Weitere ähnliche Inhalte Mehr von University of Minnesota-Horticulture (20) Kürzlich hochgeladen (20) Ventilation and Airflow in High Tunnels1. 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
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3. Ventilation of High Tunnels Needed
to Control Heat & Moisture
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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.
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5. Warm Air Holds More Moisture
Air expands as it is heated and can absorb more moisture.
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6. Moisture-Holding Capacity of Air
Every 18 F increase
doubles moisture holding
capacity
Air temperature (F)
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7. Ventilation principles
Natural Ventilation
Driving Forces –
Thermal Buoyancy
Wind
Mechanical Ventilation
Driving Force –
Fans
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8. Natural Ventilation –
Buoyancy Driven Case
Warm
Air
Cool Cool
Air Thermal Buoyancy
Air
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14. Manual Control of sidewall Inlets
High-low thermometers
Remote thermometer
(read out in home/office
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17. Seal up corners (leaks) so can
control roll up sidewall “inlets”
Before After
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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