空氣清淨機效能測試方法與濾材佳化設計研究

Abstract

在ANSI/AHAM AC-1-2020測試標準中，乾淨空氣供給率(Clean Air Delivery Rate, CADRC)可以做為評估一台空氣清淨機性能的指標。CADRC需要在特定測試艙中測量，其過程繁瑣且耗時。然而CADR也可以透過量測空氣清淨機流量和過濾效率之乘積得出，此方法於本研究稱為CADR equivalent (CADRE)，本研究進行此兩種方法比較和優缺點分析。 將空氣清淨機放置於測試艙成為50×50×60 (cm3)長方體結構的壓克力腔。使用恆定輸出器產生單一或多粒徑分布DEHS微粒進入測試艙，將初始濃度分別控制在100或5000 #/cm3，開啟混合風扇一分鐘將艙內的微粒混合均勻後關閉風扇，接著使用凝結核微粒計數器(CPC)以每秒鐘記錄1筆資料測量共10分鐘，分別量測微粒自然衰減常數(Kn)與在空氣清淨機的效率常數(Ke)，兩個常數相減後乘以測試艙體積即為CADRC。濾材過濾效率透過SMPS與APS量測空氣清淨機的上游及下游濃度，並使用乾式流量計量測空氣清淨機流量，將過濾效率與流量相乘以計算出CADRE值，最終針對兩種測試方法進行分析與比較。 對於次微米大小的微粒，因主要的過濾機制為擴散作用，當過濾風速減少時，微粒停留濾材時間變長而使過濾效率增加；對微米級微粒則隨著風速增加，慣性衝擊機制增強而使過濾效率增加。當測試微粒為單一粒徑時，CADRE與CADRC呈1:1線性關係；當CADRE使用最易穿透粒徑(MPPS)之過濾效率計算時，CADRC則維持多粒徑分布，因MPPS下過濾效率最差而導致CADRC會高估CADRE約59 %；若CADRC與CADRE皆使用多粒徑分布微粒測試，則CADRC會比CADRE平均低估約13 %。隨著空氣清淨機在測試艙內開啟的時間越長，艙內粒徑分布會越小且越趨近於MPPS，CADRC則會因測試微粒越遠離MPPS或GSD越大而被高估。 兩種測試方法在單一粒徑、多粒徑分布與MPPS下皆具有穩定的線性關係。相較於傳統AHAM測試方法，CADRE為更快速、有效且全面的測試方法，其可以獲得完整過濾效率曲線，藉此找到MPPS以計算最保守之CADR值。未來盼能將CADRE作為CADR的輔助測試方法以彌補現有測試方法之限制，並實際評估各式種類空氣清淨設備之效能。

In ANSI/AHAM AC-1-2020, Clean Air Delivery Rate (CADRC) is a measure of the appliance’s ability to provide filtered air. The CADRC measurement needs to be carried out in a standard AHAM chamber, following a tedious and time-consuming procedure. An alternative method is developed using the product of the flow rate and the filtration efficiency of the Air Cleaners (ACs). This product is named equivalent CADR (CADRE). The pros and cons of these two methods are then compared and analyzed. A small chamber, 50×50×60 (cm3) was built to substitute the standard AHAM chamber. A constant output aerosol generator was used to generate DEHS particles. The particles would be selected by DMA if the monodisperse aerosol is needed. The initial concentration was controlled at about 100 or 5,000 #/cm3 when using monodisperse and polydisperse aerosol respectively. A mixing fan was used to uniformize the aerosol concentration in the chamber. The natural decay rate (Kn) and the total decay rate (Ke) were then measured using a condensation particle counter, to determine the CADRC. The aerosol number concentration and size distribution upstream and downstream of the AC were measured using a scanning mobility particle size and aerodynamic particle sizer spectrometer to obtain the filtration efficiency as function of particle size. The flow rate of AC was measured using a gas meter with a special design to offset and balance the air resistance of the gas meter. The statistical analysis was conducted to compare the experimental data of these two performance testing methods. For a given filter, the filtration efficiency increases with decreasing velocity because of a longer retention time with the filter media. This is particularly true for submicron-meter sized aerosol particles because the main filtration mechanism is diffusion. Notice that the CADRE and CADRC should be identical if the test aerosol is monodisperse. The CADRC is always higher (59% in this work) than the CARDC if the MPPS is used. If the whole size distribution of the challenge is included, the CADRC is 13% lower than CADRE. This mismatch becomes more significant if the spread of the test aerosol increase, i.e., higher geometric standard deviation. Through simulation, the longer the operation of the air cleaner, the particle distribution would be smaller and closer to MPPS. CADRC would be overestimated if the testing aerosol is far from MPPS or lager GSD. Based on the experimental results, both performance testing methods correlate very well under monodisperse and polydisperse particles. CADRE is more robust, conservative, universal, and faster than the traditional chamber test method. CADRE can obtain the filtration efficiency curve, finding the MPPS to calculate the most conservative CADR value. We hope to use CADRE as a supplemental test method to make up for the limitations of chamber test methods and to actually evaluate the performance of various types of air cleaners.