出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2013/02/06 21:39:10」(JST)
HEPAフィルタ (High Efficiency Particulate Air Filter) とは、空気中からゴミ、塵埃などを取り除き、清浄空気にする目的で使用するエアフィルタの一種である。空気清浄機やクリーンルームのメインフィルタとして用いられる。
JIS Z 8122 によって、「定格風量で粒径が0.3μmの粒子に対して99.97%以上の粒子捕集率をもち、かつ初期圧力損失が245Pa以下の性能を持つエアフィルタ」と規定されている。
HEPAフィルタの粒子捕集効率をさらに上げたULPAフィルタというものもある。
目次
|
HEPAフィルタの濾紙は主に直径1~10μm以下のガラス繊維でできている。繊維の充填率は10%程度であり、空隙は数10μmの大きさをもつ。
粒子の捕集機構は以下の原理からなる。
この内さえぎり、慣性、重力効果は粒子が大きいほど強く、ブラウン運動、静電気効果は小さいほど強くなる。 したがってこれらの総和であるフィルタの粒子捕集効率は粒径によって異なり、ある粒径で最大値をとる。 HEPAフィルタの場合この最大値は約0.3μmであると言われている。
クリーンルームやクリーンブース用の精密空調機器、製造装置の組込み用にHEPAフィルタを採用したファンユニットが使われる。クリーン度クラス100~10,000までに対応し、高いクリーン度を要求されるような半導体や液晶、医薬品や食品などに適している。
現在の主流となっているファン式空気清浄機のハイエンド機種にはHEPAフィルタを使ったものが多い。より高性能なULPAフィルタを採用したものも発売されたが、過剰性能のため、採用する機種は少なくなっている。
家庭用掃除機の中でもハイエンド機種にはHEPAフィルタを使ったものが多い。これはハウスダストに寄るアレルギーへの関心の高まりに寄る。
原子力施設では、換気後の空気は気体廃棄物として排気設備から排出する際に、排気中の放射性微粒子を除去するためにHEPAフィルタが使用されている。
(五十音順)
High-Efficiency Particulate Air or HEPA[1][2] is a type of air filter. Filters meeting the HEPA standard have many applications, including use in medical facilities, automobiles, aircraft, and homes. The filter must satisfy certain standards of efficiency such as those set by the United States Department of Energy (DOE). To qualify as HEPA by US government standards, an air filter must remove 99.97% of all particles greater than 0.3 micrometre from the air that passes through. A filter that is qualified as HEPA is also subject to interior classifications.
Contents
|
HEPA filters are composed of a mat of randomly arranged fibres. The fibres are typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometers. Key factors affecting function are fibre diameter, filter thickness, and face velocity. The air space between HEPA filter fibres is much greater than 0.3 μm. The common assumption that a HEPA filter acts like a sieve where particles smaller than the largest opening can pass through is incorrect. Unlike membrane filters at this pore size, where particles as wide as the largest opening or distance between fibres cannot pass in between them at all, HEPA filters are designed to target much smaller pollutants and particles. These particles are trapped (they stick to a fibre) through a combination of the following three mechanisms:
Diffusion predominates below the 0.1 μm diameter particle size. Impaction and interception predominate above 0.4 μm. In between, near the Most Penetrating Particle Size (MPPS) 0.3 μm, both diffusion and interception are comparatively inefficient. Because this is the weakest point in the filter's performance, the HEPA specifications use the retention of these particles to classify the filter.
Lastly, it is important to note that HEPA filters are designed to arrest very fine particles effectively, but they do not filter out gasses and odor molecules. Circumstances requiring filtration of volatile organic compounds, chemical vapors, cigarette, pet, and/or flatulence odors call for the use of an activated carbon (charcoal) filter instead of or in addition to a HEPA filter.
HEPA filters, as defined by the DOE standard adopted by most American industries, remove at least 99.97% of airborne particles 0.3 micrometers (µm) in diameter. The filter's minimimal resistance to airflow, or pressure drop, is usually specified around 300 Pa at its nominal flow rate.
