Controlling environment by VPD

[exploziv]

Hello!
As I feel controlling temperature and humidity is not as good and efficient as controlling VPD, I started to sketch some rules for VPD control. But I am not sure of some things and I'd love some input.
- Which is the perfect VPD range?
- Do we really need to make 3 control options for seedlings/mature plants/flowering or we just go by the average range all the time?
- How aggresive do we want to be on VPD control? (Do we go for perfect environment all the time or for energy efficiency?)
- De we need a fancy big touchscreen to run this or just a lcd screen and some buttons?
- Has anyone did this before?

I am thinking of just fixing the humidity when temperature is in range, like when temp is 22 to 26 degrees C, just fix humidity so you get within 1 or 2 mbar of set VPD.
When temp is out of range fix temp first then fix humidity.
When VPD stays out of range for X hours sound an alarm. (Something is probably broken.)
Temp is fixed by increasing air movement or by a heater. Humidity is fixed by increasing air movement or by running a humidifier.
After a function has been run there is a delay before the next environment reading is taken into account. I am thinking 10 minutes.

Any input or ideea is helpful, so don't hesitate to post. Thank you!

 

[Switcher56]

I set my environment IAW this chart.

 

[Chevy cHaze]

VPD is really getting a lot of my attention lately...
One solution is buying the equipment to automate everything but that's a $$$ question and also sometimes not really doable, especially when growing small scale.
I'm trying to get VPD dialled in by a heater cable and a small mobile dehuey.
Soon with some proper controllers.
What I find confusing is the values are all over the palce when comparing VPD charts... sure veg and flower have different optimal VPDs but it's a bit off when I compare charts...
What or which charts are you using as the truth on temp vs. rh??


I'm also trying to dial in via leaf temps, not air temps ( I can only control air temps but then those will correlate with certain leaf temps)



Best
CC

 

[LEDAstray]

Key to calculating VPD is the difference between your leaf and air temps. The varying static charts you see will make assumptions as to what this difference is.

Search for a VPD calculator that allows you to input your own air/leaf temp difference and redraw the chart.

 

[Switcher56]

VPD is really getting a lot of my attention lately...
One solution is buying the equipment to automate everything but that's a $$$ question and also sometimes not really doable, especially when growing small scale.
I'm trying to get VPD dialled in by a heater cable and a small mobile dehuey.
Soon with some proper controllers.
What I find confusing is the values are all over the palce when comparing VPD charts... sure veg and flower have different optimal VPDs but it's a bit off when I compare charts...
What or which charts are you using as the truth on temp vs. rh??

I'm also trying to dial in via leaf temps, not air temps ( I can only control air temps but then those will correlate with certain leaf temps)

Best
CC

It need not cost you a fortune. This is what I use...

Left RH controller. Work1 = huey, work2 = de-huey. Right, temp controller, self explanatory.

I have a 3x3 tent in a 10x10 room. You need to treat that room (10x10) as the "environment". Because I am in the Maritimes, I don't grow between Jun-Aug (both inclusive) for 2 reasons:

• I don't need to do 3 runs in a year. AAMOF by the end of 2021, I'll have dropped that down to one run/yr; and
• Because we have large temp/RH swings here during the summer, combating the natural elements simply doesn't make sense. It's not cost effective.

That being said, your exhaust fan does need to have variable speed. Decrease extraction during lights on, because as temp rises, RH decreases and, increase extraction during lights out, as temp drops, RH increases.

As a safety measure, I "jury rigged" a home de-huey, hooked into work 2.

I sucks from the top of the tent (most hot and humid) and discharges into the room (via a charcoal filter). I used to have the return to the bottom of the tent. De-huey's discharge is 6-8 deg F higher than ambient, not a good thing, as I try to maintain a 10 deg F spread between lights on and lights off. BTW I run my 18/6 set up from 4 pm to the following 10am and, my 12/12 schedule from 10pm to 10 am the following day. <--- read same 24 hr period.

A radiant heater as required during winter, remember you are controlling your environment. The heater is oil filled, it is safer that one with an element and, unlike an element that goes cold, when it is turned off, this heater remains hot/warm for a period after power was interrupted.

