06/16/2023

Enhancing Greenhouse Ventilation: Choosing the Right Fan

Proper ventilation is essential for maintaining a healthy and productive greenhouse environment. One key component of greenhouse ventilation is the use of fans. In this blog post, we will explore the different aspects of greenhouse fans, including the type of fan needed, ideal fan placement, appropriate fan size, the necessity of leaving fans on at night, and the distinction between horizontal airflow and destratification.

What kind of fan do I need for a greenhouse?

When selecting a fan for your greenhouse, it’s important to consider the specific needs of your plants. Two common types of fans suitable for greenhouses are circulation fans and exhaust fans.

Circulation fans, also known as horizontal airflow or HAF fans, are designed to provide even air distribution throughout the greenhouse. These fans improve airflow, ensuring consistent temperatures and reducing humidity variations. By promoting air circulation, circulation fans help prevent stagnant air and provides a supply of carbon dioxide which is basic to plant health.  They also help to control disease and pest issues.

Exhaust fans are primarily used to expel hot, stale air from the greenhouse. These fans are crucial for removing excess heat and humidity, especially during the summer months. By maintaining proper ventilation, exhaust fans aid in preventing mold, mildew, and other environmental issues that can negatively impact plant health.

Where is the best place to put a fan in a greenhouse?

The placement of fans within a greenhouse significantly affects their efficiency. Consider the following guidelines for optimal greenhouse fan positioning:

For horizontal airflow fans, it’s recommended to place them at diagonally opposite corners.  Greenhouses longer than 50 feet will need more than two fans. Mounting the fans above the crop canopy or along the sidewalls helps ensure efficient air movement throughout the entire growing area.

Exhaust fans should be positioned at one end of the greenhouse slightly above bench level.  This positioning maximizes the cooler air at the plants.  It also makes it easier to work on the fans, as belts need to be maintained, blades should be wiped off twice a year, etc.  You can also install a smaller fan up in the peak for winter ventilation.  This placement allows hot air to escape effectively, drawing fresh air in from the opposite side of the greenhouse.

How big should a greenhouse fan be?

Choosing the right size for your greenhouse fan is crucial for maintaining proper air circulation and ventilation. The size of the fan depends on the volume of the greenhouse space. Follow these general recommendations:

For circulation fans, we recommend two rows of fans – four fans total in a 24 x 96 greenhouse (2,300 square feet).  You may need more if you have taller, thicker crops like hydroponic tomatoes or cannabis.  However, factors such as the specific crop requirements, greenhouse layout, and the presence of additional ventilation systems should also be considered.

The performance of exhaust fans is typically represented by the cubic feet per minute (CFM) of air they can move. Aim for a ventilation rate of one complete air exchange per minute. To calculate the required CFM, multiply the volume of your greenhouse (length × width × average height) by the desired air exchange rate. For winter ventilation, try to get two or three air changes per hour.

Should I leave a circulation fan on in the greenhouse at night?

In regions with high humidity or during specific plant growth stages, leaving fans on at a low speed can help control temperature fluctuations and reduce the risk of condensation and fungal growth.

If your greenhouse has sophisticated ventilation systems that maintain temperature and humidity levels automatically, they can be programmed to operate at night as needed, ensuring a favorable environment for the plants.

What’s the difference between horizontal airflow and destratification?

Horizontal airflow and destratification are two distinct concepts related to air movement within a greenhouse.

Horizontal airflow refers to the uniform movement of air in a horizontal plane within the greenhouse. It is achieved through the use of circulation fans strategically positioned to create a gentle breeze that evenly distributes air across the crops. Horizontal airflow minimizes temperature and humidity variations, aids in pollination, and reduces the risk of disease.

Destratification involves the mixing of air in a vertical plane within the greenhouse. It targets the stratified layers of hot air that accumulate near the ceiling and redistributes it to the lower parts of the greenhouse. Destratification fans help equalize temperatures, enhance air circulation, and improve overall climate control.

Choosing the right fan and utilizing it effectively is crucial for maintaining an optimal greenhouse environment. By selecting the appropriate fan type, positioning it correctly, sizing it adequately, and understanding when to operate it, you can ensure consistent airflow, temperature regulation, and healthy plant growth. Remember to consider the specific requirements of your plants and adapt these guidelines accordingly to maximize the benefits of greenhouse fans. If you need assistance with choosing the right fan size or type for your greenhouse operation, reach out to the ventilation experts at J&D Manufacturing.