Greenhouse Supplies

Greenhouse Ventilation – Keeping the Greenhouse Cool

When looking for greenhouse ventilation options to keep greenhouses cool, it’s important to first understand why ventilation is essential. Ventilation is the exchange of inside air for outer air. The act of ventilation can control temperature, remove moisture or replenish carbon dioxide (CO2). If you’re trying to grow the healthiest plants possible in your greenhouse, establishing a proper ventilation system is essential.

Things to remember about greenhouse ventilation:
• Ventilation systems can be comprised of several different methods. However, always be careful if mixing parts of two specific systems.
• Roof vents with side inlet vents are great forms of natural ventilation. When the warm air rises on convective currents, it can escape through the top and draw cool air in via the sides.
• Most mechanical greenhouse ventilation options use exhaust fans to move the air out of one end of the greenhouse. While this occurs, the outside air comes through the other end of the house, via motorized inlet slots. For effective control, exhaust fans should be the right size to exchange the total air volume in one minute.
• To estimate the total volume of air (for medium and large greenhouses) a gardeners can multiply the floor area times 8.0 (which is the average height). A smaller greenhouse can be estimated by multiplying the floor area by 12.
• Requirements of ventilation will change from season to season. In warm summer months, the air volume changes should be 1:1, per minute. In the colder winter months, 20 to 30 percent of air volume exchanges per minute are adequate.
Greenhouse Ventilation Options
• Most often a single-speed fan won’t be able to meet the air exchange criteria needed. Instead, two single-speed fans are best, with a single-speed fan and a two-speed fan offering the best combination of ventilation rates for year-round tending.
• If a greenhouse is sold with a manual ridge vent, you’ll still need another ventilation system. The manual vent is only meant for backup purposes and shouldn’t be the main system for ventilation.
• Even with ventilation, an evaporative cooling or shade cloth might be necessary.
Evaporative coolers with fans and an evaporative pad in one box may be good options. They evaporate water, cool the air and increase humidity. Heat is removed from the air to change the water from liquid to a vapor. Many commercial greenhouses place these pads on the air inlets (located at one greenhouse end) and use exhaust fans at the other end. This allows them to pull air through the greenhouse with minimal effort.
Overall, before choosing what greenhouse ventilation options will work best for you, it may be a great idea to do research on the type of greenhouse you utilize. Talk with local gardening experts to see what works best in your regional climate, as well.

Greenhouse Supplies

Understanding Greenhouse Fans: Heating and Ventilation Basics

Greenhouse Ventilation

Fluid ventilation within a greenhouse is possible because of a combination of roof vents, side vents and (of course) the inside/outside door. When constructing (or purchasing) a greenhouse, airflow within the greenhouse is, by far, one of the most important aspects to consider.

Low-level ventilation is essential if you are trying to produce plants with dense foliage at ground level (tomatoes for example). The heat levels must be consistent as well as airflow from the fans. You must avoid stagnant air inside your greenhouse at all costs, as it will undoubtedly bring problems such as mildew on the leaves of your plants or the fruit on your trees.

Advice on Vents

Manufacturers generally supply the appropriate number of roof vents in each separate model of greenhouse. It is important to remember, the main function of a vent is to permit the warmest air to escape the greenhouse.

Side vents also offer several different options, and you must be careful which type you choose. One type of side vent offered by some of the bigger manufactures is the top hinged vent. These are a popular alternative. The main problem with most side vents is that, when open, they protrude awkwardly from the side of the greenhouse. This makes them dangerous to people who are walking the perimeter, and there are plenty of greenhouse gardeners with the battle scars to prove it! A better alternative would be a Louvered vent.

Solar Powered Vent Openers

Automatic openers are an absolute must when it comes to roof ventilation, though automatic openers are available for side vents as well. Automatic openers fitted to roof vents can help to easily overcome the problems of rapidly changing weather conditions that can catch you off guard and ruin months worth of effort, especially during the early months of Spring.

The first few months of spring can be especially harsh. An unventilated (or poorly ventilated) greenhouse can bake young seedlings and wilt the blooms and blossoms of otherwise beautiful plants. Roof vent openers are highly recommended, but you should be careful when making your purchase. Do some homework and save yourself from a later headache. Be cautious of cheap imports, there are plenty on the market and they can be unreliable.

Understanding the ins and outs of greenhouse fans, heating, and ventilation basics can help you be the best gardener around, all year long.