Remember, I said "you" maintain your environment. Once you set up (dial in your controllers I set for either a 3 deg/% swing)) it's pretty much set it and forgot it. The heater as infinite control as well. BTW I have a passive intake via HEPA filter behind the de-huey.

The "fine tuning" happens by varying the speed (extraction rate) with the exhaust fan.

Week 6 of veg, I'm running:

• at lights on = 78 deg 60%; and
• at lights off = ambient or 70 deg 60%

The tent will remain there until 1/2 way through flower where, I will decrease my setting to 75 deg 55%, until I finish them.

my humidifier 1gal

my circ fans. I run 2 of these. One at the front of the tent, aimed @ an angle towards the opposite wall and one at the back, doing the same think. Lots of air circulation and, the nice thing, although not "aimed" at the plants, the air circulation makes the plants gently flutter, so I know they are getting the proper amount of air circulation.

There is a caveat here, you will only achieve (IMHO) a near perfect set up e.g operating parameters, without maintaining proper VPD.

I hope this helps. This is my setup, setup for my local environmental conditions, yours may differ and, that is alright. The theory and rationalization remain the same and can be applied to any growing medium.

 

[f-e]

So you want a humidity stat that's influenced by a thermostat?

I could have 5 humidifiers. Each switched on buy it's own thermostat. So the hotter the room got, the more humidifiers came on. Each of these humidifiers could have it's own stat. As a heap of kit, it's 5 thermostats and 5 humidistats for 5 humidifiers.

The next thing to do is lower the equipment count. One humidistat with an external sensor, could have resistors switched across it by the thermostats. Thermostats are just a few £ with digital screens and relay output, that use 12v so are safe. An entirely different route would be to get 5 combi stats like the sht2000 and 5 pond foggers in a level controlled tank.

It's a bit Frankinstein but you could get it going without resorting to code. Though a more effective approach might to to demand a certain temp and rh by conventional means, rather than let to meander away from perfect. Though temperature control can be demanding on power bills.

 

[Chevy cHaze]

Interesting points...
I have checked a calculator for VPD too, and it gave different results from the chart I had again.
Overall for late flower I think most agree you want a VPD of 1.2-1.6 kPa and that should roughly be achieved at 25C/ 50%-55% rh...
The same VPD can also be achieved (roughly) at 20C/35%rh or at 30C/65%rh but I wouldn't want to go there because these settings are further away from my ambient, so will result in higher costs and not sure if I want to flower at 30C. Let alone the slightly uncomfortable feeling of flowering out a thicc indica in hot humid climate hahaha.


I will be having a heater (cable) on a thermostat and a dehuey only with constant ventilation as my ambient temps over winter are cool and humid, so no need for a huey. Matter of fact, it's always humid around here so really no need to increase rh ever!
Good goings everyone, excited to start exploring VPD and hope it does something for the better!


CC

 

[Mattbho]

Problem is the grow lights dry the fuck outta the air and at the beginning of veg theres no plant matter to transpire making your 70% rh 35% under the lights . Seedlings/ clones can almost always benefit from some type of humidifier . As if there wasnt enough to worry about.

I would really like to have a vpd controlled environment just the controllers are crazy priced and the cheaper ones only control a few things . Ideally i want to control humidifier/dehumifier plus exhaust speed and ac/heat plus exhaust speed all from environment sensors and perhaps an infared leaf temp sensor.

Maybe this will help a few out i just found it last eve.

https://ledgardener.com/automate-yo...ess-temp-humidity-w-bme280-boards-ruuvi-tags/

 

[exploziv]

I have the hardware, I'm just working on the final code, some useful control rules and a good interface.

 

[ridoo]

I have the hardware, I'm just working on the final code, some useful control rules and a good interface.

https://project.seeedstudio.com/

hi
I worked before with Grove probes from seeedstudio and a Uno card I think, not sure... however something similar to Arduino

the code is very easy and many examples around to play with and adapt to your needs

If you dig a bit with arduino you can code control and display on little screens everything i guess

 

[exploziv]

Thank you man, it's always good to have new inspiration.
The thing I would need most from users of this forum is input on what the vpd/temp/humidity ranges and limits should be for different stages of plant growth.

 

[Mars Hydro Led]

Very interesting topic. Lurking for learnning something.

