利用驗證後之計算流體力學模式評估窗戶位置與排氣量對家用排油煙機效能之影響

Abstract

研究背景及目的：烹飪不僅是室內空氣汙染的主要來源之一，長期暴露於烹飪汙染物也會對健康產生負面影響。而除了使用排油煙機能有效地移除烹飪汙染物之外，文獻回顧中發現，烹飪時打開窗戶也有助於廚房內外空氣流通，稀釋汙染物濃度。而現今對排油煙機的研究多集中於探討排氣流率以及造型的影響，尚缺乏針對家戶廚房中窗戶位置對廚房排油煙機效能的影響作研究評估。故本研究目的為使用經過驗證的計算流體動力學 (CFD) 方法，將二氧化碳作為烹飪汙染物的替代物，以探討窗戶位置與排氣量對家戶廚房內氣流流動特性、汙染物濃度分佈以及排油煙機捕集效率之影響。 方法：本研究將透過二氧化碳及溫度於穩態時所測量的數值與使用CFD模擬之結果作驗證比較。而符合驗證標準後的基本模型將用於模擬12種設定條件下，廚房內氣體流動結果。設定條件包含2種高度(1.2、2.4 m)及3種方向(前、側、後)的窗戶設置位置以及排油煙機的原始高低流率 (6.72、12.16 m3/min)，共12組案例。二氧化碳將作為室內空氣品質指標以計算排油煙機捕集效率以及探討每個模擬案例之間的差異性。 結果與討論：在模型驗證的部分，模擬值與實驗值之間的差異率在四個測量點處皆小於可接受標準 (10%)。而後在12個模擬案例中，在窗戶高度方面，觀察到當窗戶高度設置在2.4 m時，可以更有效地降低CO2濃度。探討3種窗戶方位的對抽油煙機效能的影響時，廚房中汙染物在開前窗時地濃度最低，且捕集效率皆高於80%，其次是後窗和側窗。另外，隨著排氣量從6.72 m3/min增加到 12.16 m3/min，所有窗口位置的捕集效率均可達到75%以上。 結論： 整體而言，改變窗戶與排油煙機的相對位置有助於改善廚房的整體通風，降低污染物濃度。透過本研究能更進一步提供在降低排氣流率與能源成本的情況下也能減少居民暴露於烹飪汙染物的方法。

Introduction: Studies have shown that cooking emissions would influence indoor air quality and cause adverse health effects on the human body. The kitchen hood is a common and effective intervention to remove harmful substances, meanwhile, previous studies showed that opening windows could also help with kitchen ventilation in pollutant removal. However, no studies have systematically examined the impacts of window positions on kitchen hood performance, and there is insufficient information on indoor airflow characteristics and pollutant distribution from makeup air through open windows. Therefore, the objective of this study was to use a validated computational fluid dynamic (CFD) approach with CO2 as a surrogate for cooking emissions to understand the impacts of exhaust flow rate and the window opening position on the flow characteristics, concentration distribution, and capture efficiency (CE) of the hood. Method: We conducted four-point validation tests by comparing the numerical and experimental results based on CO2 concentration and temperature measurements under steady state conditions. The validated models were subsequently used in simulations to understand the effects of six different window opening positions and the two exhaust flow rates on exposure. CO2 was used as the IAQ indicator in order to understand the difference between each simulation cases. Results and discussions: The results of the model validation were considered acceptable, the difference ratio between the simulation and experimental results were under 10% at four measure points. Among 12 simulation cases, we found that the CO2 concentration could be better reduced by having windows open at the higher location. Generally, the front windows were found to be more effective with CE >80%, followed by the back and the side windows, respectively. We also found that as the exhaust flow rate increased from 6.72 to 12.16 m3/min, CE reached >75% for all window positions, where the largest increase was 1.58 times for the lower side window. Conclusion: In sum, changing the relative position of the window and the exhaust hood could help disperse the incoming airflow from the window, improve the kitchen's overall ventilation, and reduce contaminant concentration. Findings from this study provide important implications that when the architectural configuration was arranged correctly, the hood performance could be well improved to protect residents from exposure to cooking emissions, even under the low exhaust flow rate with reduced energy cost.