VentoVind PRO Special user manual
© Corroventa Avfuktning AB
2020.12
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Relative humidity and its impact on materials
All air contains a greater or lesser degree of moisture. We can’t see it with the naked eye until it
appears in the form of small water drops against a cold metal or glass surface for example. However,
before it is visible, moisture is already causing problems by affecting materials, causing corrosion and
growth of micro-organisms. It can be taken for granted that the Nordic climate is always humid.
Large areas of water, in the shape of thousands of lakes and the surrounding sea, cause a lot of
humidity.
Air moisture is measured and usually given in relative humidity (% RH). This is a measurement of how
much moisture the air contains compared to how much it can hold in total at a given temperature
and pressure. The higher the temperature, the more water the air can hold but it is the relative
humidity which is calculated, and which must be controlled.
At 100% RH the air is saturated and the moisture falls in the form of small water droplets. Steel
corrodes at 60% RH and at 70% RH there is a risk of mould. A rule of thumb is that 50% RH is a good
climate for most materials but here in Scandinavia, it is rarely that low. The annual average value in
most places is instead around 80% RH and can be equally high in both summer and winter.
