Effect of Corona Ionizers on Indoor Air Quality and Performance of HVAC Systems

FRANCISCO ROMAY, Qisheng Ou, David Y. H. Pui, University of Minnesota

     Abstract Number: 655
     Working Group: Indoor Aerosols

Abstract
Corona ionizers are currently used to enhance the effectiveness of indoor air cleaners, remove odors, and more recently to inactivate viruses attached to airborne particles. However, there is limited experimental evidence of the effectiveness of ions in indoor air quality, and many commercial products have ambiguous performance statements. The purpose of this study is to perform quantitative measurements made in a real office room, with unipolar and bipolar corona ionizers. The first part of the study determines the effect of the corona generated ions on the deposition of particles to the walls of the room, on the performance of the HVAC filtration system, and of a portable indoor air cleaner. The experiments measure the mass and number concentration decay of a polydisperse NaCl aerosol as a function of time for a variety of conditions including: (1) zero ventilation in the room, (2) HVAC system (100% outdoor air) with MERV 8 and MERV 15 filtration, (3) Indoor air cleaner at different blower settings. The experiments tested a unipolar corona ionizer operated at both positive and negative polarities, and a bipolar corona ionizer. Preliminary results indicate that for the zero ventilation case, unipolar ions enhances wall particle deposition by a factor of 2, while bipolar ions do not enhance particle wall deposition. For the HVAC system and indoor air cleaners, the aerosol decay rates in the room were increased by 10 to 20%, depending on the operating conditions (air flow rate and unipolar ionizer voltage level). Ion concentrations were also measured in the room to better understand the ion distribution as a function of distance from the ion source. This work demonstrates that unipolar ions can help improve indoor air quality, particularly in poorly ventilated environments, but have a smaller effect on the performance of HVAC filtration systems and indoor air cleaners.