Water and air. Nothing is more necessary to humans, animals and plants than these two fundamental elements of life. Water is the source of our being – where there is not enough, the consequences cannot be ignored and are usually irreversible. Air surrounds us all the time. We breathe it, we feel when it fatigues or refreshes us. Air contains water too! We can feel extremes of humidity all too clearly in the dryness of crisp, cold winter days or the oppressive humidity of the tropics, though the differences are not always as obvious as this. Humidity cannot be tasted or smelt - and frequently cannot be felt, either. These characteristics make humidity the invisible enemy of modern industry. Wherever hygroscopic materials, i.e. materials which attract water, are produced or processed, inadequate humidity jeopardizes quality and productivity. Restricted machine running times, reject production and high costs are frequently the negative outcome of less than ideal humidity during the production process.

What is humidity?
Air consists of a large number of gases, one of which is hydrogen. The quantity of hydrogen in air determines its humidity. We talk about absolute humidity when describing the total quantity of water contained in one kilogramme of air in the form of gas, e.g. 8 g/kg.


An important factor in the air/water ratio is the air's constant endeavour to absorb water (in the form of vapour) until it is saturated. For this reason, another value is of key importance in assessing ambient humidity and defining an optimum humidity value: relative humidity! Relative humidity describes the quantity of water contained in air in relation to the maximum quantity of water which can be absorbed, e.g. 55% relative humidity. This "percentage saturation" of the air with water vapour is affected by air temperature: hot air can absorb more water vapour than cold air.

The following example explains the link between temperature and relative humidity: If a room is hermetically sealed against the outside air, it has a constant absolute humidity: water can neither be absorbed from the environment, nor can it be given off into that environment. If inside temperature rises due to heating, relative humidity would drop because the warmed air from the heating system would be able to absorb more water vapour than the sealed room has available. If, in the winter, windows or doors are opened for ventilation, the inside air becomes even drier than before. The higher vapour pressure of the hot, dry internal air means that the residual moisture remaining escapes outside. Relative humidity continues to fall.

This explains why ambient air is frequently so extremely dry, especially in the winter, if air is not actively humidified.

In many branches the production factor of humidity is an underestimated one! From microelectronics to the food industry, in the most varied of industrial sectors, a constant, ideal humidity not only serves to assure quality, but also to guarantee fast, trouble-free production. If the air, for example is too dry then drying-out of material or electrostatic charging can lead to avoidable costs. The processing of hygroscopic materials such as, e.g. paper, cardboard, wood, leather is particularly sensitive. However, in administrative and office buildings a regulated humidity is gaining increasingly in significance.
 

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