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Greenhouse Cooling for Tropical and Subtropical Regions 熱帶與亞熱帶地區溫室降溫

Greenhouse Cooling for Tropical and Subtropical Regions 熱帶與亞熱帶地區溫室降溫. 方煒 台灣大學生物產業機電工程系教授 Wei Fang, Ph.D., Professor Dept. of Bio-Industrial Mechatronics Engineering National Taiwan University. Open field Rain shelter Net house. Vegetable and Flower production. Greenhouse. ?.

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Greenhouse Cooling for Tropical and Subtropical Regions 熱帶與亞熱帶地區溫室降溫

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  1. Greenhouse Cooling for Tropical and Subtropical Regions熱帶與亞熱帶地區溫室降溫 方煒 台灣大學生物產業機電工程系教授 Wei Fang, Ph.D., Professor Dept. of Bio-Industrial Mechatronics Engineering National Taiwan University

  2. Open field Rain shelter Net house Vegetable and Flower production • Greenhouse ?

  3. Cheap in construction cost Little opportunity for environment control No guarantee on quality, quantity and date of harvest Highly dependent on weather condition (high risk) Open field, rain shelter, net house露地栽培、遮雨棚、網室 • Upon entering WTO, such facilities are not acceptable in producing products to meet the highly competing international market.

  4. With the capability of environment modification is the basic requirement. Year-round production is a must. However, Outdoor T > 35 degree C is quite normal Greenhouse without proper design, indoor T > 50 degree C is possible. Crops at risk, not able to grow for at least 3 to 4 months. Greenhouse cooling is the key issue. Tropical & Subtropical Greenhouse熱帶、亞熱帶溫室

  5. Objectives • To describe • A systematic approach (ACESYS) in selecting cost effective environment modification techniques • To introduce • various environment modification techniques for tropical and subtropical greenhouses focusing on cooling

  6. Part I: Applying ACESYS on Greenhouse coolingACESYS應用於溫室降溫 • Automation • greenhouse dimension, techniques available and their limits, costs and adjustable range of each technique, • Culture • type of crops, projected quality and quantity of harvestable amount based on specific indoor weather condition. • Environment • local climate, indoor climate, etc. • Systems • budget available, market values of the selected crops, potential benefits on the quality and/or quantity of increased harvestable amount.

  7. Provide solutions to the following questions 為以下問題提供解答 • What are the affordable/effective environment modification facilities subject to available budget? 經費上限之內的最有效的環境調節方式為何？ • What are the limits on the modification of environment subject to the local agro-climate and the efficiency of the environment modification facilities? 基於當地天候與設備功能，所能調節的環境因子與範圍為何？極限為何？

  8. Provide solutions to the following questions 為以下問題提供解答 (續) • What crops can be grown in the controlled environment? 在控制環境內有哪些作物可以栽培？各自的經濟效益為何？ • What are the potential benefits that the environment modification facilities can bring? 增加環控設備可有哪些好處？增加的獲利程度為何？ • Does it cost effective to apply selected environment modification techniques in growing selected crops? 已知栽培某種作物，選擇某種環控設備是否合乎經濟效益？

  9. Part II: Environment Modification Techniques 環控技術 (強調降溫) Categories : • Design • Reducing thermal load • Ventilation • Evaporative cooling • Desiccant cooling • Refrigeration

  10. Design 設計 • Glazing • more diffuse light, less direct light • spectral selective: block NIR light • Site 避風、排水 • windbreak, • local weather, etc. • Orientation 迎風 • prevailing wind, etc. • Dimension and roof configuration • Height • % of roof vent, etc

  11. Industrial Accident

  12. Reducing Thermal Load 減輕熱負荷 • shade paint 外噴漆 • external screens and curtains 外遮陰 • internal screens and curtains 內遮陰 • screen on roof 外敷蓋 • wet screen on roof 外敷蓋(+洒水) • roof spray 屋頂洒水

  13. Shading 遮陰 外噴漆 外遮陰 外敷蓋 (+洒水) 內遮陰

  14. PAR transmitted short-wave radiation μmol/m2/s PAR per W/m2 metalized shading fabrics 20.7 % 20.5 % 2.31 multilayered film reflects near infra-red (solid) 41.1 % 33.9 % 2.78 multilayered film reflects near infra-red (screen) 43.2 % 35.6 % 2.78 Internal shading materials 內遮陰材質的比較 (PAR, 400 to 700 nm；NIR, 700 to 1100 nm) Temperature differences in greenhouse less than 0.8 degree C

  15. Shading 遮陰之降溫效果 • 外遮陰 > 外敷蓋 > 內遮陰 • 外敷蓋 + 洒水 > 外遮陰 (高度不足造成夾層通風不良) • 外敷蓋 (白) > 外敷蓋 (黑) • 內遮陰、外敷蓋 (黑)仍是最常見 • 外遮陰系統不耐強風、增加成本 • 外敷蓋系統施工容易、便宜 • 黑網便宜

