Fall 2002Biernbaum, MSU HRT 221, pg 46Air Circulation(Lecture 8)In a closed greenhouse there is little natural air movement except temperature currents fromheat stratification. The air in the greenhouse should be kept circulated to:1. Prevent temperature stratification, from roof to floor2. Provide uniform temperatures in the greenhouse3. Prevent high humidity pockets and moisture condensation on leaf surfaces4. Maintain the carbon dioxide (CO2) level around the plants.Forced air circulation should be provided. The air circulation system may be present as part of theventilation or heating system.There are three basic methods of circulating greenhouse air:1. Overhead unit heaters with horizontal fans or fan jetsFan capacity should be about one forth of the house volume.If the house width is less than 30 feet can use one, if greater than 30 feet two fansshould be used.The fans can be located in the center of the house or the ends.
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Fall 2002Biernbaum, MSU HRT 221, pg 472.Overhead unit heaters or fan jets with perforated convection tubesTube should have one square foot cross sectional area per 1000 cfm air flow.The tube is inflated and air comes out the holes.3.Horizontal air flow (HAF) (most common today)Air flow can be provided by locating several small fans around the greenhouse. The goal isto get 40 feet per minute air flow for good mixing. There usually is a fan every 50 feet withthe first fan 15 to 20 feet from the end of the house and the last one 40 to 50 feet from theopposite end of the house.Air flow can be tested by using a smoke bomb or generator in the greenhouse to check air patternsor by checking temperature uniformity around the greenhouse.