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IX. REDUCING GREENHOUSE TEMPERATURE

IX. REDUCING GREENHOUSE TEMPERATURE. A. temperature regimes range 50-80 deg, stress above 90 deg. Greenhouse effect. B. Temperature in greenhouse determined by:. 1. Solar energy Greenhouse effect: Solar energy- short wave radiation passes through glass

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IX. REDUCING GREENHOUSE TEMPERATURE

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  1. IX. REDUCING GREENHOUSE TEMPERATURE A. temperature regimes • range 50-80 deg, stress above 90 deg

  2. Greenhouse effect

  3. B. Temperature in greenhouse determined by: 1. Solar energy • Greenhouse effect: • Solar energy- short wave radiation passes through glass • Thermal radiation- longer waves trapped • shading in greenhouse • time of year • time of day

  4. 2. Exterior ambient temperature 3. Moisture transpired • Temperature in empty greenhouse greater than in greenhouse with plants 4. Evaporation of water from soil, walls etc.

  5. C. Techniques to reduce temperature • Shading - reduce energy absorbed a. Shading compound • Permanent shade after application • Removed Aug – Sept b. Shade curtain • Remove during cloudy weather

  6. 2. Greenhouse ventilation a. Definition • movement of outside air through greenhouse b. Characteristics of ventilation system 1) capacity to reduce temperature 2) uniform temperature 3) automated 4) minimum and maximum ventilation

  7. c. Time of year • Winter ventilation • Late fall, winter, early spring: • outside air cool • Minimum to maximum ventilation usually adequate • Summer ventilation • Temperature control difficult • Shading and ventilation • Maximum ventilation

  8. d. Types of Systems 1) Natural ventilation • Establish convection currents • Ridge vent and side vents • Open area -40% of floor space • Removable side wall • Removable roof

  9. Natural ventilation

  10. Natural ventilation

  11. Natural ventilation

  12. Natural ventilation

  13. 2)Motorized Systems - minimum • Mix cold with warm ghs. air • Poly tube system with vent • Low speed fan with vent • One fan or several turned on, with vent 3)Motorized systems – maximum • Outside directly into greenhouse • Temperature dependent • Air flow rate -3/4 to 1 1/4 air ex. /min -7-8° rise

  14. Air exchange vs temperature

  15. e.Control of Systems 1)Natural ventilation Manual Automatic Thermostat Computer 2) Motorized ventilation • thermostats • fan(s) 1 or 2 speed • Vents • Fully open or closed • modulating

  16. 3)End wall ventilation 1) Fans on one end wall 2) Vents on other end wall 3) Fan spacing 25’ 4) 1 air exchange/min

  17. 4) Side wall ventilation • problem mixing cold air • Air exchange rate vs velocity • 1 exchange 30’ x 100’ -end wall - 100 ft/min -side wall - 30 ft/min • Fan spacing- max 25 ft

  18. Side wall ventilation

  19. Natural ventilation

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