Ventilation and Airflow in High Tunnels
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Presented by University of Minnesota Professor and Extension Engineer Larry D. Jacobson at the 2009 Minnesota Statewide High Tunnel Conference in Alexandria, MN on Dec. 2-3, 2009.
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Ventilation and Airflow in High Tunnels
- 1. Ventilation and Air Flow in High Tunnels Presented at 2009 Minnesota Statewide High Tunnel/Season Extension Conference, Dec 2 & 3, 2009. Alexandria, MN Larry.D.Jacobson, Professor and Extension Agricultural Engineer Dept of Bioproducts & Biosystems Engineering U of Minnesota, St.Paul, MN © 2009 Regents of the University of Minnesota
- 2. Presentation Outline Ventilation principles Natural vs. Mechanical High Tunnel application Manual control Automated (temperature) control © 2009 Regents of the University of Minnesota
- 3. Ventilation of High Tunnels Needed to Control Heat & Moisture © 2009 Regents of the University of Minnesota
- 4. Target Temperatures Table 2. Approximate Temperatures for Best Growth and Quality of Selected Vegetable Crops.* Temperature (ºF) Crop Maximum Optimum Minimum 85 55-75 45 Onion, Garlic 75 60-65 40 Beet, Broccoli, Cabbage, Chard, Radish 75 60-65 45 Carrot, Lettuce, Pea, Potato Snap Bean, Lima Bean 80 60-70 50 90 65-75 60 Cucumber 80 70-75 65 Tomato, Sweet Pepper 95 70-85 65 Eggplant, Hot Pepper, Okra *Adapted from Knott's Handbook for Vegetable Growers. Lorenz and Maynard. 1988. P 70. © 2009 Regents of the University of Minnesota
- 5. Warm Air Holds More Moisture Air expands as it is heated and can absorb more moisture. © 2009 Regents of the University of Minnesota
- 6. Moisture-Holding Capacity of Air Every 18 F increase doubles moisture holding capacity Air temperature (F) © 2009 Regents of the University of Minnesota
- 7. Ventilation principles Natural Ventilation Driving Forces – Thermal Buoyancy Wind Mechanical Ventilation Driving Force – Fans © 2009 Regents of the University of Minnesota
- 8. Natural Ventilation – Buoyancy Driven Case Warm Air Cool Cool Air Thermal Buoyancy Air © 2009 Regents of the University of Minnesota
- 9. Natural Ventilation – Wind Driven Case Wind © 2009 Regents of the University of Minnesota
- 10. Natural Ventilation needs both an inlet and outlet Outlet Inlet © 2009 Regents of the University of Minnesota
- 11. Inlets for High Tunnels © 2009 Regents of the University of Minnesota
- 12. End Wall Outlet Vent © 2009 Regents of the University of Minnesota
- 13. Ridge type “Outlet” for High Tunnel © 2009 Regents of the University of Minnesota
- 14. Manual Control of sidewall Inlets High-low thermometers Remote thermometer (read out in home/office © 2009 Regents of the University of Minnesota
- 15. Automated Temperature sensor and Inlet Controller © 2009 Regents of the University of Minnesota
- 16. Mechanical Ventilation – Negative Pressure - Negative (A) © 2009 Regents of the University of Minnesota
- 17. Seal up corners (leaks) so can control roll up sidewall “inlets” Before After © 2009 Regents of the University of Minnesota
- 18. Mechanical Ventilation © 2009 Regents of the University of Minnesota
- 19. Summary Natural Ventilation is probably preferred in High Tunnels because of cost and difficulty to seal up all the leaks Temperature control is primary need for ventilation, moisture control secondary Manual ventilation control challenging but possible Simple aid might be remote thermometer Automated controller for sidewall inlets would yield tighter temperature control © 2009 Regents of the University of Minnesota
- 20. Questions © 2009 Regents of the University of Minnesota
- 21. Inlets and Outlets © 2009 Regents of the University of Minnesota