How to lower VPD?

[Rtaym22224]

I am using a 4x4 gorilla tent with a 760w LED that’s dimmable. I am using an 8” online fan above the light to exhaust air when temps exceed 84 degrees and the fan goes off when it’s 81

Fan also goes on at 50% humidity or greater until it’s at 40% or below.

Using oscillating fans. Ready to go with co2 but just need a fill.

I covered the grow tent air intakes from the inside wirh extemely fine nylon to filter out even the tiniest particles

My vpd is consistently 2 or above

Humidity was averaging 30% so i added a few buckets of water to the grow room tonup humidity . I raised temps anlottle
Increased light intensity

No dice
What do I do?

 

[Rtaym22224]

Lowering temps improved it

 

[Rtaym22224]

Still having issues withvpd of 3 how do I lower this

I have an exhaust but no air intake would that help? A 4” or 6” inline intake ?

I covered all of the fresh air vents in the tent with very fine nylon mesh to prevent any particulates from getttjf through. It does restrict airflow a bit

 

[xet]

No dehumidifier?

 

[exploziv]

Yeah, a humidifier is better than water buckets at adding water vapour to the air.

 

[xet]

 

[xet]

 

[Rtaym22224]

Do I want to increase humidity with an evaporative humidifier or decrease it with a dehumidifier?

I will be running co2 by The Weeknd

Atlas 9 co2 controlller 20lb tank

In the enclosed grow room with no exhaust fan or intake fan the temps max at about 87 degrees Fahrenheit. I believe that’s workable with co2.

My plants are all about 15” tall passed the clone stage and entering early-mid Veg

 

[Rtaym22224]

I’m buying a dehumidifier and an evaporative humidifier and a humidity controller.

 

[Three Berries]

That much airflow you need to be treating the room it's in. If you play around with the settings in the app under ports, you can change how the fans come on and off to a lower constant run. Boost the temp diff by +2F. If your problem is spikes between the fan cycling, If the fan is cycling. +700w is a lot of heat in an enclosed space.

I run a ultrasonic egg mister in the intake air of my flower tent. Still takes some manual adjustments depending on ambient air.

 

[Rtaym22224]

How do I run a mister or humidifier through an intake? I need to add at least a 4” or 6” inline fan.

 

[exploziv]

u just need negative pressure from the exhaust fan, and.. a "lung room" with the humidifier on the intake, with fresh air or whatever you are using.

 

[Three Berries]

I have mine in a big black and yellow tote. The top has a cut out for an air filter, the side has an opening that nest up against the wall. In the wall is a 6" duct that feeds into the tent. The mister just mist into the opening and it's on a timer that comes on about 20 minutes after the lights to 30 minutes before they go off. The fan is always on at a minimum speed.

 

[troutman]

I sometime hang damp towels and fill shallow trays of water when humidity drops below 50%.

 

[GrandpaMillenial]

How do I run a mister or humidifier through an intake? I need to add at least a 4” or 6” inline fan.

my tent is small so i just humidity control the basement that my tent is in.

also for a more interactive experience, checkout this site https://vpdchart.com/

you can change celsius/fahrenheit using the gear

 

[Three Berries]

I my small tent I have one of those wick type misters. They work pretty good. The first one I had the USB port broke off though. They have single and dual misters and they can be on 100% or 50/50 time wise. But high fan flow will really swing the RH as they can't keep up.

Something like this.

 

[Douglas.Curtis]

Can you keep the temps low? Like 69F steady? Can you get humidity down to 20% ish? That is my general target area for max terpene and cannabinoid production and retention. Love the furnace filter, I use the black or purple 3M ones. I have found this level of transpiration needs lower nutrient strength solutions and soils, and a lot of water.

 

[flylowgethigh]

View attachment 18735944

You are lucky to have low ambient humidity. I bust my ass to keep the lung room 40%, and the 4x4 tent will be a few % higher. 60% is great for veg, hugely important early cause the roots are still weak, but in flower - dry is what you want. I think. I can't get dry. Will time the next run to flower in winter.

BTW, I suggest to use forced filtered air with a separate fan for the air being pushed in. A simple 6" S6 with manual settings, placed in a box that is sealed up except for an opening for a HEPA air filter element (3M 1500 or better). Run the 6" hose from the fan, through the box, into the tent. I dump the hose into a 5 gallon bucket with holes around the top to distribute the flow. I tape the filter element onto the box opening so no spider mites can sneak past.

With forced air being blown into the bucket, water can be added to add humidity. I even rigged up a wick, to get a swamp cooler effect once.

Those screened flaps at the bottom of the tent are spider mite magnets. Control the air flow going in with the fan box, and the outflow with the tent filter / fan. BTW, that should also be set on a constant speed. This way you can control the pressure balance in the tent - puffed in or out.

just free opinions.

 

[Ca++]

Fan set to come on at 50%, won't aid you getting any higher.

Presuming there are plants in there, then you should have high enough RH. The issue is too much extraction. Slow it down. The fan is huge, so some controllers are not going to go slow enough. You may need to restrict the air by mechanical means. Worry less about the temp, and more about the RH

Edit: I find it odd to see 77f if the fan doesn't run at that. Does the fan have a minimum speed it never drops below?

 

[Creeperpark]

There or 2 systematic principles for mechanical systems to dehumidify the air and lower the dew point or VPD. That is to sub-cool and then reheat the area. Sub-cooling followed by reheating is the most common method of dehumidification in large grow systems to maintain VPD.