Wanting to dial in my vpd

[Smoklahoma]

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.

[Gingerbeard]

Check your local weather for dew point. Sounds like the same thing. You have to have control over humidity and temperature.

[Smoklahoma]

Weather here is always screwy. I am not venting the box with fresh air. Sealed grow.

[Insight]

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.

[golfnrl]

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?

[Insight]

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.

[Smoklahoma]

I'll check out that app. So far been going off the chart from pulse.

[Insight]

golfnrl

[golfnrl]

Thx Insight Imma check out my user manual. Apparently I missed the Transition Humidity section during set up. Thx for chart!

[Smoklahoma]

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.

[gbauto]

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.

[Smallgrow]

Yea I use a temp gun as well to check leaves, once you know your set up the leaf temp offset seems to stay about the same. I just printed the relevant chart and stuck it on the shelf next to my tent for quick reference of temp and RH readings. Ac infinity only tells you room VPD I believe , as it has no offset

[Smoklahoma]

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

[3Berries]

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.

[TjckTock]

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.

[Bowhunterwoody]

That's the chart I have.

[3Berries]

Does anyone run a dehumidifier when lights out to target VPD?

[3Berries]

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.

[Smoklahoma]

I'm not sure if my humidifier is running in the dark or not. I do drop the humidity 5% and the temp 5° when the lights go out.

[Smallgrow]

Yes my dehumidifier will run on lights off to lower RH.
If only it could anticipate the spike when the lights go out

[golfnrl]

Same here. I'm trying to hit 60% RH and about 80f. The lung room I'm trying to keep at 68-70. With lights off the tent gets to lung room temp but not below. If I don't keep adequate ventilation the RH gets sky high with lights off. It's easier for me to maintain the temp-RH in the lung room with the AC on. This time of year its hot one day and cold the next with corresponding RH. I've been pondering the whole natural world thing while trying to maintain a good atmosphere for the plants. Has me thinking the RH and temps should rise and fall, same with the lights, over a range of time, as it happens in nature. Sometimes I feel like I'm working against the laws of nature.

[3Berries]

Sometimes I mist them with rain water when the lights first come on. That usually brings the RH up to levels that require cycling of the fan.

[Smoklahoma]

I was following the pulse chart I posted earlier but now I'm using the charts the dimlux sent me. Each chart is different for compensation of the leaf temp. I increased the ppfd to 500 trying to raise the leaf temp by 2 or 3 deg. Hell I might kill this grow before I figure it all out. But I'll get it eventually.

[grouchyoldman]

Hi @smoklahoma,
You are on a righteous but difficult path on VPD.
I obsess on that indicator of optimal conditions for healthy plant respiration but the conditions for really dialing it in are daunting.

I recently finished a grow room remodel and I am finally able to put VPD pretty much wherever I want it depending on the grown stage of my plants. I don't want to dissuade your pursuit, but here's the list of upgrades that made this possible.

- Grow Room circulation with separate intake for cool dry basement air and an external exhaust that pushes stale air outside.

- AC Infinity T8 fan with the controller 67 that displays VPD directly and allows fan triggers for both temp and RH. T8 is overkill but that allows it to run quietly at a lower speed to do the job.

- Portable air conditioner large enough to cool the room to around 70 all summer

- Oil-filled electric radiator capable of warming the room to around 70 all winter.

- Four gallon warm steam humidifier capable of increasing RH up to 65% all winter. Steam is way better for our cold dry winters, check the Optimus line.

- A fairly well sealed and insulated grow room, a little leaky but good enough for all those devices to do their job.

- Last but not least, an electrical upgrade to provide 35 amp service via two circuits connected to a standby emergency generator. Losing power now and again is a "Feature" of New England Winters.

So, my advice is that VPD control is worth the effort but you should be realistic about what you are getting into.

Cheers,
-Grouchy
PS, Oh, this project also cost me a cross-my-heart pinky-promise with my Saintly Spouse that includes a moratorium on spending!!!

[Smallgrow]

Here’s a good info source for VPD if your interested. It may have been posted on GWE before I’m not sure .
https://www.dimluxlighting.com/knowl...-guide-to-vpd/
oh I forgot there is a VPD calculator in there too…