The Importance of Polytunnel Ventilation

The Importance of Polytunnel Ventilation

Understanding the temperature requirements of the plants and produce you’re working to grow is vital to a successful growing season.

When creating planting zones in your polytunnel, consider planting similar temperature produce and plants together, so that you can control the ventilation in different parts of your tunnel.

Good ventilation in your polytunnel helps to regulate the temperature inside your greenhouse and can reduce the mid-day high temperatures; providing fresh air and CO2 to your produce and plants; promoting optimum growing conditions.

There are a number of different ways in which you can ventilate your commercial polytunnel, and in this blog we’ll explain the most common.

Polytunnel Ventilation Methods

Depending on the size of your tunnel and the cooling effect you hope to achieve, some ventilation types will perform better than others. The core ventilation types are:

• Ventilation From Doors
• Louvres
• Side Ventilation (Curtains)
• Extraction Fans
• Gutter Ventilation
• Ridge Ventilation

Door Ventilation

Ventilation from doors is the easiest ventilation method, it’s simple to do and comes as a standard with most of our polytunnels. It’s pretty much what it says on the tin, opening the polytunnel door to ventilate the tunnel.

Door ventilation is most effective in smaller, shorter tunnels, as in longer tunnels the cool air from the ventilation would not reach the centre of the structure. You also need to be considerate of insects and pests entering your polytunnel, when using door ventilation, so a net is advised if using this method, or a double zip vent door.

Louvres

Louvres are also known as a D-Panel, are usually located above the polytunnel door or in the door frame, as the top of the tunnel is typically where hot air collects.

Louvres are really simple to operate and tend to have either a pull cord or a winding handle to open and close them. More advanced Louvres can be automated to work on a schedule.Whilst Louvres are great for use in smaller polytunnels, they aren’t as effective in long tunnels due to their size and positioning.

Side Ventilation (Curtains)

Side ventilation is great for single span polytunnels and in most cases will give plenty of temperature control. We offer a range of ventilation kits for our hobby / garden polytunnels with both 5ft and 6ft hoop options.

Side ventilation has a number of benefits to your temperature control, it can be manual, powered or fully automated, making its management easy, and it’s a very cost effective ventilation method. Even better, the ventilation is accessible from outside your structure, meaning you don’t need to disturb the internal temperature each time you alter the curtains.

We recommend combining side ventilation with netting, in order to keep most flying insects out and on larger, multi-span polytunnels, you may also wish to add ridge ventilation such as a Louvre to tackle heat rising to the top of the polytunnel structure.

Extraction / Intake Fans

Extraction and Intake Fans can easily be retrofitted to your polytunnel or greenhouse, offering an easy way to release excessive heat build up in your polytunnel. They tend to be fitted to the roof of your structure, and more can be added as your structure grows.

Depending on the type of fan used in your polytunnel, they can either extract the hot air or act as in intake and push fresh air in. This roof fan extracts the hot air, whilst this air intake fan helps to push fresh air into the structure.

Passive fans are ideal for garden structures, with this one being operated with a simple pull-cord. For commercial and larger polytunnels, we recommend extraction and intake fans that require power.

Gutter Ventilation

As the name suggests gutter ventilation can only be fitted to a polytunnel that has gutters, so this method of ventilation would typically only be used in commercial multi-span or superbay structures, opposed to garden greenhouses.

Gutter ventilation can be retrofitted to your structure and means that you shouldn’t have hotspots in the middle of your structure, as the ventilation can span the entire length of the polytunnel. Be aware however, that gutter ventilation can only be fitted to one side of the gutter, not both, as they would clash on opening.

Opening Ridge Ventilation

A popular addition to our commercial, traditional multi-span or superbay structures is opening ridge ventilation. This ventilation sits at the highest point in the ridge in order to allow the build-up of hot air to escape in the most efficient way possible. It’s self-regulating and ensures that there aren’t any hot spots in the centre of the tunnel, making it ideal for large structures.

Opening Ridge Ventilation requires specialist equipment to install, and requires single or three phase power.

Help In Selecting A Ventilation System

When selecting ventilation there are some general guidelines, we recommend following to ensure you get the right amount of ventilation, and select the most suitable type of ventilation to achieve this.

• Side ventilation is only effective for around 10m from the vent into the structure and is very reliant on an outside wind speed.
• Extraction, gutter & ridge ventilation is typically sized based on the number of air changes you wish to achieve per hour.
• To achieve good temperature control a ventilation system would normally provide 20-30 air changes per hour but this can be difficult to achieve on a commercial structure unless ridge ventilation is used.
• In some cases 10-15 air changes for extraction fans can provide manageable temperature control but has a tendency to saturate on the hottest days of the year.

Speak with our team about your polytunnel ventilation needs to ensure you get the best system possible for your structure, produce and plants.