Air Humidity

The measured air humidity can either be expressed as relative humidity, h_r, as wet bulb temperature (i.e. the temperature where the relative humidity is 100%), T_bulb, or as the actual vapour pressure, e_a  (see VapourAirInput). Wet bulb temperature is converted to actual vapour pressure, e_a, by:

                                            (8.8)

where e_s is the saturated vapour pressure, T_a 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, e_a, will be calculated from air temperature if the relative humidity is used and from the vapour pressure, e_a, the vapour pressure deficit, δe, is calculated:

                                                            (8.9)

and

                                                          (8.10)

The saturated vapour pressure function, e_s(T_a), is defined by:

                                   (8.11)

where e_s is calculated in (Pa) and T_a in °C.