Condensation
Condensation commonly occures when the air in the interior is saturated with vapours. Modern windows are very well sealed, a fact that leads to the energy waste elimination. Rain, wind and cold are not penetrating, but the air exchange, with the exterior is performed in a controlled way, by periodical ventilation and aeration. Condensation appearance as a consequence of the, in the interior existing air and water vapours, constitutes a problem with special repercussions. Out of the molecular point of view, the - on the ”contact surface” air and water - exchange is continuous, due to the evaporating and condensation phenomenon. In constant temperature and humidity conditions, there is an equilibrium in the liquid – vapour, water state. The condensation phenomenon appears only when the air in the interior, is vapor saturated, the quantity that can be absorbed by a certain air volume being dependent on the temperature.
According to the data registered in the following table, we can observe that the air, water vapours saturation degree, grows togather with temperature heightening.
| Temperature (C grades) | Saturation degree (g/mc) |
|---|---|
| -10 | 2,14 |
| 0 | 4,8 |
| 10 | 9,4 |
| 20 | 17,3 |
| 30 | 30,3 |
If a water recipient filled with water, is let open, the air quantity which can absorb molecules, on its surface, is very large. In case the maximum absorbtion degree (generic named ”relative humidity”) hasn’t been yet reached, the air remaines” unsaturated”. The water saturated air, has a relative humidity of 100%. Its calculation can be made on the basis of a formula. According to effectuated tests, it has been determined that air with a 20 ºC temperature can absorb a maximum of 17,3 g/mc. If it containes only 8,7 g/mc, then the relative humidity is : f = 8,7 / 17,3 * 100%, this is 50%.
The dew point appears, in case the air which has a certain temperature and relative humidity, can’t absorb any additional vapor quantity. The air in a room, with a temperature of 21 ºC and a relative humidity of 50% may still absorb half of the maximal pemissible vapor quantity . If the air is cooled to 9,3 ºC the relative humidity will grow to 100%. The air is thus completely vapor saturated and reaches the dew point.
Further cooling under this level (9,3 ºC) will result in condensation pop up, because the air shall not be able to absorb anymore water. The air with a temperature of 20 ºC, saturated with 17,3 g of vapors/mc, by cooling to 10 ºC (maximal absorbed quantity being of 9,4 g of vapors/mc), determins a 7,9 g condensation enhancement.
