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Monday, 04 May 2015 08:35

How to Improve Greenhouse Ventilation

Systems Used:

The types of vents used have ranged from:

  • Manual opening band
  • Opening of joints planes greenhouses
  • and then in the "scrapes and amagado" failed trials of small manual roof windows (they were insufficient and wind could broke them)
  • Rolling vents, also widely used in greenhouses (the bonus was the mechanization but still not ventilate well the roof).
  • Currently casement longitudinal windows are being installed with pipe-rack system and roll bands.

High flow axial fans:

Another type of solution is the installation of high flow axial fans (forced ventilation). This system can support to help evacuate heat accumulation zones, as in the upper reaches of the sloping greenhouse, also to dry the air when the humidity inside the greenhouse is high, introducing outside air drier, and preventing water condensation occurring in the fruits which causes problems in the culture. You can also evacuate heat sources removing the hot air.

For optimum ventilation (45-60 renewals per hour) it is requiere a large numer of them, but depending on the number of renovations that want to get is a good choice, and a good distribution that ensures a continuous flow of air throughout the greenhouse. The placement of these devices is limited by the scope of airflow and it is usually about 30-40 m.

Recommendations about the use of Ventilation in Greenhouses:

The use of fans allow more precise temperature control in greenhouses, than can be achieved with passive ventilation control. However, in Mediterranean climates it is rare to find such equipment, because the farmer ruled out so far because of its price and power consumption.

Recommendations for installation:

  • The fans must circulate the previously calculated air flow static pressure of 0.03 kilopascals.
  • The distance between two adjacent fans must not exceed 25 meters to ensure uniformity in the airflow.
  • Whenever possible, fans should be located downwind of the prevailing winds in summer. If it is necessary install them upwind, volume for each fan should be increased to ventilate 10%.
  • There must be a minimum distance unhindered air outlet 1.5 times the diameter of the fan. The fans can be placed on the roof if there is interference on the sides.
  • To avoid unwanted air input when fans are not operating, the inlet openings must be motorized louvers that open outwards and be opened only when the fans come online. Outlet grilles also open outwards moved by the pressure of the fans.
  • The blades should be protected with wire mesh wire at least 1.5 mm thick and 13 mm openings. This kind of screen should be at least 100 mm away from any moving parts to prevent accidents.
  • It is preferable to control the air volume renovated in several phases. For this purpose, two speed fans can be use or to connect different numbers of them depending on the temperature in the greenhouse.
  • The measurement and control instruments should be fully protected from solar radiation. We have to make sure that air circulation should be around the controls speed 3 to 5 m / s. To that end, mechanical ventilators can be installed to extract air from the box containing the sensors.