Getting Started Greenhouse Ventilation Systems With Exhaust Fan

There are many reasons for growers to choose a greenhouse growing environment. Perhaps he uses greenhouse to start seedlings and protect them in their early stages. Maybe she use it to extend the growing season of plants and increase her production or grow plant species that wouldn’t naturally thrive in growing region. 

Besides, as the weather gets colder, you will see more and more greenhouses. Have you ever wondered why? Actually, it's not just because most plants can't survive in cold weather, but if you look closely you will find greenhouses all year round. The most important thing in a greenhouse is air temperature and humidity, where ventilation is always neglected, this article will let you know the importance of a ventilation system with exhaust fans.

Greenhouse Overview

A greenhouse is an outdoor structure used to house and nurture plants. Greenhouses have mylar or glass walls that allow sunlight to enter the house while preventing heat from escaping. This helps create the ideal growing climate for flowers, fruits and vegetables, especially in cold areas or seasons. 

The Main Issue of Using Greenhouse Without Ventilation Systems

As light hits the walls of a greenhouse, some of that energy is absorbed and converted to infrared energy or heat. While infrared energy wavelengths can easily pass through greenhouse walls, their makeup makes it hard to escape once inside. The trapped infrared energy or heat creates warmth within the greenhouse, helping to create optimal growing temperatures. However, if there’s nothing to cool down the greenhouse, the interior temperature will continue to rise and become too high, which will result in scorched crops. When crops suffer, so do greenhouse operation profits.

Poor Ventilation

Inadequate ventilation can lead to excessive heat and humidity. High temperatures can lead to plant stress and reduced yields, while high humidity can lead to fungal diseases. If you are experiencing high temperatures and exhaust fans are constantly running, or all passive ventilation is fully open, you likely have inadequate ventilation. If you are seeing widespread fungal disease, you likely have an inadequate ventilation problem. As vegetation increases and air flow becomes more restricted, the effectiveness of your ventilation system will change over the growing season. You should be able to stand in the middle of a tunnel or greenhouse and feel a comfortable breeze.

Poor Circulation

Inadequate circulation can lead to inconsistent conditions throughout the tunnel or greenhouse. This can manifest itself as hot spots with high temperatures, cold spots with low temperatures, areas of high humidity, and condensation. Look for leaf movement in each section of the tunnel or greenhouse as a sign of air circulation. Cutting survey tape to equal lengths and tying it to the tunnel frame to hang down also helps to show where air is moving and where it is not.

The Solution

In order to cope with the rise in temperature inside the greenhouse, proper ventilation is necessary. Greenhouse ventilation design is the key to ensure optimal ambient temperature for crops. The two types of greenhouse ventilation are natural ventilation and mechanical ventilation. These systems both work on the principle of thermal buoyancy, using cold, dense air to push hotter air outside the greenhouse.

4 Reasons for Why Greenhouses Need Ventilation?

Ventilation serves four crucial functions in the growing process: temperature control, improved air circulation, humidity control, and carbon dioxide/oxygen substitution.

1. Temperature control

Greenhouses receive and capture solar radiation, resulting in an increase in temperature in the growing environment. This is beneficial to a certain extent, but allowing temperatures to climb too high can be detrimental to plant growth and plant health. Greenhouse ventilation systems allow growers to vent excess heat and allow their plants to thrive at optimal temperatures.

2. Improved air circulation

Plants benefit from breezes in terms of transpiration and cell wall strengthening. Air flows and mixes throughout the greenhouse, balancing temperature, humidity, carbon dioxide and oxygen, helping to create uniform conditions to which plants respond better.

3. Humidity control

Without adequate ventilation, humidity can build up in the greenhouse. Naturally occurring transpiration (evaporation of water from plants) and condensation as part of the water cycle increase humidity levels in thermodynamic structures. High humidity levels in a greenhouse can invite pathogens, molds and fungi that can interfere with plant growth. With automatic ventilation systems, humidity control can be achieved by replacing wet, warm air with dry, cool air as needed.

4. Carbon dioxide/oxygen substitution

Fresh air from ventilation provides plants with carbon dioxide, which is essential for photosynthesis, and oxygen, which is needed for root growth. Greenhouse ventilation systems introduce fresh air and expel stale air, improving the health and quality of crops. Without ventilation, the interior air becomes over-saturated with oxygen and plant life suffers. 

In addition, ventilation contributes to other factors that are important for healthy growth.

Pollination - In a natural growing environment, plants rely on the wind to spread their pollen. In a greenhouse, ventilation is necessary for the movement of plants and the release of pollen.

Resistance to pests - Poor ventilation weakens plants and makes them more susceptible to pest damage. Improper ventilation also creates moist conditions that are perfect for pests to lay their eggs. 

Types of Greenhouse Ventilation-Mechanical & Natural

To choose the right type of ventilation for your greenhouse, it is important to gain insight into the description and cost effectiveness of each type.

What is mechanical ventilation?

In mechanical ventilation, fans are installed in the greenhouse to exhaust the rising hot air. This creates a vacuum that draws cooler air through the louvers on the side of the greenhouse. When properly designed, this type of ventilation can maintain ideal greenhouse interior temperatures, even when operating in different locations and weather conditions. 

Multiple greenhouse ventilation fans should be installed to provide different rates of ventilation. Ventilation motors should also have multiple speeds to allow the user to control the ventilation rate. 

What is natural ventilation?

Natural ventilation, or curtain ventilation, uses a series of roof and sidewall vents. As the temperature inside the greenhouse rises, hot air rises and exits through the roof vents. This creates a vacuum that draws cooler air into the greenhouse through sidewall vents near the floor.

The curtain ventilation system allows air to flow across the width of the greenhouse. Since the width is the shortest dimension, the new air will stay colder than air moving along the entire length of the greenhouse, which is common in mechanical systems.

Because these systems do not require fans, they are more energy efficient and help reduce operating costs. They are also easily automated through climate control to improve crop yields and labor efficiency.

Natural vs. mechanical ventilation in greenhouses - which is better?

The costs

Cost is one of the main factors that growers use to choose the best ventilation system. While the initial set-up costs for both types of greenhouse ventilation systems are comparable, the climate controller and roll-up motor used in a curtain ventilation system consume much less electricity than a fan. This makes the daily operation of the greenhouse energy efficient and cost effective.

The size of the greenhouse

The size of the greenhouse is another factor when choosing between natural and mechanical ventilation systems. In a smaller greenhouse, less than 40 square feet, maintaining a fan ventilation system will prove to be too expensive. In greenhouses larger than 100 square feet, a mechanical system does not have the ability to effectively maintain both ends of the greenhouse at optimal temperatures. 

The season

Seasonally, there are advantages to each ventilation type. Fan cooling systems can be particularly useful in early spring when you can't open the side curtains because of snow on the ground. Meanwhile, running fans in an empty greenhouse after summer harvest to keep plastic from melting can waste electricity and push up your utility bills. During these times of the year, natural ventilation allows you to open the curtains, set it, and forget it.