VPD (nerds) Formula

Tips & Tricks
#1

Hello,
In the quest of a perfect dial VPD i try to create/implement a program in my climate computer.
The goal here, is to modulate the temperature in order to stay in the right set VPD.

Note : Much easier/responsive in my set up to play with the temperature to control VPD rather than play with RH (Or try to play with both RH and Temperature)

So we know, we have the following formula (in Celcius) :
VPD = 610.78 x e^(LeafTemp / (LeafTemp +238.3) x 17.2694)) - 610.78 x e^(AirTemp / (AirTemp +238.3) x 17.2694))*RH/100
Where LeafTemp = AirTemp - 2
And e=2,71828

Is there anybody who did extract Air temp from that equation?
With that we will be able **to calculate the desired Airtemp according to a setpoint VPD and RH **. It will look like :
AirTemp = f(VPD, RH)

Peete I think you did use this equation in your excell sheet? Will it be possible to get it? My math course are too far to solve this one in a decent amount of time:)

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#2

Hey Godi - i believe this is what i ended up figuring out to be the equation (js code below):

    // takes rh as a % and VPD in kPa
    // returns temp in F
    function calcTemp(vpdAir, rh){
      let t = 9621 / ( 17.863 - Math.log(vpdAir / ((1-rh/100) * 3.386))) - 460;
      return t;
    }
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#3

Great!
Thanks, you rock.
You re always very fast, helpful and willing to share.
Very appreciated.
I will try this.

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#4

Wow, are you able to modulate your environmental controls with this code? Tell me how.
Im a software engineer, and would love to tinker with this.

#5

We don’t do anything with controls, but you can definitely theoretically do that.

#6

Epic, any examples online of how someone did that?
I guess with the API I can access the data, but then Godi, you’re pulling that data into a chunk of code to decide how to set your controls, are you then able to push that code to a controller? If so, which one? How do the pieces fit together?

#7

SmartBee Hive does the controlling, very expensive but if you have the money, Pulse Grow monitor combined with a Smartbee hive would be awesome! I would expect to see something similar come from pulse, as Pulse gives you the data but not the ability to controll the equipment involved in maintaining a sweetspot atmosphere or environment!
In my case, I have the Pulse grow monitor, now I need a heater and better dehumidifier to control the environment during nighttime hours to help growth during nighttime!

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