 

[Switcher56]

Thank you man, it's always good to have new inspiration.
The thing I would need most from users of this forum is input on what the vpd/temp/humidity ranges and limits should be for different stages of plant growth.

See post #2

 

[f-e]

From a random veg chart I see 42% is nice for 20c. While at 25c 55% is recommended.

Looking at a real grow room, you could have 20c air but the lit areas at 25c. This kind of difference is common enough with leds and with hids the temperature gap between air and canopy can be much greater. It's almost a minimum temperature differential. Yet requires a quite different RH. We see the warmer area needs the greater RH but we know it's actually going to be lower under them lights.

If we favour the canopy and give it 55% at 25c then the room at 20c may have an RH of 70-75%. We actually wanted 42. So getting a canopy right, with a 5C differential, drowns the room. The greater the canopy to room differential the greater the issue.

Outdoors the air temp isn't effected by sun or shade. You may bake in the suns solar radiation, but the air temp isn't effected by the sun shining through it.

My little LED grow has a 22c air temp, with 25c canopy and 29c being extracted from the 42c lights. Having reached the lights at 25c and picked up 4c across their ducted heatsinks. I think this 3c differential could be the lowest on this site but still puts me in an impossible position. I have to decide just where I want the vpd correct. It won't be right for the whole plant.

Before I seem to be getting somewhere with the science, we don't actually know what humidity we want, where. I always have mixed crops, fed together. I know some want high RH or turn into stick men. While others given that RH are cabbage. Rotten cabbage given chance.

There really is no answer to what your plant wants. Just saying it's cannabis isn't particularly helpful. So looking at these charts of vpd like they're the holy grail is rather floored when we are growing in confinement under lights.

It would seem reducing the temperature differential is a large goal. While keeping their feet cool. So maybe HID users can forget it unless in greenhouses with high-bays.

The idea of room RH tracking temperature is about all I can take away from the vpd debate. Also our plants seem pickier about vpd in the lower 20s to the upper 20s. As an example, that 20-25c change called for 13% more RH. While 27-32c calls for 8% more RH. Thus a room that usually sits in the upper 20s is happy enough with a fixed RH and a couple of C drift. Which just favours one plant over another, to such a small degree it's meaningless.

If I had a big pollytunnel who's temperature changed a lot from dawn till dusk then I would profit from having the RH track the temperature. Dragging out the humidity with big fans in the morning. Slowing through mid day as temps picked up, then increasing again towards dusk as it cooled down perhaps. Them big fans/shutters would pay.

Indoors my temps are too consistent. The changes I might make too small to matter. Lost in the technicalities of confinement/temp deltas/strains.

 

[ridoo]

I guess that every serious grower fall once in the vdp vortex... ??

you have the charts with the numbers, this is it, the optimal thing and so on...

but you have your setup first, your genetics, closet, room, light, vent, extractors

and your environment, weather

then the equation should look like : how much energy /space time power money tools brainwork /are you able to spend to adapt and monitor your grow area environment ?

what i remember about vdp, the larger the room the easier you can manage it, positive pression and nearly passive extraction works better to keep the hygrometer in the right numbers, sealed room, lots of vents makes you able to work at high HR with reducing molds issues

when using a tent, a small grow space with strong hps light, vdp gets tricky... i tried those ultrasonic mister and they works fine but... the vapor is cold, if you use strong extraction it will suck all of it... i get better result at slowly boiling a big water pan in the next room, this make the room air wet and so the closet in the room get a fairly good hr, but i still use the foggers for fight high temp...

 

[Switcher56]

From a random veg chart I see 42% is nice for 20c. While at 25c 55% is recommended.

Looking at a real grow room, you could have 20c air but the lit areas at 25c. This kind of difference is common enough with leds and with hids the temperature gap between air and canopy can be much greater. It's almost a minimum temperature differential. Yet requires a quite different RH. We see the warmer area needs the greater RH but we know it's actually going to be lower under them lights.

If we favour the canopy and give it 55% at 25c then the room at 20c may have an RH of 70-75%. We actually wanted 42. So getting a canopy right, with a 5C differential, drowns the room. The greater the canopy to room differential the greater the issue.

Outdoors the air temp isn't effected by sun or shade. You may bake in the suns solar radiation, but the air temp isn't effected by the sun shining through it.

