Simulating the impact of air purifiers on indoor PM2.5 concentration and optimization of natural ventilation schedules: the case of a public office building in Bolzano, Italy

A growing attention has been paid in the last years to the indoor pollutants’ concentrations. In particular, several European Administrations focused on the Particulate Matter with less than 2.5 µm in diameter, i.e., the PM2.5, since it can cause severe respiratory and other health hazards. In the early 2024, the European Union tightened IAQ standards by lowering the annual average PM2.5 threshold value from 25 to 10 µg/m3. Even if PM2.5 generation in the indoor environments is typically linked to printers and office appliances, a significant share is due to natural ventilation through openings adjacent to congested streets or factories.

Recently, attention has been paid also to air purifiers, which can contribute to removal of PM2.5, reducing the need for window opening and, consequently, ventilation heat losses. Impact of air purifiers on the energy performance of naturally ventilated buildings, however, has not been investigated in detail, with primary focus put solely on IAQ.

In order to discuss the potential of air-purifiers to improve IAQ while optimizing natural and hybrid ventilation strategies, in this research we analyzed a public office building located in Bolzano, Italy, representative of offices designed and constructed in the 1990s in the Italian northern regions. Although the building is equipped with mechanical ventilation system, this is operated only for the removal of pollutants one hour during lunch break, before and after occupancy. In the remaining worktime, employees rely on natural ventilation solutions to improve the IAQ conditions, increasing in such a way thermal losses during the heating season. Furthermore, part of the offices are adjacent to a congested street, meaning that windows opening may allow ingress of outdoor PM2.5 in those spaces. Given these premises, in this research we explored the potential of hybrid ventilation strategies based on optimal window opening schedule and installation of portable air purifiers to improve both IAQ and building energy performance.

Whole annual building simulations with a calibrated TRNSYS and TRNFLOW model were performed to estimate energy consumption and CO2 and PM2.5 concentrations in all considered scenarios. Results confirmed that outdoor sources contribute significantly to the increase of indoor PM2.5 concentrations and internal air flows to their distribution to adjacent environments. Air purifiers proved to be effective in controlling PM2.5 in the room where placed, as well as to reduce energy consumption while keeping adequate air changes and CO2 concentrations, with an overall improvement compared to the current practice in the building.