Thermo-physical Properties of Air

Psychrometric Conversions

The modelling of psychrometric processes in ApacheSim, MacroFlo and ApacheHVAC requires a set of calculation procedures for converting between such quantities as:

Dry-bulb temperature
Wet-bulb temperature
Dew-point temperature
Relative humidity
Percentage saturation
Humidity ratio
Water vapour pressure
Enthalpy
Air density
Atmospheric pressure

For these conversions ApacheSim, MacroFlo and ApacheHVAC use published procedures set out in Reference 9.

Air Moisture Content Dynamics

The storage of water vapour in the room air mass is represented by

( 40)

where

is the air density (kg/m ³)

is the net water vapour gain to the air (kg/s)

is the room air humidity ratio (kg/kg)