  16. 通風量 才是關鍵 500 W/m2可使2m高溫室內溫度提高12度C

  17. Air changesper minute Indoor – Outdoor Temperature PE 2 5 ° C PE +外敷蓋 2 2.5 °C PE + 外敷蓋 +洒水 2 1 °C 強制通風下有無外敷蓋之比較外溫 34.5 oC

  18. Ventilation 通風 • Natural ventilation 自然通風 • location • % of side vent and roof vent • wind speed • With(out) insect screen • Forcedventilation 強制通風 • Air change per minute • With(out) insect screen • Pressure drop of the system • Fan selection/maintenance

  19. Natural Ventilation自然通風 • 自然通風溫室仰賴風速與煙囪效應來降溫，後者在熱天與低風速時主導空氣之流動。 • 屋頂有熱氣滯留時會影響下方熱氣的上升，以熱天、低風速時影響最嚴重。 • 屋頂處最好沒有熱氣滯留區，換言之，有連續的屋頂空氣出口(continuous roof vent)為最佳，開口面積愈大愈好。

  20. Natural Ventilation –自然通風continuous roof vent Ridge wing gutter wing mid. wing

  21. 太子樓 Natural ventilation –自然通風roof vent - double frame 防蟲兼通風良好

  22. Natural Ventilation –自然通風2/3 to 100% open top

  23. Natural Ventilation自然通風 • 自然通風溫室仰賴風速與煙囪效應來降溫，前者在風速高於2 m/s 情況下居主導地位。 • 設計良好的自然通風溫室需具備至少一個空氣入口與多個空氣出口，換言之，要有側窗作為空氣入口。 • 具上方開口的自然通風溫室，在迎風面與背風面的側開口關閉與打開時，在試驗條件下空氣交換率分別為 0.38 A.C./min 與0.9 A.C./min。前者之室內外溫差可高達10度C且室內空氣流通情況差，後者室內外只有 3度C溫差且室內空氣流通情況良好。

  24. Natural Ventilation自然通風 • 側開口的位置若高出作物許多且接近出口高度，將完全無法對作物達到降溫效果。空氣由側開口進入溫室至由出口離開，應經過作物區，以發揮降溫效果。 • 自然通風溫室配備內遮陰時，應確保由側窗進來的空氣可通過遮陰由上方開口逸出。

  25. Side vent Side vent greenhouse Side vent Side vent Natural Ventilation –自然通風trends forside vents at 4 ends 外舉式 Push type 捲揚式 Roll-up type

  26. fan Side vent Greenhouse Forced Ventilation強制通風 • Negative pressure type 負壓式 • Positive pressure type 正壓式 net fan Side vent Greenhouse

  27. 風扇 風扇 Insect-proof nets 防蟲網 • 熱帶、亞熱帶地區的溫室應安裝防蟲網 • 但防蟲網增加的壓降會大幅降低通風量， • 增加防蟲網面積或加大風量是必要的設計。

  28. Positive pressure ventilation正壓式強制通風 • Advantage is that airflow is out through breaks in glazing and open doorways • Design should be for internal pressure sufficient to create outward velocities greater than the flight speed of insects • Challenge is to provide uniform distribution of incoming air

  29. Insect proof nets fans Positive pressure ventilation Adapted from Mears, 2001 (Rutgers Univ.)

  30. Evaporative cooling 蒸發冷卻 • Negative pressure type 負壓式 • spray/misting • fogging • pad and fan • Pad substitutes • Positive pressure type 正壓式 • Package evaporative cooler

  31. Spraying/Misting

  32. outlet Water lines with nozzles Air inlet Fogging - nozzles sensor 動力噴霧機提供高壓 過濾器提供良好水質

  33. Fogging - nozzles

  34. Fogging - spinning atomizer

  35. Fogging fan I

  36. Fogging Fan II

  37. Fogging Fan III

  38. Fogging Fan IV

  39. Fogging Fan V

  40. Pad and Fan – 2 wrong messages

  41. T: 10 ~ 40 oC RH: 50 ~ 100% Weather of Taiwan’s plain area

  42. oC % WBD (Wet Bulb Depression) = dry bulb Temperature – wet bulb Temperature T = WBD * Efficiency Limits of temperature drop with evaporative cooling under various Tdb & RH combinations

  43. Tdb 38 C RH 55% Twb 30 C T gradient 5 C Tdb 31.6 C RH 87.5% 80% pad efficiency Fan Fan Pad and Fan – Actual condition in extreme weather of Taiwan

  44. Pad: powerful but …..

  45. Drawbacks of Pad • Expensive/Imported • Algae/deposition/mouse • Short usable life

  46. Pad substitutes - Palm tree fibers 科威特

  47. Pad substitutes – hollow Brick with fiber View from inside Fibers or scrub pads were used to fill the holes

  48. Pad substitutes –plastic cage with fiber View from inside

  49. Pad substitutes – Rolling Nets I

  50. Pad substitutes – Rolling Nets II

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