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Wanting to dial in my vpd

Smoklahoma

Smoklahoma

New member
How many of you folks worry about the vapor pressure deficit? I would like to try and keep it in range for this new grow. I'm no mathematician, I don't even know what half the symbols are in the formula. Pulse has a monitor, but it works on wi-fi, which I don't have. I can read their chart to get the right temperature and humidity but not sure about the leaf temp adjustment. Any ideas? I just thought it would be a useful tool in the grow.
 
Check your local weather for dew point. Sounds like the same thing. You have to have control over humidity and temperature.
 
I've been trying to do the same, dial in my VPD.

I've been successful using the following fan and controller. I set the RH% trigger point to maintain the VPD I'm shooting for.
By playing around with the RH% and Transition Humidity I've been able to maintain the VPD I'm looking for.

AC Infinity CLOUDLINE S6

AC Infinity Controller 67

Both available on amazon.
 
Smoklahoma I'm trying to pay attention to VPD this grow. If you can download an app that might help. I've been toying around with VPD Buddy. There's not much documentation but it's easy to use.

Insight I've got that Infinity set up in the 4". What is Transition Humidity? I have mine to increase the fan speed at 62% High Humidity and 81f High Heat. That seems to keep the RH and temps in the range I'm wanting. Do you do something similar?
 
golfnrl If you are using the Model 67 controller, there is a setting called Transition Humidity (and Transition Temperature) customizes how the fan will ramp up in speeds when triggered to run in AUTO mode. ie....if Transition Humidity is set to 3%, the fan will turn on at speed 1, at my specified Humidity Trigger point, and it will then ramp up to speed 2 if the humidity continues to rise by 3% RH, then speed 3 if another 3% rise...can do the same with temperature. It helps keep the tent at my desired humidity, my temperature stays somewhat stable regardless of fan speed. I'm mainly trying to stay within a certain VPD range.
 
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This is the chart I am running off of. I cranked up both temp and humidity about 12 hrs ago to 86° and 76%, they grew alot today.
 

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I am running a sealed grow with no fresh air. Had to add a second humidifier to keep up.
few details as of today-
Temp 86°
Humidity 76%
Leaf temp 81°
Co2 1200 ppm
Lights 410- 430 ppfd
plants are in early veg
 
I use the same data.
Using an IR temp gun will let you measure the exact leaf surface temp.
Plug that into the vpd chart with the rh% in the grow and you have the info you need.
 
I never even heard of it a year ago but since getting tents it's what I pay attention too. Been growing inside since 2015. I have the AC Infinity controllers. Use to just worry about temperature.

Some days I need to add humidity. Really depends on temp as when it gets over 80F then the plants can't keep up it seems.

Yesterday it was hitting the high temp point of 85F and exhausting to cool down but drove the humidity so low I had to crank up the egg shape mister one I use. Veg tent needed a wet towel.
 
I keep a printout of this chart tacked to my wall and deal with it by turning on an evaporative cooler when I drift too far into the lower right. I live in the desert. Hot and dry so the evap cooler helps get the temp lower and humidity higher which is what I need but still tend to hover in the yellow.
vpd-chart.gif
 
Yes, sometimes I do depending on the weather. Also use a humidifier with lights out if necessary. This time of year where I am the RH is all over the map. I have a humidifier and de-humidifier for the lung room and if necessary I can also add both to my tents. I have a 3x3x6 with a 4" AC fan that works well to control temps etc. I have a 6" jet fan, two oscillating fans, and added fresh air for the 4x4x6 and I'm really struggling trying to keep the atmosphere consistent in that tent.
 
So do you see much transpiration with lights out? All I can do now is maintain under 80%, usually 70%. But the temp drops in to the 60fs now, sometimes 50fs in the dead of winter when lights out.
 
I have not gotten that far. What I've seen but haven't tried is covering part of the plant with a plastic bag and watching for moisture droplets. Is that what you mean?
 
My lights off time requires some constant flow ventilation to maintain 70% RH, so the temps drop down to under the house room temp, much more than when the lights are on. So my VPD drops to around .50 or so sometimes.

I believe the plant is using sugars when lights are off and stull functioning somewhat, whatever it can do without light. But I would guess that a high humidity would suppress that. But then again in the natural world around me, high humidity at night is the norm, to the point of fog.
 
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