使用計算流體力學分析臺灣負壓水簾隧道式通風籠飼蛋雞舍的室內空間配置

Abstract

臺灣位處北回歸線副熱帶地區，長年氣候高溫多濕，然而，高溫多濕的氣候並不適合蛋雞，雞隻遭受熱緊迫時將造成呼吸急促，需耗費大量額外能量來散熱，破壞動物體的持衡，導致產能下降，甚至最終產生疾病或死亡。本研究選擇籠飼蛋雞舍 原因是蛋雞在臺灣的產蛋服役時間長達 1.5 年甚至更久，且臺灣蛋雞在養隻數將近全國人口數的兩倍，於民國 110 年已達 43,831 千隻，雞蛋可完全自給，而籠飼是臺灣主要飼養蛋雞的形式，籠飼的飼養密度於同一空間的飼養比平飼高，要達到蛋雞舒適的環境更為困難。蛋雞的養成需要 18 週以上，若因舒適度不佳發生疾病或死亡，將會是農民巨大的損失，同時也違反了動物福祉五大自由中的四項自由 - 免於身體不適的自由、免於身體不適的自由，免於痛苦、傷害和疾病的自由， 以及表現自然行為之自由。 目前較先進的負壓水簾隧道式通風環控雞舍，能透過感測器來自動調整風扇開關的模式、水簾的開關、屋頂擋流板的升降、側窗的開啟角度等。負壓水簾隧道式通風環控雞舍僅能利用水簾進行直接蒸發降溫，也就是利用冷水吸熱蒸發帶走空氣熱能的方式來降低進入室內的空氣溫度。我們認為水簾在副熱帶地區的效果需要被重新檢視，副熱帶的氣候潮濕，大氣濕度往往很高或接近飽和，這使得水簾降溫的效果大幅下降，臺灣尚無研究負壓水簾隧道式通風環控蛋雞舍最佳化配置的文獻，即便此類雞舍在國外有相當數量的研究，我們認為副熱帶的氣候是獨特的，與國外相同的雞舍設計在副熱帶氣候下運行的狀況值得另外研究探討臺灣環控雞舍現況為沒有使用任何除濕設備 (例如 : 添加乾燥劑的水簾、除濕機)，僅透過通風來調節舍內濕度，雞舍基於成本考量不可能使用空調降溫，僅利用水簾及通風來降溫，冬季則會燃燒瓦斯來給雞隻保溫。 本研究致力於利用計算流體力學 (CFD) 模擬負壓水簾隧道式通風環控雞舍在副熱帶地區夏季的實際降溫效果，進一步找出最適合的室內通風配置，例如改變水簾裝設位置、調整水簾之水溫與用水量、調整蛋雞舍高度及風扇來提升室內雞隻平面的舒適度 (風速、溫度及濕度)。 我們得出的結論是，安裝一個前置水簾和兩個側邊中間水簾（Model A-1.4，Pad 1&4&5）在這個雞舍模型中可以得到最佳的 THI。在臺灣夏天，這個負壓水簾隧道式籠飼蛋雞舍最佳每平方米水簾面積的質量流速為1.28×10-3 (m-2 kg s-1)。在本研究中，空氣和水簾出水之間的溫差為 8℃ 時可以產生最佳的蒸發冷卻效果。保留籠頂與天花板之間的空間亦很重要，我們建議在籠子上方保留 2.3 米的空間，相比 0.8 米的空間顯著改善風速的均勻性。風扇安裝在下排（在動物層）可以為蛋雞創造更佳的熱舒適指數，比在上排安裝風扇更理想，但差異不顯著。 綜上所述，水簾的位置、雞舍的高度（籠頂和天花板之間的距離）和水簾的水溫是三個最重要的變量，對雞舍內部環境舒適度影響顯著。我們發現研究案例中探討的所有因素皆相互緊密關聯，共同影響室內環境，這表示每個負壓水簾隧道式籠飼蛋雞舍應進行獨立的模擬才可以確定最適合自己具體條件的配置。 本研究的貢獻為提供臺灣及副熱帶地區現有或未來雞舍配置與通風設備運作模式建議，以達到最佳產蛋量、農民經濟效益以及蛋雞動物福祉的三贏局面。

