Switcher56
Comfortably numb!
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Controlling environment by VPD
- Thread starter exploziv
- Start date
ButterflyEffect
Well-known member
What sensors do you use? I currently use DHT22s and they tend to over-report humidity by at least 10% within a short period of time.
If you're able to share any lines of code, that'd be very helpful!
Very interesting topic related to VPD!
I have some doubts about the scheme and the pressure of the kPa tent. Depending on the humidity and temperature for example on 1.44m2 with 2.0m height. What kPa pressure would be ideal for a controller set at 26-27 ° C during the day with a humidity of about 60-70rh?
I have an open treath connected to a certain controller and I need help for a better configuration. What I failed to understand .. how to connect / use this sensor correctly?
Growbase Pro
https://www.icmag.com/ic/showthread.php?t=378741
Pressence sensor
I have some doubts about the scheme and the pressure of the kPa tent. Depending on the humidity and temperature for example on 1.44m2 with 2.0m height. What kPa pressure would be ideal for a controller set at 26-27 ° C during the day with a humidity of about 60-70rh?
I have an open treath connected to a certain controller and I need help for a better configuration. What I failed to understand .. how to connect / use this sensor correctly?
Growbase Pro
https://www.icmag.com/ic/showthread.php?t=378741
Pressence sensor
@ZV: Vacuum depresure is not related to temperature or humidity. You just need to keep NEGATIVE pressure inside that is constant. 100 kpa = 1 bar (atmospheric pressure). I would keep at least 20-to 30% of that at all times to ensure smell is not going out.
About the sensor you call Pressence, I am not sure in the picture it writes pressence or other name, but has no logic with that name. What pressence is and what should that sensor measure? Any info from the manufacturer on it?
Only think I can throw out there, and it's just a guess, maybe it's the vacuum presence sensor? Or is this a different sensor?
Anyway please note that the vacuum kPa should be a negative value, and not positive one, as vacuuum is negative pressure.
@Butterflyeffect:
I am about to scratch the vpd control code and rethink it. I am not happy with it, even if it works, I want it much better planned and written. Might even get a code guy to have a try at optimising it once it's done. Sorry, won't share it for now, as I consider there is nothing to be proud of.
About the sensor you call Pressence, I am not sure in the picture it writes pressence or other name, but has no logic with that name. What pressence is and what should that sensor measure? Any info from the manufacturer on it?
Only think I can throw out there, and it's just a guess, maybe it's the vacuum presence sensor? Or is this a different sensor?
Anyway please note that the vacuum kPa should be a negative value, and not positive one, as vacuuum is negative pressure.
@Butterflyeffect:
I am about to scratch the vpd control code and rethink it. I am not happy with it, even if it works, I want it much better planned and written. Might even get a code guy to have a try at optimising it once it's done. Sorry, won't share it for now, as I consider there is nothing to be proud of.
CrushnYuba
Well-known member
So what is it exactly? I am no expert on vpd. I get the basics i think.
So instead of controlling humidity and temperature separately based on a vpd chart... You choose your vpd level? What is the point?
Or is it more like a gauge? Howis this used in practice
So instead of controlling humidity and temperature separately based on a vpd chart... You choose your vpd level? What is the point?
Or is it more like a gauge? Howis this used in practice
PresSence data sheet:
The negative pressure sensor measures the current negative pressure value at the end of the connected pressure measuring hose. The digital climate controller receives the negative pressure values ??and regulates the speed of the supply air fan so that the negative pressure is kept at the desired value.
The vacuum sensor is connected to the controller with the 5m cable with RJ45 plug. The hose supplied is connected to the socket labeled "Inside" on the sensor, which is led into the box or room in which the negative pressure is to be regulated.
If the sensor is located in the room in which the negative pressure is to be regulated, a hose can be led to the outside via the nozzle labeled "Outside".
Scope of delivery:
Pressure sensor with 5m cable
4m hose for pressure measurement
Wall mounting (Velcro)
Technical specifications
Dimensions without cable (LxWxH) 110mm x 36mm x 20mm
Cable length 5m
Measuring interval 1 s
Measuring range 0-40 Pa negative pressure
Degree of protection IP40
Permissible operating temperature 10-40 ° C
The controller came set to 5kPa and I couldn't understand its exact use!
Thank you exploziv!
The negative pressure sensor measures the current negative pressure value at the end of the connected pressure measuring hose. The digital climate controller receives the negative pressure values ??and regulates the speed of the supply air fan so that the negative pressure is kept at the desired value.
The vacuum sensor is connected to the controller with the 5m cable with RJ45 plug. The hose supplied is connected to the socket labeled "Inside" on the sensor, which is led into the box or room in which the negative pressure is to be regulated.
If the sensor is located in the room in which the negative pressure is to be regulated, a hose can be led to the outside via the nozzle labeled "Outside".
