Retrofitting of an Air Handling Unit by a Two-Stage Electrostatic Precipitator

A two-stage electrostatic precipitator (ESP) was developed using carbon brush ionizers and lightweight plastic electrodes to be used in an air handling unit (AHU). In a pilot study, the developed ESP emitted near-zero ozone (<10 ppbv) and achieved a PM
_2.5
collection efficiency higher than 90%. Theoretical analysis revealed that diffusion charging was as important as field charging in the particle charging mechanism. Based on the results of the pilot study, a real AHU of Yuseong Oncheon subway station, South Korea, was retrofitted with the developed ESP. In the field study, a flow distributor was required to achieve uniform flow and minimize the spatial standard deviation of the air flow velocity. Compared to a filter with a minimum efficiency reporting value (MERV) = 14, typically used for particle removal, the pressure drop decreased from 157.1 to 15.2 Pa, and the PM
_2.5
collection efficiency increased from 72.7% to 75.0% by the retrofitting of the AHU. The modified quality factor improved more than three-fold, and the required power consumption to operate the device and the fan decreased from 2.49 to 0.85 kW. During ESP operation, the indoor ozone concentration increased by only 1.1 ppbv, whereas the outdoor ozone concentration increased by 30 ppbv. Thus, ESP operation in this study barely increased the indoor ozone concentration.