風管中即時殺菌單元風洞暨實場測試

Validation of Real-Time Sterilization Unit Using in Ventilation Duct under Wind Tunnel and Field Study

溫欣然(Hsin-Jan Wen)

指導教授 ： 賴全裕

中山醫學大學/健康管理學院/職業安全衛生學系碩士班/碩士(2015年)

https://doi.org/10.6834/CSMU.2015.00160

摘要

一般通風管道內潛藏多種細菌及真菌，顯見通風管道雖在進氣口設有高效率濾材，但在冗長的通風管道內可能因有其他污染，導致空調設備在室內新鮮空氣出風口端，可採集得數量不少的細菌及真菌。而醫療院所隨時皆有住院及門診病患，並無法如同一般工廠可以停廠或歲休進行消毒工作，所以在通風管道內之消毒殺菌工作益顯困難。

本研究以即時殺菌單元進行風洞測試及實場測試。在風洞測試方面：實驗使用大腸桿菌及枯草桿菌作為挑戰氣膠，並配合卡里遜噴霧器（Collison nebulizer）產生挑戰氣膠。實驗中並使用Am-241，將剛產生之氣膠微粒中和至波茲曼電性中和分佈（Boltzmann charge equilibrium），採用海綿及鎳篩網捕集細菌，並輔以紫外光作為殺菌單元。生物氣膠殺菌效率之比較方面，利用安德森（Andersen）單階採樣器及安德森（Andersen）六階進行採樣培養。實驗結果顯示此即時殺菌單元搭配海綿濾網或是鎳篩網皆有良好的殺菌能力。

在實場測試方面：選擇中部某部立醫院兩間病房及一間護理站，先進行安裝殺菌單元前背景細菌、真菌分佈濃度測試，並接著選擇安裝鎳篩網－紫外光殺菌單元，進行安裝後細菌、真菌分佈濃度測試。生物氣膠粒徑分佈、殺菌效率之比較方面，主要利用安德森單階採樣器（Andersen 1-stage sampler）、安德森六階採樣器（Andersen 6-stage sampler）、AGI-30、Biosampler及氣動粒徑分析儀（aerodynamic particle sizer, APS）進行採樣及培養計數。本研究選擇不同管道表面風速進行比較測量，也量測管道內濕度、溫度變化，並比較紫外光殺菌率、燈管衰減率與損耗功率，以及鎳篩網老化程度。

結果發現安裝殺菌單元的病房，鎳篩網在未披覆矽油時，在風管風速2.4∼3.5 m/s時會造成氣膠彈跳現象，使得4.7 μm (以六階安德森採樣器截取粒徑為例)以上大粒徑範圍氣膠捕集率下降；而在風管風速1.4∼1.9 m/s時，反而因為機械力之過濾捕集機制無法發揮，無法針對小於1.7 μm以下之生物氣膠進行捕集殺菌。因此在鎳篩網未披覆矽油時，風管風速1.4∼3.5 m/s範圍內，最佳生物氣膠捕集殺菌範圍為1.7∼4.7 μm，而安德森六階生物氣膠採樣器在三間採樣地點評估平均細菌殺菌率為67.7 %；安德森單階採樣器評估細菌殺菌率平均約為40.8 %；AGI-30採樣器評估細菌殺菌率平均約為99.3 %。紫外光的能量功率則在90小時之後衰減至原有功率4∼9 %左右。另外將經暴露123小時之後的鎳篩網聯片進行抗拉試驗，結果所測得的抗拉荷重只剩原有強度約78 %。研究建議鎳篩網殺菌裝置應有矽油披覆，以防止大粒徑生物氣膠彈跳，並應裝載於中央空調系統之主要高速管道，以提升鎳篩網機械力捕集過濾機制。而殺菌單元可以選擇性開啟紫外燈數分鐘進行殺菌，不必持續開啟，避免紫外光快速衰減能量，及降低鎳篩網之強度結構，也可以減少能量損耗。

關鍵字

中央空調 ； 風洞 ； 醫院 ； 殺菌

並列摘要

The recent studies have shown high concentration of bacterial that sampled from the HVAC (heating, ventilating, and air conditioning) system was observed in the hospital, included clinics, wards, emergency department, and dentistry clinics. Obviously, the HVAC systems in above cases were poorly sterilized and had bred microorganisms in the ducts. However, an ideal HVAC system not only can provide comfortable environment for medical employees, but also should reduce the concentrations of bioaerosols. As it is hard to evacuate the whole hospital patients and then sterilize the ventilation ducts, a real-time sterilization unit that located in the ventilation ducts is a critical method to control the bioaerosol-transmitted infections in hospitals.

The objective of this research was to develop a real-time sterilization unit and evaluate the unit under wind tunnel system. The real-time sterilization unit consists of porous filter media and UVGI (ultraviolet germicidal irradiation) modules. A Collison nebulizer was used to generate Bacillus subtilis spores and Escherichia coli as challenge aerosols. A radioactive source, Am-241, was used to neutralize the challenge particles to the Boltzmann charge equilibrium. Andersen 6-stage samplers were used to sample bacteria concentration upstream and downstream of the new real-time sterilization unit. The results showed the new real-time sterilization unit could be used to reduce the bacteria concentration; however, the unit still needs to be studied under field conditions.

The research installed real-time sterilization units in the ducts of the HVAC system. Two hospital wards and one nurse station located in central Taiwan were recruited in the experiment. Andersen 1-stage, 6-stage samplers, AGI-30, Biosampler and aerodynamic particle sizer were used to measure bacteria and fungi concentration from supplying air before and after installing the real-time sterilization units. The test conditions included different face velocities, and measured the duct condition: relative humidity and temperature. The attenuation rate of ultra violet germicidal irradiation (UVGI) and ageing effect of Nickel-filter-based real-time sterilization unit had also be taken into account.

The result showed that the non-coating Nickel-filter-based real-time sterilization unit revealed large size aerosol bounce during air duct velocity between 2.4 to3.5 m/s. This phenomenon decreased the collection efficiency when aerosol larger than 4.7 μm (based on the cutoff size of six-stage Andersen impactor). However, the non-coating Nickel-filter-based real-time sterilization unit revealed small size aerosol penetrating through it during air duct velocity between 1.4 to1.9 m/s. The fact decreased the collection efficiency when aerosol smaller than 1.7 μm, and this could be concluded as failure of mechanical filtration force for the period of low sampling velocity. Therefore, the possible collection and disinfection range of the non-coating Nickel-filter-based real-time sterilization unit was about 1.7 to 4.7 μm. The average bacteria disinfection rate of two wards and nurse station of six-stage Andersen impactor, single-stage Andersen impactor, and AGI-30, was 67.7 %, 40.8 % and 99.3%, respectively. The attenuation rate of four-9W-UVGI after 90-hour-irradiation was between 91 to 96 %. Moreover, the tensile strength of Nickel-filter was decreased to 78 % after 123-hour-UVGI-irradiation. The results recommended that the Nickel-filter-based real-time sterilization unit should coat with silicone oil to avoid the large aerosol bounce effect, and was better to use the unit in main ducts under high face velocity. Furthermore, in order to avoid the attenuation of UVGI, to save the energy, and to maintain the tensile strength of Nickel-filter, the UVGI of the Nickel-filter-based real-time sterilization unit was suggested not lighting on all the time.

並列關鍵字

HVAC ； wind tunnel ； hospital ； sterilization

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