Phyto said:

Don't live and die by VPD, it's a range. In the outdoors you can;t control it and the plants do just fine. Last summer I grew at 4000 ft elevation, in June-September the daytime temps ran from 70-95 degrees with 10-20% r/h. At night the temps were anywhere from 40 to 60 degrees with 70% r/h. Once Mid-September hit the daytime temps rarely got above 65 degrees with 20% humidity, at night 30 degrees with 70& r/h. I harvested in mid Oct, the two weeks before harvest the nightime temps were anywhere from 24 to 34 degreesm daytime in 50's. The morning I pulled them it was 18 degrees. The plants did fine, good harvest, good smoke.

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WinJr63 said:

So than, u grow indoors, like how the plants grow outside ?

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JIMKSI64 said:

Indoor growing plants seem to appreciate long hours of stability with minimal changes in temp and humidity.
If using VPD for your tracking ensure a stable VDP that tracks withing .08 or less.
It will not help your grow if you have wide changes by the hour. Humidity bouncing up and down will show on your VPD trace as highs and lows in your numbers.
If aiming for 1.0 VPD the trace should be less than .05 up and down.
Running a tent where the humidity moves up and down 4% multiple times an hour is not a stable environment although the average VDP may show your target of 1.0 you are actually rolling from 1.1 to .9 over and over.......

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Trash_2002 said:

considering the best dehumidifiers can only be +/- 3% RH at best from factory controller, you will have at least +/- 3% swings every X minutes or X hours anyway tho.
yes you can use a professional controller and an inverter dehumy to get within 1% but that's LAB grade stuff lol.

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JIMKSI64 said:

I run a .04 variance on vdp all the time using ACI thermoforge and 2 sweep fans.
Current ACI trace. .07 variance +- 1% humidity
View attachment 2609953

Verified by Vivosun app same numbers.
View attachment 2609954
I can show the cube sensors but this looks to be enough.

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Trash_2002 said:

yep that's true those ac infinity controller systems that integrate light power, exaust/intake power and can also be prioritized by temp, humidity or VPD is efficient for sure. Cheap tech doing great things
still a 2% variance tho.
last post i mean a 3% variance in total not a +/- 3%. typo. Lab grade would be a total of 1% +/- 0.5%RH

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JIMKSI64 said:

This is the 69pro controller. It controls thermo and cloud forge only.
It also has lots of other data to show you how good or how bad it can get.
This shows that for this hour about 60% of the time it was withing .5% up and down and then shows the time in the peak and low.
View attachment 2609957
The lights are on a schedule and the fans are on local control because the app will bundle the sweep fans and the fans in the lights and they run totally different.

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Trash_2002 said:

yep gotcha, what i really want to pass on is that a 50-70% RH in veg is totally fine and a 30-55% rh is also totally fine for flower. You really don't need to chase VPD so hard, its just something to think about that can help grow quality overall and one more data point to see if your not streessing too much the plants. But VPD swings within limits are totally healthy for the plants, they are dynamic living beings they are not robots. Also you have to take in account LST (Leaf Surface Temperature) to get the leaf VPD (witch is the important one stress/transpiration related) not the Air VPD.

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