Taiwan is located in tropical region where the climate is hot and humid all year round. However, Taiwan's high temperature and high humidity is not suitable for laying hens. The reason why we choose the caged laying hen as a research object is that it takes about 1.5 years for laying hens to produce eggs, and the number of laying hens in Taiwan was increasing and had reached 43.8 million in 2021, nearly twice the national population. In Taiwan, the most prevalent way to raise laying hens is cage housing, yet cage housing requires more effort to maintain the thermal comfort due to the higher raising density than floor raising. When chickens suffer from heat stress, it will cause Tachypnea, dissipate heat by draining excessive energy, reduce production efficiency, destroy the homeostasis of hen body, and cause diseases or deaths in a predictable future. It takes more than 18 weeks for laying hens to reach puberty and lay the first egg. If the disease or death occurs due to environmental issues, it will be a massive loss for farmers and violate the concept of raising comfort mentioned in the Five Freedoms of Animal Welfare (FFAW) at the same time. At present, the standardized Negative Pressure Tunnel Ventilation (NPTV) laying hen houses consist of two systems: Evaporative Cooling Pad System (ECPS) and Tunnel Ventilation System (TVS). Cooling pads can be used for direct cooling, and the cold water in them takes away the heat in the air by evaporation to help lower the inlet air temperature of laying hen houses. However, the climate in Taiwan is humid, and the Relative Humidity (RH) of ambient air is usually very high and close to saturation, which greatly reduces the cooling efficiency of cooling pads. Therefore, the effectiveness of cooling pads and the layout need to be improved. Though, there are a considerable number of studies on how to improving the layout of Negative Pressure Tunnel Ventilation (NPTV) laying hen houses, no similar research has ever been conducted in Taiwan. For the reason that the climate in Taiwan is like that of many countries in Southeast Asia, the environment for the raising comfort we try to create in laying hen houses needs to fit in with the hot and humid climate of Taiwan, so further researching and analyzing is necessary. Concerning the raising cost, the current industry status of domestic laying hen houses can neither use air-conditioners to cool down indoor air, nor dehumidifying equipment (such as cooling pads with desiccant, dehumidifiers, etc.) to improve the effectiveness of evaporative cooling. Farmers can only use NPTV and ECPS to improve the indoor comfort level. This study is devoted to using Computational Fluid Dynamics (CFD) to simulate the actual NPTV cooling effect in a Negative Pressure Tunnel Ventilation (NPTV) laying hen house equipped with cooling pads, find the most suitable indoor ventilation configuration for summer by changing the installation position and location of the Evaporative Cooling Pad System (ECPS) that works with NPTV, and the process to go through is to adjust the house height, fan positions, and lower the water temperature of cooling pad to improve the comfort level of the laying hens in the house (temperature, relative humidity, air velocity and uniformity). We conclude that the install one front pad and two side middle pads (Model A-1.4, Pad 1&4&5) can meets the best THI. We have identified the optimal Mass Flow Rate per Pad's Vertical Face Area is 1.28×10-3 (m-2 kg s-1) in this NPTV laying hen house in summer. Temperature difference of 8℃ between air and Pad water in this study can perform best evaporative cooling effect. Maintaining space between the cage top and the ceiling is crucial, and we suggested 2.3m space above the cages significantly improved the uniformity of the air velocity compared to 0.8m space. Installing fans in the lower row (at the animal level) can create a more favorable thermal comfort index for laying hens compared to installing them in the upper row, but shows no significance difference. The placement of evaporative cooling pads, the height of the house (specifically, the space between the top of the cages and the ceiling), and the water temperature of the evaporative cooling pads are three significant variables that substantially affect the internal conditions of the laying hen house. The factors explored in our case studies are interconnected and together affect the indoor environment, suggesting that each NPTV laying hen house should carry out individual simulations. This way, they can determine the most suitable configuration tailored to their specific conditions. The contribution of this study is to provide suggestions of existing or future laying hen house configuration that includes ECPS working with NPTV in Taiwan, in order to achieve a win-win situation for farmers and laying hens - economic benefits for farmers and animal welfare for laying hens.