Humidity refers to the water content in air or another substance. Air is composed of:
• Nitrogen 78 %
• Oxygen 21 %
• Argon 0,9 %
• Carbon dioxide 0,04 %
• Water vapor 0,04 %
As with temperature, humans have a sense of moist or dry air. However, unlike estimating air temperature, it is much more difficult to assign an approximate value to the moisture content of air. Among other reasons, this is because air humidity is less common in everyday use.
Air quality contributes significantly to the quality of life. If the quality of the air is not good, for example, because it contains too little oxygen, we quickly become tired, get headaches and feel listless. One solution in this case is to open the windows and let fresh air into the room. However, this solution is not so easy to implement in every situation and environment. Also, air in itself is a complex matter, where simply opening the window does not always help.
Like any other substance, air has a limited capacity to absorb water. This limit is called saturation. Below saturation, moist air cannot be easily distinguished from dry air; above saturation, the excess water precipitates as mist in the form of fine water droplets (condensate).
The amount of water absorbed at saturation is temperature-dependent and increases strongly progressively with it. At 0°C, saturation is 4.8 grams of water/volume of moist air [unit: g/m3], at 20°C it is already 17.3 grams of water/volume of moist air [unit: g/m3]. The absolute humidity [fabs] is thus calculated from the following formula:
Weight of water contained in air [mass of water] / volume of air considered [volume of humid air].
The term relative humidity is used to describe the following ratio: actual absolute humidity [fabs] to the maximum possible absolute humidity [fmax] (in a given room at the same temperature).Relative humidity is defined as the absolute water content in the air in relation to the water saturation content of the air. This is about 15 g/kg (20°C air temperature) and increases exponentially with temperature.
On average, the air humidity is 30% - 55% (winter/summer). Inadequate ventilation can cause water to accumulate on/in the walls. At high humidity (>70%) molds develop. Especially in poorly ventilated areas (corners of rooms) high humidity can develop locally. Per hour, humans release 30g - 60g of water into the environment during light activity.