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Activated Carbon Fiber (ACF) Filters Prove Effective in Removing VOCs

While formaldehyde is a key indoor air pollutant, high concentrations of other VOCs in indoor spaces also pose health risks and inhibit the ability to decrease ventilation rates and energy use. In a separate study focusing on reducing ventilation and energy consumption while maintaining or improving indoor air quality, Fisk, Destaillats, and Sidheswaran evaluated the use of a commercial activated carbon fiber (ACF) media as a filter for cleaning air in heating, ventilating, and air conditioning (HVAC) systems.

Volatile organic compounds in the air flow adsorb to the ACF filter, removing them from the indoor air. To create space on the filter for more VOCs to adsorb, the VOCs must be desorbed from the filter periodically and exhausted outdoors—a process known as "regeneration." The research team studied three different regeneration methods for the filters, using outdoor air under ambient conditions, with humidified air, and with the filter or regeneration air heated. The best performance occurred when the ACF filter was regenerated for 15 minutes once every 12 hours using air heated to 150°C. The air flow during regeneration is only 1 percent of the airflow during the 12-hour period of air cleaning, so only a very small amount of air must be heated, and the amount of energy required for regeneration is small.

The research team studied ACF system performance with mixtures of VOCs, with VOC properties ranging from those of formaldehyde (with a molecular weight of 30 and a boiling point of -21°C) to undecane (with a molecular weight of 156 and a boiling point of 196°C). For all VOCs other than formaldehyde, the time-averaged VOC removal efficiency was above 70 percent. The efficiency of formaldehyde removal was approximately 20 percent. However, using a double layer of the ACF cloth, the efficiency of formaldehyde removal jumped to 40 percent, and the efficiency for other VOCs exceeded 90 percent. The ACF system imposed a low airflow resistance, so the system will have only a minor impact on fan energy use.

Modeling indicates that the combination of ACF air cleaning and a 50 percent reduction in ventilation can decrease indoor concentrations of VOCs by 60 to 80 percent and reduce formaldehyde concentrations by 12 to 40 percent. Thus, the system reduces exposures to VOCs and formaldehyde, while allowing the ventilation rate to be cut in half to save energy

"Energy modeling indicated the potential to reduce the energy required for heating and cooling of ventilation air by 35 percent to almost 50 percent," says Sidheswaran.