Ventilation for greenhouses, what do you need to know?

Optimal ventilation in greenhouses is one of the keys to achieving the desired results in crops. These systems have certain characteristics and offer certain features for every need, so in this article we tell you everything you need to know about proper ventilation in greenhouses.

Having an efficient ventilation system in a garden greenhouse ensures high yields and good quality in the crop you are working with. Both temperature and humidity are very important for fruit and vegetable production and ventilation is part of the key to a successful harvest.

In the face of high temperatures and excessive humidity inside the greenhouses, it is essential to have good ventilation in the greenhouse to mitigate the negative effects of both factors and to achieve a high yielding season.

  1. Greenhouses need ventilation?
  2. Types of ventilation in greenhouses
  3. Ventilación de invernaderos con extractores
  4. Pressurised greenhouse fans on front walls
  5. Natural ventilation systems in greenhouses
  6. How to ventilate a greenhouse in winter?

Greenhouses need ventilation?

In the mornings, after sunrise, the air in the greenhouse warms up, but the night dew sticks to the fruit and the plant and can cause diseases.

Ventilation is necessary in greenhouses. These systems can prevent complications and the deterioration of the plants and their fruit by renewing the air and thus removing the excess water vapour generated by the climatic phenomena of the sun’s heat and the night dew.

Properly installed ventilation circulates the air, lowers the humidity and temperature, which is why a good combined overhead and/or side ventilation system is necessary.

For example, at midday during the summer months, the air must circulate evenly and limit the rise in temperature. If the greenhouse is poorly ventilated, it will not distribute the CO2 properly.

In the case of winter, humidity accumulates on the inner cover and after condensation drips into the crop. To mitigate this, the vast majority of greenhouses have ventilation systems on the roof or ceiling and on the sides to allow air to enter and help to reduce the high temperatures that are generated inside the greenhouse.

Types of ventilation in greenhouses

The types of ventilation in greenhouses are divided between natural and mechanical ventilation. In addition, mechanised systems can be simple or wet.

Below we look at the types of greenhouse ventilation currently in use.

Ventilating greenhouses with extractor fans

Greenhouse ventilation with exhaust fans is widely used within forced ventilation systems.

It works as follows: air enters through the motorised louvre and is drawn through the greenhouse by the extractors, which must be able to move small volumes of air without draughts and provide adequate ventilation for rapid air exchange within the building during the summer.

Greenhouse ventilation with exhaust fans is used for greenhouses up to 40 metres long, although it is also successfully implemented in ventilation systems for greenhouses up to 80 metres long.

Temperature variations are greater the larger the greenhouse, so a higher ventilation rate is desirable.

Pressurised greenhouse fans on front walls

Greenhouse pressure fans on the front walls are most commonly used in small structures with pressure fans.

They are used for greenhouses of less than 30 metres and can be achieved by mounting pressure fans that push air into the greenhouse at the top of the front walls. The system usually has two speeds and is controlled by independent thermostats.

To prevent the air from hitting the plants, a deflector is installed in front of the fans to direct the air in the desired direction. In addition, the fans contain a protective hood to prevent rain from entering the tunnel.

It is also possible to make a pressure ventilation system in which evaporative cooling is achieved. For these cases, the pressure fans should be placed on the side wall.

The pressurised system with fans on the side wall does not provide good performance when the foliage is dense and there are many tall plants growing.

The air outlet and air inlet are on the same side of the house in this case, with a box enclosure around the fan in which cooling pads are installed.

Natural ventilation systems in greenhouses

Natural ventilation systems in greenhouses are basically openings strategically located on the greenhouse roof. They are usually located both on the roof and on the sides, and can be opened and closed manually or mechanically according to the needs of the farmer and the demand of the plantations.

The basic composition of these systems is as follows:

  • Windows. These are the openings and their different options such as casement, roll-up, sash, among others.
  • Mosquito nets. This is the element that acts as an anti-insect and anti-bird screen. In general, they cover the opening surfaces to prevent the entry of external agents that could damage the crops.
  • Traction systems. These can be controlled manually or mechanically and are used to open and close the openings: they include iron fittings, pulleys, geared motors, among other elements. 
  • Electrical installation. In cases where mechanised systems are used to open doors and windows, it is necessary to have an electrical installation in accordance with the system.

Advantages of natural ventilation in greenhouses

The main advantages of natural ventilation in greenhouses can be listed in a simple way. We will go through them in the following.

  • It is an economical option for the ventilation of any greenhouse.
  • The manual option does not require the use of electricity, which results in reduced installation, operating and maintenance costs.

Disadvantages of natural ventilation in greenhouses

Natural ventilation systems in greenhouses also have disadvantages. These can be simplified as follows.

  • They offer very little control over the climate inside the greenhouse.
  • The farmer is more dependent on external weather conditions.

Tips for naturally ventilated greenhouses

When building a greenhouse with a natural ventilation system, a number of particularities must be taken into account in order to achieve an optimal installation and the desired efficiency.

Here are some useful tips for the correct implementation of natural ventilation in greenhouses:

  • It is advisable to control the height at which wall openings are placed depending on the crops.
  • The air flow should be increased during the night to take advantage of the drop in temperatures and to eliminate the heat absorbed by the structures and the roof.
  • Install the openings strategically, so that they face each other in order to favour the generation of air currents and thus increase aeration.
  • Make the most of the topography to favour the redirection of air flow towards the greenhouse.

How to ventilate a greenhouse in winter?

To achieve efficient ventilation of the greenhouse in winter, the system must be designed to avoid hitting the plants with cold draughts.

This is the main problem with some systems that use louvres at one end of the greenhouse and an exhaust fan at the other end. To minimise the situation, the inlet can be placed at the top of the gable and baffles can be used to deflect the incoming air, as mentioned above.

For draught-free ventilation, the convection tube system can be used. This consists of exhaust fans and fresh air inlets located in the gable and end wall.

It consists of connecting a thin plastic tube that runs the length of the greenhouse. This tube is suspended on a cable near the ridge and has holes along its entire length and thus brings in the corresponding air. The fans are thermostatically controlled.

The fan produces a slight drop in air pressure inside the greenhouse, which causes fresh air to flow into the inlet and inflate the tube, which delivers the air inside through the holes in the tube.

The holes that deliver the air must be projected horizontally for proper distribution and mixing with the warm air before it reaches the plants.

The job of the thermostat is to stop the fans when the desired temperature is reached; the tube collapses and ventilation stops.

In the case of a hermetically constructed greenhouse, the location of the fans in the ventilation is by convection tubes. In such cases less ventilation capacity is required than any other winter ventilation system.

As the outside temperature rises, additional air is needed, up to the point where the full capacity of the tube is reached.

It is possible to add fans and even combine with a cooling pad for use in evaporative cooling. Air can even be drawn through the pad with or without water in the pad.

The solution to achieve efficient and adequate ventilation for each crop is to install garden greenhouses, such as the minitunnel greenhouse from Fertri. An ideal greenhouse for beginners in the world of agriculture, it also offers the necessary performance in small plots due to its small size and structural strength.

Another option that allows cultivation at any time of the year under the different climatic conditions, is the straight walls tunnel greenhouse from Fertri. It is easy to install, maintenance-free and very durable. It is a perfect structure for optimal ventilation in all geographical and climatic conditions.