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.

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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  • 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