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How To Size Your Greenhouse Solar Fans

Updated: Apr 13, 2022

Greenhouses have been one of the biggest trends in agriculture for a long time. Farmers using greenhouses come into many challenges while trying to perfect the crops they are growing - temperatures, humidity and fresh air are some of those challenges.

While some of us rely only on natural ventilation to suppress the high temperature inside the greenhouse, we can see more and more enthusiasts are turning to a good solar fan for a better active control over the living environment of the plants.

When solar fan is used, it also helps to remove high levels of humidity by removing vapors generated, preventing mold and improving the plant quality.

Create The Best Microclimate for Your Plants Using Solar Fans

The hot air accumulated inside the greenhouse will result in poor growth for the plants. Solar fan helps you to remove the excessive stale air effectively under any weather conditions, creating a slight vacuum and replenishing the air with fresh and cool breeze in the surrounding through the openings and cracks (or a designated inlet). This can be achieved by installing the exhaust closer to roof (and inlet closer to floor, if any), as the hot air will float due to the buoyancy. To maximize the air exchange rate (which is usually expressed in CFM — Cubic Feet per Minute), we can make the inlet and exhaust on walls opposite to each other such that most of the air inside the greenhouse can get replaced.

The Math Behind to Optimize the Ventilation

Improper sizing of the solar fan or having the wrong setting will probably either shoot up the electricity consumption or just have ineffective ventilation. Are you getting headache for the numbers and calculations coming up? No worries, we will walk through the math here step by step and help you to get the correct numbers.

1. Get the Total CFM You Need

The CFM required is always decided by the size of your greenhouse. A study of University of Massachusetts suggested the CFM should be twice of the floor area. For example, the CFM required for a 30’×30’ greenhouse will be 30×30×2 = 1,800 CFM. Some other bloggers would suggest an even higher multiplication factor - like 5 times or even 7 times of the floor area for larger greenhouse, that is 30×30×7 = 6,300 CFM - depending on the crops growing in the greenhouse.

It is always good to have 10% more CFM to make up for the size of the openings and the number of plants you have.

2. Knowing the CFM of Fans

The total maximum CFM can be provided by the fans should be larger than the CFM required obtained in Step (1) to accommodate the unpredictable extra demand on ventilation when needed. It is good to install more than one fan such that achieving different levels of ventilation can be easier. Taking the 30’×30’ greenhouse as an example, to get 1,800 CFM, we can install 2 units of 14” OmniPV solar fan with 1,200 CFM each to easily achieve 2,400 CFM. For increasing air exchange demand, 24” OmniPV solar fan for intense cooling is also available, providing maximum of 5,885 – 7,652 CFM which is best working with larger greenhouse. The OmniPV solar fans are all very easy to install. With brushless DC motor equipped, they can have longer service life and bring quiet operation to your greenhouse. The fans are also specially designed to serve in high humid environment without getting corrosion too.

The sun doesn’t shine 24 hours a day so having a battery backup is important. With our battery upgrade you are able to use The OmniPV solar fans up to 24hrs a day and they also have a unique optional thermostat you can set to 75 degrees F.

Still confused? Feel free to contact us and our specialist will be more than happy to assist you with the full set of solution.

“OmniPV is a team of clean energy enthusiasts who has a strong commitment to provide the best service and high-quality products to our customers”

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