RH, Temp & Air Flow

[stardawg17]

So my indoor grow setup is in my garden shed in the back yard. I have insulated as best I can and with a small space heater and a small window AC unit I can maintain temperature in there pretty well. In the summertime, the air in this area gets quite humid, but, I can control RH with a portable dehumidifier. This time of year, however, controlling RH is quite a problem. The air gets cold and dry and running heaters just makes things worse.

I have a 4" intake fan pushing air through a filter into my grow tent and a 6" exhaust fan pushing air out of the tent and into the attic space. I have these fans running 24 / 7 and even with 2 small humidifiers inside the tent I have a hard time raising RH inside the tent more than a few %. I'm currently very close to harvest and I'm struggling to get RH above 30% (chart of last 24 hrs below). I'd also like to use the same tent after harvest for drying, and we all know this just isn't gonna do.

Is it necessary to run the intake and exhaust 24x7 or can I just cycle them periodically to let humidity build up in there. I also have 3 small fans inside the tent to keep the air inside it circulating. Any advice would be greatly appreciated.

 

[AdaminCO]

Usually don’t run exhaust when having RH issues. Bring in fresh air and let it vent naturally.
Temps are on point though.

 

[Reave]

Usually don’t run exhaust when having RH issues. Bring in fresh air and let it vent naturally.
Temps are on point though.

Came here to say this. I live where it’s very dry. I use inkbird humidity controllers and only exhaust when it hits a certain rh.

 

[Backyardigan]

Usually don’t run exhaust when having RH issues. Bring in fresh air and let it vent naturally.
Temps are on point though.

You grow in a tent, you follow VPD?

EDIT : If you get room, add more plants to increase RH.

 

[Phytoplankton]

Basically, the RH range for cannabis is 40-70%, quite a range. It should be on the higher side in veg, lower (down to 30%) in flower. If you can get to 40% you’ll be fine. That 30% will serve you well in flower. I have a current grow going now, and like you it’s cool and dry, my tent rh never got above 50% and has mostly been around 40%, no problems, great growth and flowers.

 

[stardawg17]

You grow in a tent, you follow VPD?

EDIT : If you get room, add more plants to increase RH.

These 2 clones were the only survivors out of 5 which is the max the great state of IL will permit. The others died off when my ac circuit breaker popped and the shed got over 100F.

I just read about VPD for the first time tonight, I'm gonna need to create some new sensors for canopy temp and figure out how to position them without blocking out the light. I also need the dataset used to create the chart so I can do lookups when I preform the calculations. If someone has the data in a spreadsheet or knows a web service I can query that would be

 

[stardawg17]

Came here to say this. I live where it’s very dry. I use inkbird humidity controllers and only exhaust when it hits a certain rh.

Thanks for the tip.i can put the exhaust fan on a relay and kick it on and off based on RH level. I think a PID controller will work but I'll need to factor in the duty cycle. Don't want that fan kicking on and off too frequently.

 

[Backyardigan]

These 2 clones were the only survivors out of 5 which is the max the great state of IL will permit. The others died off when my ac circuit breaker popped and the shed got over 100F.

I just read about VPD for the first time tonight, I'm gonna need to create some new sensors for canopy temp and figure out how to position them without blocking out the light. I also need the dataset used to create the chart so I can do lookups when I preform the calculations. If someone has the data in a spreadsheet or knows a web service I can query that would be

Think outside the cannabox, get a lot of other plants that thrive on the same nutes regimen... just to help your humidity climb.

 

[AdaminCO]

You grow in a tent, you follow VPD?

EDIT : If you get room, add more plants to increase RH.

I have a 5x5 tent and a room.

 

[AdaminCO]

These 2 clones were the only survivors out of 5 which is the max the great state of IL will permit. The others died off when my ac circuit breaker popped and the shed got over 100F.

I just read about VPD for the first time tonight, I'm gonna need to create some new sensors for canopy temp and figure out how to position them without blocking out the light. I also need the dataset used to create the chart so I can do lookups when I preform the calculations. If someone has the data in a spreadsheet or knows a web service I can query that would be

Basically whatever your temp is (75F), tty to be 10 less for your RH (65%).
That’s the rule of thumb is us until flower. Then it goes down more.
I like to be 45-50% in full bloom.

 

[BigDannel]

Here's a VPD chart, I'm a visual learner and have this printed and posted right outside my tent. I have my AC Infinity set to run only above a certain temp and humidity so it will stay pretty locked into the range I want it at without adding humidifiers/heaters/etc.

 

[AdaminCO]

The one I use shows the different stages of the plant life cycle. Can’t remember who gave it to me years ago.

 

[BigDannel]

The one I use shows the different stages of the plant life cycle. Can’t remember who gave it to me years ago.

Of course as soon as I print and laminate mine you post your chart which I like way better

 

[Backyardigan]

Ooh, my turn! Share chart, share chart!! Haha!

 

[Reave]

NINE ITS MINE!!!!

 

[SmokingWings]

I have a 4" intake fan pushing air through a filter into my grow tent and a 6" exhaust fan pushing air out of the tent and into the attic space. I have these fans running 24 / 7 and even with 2 small humidifiers inside the tent I have a hard time raising RH inside the tent more than a few %. I'm currently very close to harvest and I'm struggling to get RH above 30% ....

Out of curiosity I started reading this thread and the problem you are experiencing has become interesting. So, a couple of questions.

You posted this in the hydroponic section. I would think that the water from the buckets or from the saturated growing medium would help add to the humidity levels.

Most people use a filter to reduce the smell of the ripening flowers so they tend to move the air through the filter as it leaves the tent and not on its way in. I am not sure how much it will affect the humidity level but what happens if the exhaust is vented back into the room instead of into the attic?

I have read many times on this message board that the best way to start to solve a temperature and/or a humidity problem is to start by working with the room the tent is in first. As in, raise the humidity in the shed first and that rise in level will make it easier to bring up the level in the tent when the vent fans draw air in.

Plus venting back into the room keeps the heat inside which is something you and many of us midwesterners will need this coming week. Any heat that can be kept inside will help reduce the load being put on the heaters.

 

[stardawg17]

@SmokingWings not sure how much humidity escapes the from the dutch / bato buckets. They hold about 1/2 gallon each. The idea of venting back into the shed is interesting. I have changed my setup so that the exhaust fan is run by a PID controller. It runs ALOT less now and the humidifier virtually never kicks on. I have noticed a much stronger smell in the back yard now that the exhaust isn't constantly pushing air through the charcoal filter. Here's the chart for the past 24 hours as I try to tune the PID controller. The anomaly shown today is where I had the tent open for a couple of hours while I harvested a few branches.

Not a bad haul so far.

They went straight into the MagicalButter extractor with some vegetable glycerine to make some vape juice for the mrs. The tops look pretty nice.

 

[stardawg17]

And to everyone posting VPD charts

I've seen a lot of these. How do you know which chart to use?

Also I've found a good post on how to calculate VPD. However, I can't find the chart in a data set I can use to automate it or set alerts. I guess if I knew which chart to use I could create my own data set.

 

[Reave]

All the charts are the same unless they have an offset for leaf temp at x degrees. Problem with that is without checking g leaf temp you are just guesstimating.

 

[stardawg17]