Looking to figure out how to decrease my VPD rating in my grow tent currently running 1.9 range for new seeding need to decrease it temps running around 81 and humidity around 45% would boosting humidity with some water containers in grow tent help?
Yes. I use a poor man’s humidifier in my veg tent for that very reason. A quart jar filled with distilled water, with a microfiber cloth “flowered” above the jar’s rim. You can see it here:
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Distilled water I’m assuming to protect plants? Tap water a no go?
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I use distilled, because I am concerned that with a fan blowing over it, there could be some residue from tap. But frankly, I’m not sure if that could be an issue.
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Tap water will work fine if you’re not misting it and just using evaporation.
It will sometimes leave a whiteish dust on leaves when using a misting type of humidifier is why most use distilled or ro.
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Light cycle opposite sunlight cycle.
Slow down aircirculation may assist.
LASAR LEAF TEMPS?
My VPD ususally calibration is -3 to -5with leaf temps lower than measuring devices at same crown level. Good luck.
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Makes sense.
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So less air circulation inside you say? So essentially vpd is a cumliation of humdity and temp in tent correct? Im using a ac infinity cloudline t6 the reading im getting is from that monitor, not sure how accurate it is.
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The ACI sensors seem to be fairly accurate, assuming the probe is at canopy height.
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Add a small humidifier inside maybe to push up humidity? Temps during daytime with lights running 81-83 hummidity 43-44 consistently
You can use RH & air temp to calculate ‘Room VPD’ at the sensors location. But you need to be targeting your ‘Leaf VPD’, & you need to know your leaf temp as well as the RH & the air temp to calculate your ‘Leaf VPD’.
Whats best to calculate RH ? Recommend tool to measure temps of leaves?
@TrapPlay26 an infrared thermometer like this to measure leaf temps
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@TrapPlay26 there are a ton of sensors to measure temps and RH. I like this one, comes with 3 sensors. I set one at floor, canopy and ceiling to get a sense of temp and rh throughout the tent. Seems to be fairly accurate. I have the ACI sensor in the tent too. So you can guage you RH by that as long as its at canopy height like @Newt said.
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Thanks sir ill look into it.
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Perfect thanks again
Yes, BUT each measuring device responds to the tent conditions differently and there are micro fluctuations. If Lights are too low, plant leaf tem increases using the AC-I Cloudline software, VPD is automatically calculated by internal software. The software allows user calibration adjusting for a more accurate VPD measurement. My issue with measuring is a result of learning my grow and devices.
TWO AC-I infinity temp/Rh probes, tethered together, hung together, will measure independentlyand often differently. Bundled together the plastic air thermometer, the GOVEE remote measuring sensor and the two AC-I sensors, all measure differently. Construction material, design, what-ever.
I know the zone of response close. I control the temp, often dialed to a degree. Temp and RH limits can be set for changing my air circulation levels. LSS VPD is a measure of how stressed you plants are and charts recommend ranges for optimum growth conditions. Screw TEMP and VPD in this heat, more lights off is the best way I have to lower VPD.
Piece of mind.
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So looking at your settings on your cloudline t6 im assuming with 80 temp 50 humidity your vpd is roughly 1.8 range maybe? So your saying tone down your lights to best control it? Problem here is im using 2 unit farm UFS3000 lights with no dimming abilty so its either run one of them in mu 2x4 tent or both.
If his air temp is 80f & the RH is 50%, then his ‘Room VPD’ is somewhere around 1.8kPa (at least, at the location of the sensor), but you mainly want to be targeting your ‘Leaf VPD’, & you mainly want to be targeting the ‘Leaf VPD’ during lights-on. ‘Lights off Leaf VPD’ is important, but maybe 10% as important compared to ‘Lights-on Leaf VPD’.
From what I understand, the leaf temperature offset calibration in the ACI controllers should be set after the user records their actual leaf surface temps & then calculates what their leaf temperature offset really is. Then they can put their air temp & RH sensor(s) where they recorded the leaf temps (ideally at the hottest leaves at the top of the canopy), & it then will be giving you the ‘Leaf VPD’ from that location (provided the actual offset stays the same as it is in the controller).
As far as I can tell, if the sensor offset in the controller is set to zero offset, then the sensor will always give you the ‘Room VPD’. It’s not going to adjust the offset for you on the fly, you have to find out what the leaf temp actually is with the IR thermometer, calculate the offset using your air temp & leaf temp, & then set the offset in the controller to match the actual offset. Does that sound about right?
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First thing I did when I started dialing in VPD was went lights out during the hottest part of the day.
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