Air Cleaners for Indoor Air Pollution Control

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Abstract
Indoor air pollutants include both particles and gases, and different technologies are required to control these pollutants. An experimental study was conducted to evaluate the performance characteristics of currently available control technologies. One aspect of the study was to evaluate the particle-size dependent collection efficiency of seven commercially available devices for control of particles: one common furnace filter, four industrial-grade filters, and two electronic air cleaners (EACs). The furnace filter had negligible effect on particles in the size range 0.1 to 1 mm (i.e., those that penetrate deep into the human lung). The industrial-grade filters, which had ASHRAE ratings of 95, 85, 65, and 40%, exhibited a minimum efficiency at approximately 0.1 mm, which was substantially lower than the ASHRAE efficiency. Of the two EACs, one was essentially a furnace filter with a high-voltage electrode while the other was similar to an industrial electrostatic precipitator (ESP). The furnace-filter type of EAC reached a maximum efficiency of 30% at low flowrates (7 m3/min); however, it had Ra negligible effect at higher flowrates (14 and 20 m3/min). The ESP-like EAC exhibited efficiencies from 80 to 90% over the entire size range at low to moderate flow rates. At the highest flowrate, a minimum efficiency of 60% was detected at 0.35 mm. Measured ozone emission rates for the EACs were used to estimate a worst-case ozone exposure in a typical residential environment. The worst-case scenario yielded a maximum concentration of 60 ppb. Actual concentrations would be much lower. Another aspect of the study was to evaluate the suitability of commercially available carbon-based sorbents for removing low concentrations of volatile organic compounds (VOCs). A laboratory experiment was conducted to measure the capacity of three different carbons (wood-, coal-, and coconut-shell-based carbons) for three different VOCs (benzene, acetaldehyde, and 1,1,1-trichloroethane) at low concentrations (100–200 ppb). Measured capacities ranged from 10−8 to 10−6 g-mol/g carbon. Model calculations based on a challenge concentration of 150 ppb and a breakthrough concentration of 50 ppb indicated that commercially available 15 cm (6 in) thick in-duct carbon filters would have a bed life on the order of minutes.

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