The measured air humidity can either be expressed as relative humidity, hr, as wet bulb temperature (i.e. the temperature where the relative humidity is 100%), Tbulb, or as the actual vapour pressure, ea (see VapourAirInput). Wet bulb temperature is converted to actual vapour pressure, ea, by:
where es is the saturated vapour pressure, Ta is air temperature and γ is the psycrometric constant.
If the humidity is not supplied as measured time series, a constant value of the relative humidity can be specified as a parameter (see HumRelInput). The vapour pressure, ea, will be calculated from air temperature if the relative humidity is used and from the vapour pressure, ea, the vapour pressure deficit, δe, is calculated:
The saturated vapour pressure function, es(Ta), is defined by:
where es is calculated in (Pa) and Ta in °C.