Air quality in care facilities: Possibly infectious particles

Sammanfattning

This study investigates how air cleaning reduces airborne particle and bacterialconcentrations in healthcare environments, aiming to lower infection risk withoutincreasing mechanical ventilation rates. The study combines laboratory experiments,infection risk modelling, and field measurements in a hospital waiting room.Under laboratory conditions, the Clean Air Delivery Rate (CADR) of the electrostaticair cleaner was determined using particle concentration decay measurements, yieldingan average value of approximately 400 l/s, depending on particle size. These resultswere used to estimate equivalent air change rates and to model infection risk using theWells–Riley approach via the REHVA calculator. The modelling indicates that addinga single air cleaner with a CADR of 400 l/s can reduce the theoretical probability ofairborne infection by approximately 75–80% compared to a baseline ventilation rate of5 air changes per hour (ACH), outperforming an increase to 8 ACH.Field measurements in a waiting room at Karolinska Universitetssjukhuset confirmedthat high-CADR air cleaning significantly reduces airborne particle concentrations (upto 60–70%) and bacterial levels (approximately 40–55%) under real operatingconditions. However, bacterial reductions showed greater variability due to changes inoccupancy and activity levels. The results also demonstrate that air cleaners providesubstantial improvements in indoor air quality at relatively low energy consumption.The estimated annual energy use is significantly lower than that required to achieveequivalent ventilation rates.Measured ozone levels, a potential by-product of electrostatic air cleaning (used duringthe experiments) remained well below recommended limits, indicating safe operation.Noise levels increased moderately but remained within acceptable ranges forhealthcare environments.Overall, the findings demonstrate that electrostatic air cleaning can serve as aneffective and energy-efficient supplementary strategy alongside ventilation forreducing airborne contaminants and infection risk in healthcare facilities, particularlyin spaces with high occupancy or limited ventilation capacity.