Scope of delivery:
Pressure sensor with 5m cable
4m hose for pressure measurement
Wall mounting (Velcro)
Technical specifications
Dimensions without cable (LxWxH) 110mm x 36mm x 20mm
Cable length 5m
Measuring interval 1 s
Measuring range 0-40 Pa negative pressure
Degree of protection IP40
Permissible operating temperature 10-40 ° C
The controller came set to 5kPa and I couldn't understand its exact use!
Thank you exploziv!
Hey Yuba,
The point is I believe that at a certain temp/rh ratio the plant metabilsm runs on maximum as the transpiration rate is ideal and therefore the plant is best supplied with nutes and water from the soil?
Lots of of people swear by it and say everything else, boosters vitality supplements, stimulants etc. is bollocks and the correct vpd does much more for the plant than all extra stimulants combined. Of course the correct nutes have to be available for the plant at any time.
(I'm also giving it a try after inspiration from the brother exploziv, but I'm not a computer expert and I have a very low ambient rh, so all I do is run a mister on a hygrostat and try to adjust rh to the given temperature in the house which is very stable.)
CC
Switcher56
Comfortably numb!
+1 
Switcher56
Comfortably numb!
During winter months here ambient RH is around 22% I have to run a household humidifier to raise it to 40%. Dry air is not good for humans either. I go through 3gal of H2O/day. It greatly assists my tents. Humidifier is is front hallway.
ButterflyEffect
Well-known member
I hear you. It took me a year to get my current code to where I was OK with it. Still ugly, but it works.
Keep us posted.
CrushnYuba
Well-known member
So this will factor air pressure? I have never figured out how to do that. I have gotten good results just looking at a vpd chart when i choose my temp and rh.
How far off am i not factoring air pressure?
How far off am i not factoring air pressure?
When I pondered on Pressure, I realised whatever the air does, so does the plant. So the differential is unaffected, presuming your pots are in the room. Reading studies where 20 varieties (of wheat) were looked at in various conditions, they also addressed and walked away from the atmospheric pressure part of any equations. All we need worry about is the big issue of how much more water the air around the plant can take on.
Once stacked, my plants like it drier than most of the graphs specify. Likely because I have no radiant heat driving transpiration. A regulating factor of great proportion, also not in the VPD studies being made.
The studies are good guidance offering ranges of results seen that we can think about. No plant will want you perfectly in the middle of these ranges with pinpoint accuracy. This is why the data is interpreted into RH ranges. This is where we can make use of the figures. RH tracking air Temperature. With a nod towards the air to leaf temperature differential.
RH v Temp is a very small closed loop system. Most people will find keeping the temperature constant is easy with whats on the shelves. Then the RH requirement is a constant, and needs just a humidistat. Its rare that you would move the RH around because you can't keep an even temperature. It's an issue of scale and location. Greenhouse growers can make real use of changing RH instead of Temperature.
Once stacked, my plants like it drier than most of the graphs specify. Likely because I have no radiant heat driving transpiration. A regulating factor of great proportion, also not in the VPD studies being made.
The studies are good guidance offering ranges of results seen that we can think about. No plant will want you perfectly in the middle of these ranges with pinpoint accuracy. This is why the data is interpreted into RH ranges. This is where we can make use of the figures. RH tracking air Temperature. With a nod towards the air to leaf temperature differential.
RH v Temp is a very small closed loop system. Most people will find keeping the temperature constant is easy with whats on the shelves. Then the RH requirement is a constant, and needs just a humidistat. Its rare that you would move the RH around because you can't keep an even temperature. It's an issue of scale and location. Greenhouse growers can make real use of changing RH instead of Temperature.
You don't need to factor in air pressure for vpd control. That's for smell controll.
eyesdownchronic
Active member
Feel free to call me out if im wrong...
but its my impression that growers who simply try to control their environment for vpd are missing part of the picture.
VPD is a wonderful measure, but it only ties in temp with humidity, which is related to a plants water potential and therefore rate of transpiration (water uptake) . it doesn't account for variations in rate of respiration vs. photosynthesis. ie energy creation vs. energy use.
a practical example of this would be someone trying to set high temps / high humidity, but under low light conditions. in this situation the plants would be transpiring and respiring at very high rates, but without enough photosynthesis the plants would not have enough sugar creation to back that kind of growth. this person will very likely run into problems with stretch and mold and have a decreased yield. however, same vpd under high light conditions and these problems will more or less disappear.
a more complete view would be tying in some measure of DLI (daily light interval) vs ADT (average daily temp) in conjuction with VPd. so pretty much energy budget alongside water uptake. in theory, the DLI v ADT measure is directly related to yield, sugar (energy ) creation vs. use.
just my
but its my impression that growers who simply try to control their environment for vpd are missing part of the picture.
