Calculating Airflow Rate in Case of Humidity Load

The resultant humidity load usually comes from two different sources. One of them is the human occupation, and the other is some kind of water surface, e.g. a swimming pool, or a fountain in a supermarket.


m1p – is the humidity load of one person [g/h,person; kg/h,person]
A water – is the free surface of evaporating water []
β –is the evaporating factor, which depends on the liquid’s material
pvapour,saturation– is the saturation pressure of vapour [Pa].
pvapour – is the partial vapour pressure [Pa]

An average adult person’s humidity load in winter state is about 50 [g/h,person], while in summer it is about 65 [g/h,person] due to standard CR 1752. It actually consists of sweating and evaporation.

Based on the above, the calculated airflow rate of supply air in summer is:

xex – is the humidity ratio of exhausted air [g/kg; kg/kg]
xsup – is the humidity ratio of supply air [g/kg; kg/kg]

The airflow rate of supply air in winter is:

In most cases, this value is higher in summer than in winter due to the bigger number of summer’s humidity load.

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