Dew Point

Hot air can contain more water vapour than cold air. When hot air cools down, without a change in absolute air humidity, the air will be saturated with water vapour at a certain temperature and condensation will occur. This temperature is called the dew point.

Greenhouse: When greenhouse temperature increases faster than plant temperature, condensation can occur. A critical point for this is when the sun is rising quickly in the morning. Also, when the sky is clear and bright at night, plants emit thermal radiation. Through this process, plant temperature can become lower than the dew point in the (plastic) greenhouse and this can cause condensation. This is similar to when a car roof becomes wet in the night without any rainfall. By increasing greenhouse temperature by heating and thus increasing plant temperature, condensation can be avoided.

A good heating strategy, which increases plant temperature effectively, should be chosen. This is because when greenhouse temperature rises it leads also to an increase in plant transpiration. This means air humidity of the greenhouse will rise and this can enhance the chance on condensation.

Sigma has available a wide range of dew point transmitters and instruments for this application.