J Air Waste Manag Assoc. 2006 May;56(5):666-74.Yu KP1, Lee GW, Huang WM, Wu CC, Lou CL, Yang S.Author information1Graduate Institute of Environmental Engineering, National Taiwan University, Taipei, Republic of China. f89541105@ntu.edu.twAbstractNowadays, the heating, ventilation, and air conditioning (HVAC) system has been an important facility for maintaining indoor air quality. However, the primary function of typical HVAC systems is to control the temperature and humidity of the supply air. Most indoor air pollutants, such as volatile organic compounds (VOCs), cannot be removed by typical HVAC systems. Thus, some air handling units for removing VOCs should be added in typical HVAC systems. Among all of the air cleaning techniques used to remove indoor VOCs, photocatalytic oxidation is an attractive alternative technique for indoor air purification and deodorization. The objective of this research is to investigate the VOC removal efficiency of the photocatalytic filter in a HVAC system.

Toluene and formaldehyde were chosen as the target pollutants. The experiments were conducted in a stainless steel chamber equipped with a simplified HVAC system. A mechanical filter coated with Degussa P25 titania photocatalyst and two commercial photocatalytic filters were used as the photocatalytic filters in this simplified HVAC system. The total air change rates were controlled at 0.5, 0.75, 1, 1.25, and 1.5 hr(-1), and the relative humidity (RH) was controlled at 30%, 50%, and 70%. The ultraviolet lamp used was a 4-W, ultraviolet-C (central wavelength at 254 nm) strip light bulb. The first-order decay constant of toluene and formaldehyde found in this study ranged from 0.381 to 1.01 hr(-1) under different total air change rates, from 0.34 to 0.433 hr(-1) under different RH, and from 0.381 to 0.433 hr(-1) for different photocatalytic filters.PMID: 16739804 [PubMed - indexed for MEDLINE] Publication TypesResearch Support, Non-U.S. Gov'tMeSH TermsAir Conditioning*Air Pollutants/chemistryAir Pollutants/isolation & purificationAir Pollutants/radiation effectsAir Pollution, Indoor/analysisAir Pollution, Indoor/prevention & control*CatalysisEnvironmental MonitoringFiltration/methodsFormaldehyde/chemistryFormaldehyde/isolation & purification*Formaldehyde/radiation effectsHeating*HumidityPhotochemistryTitanium/chemistryToluene/chemistryToluene/isolation & purification*Toluene/radiation effectsUltraviolet RaysVentilation*VolatilizationSubstancesAir Pollutantstitanium dioxideFormaldehydeTolueneTitaniumOther Literature SourcesCited by Patents in - The LensMedicalIndoor Air Pollution - MedlinePlus Health InformationMiscellaneousTOLUENE - Hazardous Substances Data BankFORMALDEHYDE - Hazardous

Substances Data BankTITANIUM - Hazardous Substances Data BankTITANIUM DIOXIDE - Hazardous Substances Data Bankaircon servicing singapore toa payohHEPA filters are one ofbionaire portable air purifier review the most widely-known methods of air cleaning. sharper image air purifier hybrid gpIn fact, when most people think of an air cleaner, they think of a HEPA filter. HEPA filters - and ALL filters, for that matter - have limitations that must be taken into consideration when choosing an air cleaning unit for your home or office. Because filtration systems (HEPA and other filters) dilute contaminated air with cleaner air, their effectiveness depends largely upon how much filtered air they deliver over a given

period into a specified space. air cleaners (they are NOT air purifiers because the cannot purify the ambient air of very small contaminants like viruses!) have large, often loud fans because they only clean the air they can actually filter through them. is an acronym for High Efficiency Particulate Air Filter, which was used in U.S. military specifications beginning around World War II. The precise definition of a HEPA varies somewhat from country to country and from specifier to specifier with respect to the efficiency for a particular test method. A conventional HEPA filter consists of a continuous sheet of a special paper-like, glass-fiber filter medium which is pleated into a "V" configuration with corrugated aluminum separators between the pleats. the filter element, which is then bonded into a rigid frame using a special polyurethane compound. Standard filters are produced in a range of face dimensions and in two standard depths of nominally

150 mm and 300 mm. HEPA filters cannot be cleaned to remove particulate and dust loading and must be replaced as a complete assembly, often at significant yearly cost. particle load increases, so will the resistance to flow and hence the pressure drop across the filter. In some applications, uneven filter loading will cause non-uniform airflow through the filter filter systems often do not seal the filter chamber properly, so contaminated air simply passes through the holes and back into the ambient air. Some manufacturers will void your warranty on filtration systems if you do not replace the filter according to a very specific schedule, and most will not cover damage caused to the unit by clogged filters, which can cause the fan motor to burn up. Even the larger HEPA air filters cover only a single room, or at most a small apartment. This is because in order for the air to be cleaned, it must pass through the filter.

As a result, they can only clean the air that is nearby. While some filtration systems do incorporate flimsy charcoal or other filtration media that can absorb odors, they tend to have little effect on odors and virtually none on bacteria, viruses, germs and fungi like mold. A key point to consider is that HEPA filters are simply that -- filters -- and are designed ONLY to FILTER larger (0.3 and above) micron-sized particulates from the air, and they can do it quickly. It is true that they can remove mold spores and bacteria from the air, but unless the filter is treated with an anti-microbial substance -- which is often, in itself, a contaminant -- still-living microbials continue to grow and multiply on the HEPAAnd when you pull out the filter to change it, guess where Some air cleaner models offer optional filters for smoke and odors, but these simply trap chemicals and odor vapors in activated charcoal or carbon, and are not very effective unless

they have a sizeable carbon, like in the Airpura models. it is nearly impossible to know at what point the carbon becomes saturated and can no longer absorber chemicals and odors. By contrast, filter-less air purification devices based on Germicidal UV technology, like the Air Oasis, oxidize odors and vapors, removing them permanently, and they are effective on even microscopic particulates, bacteria, and viruses as small as .001 microns (many viruses, herbicides and pesticides are that small). HEPA filter effectiveness significantly diminishes as the particles become smaller. As particles become very small, they cease to behave so much like particles as they do gas phaseIt is difficult to tell whether such small particles are actually suspended in air (particles) or diffused throughout it (gasThe bottom boundary where particles act as true particles is about 0.01 micron. The normal theory of separation does not apply to particles below this size and removing them from air requires techniques