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What Are The Types Of Greenhouse Ventilation?

In Ventilation by Ana M

Air flow not only plays an important role in greenhouse cooling but also maintains humidity levels.

Although ventilation helps to cool a greenhouse, a proper air circulation should take place in winter to keep the plants healthy.

What is a greenhouse ventilation?

Ventilation is an air circulation in a series of rapid air changes. When the temperature inside the greenhouse rises above 80 degrees F or humidity levels are reaching 100 per cent, you need to ventilate it.

The general guidance is to have about 40-60 air changes per hour. The total ventilator area should be 16-20% of the total floor area along the ridge.

Do you need to vent a greenhouse?

Yes, when you vent a greenhouse a fresh air provides plants with carbon dioxide which they use for photosynthesis.

The air enters a greenhouse through the vents and then moves around the entire structure with a help of circulation fan.

Types of Greenhouse Ventilation

There are two types of greenhouse ventilation:

  1. Natural Ventilation – roof vents on both sides of the greenhouse and louvered side vents set low down.
  2. Fan ventilation – electric fans set into the ends of the wall or in the roof of the greenhouse.

In natural ventilation cold air from the outside enters a greenhouse via louvered vents at the bottom where it warms up.

Greenhouse Ventilation In Winter

As the temperature inside greenhouse rises, warm air moves and stays near the open windows and roof vents.

Then a wind from outdoors pushes cool air from outside inside a greenhouse and warmer air exits the structure.

In fan ventilation circulation fan set up in the end of the wall or in the roof of the greenhouse moves the air throughout the structure.

greenhouse exhaust fan system

That way fresh air reaches every plant and then is moved out of the greenhouse.

How much ventilation does a greenhouse need?

A standard greenhouse needs at least one roof vent also known as ridge vent and one side vent on each side of the greenhouse walls.

As a guidance the combined sidewall vent area needs to be the same as combined roof vent area and each should be 16-20% of the floor area.

When to open greenhouse vents?

The roof vents should be open to at least 55 degrees. Side vents should not b open so widely and louvred vents are better than hinged vents.

The minimal rate for ventilation during summer is one air change per minute. In winter the minimal ventilation rate is one air change every 20 minutes.

With the natural ventilation you need to come to greenhouse a few times a day and check if you need to close or open vents more.

Although natural ventilation system is free, it is more time consuming and not very accurate.

Make sure to close the vents at night so the frost won’t damage your plants. I would suggest installing automatic vent opener to ensure proper ventilation.

Automatic greenhouse vent opener

It is a non-electrical item which is heat activated. Most of the models are installed easily with the clamps or screws on most of the greenhouse windows.

How does an automatic greenhouse vent work?

All types of automatic greenhouse vents openers work according to the temperature changes. The reference range for the majority of models is 15 to 25°C.

So you need to set up the temperature when you want a vent to close and when you want is to open. If the temperature inside the greenhouse reaches 25°C, the automatic will open.

If the temperature goes lower than 15-18 degrees Celsius, the opener will automatically shut the vents completely.

An opener has a tube which contains a heat-expanding compound, for example, mineral wax as a control unit.

With the raise of temperature wax expands and moves the plunger within the tube which will open the vent.

Alternatively, when the temperature drops wax contracts so the piston moves back to the tube closing the vent.

What is the best greenhouse automatic vent opener?

The best greenhouse automatic vent opener should be non-electric and easy to set up. You will find lots of options on the market. The main difference is in the material used for a heat control.

For example, this option has oil-filled cylinder which expands or contracts when temperatures change.

Also, look for the opener which can lift up to 15 lbs and made of galvanized steel to withstand harsh weather conditions.

Recently I came across an opener with a solar sensor so it uses solar energy to close or open greenhouse vents when temperature drops or rises.

Make sure that an opener can be easily clamped or screwed onto a greenhouse frame.

Look for the option which can be set up on a wood and aluminum frames as well as screwed to polycarbonate panels.

What exhaust fan is suitable for a greenhouse?

If you have a big greenhouse and are concerned about the humidity and temperature control, an exhaust fan is a good option.

You can either get an electric option but your greenhouse has to have a connection for power supply.

Alternatively, you can get a solar powered exhaust fan for your greenhouse. I would not recommend getting a fan powered by batteries.

This can run out of power at any time so the permanent temperature and humidity control messes up which can lead to the plant lethargy.

Here is a good electric exhaust fan option for a greenhouse. It is weather resistant and made of the galvanized steel frame with aluminum shutters.

You can choose from a speed mode suitable for your greenhouse. Also, you can get a thermostat and a speed controller to automate the fan.

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