Temp and humidity fluctuations while cycling

Kindon67 · May 24, 2025

I spend a lot of time making changes to UIS controller and tent configuration in order to keep temp, humidity and VPD at a desired level. Sometimes I have to open flaps or close one. I have a fan hanging that I blow out using ventilation tubing sometimes to get heat and humidity down when in-line fan isn’t enough. This takes a lot of time and things change daily depending on weather, even though tent is indoors. I usually can get temp to fluctuate +/- .5 degrees; humidity +/- 2% and VPD +/- .3 kpa. I am wondering if I’m being too anal about the fluctuations. I know that the least fluctuations is obviously going to be most ideal. But is there a larger range that is acceptable? Am I spending too much time tweaking this and that? Any thoughts?

Kindon67 · May 24, 2025

Kindon67 said:
I spend a lot of time making changes to UIS controller and tent configuration in order to keep temp, humidity and VPD at a desired level. Sometimes I have to open flaps or close one. I have a fan hanging that I blow out using ventilation tubing sometimes to get heat and humidity down when in-line fan isn’t enough. This takes a lot of time and things change daily depending on weather, even though tent is indoors. I usually can get temp to fluctuate +/- .5 degrees; humidity +/- 2% and VPD +/- .3 kpa. I am wondering if I’m being too anal about the fluctuations. I know that the least fluctuations is obviously going to be most ideal. But is there a larger range that is acceptable? Am I spending too much time tweaking this and that? Any thoughts?

Just want to add that the fluctuations in the humidity is my main focus. That 2% fluctuation causes a big change in VPD. (Like .6 kpa) Before I got this UIS Controller I’d set fan and humidifier and leave it. I’m sure these numbers were all over the place back then. Yet my plants have always thrived. My main focus now is to learn the proper way to prune. I’ve been doing a little here and a little there but recently read that this could keep plant in recuperation mode. They said it’s better to do complete prunes at 2-3 points in time. In another post I mention that I’m trying to tuck fan leaves down to expose bud sites instead of clipping them. That was yesterday and today I had to do it again, they find their way back up. However, I bet that after doing this for a week those bud sites will become dominant. Any thoughts?

Grownsince95 · May 24, 2025

Without getting into too much detail right away it does sound like you are being a bit too "anal" about things. Your words not mine btw lol.

There's some nuance to the numbers. The appropriate vpd for your grow at any given time is based on what's going on in your grow. You said that "things change daily depending on weather, even though tent is indoors." This means you don't have enough control of you environmentals yet to be concerned about VPD even though you claim to be able to make micro adjustments.

It's either one or the other. Either way a more thorough explanation is necessary.

If you post up some pics of your setup and plants with some basic info, most of the good folks here can give really useful advice based on their experience.

Kindon67 · May 24, 2025

Grownsince95 said:
Without getting into too much detail right away it does sound like you are being a bit too "anal" about things. Your words not mine btw lol.

There's some nuance to the numbers. The appropriate vpd for your grow at any given time is based on what's going on in your grow. You said that "things change daily depending on weather, even though tent is indoors." This means you don't have enough control of you environmentals yet to be concerned about VPD even though you claim to be able to make micro adjustments.

It's either one or the other. Either way a more thorough explanation is necessary.

If you post up some pics of your setup and plants with some basic info, most of the good folks here can give really useful advice based on their experience.

The fan up top on right I use when humidity gets out of control. I haven’t gotten a decent dehumidifier yet. I can’t find one that is UIS controlled. I think AcInfinity is out of stock and can’t find anywhere else. I wrapped the heater hose with old bath mat to insulate. I have a Vivosun dehumidifier and another one but they suck. My question is mainly about the fluctuations in VPD and what is considered tolerable. Seems no matter what I do the humidity fluctuates 2% and that changes VPD like .6 kpa. Is that acceptable?

Kindon67 · May 24, 2025

Kindon67 said:
View attachment 2440212 View attachment 2440213 View attachment 2440214 View attachment 2440215

The fan up top on right I use when humidity gets out of control. I haven’t gotten a decent dehumidifier yet. I can’t find one that is UIS controlled. I think AcInfinity is out of stock and can’t find anywhere else. I wrapped the heater hose with old bath mat to insulate. I have a Vivosun dehumidifier and another one but they suck. My question is mainly about the fluctuations in VPD and what is considered tolerable. Seems no matter what I do the humidity fluctuates 2% and that changes VPD like .6 kpa. Is that acceptable?

The in-line fan is vented out the window. Once plants are a couple feet tall I can’t vent in room anymore or humidity gets too high to handle.

Grownsince95 · May 24, 2025

Kindon67 said:
View attachment 2440212 View attachment 2440213 View attachment 2440214 View attachment 2440215

The fan up top on right I use when humidity gets out of control. I haven’t gotten a decent dehumidifier yet. I can’t find one that is UIS controlled. I think AcInfinity is out of stock and can’t find anywhere else. I wrapped the heater hose with old bath mat to insulate. I have a Vivosun dehumidifier and another one but they suck. My question is mainly about the fluctuations in VPD and what is considered tolerable. Seems no matter what I do the humidity fluctuates 2% and that changes VPD like .6 kpa. Is that acceptable?

With that much plant matter in that little space, humidity is almost uncontrollable at certain points. Turn the lights off? Yeah expect a giant jump. It's all about the amount of air you move and where that air is coming from.

Your tent looks like it's in a house in a room so yeah, the exhaust needs to vent outside. Let's start from there.

JIMKSI64 · May 24, 2025

Cool topic and I had to work a lot to stabilize my tent. Plants were growing ok but they just did not have the presentation I see in other tents. The upward tilt to the smaller leaves and the fans out like tables.
After spending a lot of time documenting in my diary I found that a steady vpd of no more then .08 wave was needed to get transperation up high enough to raise the internal pressure in the plant to get the reaction than I wanted.

