Experimental characterization of the efficiency and energy consumption of various central ventilation air cleaning systems

The present study aimed at assessing six commercially-available in-duct air cleaning devices which are designed to be mounted in the central ventilation system of offices or commercial buildings. The selected devices use different air cleaning technologies: mechanical filtration, electrostatic precipitation, gas filtration, ionisation / cold plasma, photocatalytic oxidation (PCO) and catalysis under UV light. They were tested against particles, a mixture of volatile organic compounds containing acetone, acetaldehyde, toluene, heptane and formaldehyde, and two bio-contaminants: Aspergillus brasiliensis (fungus) and Staphylococcus epidermidis (bacteria).
Two different test rigs were used for the tests. The single pass efficiency of each device was determined for 3 airflow rates, ranging from 1200 m3/h to 3600 m3/h, and two sets of temperature and humidity that are representative of wintertime and summertime indoor air conditions. The concentrations of the challenge VOC were also varied in the range from 30 to 100 g/m3 as a way to characterize their influence upon efficiency at realistic concentration levels for non-industrial buildings. Ozone and formaldehyde concentration measurements downstream of the air cleaners were achieved to determine the rate of harmful by-products that are released. Finally, the energy issue was addressed by measuring the electric consumption (if any) and pressure loss of the devices.
The results show that single pass efficiencies can vary in a wide range from one system to another. For a same device, it can also vary a lot from one challenge contaminant to another, which is somewhat a more intuitive conclusion. Two systems have no efficiency at all, or negligible impact on the concentrations of the challenge pollutants. The air handling unit containing a F8 class mechanical filter, a PCO reactor and a gas filter proves to be quite efficient in removing pollutants. However, photocatalytic oxidation isn’t effective while tremendously adding to the energy consumption. Finally, two devices show from moderate to high efficiency for a wide range of contaminants and acceptable energy consumption. In a general way, the study provides a methodology to assess the benefits of using central ventilation in-duct air cleaners, and then to determine which system is most suited for a building, based on indoor air quality, cost and energy criteria.