 # VPD (nerds) Formula

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:)

1 Like

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;
}``````

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

1 Like