Computing VPD For Plants in A Greenhouse
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
where:
is the saturation vapor pressure in kPa
Temperature of the air in Kelvin
To convert between Kelvin and Celsius:
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 :
relative humidity/100
and finally VPD using or canopy sat when the canopy temperature is known.
Read more about this topic: Vapour Pressure Deficit
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