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

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

Open field, rain shelter, net house 露地栽培、遮雨棚、網室 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) Upon entering WTO, such facilities are not acceptable in producing products to meet the highly competing international market.

Tropical & Subtropical Greenhouse 熱帶、亞熱帶溫室 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.

Objectives To describe To introduce 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

Part I: Applying ACESYS on Greenhouse cooling ACESYS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.

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？

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？

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

Design 設計 Glazing Site 避風、排水 Orientation 迎風 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

Industrial Accident

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

Shading 遮陰 外噴漆 外遮陰 內遮陰 外敷蓋 (+洒水)

Internal shading materials 內遮陰材質的比較   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 % (PAR, 400 to 700 nm；NIR, 700 to 1100 nm) Temperature differences in greenhouse less than 0.8 degree C

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

通風量 才是關鍵 500 W/m2 可使2m高溫室內溫度提高12度C 室外溫度 35度C PE 溫室內溫度 (無通風) 52度C 通風量 才是關鍵 室外溫度 35度C PE 溫室內溫度 (無通風) 52度C 玻璃溫室內溫度 55度C 500 W/m2 可使2m高溫室內溫度提高12度C

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

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

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。

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

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

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

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。

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。

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

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

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。 風扇

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

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

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

Spraying/Misting

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

Fogging - nozzles

Fogging - spinning atomizer

Fogging fan I

Fogging Fan II

Fogging Fan III

Fogging Fan IV

Fogging Fan V

Pad and Fan – 2 wrong messages

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

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

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

Pad: powerful but …..

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

Pad substitutes - Palm tree fibers 科威特

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

Pad substitutes –plastic cage with fiber View from inside

Pad substitutes – Rolling Nets I

Pad substitutes – Rolling Nets II

Pad substitutes - Multi-layer Nets View from outside View from inside Fogging is better than spray

複合式蒸發冷卻 風扇+多層網 + 中間噴霧 + 濕式外敷蓋 外敷蓋之遮陰比例視作物需光量而定

Package evaporative cooler Downward model: Wood wool at 4 ends Sideward model: Wood wool at 3 ends 木絲

Package evaporative coolers work well with plastic tubes

Package evaporative cooler positive pressure type

Desiccant cooling 除濕冷卻 Dehumidification of incoming air using desiccant Collect thermal energy from greenhouse attic (between inside curtain and roof) Use collected thermal energy to recover desiccant

Schematic diagram of desiccant cooling Dehumidifier Regenerator Pump Hot water or air Cold water Fresh air Fresh dried air to greenhouse Outdoor air in Outdoor air out

Application of desiccant cooling in greenhouse Attic Hot air Heat exchanger weak solution dark solution Regenerator Dehumidifier

Refrigeration – water chiller Water chiller with evaporator in greenhouse flower forcing of Phalaenopsis (蝴蝶蘭催花) 金針菇栽培 木耳、香菇、秀珍菇等在夏季維持適當的日夜溫差

Inside shading closed when AC turned on.

Flower stalk forcing in greenhouse

Refrigeration – Bottom cooling Bench top lines of tubes filled with cold water (使用冰水機) switching between hot and cold water whenever in need (配合使用熱水機) Seedling production only

Refrigeration – Bottom cooling Concept borrowed from floor heating Temperature in degree F

Conclusions I Greenhouse capable of continuously year-round production is the basic requirement in the highly competing international market.

Conclusions II Technically feasible is not enough, economically feasible is vital. An ACESYS systematic approach in looking for cost effective cooling system was introduced. Various cooling methods were described. Combinations of systems can be effective. Evaluation of cooling system must based on value engineering

Value Engineering Value = Capability (problem * cost) 方煒 台灣大學生物產業機電工程系