A greenhouse provides the ideal climate for optimal plant growth. While every species of plants have their own growth needs, generally, a greenhouse should maintain a steady day temperature between 70-80 degrees Fahrenheit. Depending on the time of year, maintaining this temperature can be challenging.

In summer months, increased solar radiation from longer days can cause greenhouse temperatures to quickly rise beyond what’s healthy for optimal plant growth. This is why it’s crucial to use proper greenhouse ventilation and cooling systems.

In this blog, we’ll give a quick overview of greenhouse ventilation basics, then offer some tips for keeping your greenhouse cool when outside temperatures begin to climb.

The Two Types of Greenhouse Ventilation

Whether it’s a greenhouse, a barn, or any other structure, ventilation comes in two general varieties: passive and active. Let’s take a look at both types in more detail.

Passive Greenhouse Ventilation

Passive ventilation has been used for centuries. Simply put, passive ventilation is a means of providing indoor airflow without mechanical means. It’s sometimes also known as natural ventilation. The biggest benefit of passive ventilation is cost: most passive ventilation systems require little to no energy consumption. However, they can be ineffective in adequately cooling a greenhouse.

Natural ventilation relies on the basic physics of thermal gradients: hot air rises and cool air falls. One of the most common passive ventilation techniques is to install ridge vents in the roof of a greenhouse.

The vents can be opened, allowing rising hot air to exit the greenhouse. In turn, this pulls air into the greenhouse through strategically placed inlets, creating a natural airflow. By adjusting inlet and roof vents, airflow can be controlled.

Natural ventilation does have some disadvantages. Most importantly, it’s subject to ambient temperatures outside of the greenhouse. If the temperature outside of the greenhouse is too high, then natural ventilation won’t be able to efficiently lower temperatures inside of the greenhouse. Additionally, other environmental conditions, like prevailing winds, can impact passive systems. This means there are a lot of factors that are outside of the grower’s control.

In situations where passive ventilation is inadequate for proper climate control, active ventilation is a suitable option.

Active Greenhouse Ventilation

Active ventilation is also called mechanical ventilation. As both names imply, this type of ventilation uses mechanical systems, generally fans, to actively create airflow. The upside to active ventilation is it can be used to directly influence airflow inside of a greenhouse. The downside is it usually costs more than passive means.

The most common type of active ventilation are exhaust fans. These are used in conjunction with air inlet vents to exhaust hot air, pull in cooler air, and take advantage of the wind chill effect.

Fan Positioning

Greenhouse exhaust fans should be positioned no more than 150 feet away from inlets.

In greenhouses where opposite walls are greater than 150 feet apart, exhaust fans can be installed in the middle of the greenhouse. In this case, air inlets are installed on the remaining walls to help facilitate the greatest airflow.

Fan Sizing

Fan capacities are measured by the cubic amount of air they can exchange per minute. For a greenhouse, the necessary air exchange rate is found by multiplying the greenhouse floor area, in other words, the length and width of the greenhouse, by 8 feet in height. In warmer climates, the floor area can be multiplied by a height of 10 feet.

Often, mechanical ventilation is enough to help cool most greenhouses during the warm months. However, sometimes a grower will need to do more to help maintain a suitable growing environment.

Other Tips For Cooling A Greenhouse

While ventilation goes a long way in helping cool a greenhouse, there are other ways you can help control its temperature.

Use Evaporative Cooling

Evaporative cooling uses the natural cooling effect of water evaporation to dissipate heat. There are several ways greenhouses can use evaporation to aid in cooling. A simple way is through a misting system.

Misters can be installed, and if the ambient temperature becomes too high, they can be turned on to use in conjunction with exhaust fans to enhance the wind chill effect.

Cooling Pads

Another form of evaporative cooling uses pads soaked in water to help naturally cool air through evaporation. Generally, evaporative cooling pads are placed in front of intake fans to cool air as it’s pulled in from the outside. When used in a greenhouse, cooling pads can be installed in front of air inlets.

Damping

A simple method of using evaporation to cool a greenhouse is damping.Simply spraying water on hard surfaces, like concrete or cement pad flooring, will cause the water to evaporate, increasing humidity and potentially lowering ambient air temperatures in the process. However, if the climate is already too humid, this is less likely to have a meaningful impact.

Clean Insect Screening

Insect screening should be installed with any inlet, exhaust venting, or fan. It’s important to keep this screening clean. If left unchecked, debris can build-up on the screen, sometimes dramatically reducing airflow through the greenhouse.

Create Shade

Shade can be used to help cool a greenhouse when temperatures rise too quickly. However, plants need sunlight to grow, so don’t overly rely on shade to cool your greenhouse or it may negatively impact growth.

Blinds can be installed both on the inside and outside of the greenhouse. On cooler days the blinds can be raised or removed, depending on their design. Keep in mind, depending on the material and placement, blinds can hinder airflow by blocking air inlets. One solution is to use a mesh or netting to create shade without being too restrictive on airflow.

Find Greenhouse Cooling & Ventilation Solutions

Whether you’re a first-time greenhouse operator or an experienced grower, Farmer Boy has the tools and equipment you need to keep your greenhouse running smoothly.

View our full selection of agricultural and greenhouse ventilation equipment. We also have a wide range of cooling products - from misters to cooling pads.

If you need help with a large, custom ventilation or cooling system, give our sales team a call at [1] for assistance.

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