VPD During Off Hours

Is VPD important during lights off?

I think less so but let’s ask @dbrn32 @Nicky @Low @Covertgrower @MattyBear maybe @PurpNGold74 @OGIncognito ?

VPD - lights on only or 24hr concern?


I don’t worry a lot about VPD at night, but if your day time temps are in line, your night temps will be more than likely be close.


Negative. There are still some very good reasons to keep your temperature and relative humidity at reasonable levels, but vpd is not as critical during dark time.


@dbrn32 has my vote. [quote=“dbrn32, post:4, topic:86450”]
vpd is not as critical during dark time.
First day with VPD monitoring capability. Flower tent 63 degrees, VPD .33 (not good)
All day fan movement up speed or down speed-controlled fan remotely, nicely, but RH 78% probably high due because rain all night. Last AM yesterday morning watering 1-2 quarts of brew (1/4 feed PH 6.5 with PPM 850). As soon as LED lights came on, VPD went to zero-point 9 (perfect for today) RH dropping as night approaches (outside). LSS, I water too much.
Who knew?
DeepDiverDave has lots of water in the background. ABOVE, ON, and UNDER.

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I live in the high desert and I run the light from 8pm to 8am. Unfortunately, my wife has set the law that the tent must stay in the garage. So during the day, the garage is already in the low 90’s and the tent hovers in the high 70’s or 81ish degrees. When the overnight temperature drops, I will hit my target humidity very easily, but during the day (lights off), my humidifier struggles to keep 35%RH. I have just a cheap dialed humidifier. Today my VPD hit 2.0 around 6pm.

I guess the simple solution is to purchase a better humidifier where X% can be set and have the humidifier control the RH vs trying to control RH with my AC Infinity?

Thank you for all of the replies and insight, I do really appreciate it.

FYI, my garage humidity hit 10% today.


To be honest…temps and RH were my biggest concerns and keeping those in range :love_you_gesture:


The lowest RH I’ve experienced is the winters here in the good old south and around 25%. It’s not ideal but I’ll put a soaked towel on the tent floor and can get a boost in RH of 10-15% :love_you_gesture:


I have just set up the AC Infinity Cloudline system. I like it so much, I ordered the second T6 (6-inch) fan that connects to the controller (Intake and exhaust both controlled, together). I firmly believe their product meets my needs. The advertising says so, but that’s just marketing. Supposedly, more economical to operate and a blessing on DBM caused ear pain. I do have a Frigidaire Dehumidifier
for implementation tonight (old equipment, like me). Haven’t researched an Infinity controlled dehumid system, yet

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@Unexpected Frigidaire Dehumidifier has % setting available 60-35 or full on. Removable bucket reservoir holds over a gallon. Most importantly, the unit we use has been in house service for 7 years, mostly on at least 12 hours a day. Temporarily tropical residence with high humidity. We have an older version of the middle model (22pint)

What enables you to monitor now?
If I want to check I look at my thermometer and hygrometer and find them on a VPD chart. But I have thought about getting a Pulse 1 or something. Now that the plants are in late flower I check the hygrometers and turn on or turn off the dehumidifiers.

The AC Infinity inline fan systems will monitor VPD automatically.

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This might be an upgrade. LOL


That’s definitely an upgrade! I like it :love_you_gesture:

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Dehumidifier in flower tent, set at 50%. AC Infinity Cloudline T-Series w/ #67 Controller. User
calibrated with available information and other standards (thermometer, for ambient calibration and laser gun, for leaf temperature measurement). Trouble-call to AC Infinity about manual deficient explanation for sufficient Humidity Calibration procedure received by moronic deaf support person. All social media videos BREEZE over procedure with meaningless “Humidity Calibration procedure available”. However, manual manipulation of multiple factors utilizing SWAG procedure, System can be monitored, balanced, and data analyzed for optimum control of environmental factors. Speed/Volume changes in the intake and/or exhaust fans can be manipulated and monitored for tent temp and RH swings. Tent volume expansion vs contraction supports recognizable air flow patterns. The Frigidaire dehumidifier set at 50% RH can be audible and environmentally monitored for operation inside the flower tent. Temp and RH fluctuation can be manipulated, and results instantly adjusted for smoother temp and RH swings. RH changes varied from 10% to 16% swing in 3-5 minutes. Unit operation set at 50% results in swings from High 66% to 28% Low and adjusted to High 58%-28% Low. Awaiting second unit for outside tent environmental monitoring, to be used for calibrating inside probe. Additional Amazon purchase of Bluetooth Temp/RH completed, awaiting delivery. Also waiting for LIGHTS ON system manipulation opportunities. Exhaust T6 fan does 90-degrees bend out of tent 5 feet into attic. Large charcoal filter, available and not required at this time. Too much air flow changes temp and RH too much.

Hot damn, it sure does.

I set my app and forgot about it for 6 months because it maintains itself. Didn’t even see the VPD sneak in the updates

@Sorceress above is an update for the humidity issue.

@Graysin First day with new devices, installed, working together? Almost as much fun as first date, in 1968, with DS. Engineering changes and upgrades required, for system integration into the new world. Do i need a license for grow in META?

Absolutely. Every time I get a new toy to add to the grow room, I’m a kid in a candy shop all over again.

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Each piece of hardware requires another hardware purchase to balance and ensure optimum integration or determine the engineering change necessary for utilization in my system. In for a penny, in for a pound.

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