No abstract

Nowadays, 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 Ϫ1 , 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 Ϫ1 under different total air change rates, from 0.34 to 0.433 hr Ϫ1 under different RH, and from 0.381 to 0.433 hr Ϫ1 for different photocatalytic filters.

Currently silver nanoparticles (AgNP)-modified filter are widely used to inactivate airborne microbes in indoor environment. However, AgNP is extremely small and thus will penetrate cells membranes to cause cytotoxicity. AgNPs/NSP has been proven to be less cytotoxic to human body. In this study, it was the first time that AgNPs/NSP was used to develop a new antimicrobial air filter with low cytotoxicity. The AgNPs/NSP filter was made by dip-coating of filter with AgNPs/NSP and acrylic resin solution and three different amount of silver on filter were obtained including 12.6, 31.5 and 63 ppm. The filtration efficiency and the antimicrobial activity of AgNP/NSP filter were evaluated by bioaerosols including Escherichia coli and Candida famata in testing chamber and HVAC simulation system under 30% and 70% relative humidity (RH). The results showed that filtration efficiency of AgNPs/NSP-modified filter increased by about 13 to 20% compared to unmodified filter for E. coli but remained almost the same for C. famata. The antimicrobial efficiency of AgNPs/NSP modified filter of 63 ppm was 95.1% for E. coli at RH of 30%. In addition, 91% of antimicrobial efficiency for C. famata was found at RH of 70%. On the other hand, the antimicrobial efficiency of yeast for AgNPs/NSP-modified filter was 97.8% and 86.4% for RH of 30% and 70% respectively when yeast just started to contact with filter in HVAC system. The results suggest that AgNP/NSP-modified air filter can effectively inactivate microorganisms retained on. Therefore, emission of bioaerosols from air filter can be avoided in order to improve the air cleaning technology in indoor environment.