The specification usually used in the European Union is the European Norm EN 1822:2009. It defines several classes of HEPA filters by their retention at the given Most Penetrating Particle Size (MPPS):
HEPA class | retention (total) | retention (local) |
---|---|---|
E10 | > 85% | --- |
E11 | > 95% | --- |
E12 | > 99.5% | --- |
H13 | > 99.95% | > 99.75% |
H14 | > 99.995% | > 99.975% |
U15 | > 99.9995% | > 99.9975% |
U16 | > 99.99995% | > 99.99975% |
U17 | > 99.999995% | > 99.9999% |
The original HEPA filter was designed in the 1940s and was used in the Manhattan Project to prevent the spread of airborne radioactive contaminants. It was commercialized in the 1950s, and the original term became a registered trademark and a generic term for highly efficient filters. Over the decades filters have evolved to satisfy the higher and higher demands for air quality in various high technology industries, such as aerospace, pharmaceutical processing, hospitals, health care, nuclear fuels, nuclear power, and electronic microcircuitry (computer chips).
Today, a HEPA filter rating is applicable to any highly efficient air filter that can attain the same filter efficiency performance standards as a minimum and is equivalent to the more recent NIOSH N100 rating for respirator filters. The United States Department of Energy (DOE) has specific requirements for HEPA filters in DOE regulated applications. In addition, companies have begun using a marketing term known as "True HEPA" to give consumers assurance that their air filters are indeed certified to meet the HEPA standard.[3]
Products that claim to be "HEPA-type", "HEPA-like", "HEPA-style" or "99% HEPA" do not satisfy these requirements and may not have been tested in independent laboratories. Some of these sub-par quality filters may come reasonably close to HEPA filtration, while others will fall significantly short, making them truly inferior.[4]
HEPA filters are critical in the prevention of the spread of airborne bacterial and viral organisms and, therefore, infection. Typically, medical-use HEPA filtration systems also incorporate high-energy ultra-violet light units to kill off the live bacteria and viruses trapped by the filter media. Some of the best-rated HEPA units have an efficiency rating of 99.995%, which assures a very high level of protection against airborne disease transmission.
Many vacuum cleaners also use HEPA filters as part of their filtration systems. This is beneficial for asthma and allergy sufferers, because the HEPA filter traps the fine particles (such as pollen and dust mite feces) which trigger allergy and asthma symptoms. For a HEPA filter in a vacuum cleaner to be effective, the vacuum cleaner must be designed so that all the air drawn into the machine is expelled through the filter, with none of the air leaking past it. This is often referred to as "Sealed HEPA" or sometimes the more vague "True HEPA." Vacuum cleaners simply labeled HEPA have a HEPA filter, but not all air necessarily passes through it. Finally, vacuum cleaner filters marketed as "HEPA-like" will typically use a filter of a similar construction to HEPA, but without the filtering efficiency. Because of the extra density of a HEPA filter, HEPA vacuum cleaners require more powerful motors to provide adequate cleaning power.
Newer models claim to be better than the first models because of being "washable". Generally washable filters are expensive. Some manufacturers claim filter standards such as "HEPA 4", without explaining the meaning behind them. It refers to their Minimum Efficiency Reporting Value (MERV) rating. These ratings are used to rate the ability of an air cleaner filter to remove dust from the air as it passes through the filter. MERV is a standard used to measure the overall efficiency of a filter. The MERV scale ranges from 1 to 20, and measures a filter's ability to remove particles from 10 to 0.3 micrometre in size. Filters with higher ratings not only remove more particles from the air, they also remove smaller particles.
Some new model cars have cabin air filters that look like HEPA filters, but are not. The confusion is perpetuated by guides on how to change your car's air filter, misnaming it as a HEPA filter. The performance of these filters is obscured by manufacturers and difficult to evaluate, as they are not rated with the MERV system. They are typically close to MERV 8 performance.
Modern airliners use HEPA filters to reduce the spread of airborne pathogens in recirculated air.[5]
Wikimedia Commons has media related to: High-Efficiency Particulate Arresting |
全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.
拡張検索 | 「HEPA filter」 |
関連記事 | 「HEP」 |
.