My little LED grow has a 22c air temp, with 25c canopy and 29c being extracted from the 42c lights. Having reached the lights at 25c and picked up 4c across their ducted heatsinks. I think this 3c differential could be the lowest on this site but still puts me in an impossible position. I have to decide just where I want the vpd correct. It won't be right for the whole plant.

Before I seem to be getting somewhere with the science, we don't actually know what humidity we want, where. I always have mixed crops, fed together. I know some want high RH or turn into stick men. While others given that RH are cabbage. Rotten cabbage given chance.

There really is no answer to what your plant wants. Just saying it's cannabis isn't particularly helpful. So looking at these charts of vpd like they're the holy grail is rather floored when we are growing in confinement under lights.

It would seem reducing the temperature differential is a large goal. While keeping their feet cool. So maybe HID users can forget it unless in greenhouses with high-bays.

The idea of room RH tracking temperature is about all I can take away from the vpd debate. Also our plants seem pickier about vpd in the lower 20s to the upper 20s. As an example, that 20-25c change called for 13% more RH. While 27-32c calls for 8% more RH. Thus a room that usually sits in the upper 20s is happy enough with a fixed RH and a couple of C drift. Which just favours one plant over another, to such a small degree it's meaningless.

If I had a big pollytunnel who's temperature changed a lot from dawn till dusk then I would profit from having the RH track the temperature. Dragging out the humidity with big fans in the morning. Slowing through mid day as temps picked up, then increasing again towards dusk as it cooled down perhaps. Them big fans/shutters would pay.

Indoors my temps are too consistent. The changes I might make too small to matter. Lost in the technicalities of confinement/temp deltas/strains.

I guess that every serious grower fall once in the vdp vortex... ??

you have the charts with the numbers, this is it, the optimal thing and so on...

but you have your setup first, your genetics, closet, room, light, vent, extractors

and your environment, weather

then the equation should look like : how much energy /space time power money tools brainwork /are you able to spend to adapt and monitor your grow area environment ?

what i remember about vdp, the larger the room the easier you can manage it, positive pression and nearly passive extraction works better to keep the hygrometer in the right numbers, sealed room, lots of vents makes you able to work at high HR with reducing molds issues

when using a tent, a small grow space with strong hps light, vdp gets tricky... i tried those ultrasonic mister and they works fine but... the vapor is cold, if you use strong extraction it will suck all of it... i get better result at slowly boiling a big water pan in the next room, this make the room air wet and so the closet in the room get a fairly good hr, but i still use the foggers for fight high temp...

It is a starting point, vice tossing a bean in whatever medium you choose, including glass, <--- yes you can grow in granite or glass, providing you see to their nutritional/water needs.

From there, you adjust your needs as required. Never heard of the term VPD, prior to or during my 1st grow. The delta after applying its principles, have been night and day, under "my" growing conditions and environmental factors.

That being said, properly positioned circulation fans, will ensure a homogeneous environment across the volume of your growing chamber.

It can be argued that we can control VPD at both intervals, lights on and lights out, each having their own setting parameters of the manipulated variable based on current environmental conditions inside the grow chamber.

That is on my list of things to try out down the road. I am early veg and my temps are between 70 & 80 deg F and 60% RH (early flower)./ I will finish them off @ 55% RH. Using those numbers, we are definitely in the ball park for a personal grow. I am at the "tweaking stage", but it is nice to have something readily available to build on that foundation

 

[ButterflyEffect]

Any updates on this project?

I've been running my 3 flower rooms with arduinos for 3 years now and I'd love to take it to the next level with some VPD coding. Currently I control heat, ac, dehuey and a line pressure mister.

 

[exploziv]

Concept works but i am still thinking on the right code for energy efficiency and stable enaugh environment.
If you are already controlling temp and humidity 90% of the work is done. Just make those checks 3 way (to factor in both humidity and temp) and not 2 way.
Soon i will package my controller in a box to start working on code alone, cause the hardware already been checked and it's working good.
My code is more of a sketch now, I want ro make it smarter.

 

[Chevy cHaze]

Oh man I have fired up the TS1000s in my new spot and also added a hygrostat and mister to the equation.
VPD for the win!
CC

 

[exploziv]

Oh man, keep a thread subscription spot open for my TSW2000 grow that's gonna start soon..