How do you calculate the condensation pressure deficit?
How do you calculate the condensation pressure deficit?
To compute the VPD we need the ambient (greenhouse) air temperature, the relative humidity and if possible, the canopy air temperature. We must then compute the saturation pressure. Saturation pressure can be looked up in a psychrometric chart or derived from the Arrhenius equation, a way to compute it directly from temperature is
kPa
where
A = − 1.88x104 B = − 13.1 C = − 1.5x10 − 2 D = 8x10 − 7 E = − 1.69x10 − 11 F = 6.456
T – Temperature of the air in K, T(K) = T(°C) + 273.15
We compute this pressure for both the ambient and canopy temperatures.
We then can compute the actual partial pressure of the water vapour in the air by multiplying by the relative humidity [%]:
vpair = vpsat * relative humidity/100
and finally VPD using vpsat − vpair or vpcanopy sat − vpair when the canopy temperature is known.
BOOOOOOOOOOOOOOOOOM
Is VPD the same as CPD?