

The easiest way to pressurize a space is to blow more air into it than is going out of it. Negative pressure is caused by taking out air more quickly than it can be replaced. That's why I was trying to find out how much air your taking out of the space./Where the negative pressure is being created.

Let me show you:

• The orange arrows show where air can go in and out. I.e. the Windows
• The 3 blue blocks are the three tents.
• Only the big 2.4 x 1.2 tent has an extractor fan that goes to the outside. But the problem is that where the fan is blowing out, it's blowing into the back of this:
  
  
  
  Which means, not all of the air is going out, some of it is coming back into the room and some of it might even go back into the extractor somehow. Ask yourself, what would happen to an extractor fan if it was blowing against a wall? Now, mine is basically blowing against a wall with a few slits in it. Which I assume would cause some kind of back pressure against the extractor fan
• The other two tents also have extractor fans each, but the fans blow out into the room. In fact, those two tens have both their extractor fans positioned on TOP of the MIDDLE tent. So they blow out towards the door's side.

I believe this is where my problem lies. I need to perhaps make the two smaller tents also extract the air outside of the actual grow room via the small window. And I need to make the main tent extract out of the room via the other window. But I dont know how to physically build something that will solve the problem. Let me know if this explains it better? I'll see if I can't get a picture of the window itself.

Blowing air from the rest of the house into there will help the pressure issue but you still have to cope with all the moisture/heat that may come in with that air %70 Rh is pretty wet

Nothing can "blow from the rest of the house". This basement has a one door, that is on the side of the house. Nothing connects it to the rest of the house. So just outside the room, is the actual outside world. So RH is coming in is literally coming from outside.

 

[keith1975]

I also just read this:

“Plants need outside air for one very basic reason: CO2. Plants absorb CO2 throughout the day as part of their nutrient cycle. If your grow tent setup is sealed, this means that the level of CO2 in the room gradually decreases, limiting your plants’ growth. Ventilation brings in fresh air and fresh CO2 from outside and removes the old air from your grow room, boosting growth and yields.”

So perhaps i just need one-way vents? Do you get something like that? So that no air can come in from outside but still leave. And then i need to find a way to substitute co2? Could that sound like a good next move?

 

[TurboBucket]

Ok. Catching up now. Your extractor fan is creating your negative pressure by blowing air outside past the vents that are in it's way.

It's staying humid because it's humid outside and it's pulling in all this wet air from outside. All the air that blows out the vent is replaced by outside air coming in through the cracks around windows, doors, outlet boxes etc.

Your current dehumidifier can not keep up with the amount of humidity being brought into the room.

Exhaust less air out, which would bring less air in. Probably not an option (heat)

Add an ac seal the window use the exhaust fan on your veg space where humidity is more tolerablet o slightly positively pressurize the space by using it to draw air in from outside through the window or the vent, to help limit infiltration but still provide fresh air.

Seal the room add a good ac and co2. You can't seal a room full of plants without co2 they will suffocate like fish out of water. Less dramatically of course. If it's a big space with a couple of plants that gets opened occasionally you can get away with it. A small space with a lot of plants they will absorb all the co2 too rapidly without new fresh air, or co2 supplementation.

 

[TurboBucket]

So that no air can come in from outside but still leave

Whatever you blow outside has to come from somewhere though. The air gets inside the room before you can blow it out.

 

[keith1975]

Okay, so now I'm on the fence again. Inside the room it is 31 degrees, while outside it is 21 degrees. So surely air is not getting inside? And therefore I should perhaps look at installing an aircon? Or I need to open those windows?

All remaining changes are drastic and expensive, so I'm a bit stuck as to where to go from here.

 

[TurboBucket]

So surely air is not getting inside?

We're pretty sure with the amount of water coming out of the room that extra humidity is being introduced.
Also if your venting air out it has to come from somewhere. Think about blowing through a straw, you can only blow air out until your lungs are empty and then you have to breathe in more air before you can exhale again, same idea. It's just not enough to cool down all the lights.

1000w of led lights is around 1800 btu/hr.
1000w hps is closer to 3000 depending on how efficient it actually is.

All remaining changes are drastic and expensive, so I'm a bit stuck as to where to go from here.

Welcome to the world of indoor growing. It's a balance game, trying to give your plants the best you can with what you have.

If you put an air conditioner in a leaky room you'll pay extra in run costs cooling air that doesn't need to be. Seal it up too tight and the plants can't breathe. A lot of people only grow during the cooler seasons so heat is less of a concern.

But yes putting an ac unit that actually vents the heat out of the space would help with your temperature and humidity issues.