VPD is a wonderful measure, but it only ties in temp with humidity, which is related to a plants water potential and therefore rate of transpiration (water uptake) . it doesn't account for variations in rate of respiration vs. photosynthesis. ie energy creation vs. energy use.
a practical example of this would be someone trying to set high temps / high humidity, but under low light conditions. in this situation the plants would be transpiring and respiring at very high rates, but without enough photosynthesis the plants would not have enough sugar creation to back that kind of growth. this person will very likely run into problems with stretch and mold and have a decreased yield. however, same vpd under high light conditions and these problems will more or less disappear.
a more complete view would be tying in some measure of DLI (daily light interval) vs ADT (average daily temp) in conjuction with VPd. so pretty much energy budget alongside water uptake. in theory, the DLI v ADT measure is directly related to yield, sugar (energy ) creation vs. use.
just my
ButterflyEffect
Well-known member
Feel free to call me out if im wrong...
but its my impression that growers who simply try to control their environment for vpd are missing part of the picture.
VPD is a wonderful measure, but it only ties in temp with humidity, which is related to a plants water potential and therefore rate of transpiration (water uptake) . it doesn't account for variations in rate of respiration vs. photosynthesis. ie energy creation vs. energy use.
a practical example of this would be someone trying to set high temps / high humidity, but under low light conditions. in this situation the plants would be transpiring and respiring at very high rates, but without enough photosynthesis the plants would not have enough sugar creation to back that kind of growth. this person will very likely run into problems with stretch and mold and have a decreased yield. however, same vpd under high light conditions and these problems will more or less disappear.
a more complete view would be tying in some measure of DLI (daily light interval) vs ADT (average daily temp) in conjuction with VPd. so pretty much energy budget alongside water uptake. in theory, the DLI v ADT measure is directly related to yield, sugar (energy ) creation vs. use.
just my
That's a serious knowledge drop my friend! More proof that context is everything!
I get my rooms to run fairly close to optimal so I'm less incentivized to get the code for VPD, let alone DLI & ADT. But I'd sure as shit run it if I had it.
Goes to show how much we've been missing out knowledge-wise. As I look back at posts on all of the boards over the years, I see so much info lacking context and people eating it up like gospel. Many growers never thought to adapt the advice to their own specific circumstances.
eyesdownchronic
Active member
people usually like easy answers, but its often times not the case.
i knew an old greenhouse research and extension professor whose favorite answer to just about every question was , "it depends," and he was never wrong haha.
While I totally agree VPD doesn't take in the whole picture, I personally feel it's much better than keeping RH and temperature at fixed points. If not for the plants, then for electricity use it's better for sure. My experience tells me it was better than just keeping temp and RH, anyway.
I used VPD because that is what i can read for cheap and also control with just unexpensive added hardware. To a point, I bet VPD can work for most growers ro raise their respective bud quality bar a bit higher (or way higher for some, maybe).
But I thank you for coming in on this, I enjoy talking to people that go the distance and suck in any piece of knowledge that they came across.
As more advanced environment and phytosensors get cheaper and easier to use I bet we can have more insight into our future grows parameters, but for now I feel this is more than enaugh for small time growers like myself.
Actually, I bet it can help some of the commercial growers as well. Better bud and more of it means more money for them right? It's also easier to know when something fails or goes wrong, the recorded parameters tell the story better than the eye can see them in real time.
I used VPD because that is what i can read for cheap and also control with just unexpensive added hardware. To a point, I bet VPD can work for most growers ro raise their respective bud quality bar a bit higher (or way higher for some, maybe).
But I thank you for coming in on this, I enjoy talking to people that go the distance and suck in any piece of knowledge that they came across.
As more advanced environment and phytosensors get cheaper and easier to use I bet we can have more insight into our future grows parameters, but for now I feel this is more than enaugh for small time growers like myself.
Actually, I bet it can help some of the commercial growers as well. Better bud and more of it means more money for them right? It's also easier to know when something fails or goes wrong, the recorded parameters tell the story better than the eye can see them in real time.
Last edited:
Switcher56
Comfortably numb!
It's a starting point. Nothing more nothing less. That being said... a necessity.Feel free to call me out if im wrong...
but its my impression that growers who simply try to control their environment for vpd are missing part of the picture.
VPD is a wonderful measure, but it only ties in temp with humidity, which is related to a plants water potential and therefore rate of transpiration (water uptake) . it doesn't account for variations in rate of respiration vs. photosynthesis. ie energy creation vs. energy use.
a practical example of this would be someone trying to set high temps / high humidity, but under low light conditions. in this situation the plants would be transpiring and respiring at very high rates, but without enough photosynthesis the plants would not have enough sugar creation to back that kind of growth. this person will very likely run into problems with stretch and mold and have a decreased yield. however, same vpd under high light conditions and these problems will more or less disappear.
a more complete view would be tying in some measure of DLI (daily light interval) vs ADT (average daily temp) in conjuction with VPd. so pretty much energy budget alongside water uptake. in theory, the DLI v ADT measure is directly related to yield, sugar (energy ) creation vs. use.
just my
Isn't the tent / room negative pressure just the same as going to a higher elevation?
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