AC Infinity">

If you look at the vdp high and low you see how close to settings I have it. .02 down and .03 up
If your vdp is going from say 1.0 to 1.7 vdp that is a huge swing. Do you have a graph trace to post?

Kindon67 · May 24, 2025

JIMKSI64 said:
Cool topic and I had to work a lot to stabilize my tent. Plants were growing ok but they just did not have the presentation I see in other tents. The upward tilt to the smaller leaves and the fans out like tables.
After spending a lot of time documenting in my diary I found that a steady vpd of no more then .08 wave was needed to get transperation up high enough to raise the internal pressure in the plant to get the reaction than I wanted.
View attachment 2440236
If you look at the vdp high and low you see how close to settings I have it. .02 down and .03 up
If your vdp is going from say 1.0 to 1.7 vdp that is a huge swing. Do you have a graph trace to post?

After playing around for hours I finally stabilized the humidity. That is the purpose of my posts. I don’t know if I’m being overly concerned. Earlier today the swings were .7 kpa difference. I then spent a few hours getting it under control. As you probably know, just opening a flap can make a big change. Anyhow you can see my struggle and then about half hour ago I got VPD much more stable.

This is earlier

This is now

Kindon67 · May 24, 2025

Kindon67 said:
After playing around for hours I finally stabilized the humidity. That is the purpose of my posts. I don’t know if I’m being overly concerned. Earlier today the swings were .7 kpa difference. I then spent a few hours getting it under control. As you probably know, just opening a flap can make a big change. Anyhow you can see my struggle and then about half hour ago I got VPD much more stable.

View attachment 2440251
This is earlier

View attachment 2440252

This is now

The difference was me setting the fan to 7 min and 8 max so it doesn’t swing a lot. Then I gave the humidifier nor room to move around. (0 min and 5 max) Earlier I was trying to stabilize by having fan adjust more.

Kindon67 · May 24, 2025

Grownsince95 said:
With that much plant matter in that little space, humidity is almost uncontrollable at certain points. Turn the lights off? Yeah expect a giant jump. It's all about the amount of air you move and where that air is coming from.

Your tent looks like it's in a house in a room so yeah, the exhaust needs to vent outside. Let's start from there.

The tent is in my bedroom. (Only have 1 bedroom apt) The humidity in room today is 48%. I have ac in apt set on 72. The tent is against a bay window that faces west. In afternoon-evening that wall/window does warm up noticeably. Next harvest I might put some board insulation behind tent. The kind they use when siding a home. That should help keep the outside environment from affecting my tent. I think that setting in-line fan to stay at close to same speed (7-8) and having humidifier do most the changing helped me a lot today. Earlier I was having trouble keeping the heat from falling while fan was up. That’s why I wrapped the heater hose. Seemed to help.

JIMKSI64 · May 24, 2025

By looking at your trace I can see you are doing what's called running on your lung room . The very low input from heater and humidity control means your lung room specifications are very important. This is the same thing I found out with the 4x4. Even after squaring away the tent my trace would creep up from 6am until about 2 pm then go to crap. I had outrun my lung rooms capacity to absorb the heat from the tent .
A simple powered duct cover in the wall temp controlled keeps my lung room within 3 degrees of tent need. Best upgrade this run.

Week4Bytch · May 24, 2025

If that's a 4 inch fan in there.. a 6 inch fan might help remove humidity, or invest in a nice dehumidifier.

Kindon67 · May 24, 2025

JIMKSI64 said:
By looking at your trace I can see you are doing what's called running on your lung room . The very low input from heater and humidity control means your lung room specifications are very important. This is the same thing I found out with the 4x4. Even after squaring away the tent my trace would creep up from 6am until about 2 pm then go to crap. I had outrun my lung rooms capacity to absorb the heat from the tent .
A simple powered duct cover in the wall temp controlled keeps my lung room within 3 degrees of tent need. Best upgrade this run.

I heard the term lung room today but not sure what you want me to do. Can you explain what you mean a little better? Thanks my room is 48% rh and 72 degrees

JIMKSI64 · May 24, 2025

You do not need to do anything from the info I see on your trace. As long as your minimum and maximum vdp stay within .08 you will pretty much have a dialed up system. lung room refers to the room your tent is in and where you draw your air into the tent. The closer your lung room is to what you are running the tent at the easier your controller will have it. There are limits as you want to have a buffer of a few degrees to remove the heat from lights.
The points to look out for are the tendency of the tent humidity to spike right at lights out because the air drops quicker than the tent walls. You can check your history trace around when your lights go out. I have my lung room scheduled to start dropping temp by 11:15 for midnight lights out. Before I was controlling my lung room I was scheduling the tent duct fan to step up one notch for 20 minutes at midnight to clear the tent walls.
Good luck

Temp and humidity fluctuations while cycling

Temp and humidity fluctuations while cycling

Kindon67

Kindon67

Grownsince95

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Kindon67

Kindon67

Grownsince95

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JIMKSI64

Kindon67

Kindon67

Kindon67

JIMKSI64

Week4Bytch

Loyal To The Soil

Kindon67

JIMKSI64

Temp and humidity fluctuations while cycling

Temp and humidity fluctuations while cycling

Kindon67

Kindon67

Grownsince95

🤘😆👍

Kindon67

Kindon67

Grownsince95

🤘😆👍

JIMKSI64

Kindon67

Kindon67

Kindon67

JIMKSI64

Week4Bytch

Loyal To The Soil

Kindon67

JIMKSI64

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