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Monday, 04 May 2015 08:24

Most frequent problems of ventilation in Greenhouses

Currently most of greenhouses, located in the country, have ventilation problems from various causes such as:

  • Lack of surface ventilation
  • Inadequate height of most of greenhouses
  • Poor structure (as general rule)
  • The use of anti-trips meshes that interrupts the air flow, etc.

Best conditions for Greenhouse Ventilation:

Ventilation rates should tend to:

  • Reach between 0.75 and 1 renewals of the air volume of the greenhouse per minute.
  • A surface ventilation 20-25% compared to the cultivated surface (by lateral and zenithal windows) and a suitable management strategy, can be enough.

The efficiency of this ventilation is generally very limited because the plant health problems forced farmers to install dense meshes anti-insects that hinder the passage of air.

Theoretical Aspects about ventilation in Greenhouses:

Other aspects to consider are:

The distance between the side windows, the zenith and the height of the crop, as these factors will limit the airflow, especially when the wind speed is low, the shape and orientation of the windows (depending on the prevailing winds) is not suitable etc. In any case, the issue of ventilation is very complex and it is necessary to delve into each area.

Air exchange between inside and outside the greenhouse clearly affects to crop climate. Not only changes the balance of power, and therefore the air temperature, but also affects the content of water vapor and carbon dioxide.

Passive or Active Ventilation?

Even though the importance of passive or natural ventilation, few studies have been dedicated to this phenomenon in connection with greenhouses. The calculation methods of ventilation are inaccurate because they are based on a number of simplifying assumptions that do not correspond to reality. For this reason it is often called upon experimental measurements of the renewal fee to obtain empirical models.

Passive ventilation starts because of these two factors:

  • The pressure distribution on the surface of the structure due to wind.
  • The difference in temperature, and therefore pressure, between the greenhouse and the outside.

It is also necessary to consider the resistance of the mesh of the window to the air flow, depending on the geometry of the holes.