Ventilation and air cleaning to limit aerosol particle concentrations in a gym during the COVID-19 pandemic

Abstract

SARS-CoV-2 can spread by close contact through large droplet spray and indirect contact via contaminated objects. There is mounting evidence that it can also be transmitted by inhalation of infected saliva aerosol particles. These particles are generated when breathing, talking, laughing, coughing or sneezing. It can be assumed that aerosol particle concentrations should be kept low in order to minimize the potential risk of airborne virus transmission. This paper presents measurements of aerosol particle concentrations in a gym, where saliva aerosol production is pronounced. 35 test persons performed physical exercise and aerosol particle concentrations, CO₂ concentrations, air temperature and relative humidity were obtained in the room of 886 m³. A separate test was used to discriminate between human endogenous and exogenous aerosol particles. Aerosol particle removal by mechanical ventilation and mobile air cleaning units was measured. The gym test showed that ventilation with air-change rate ACH = 2.2 h^-1, i.e. 4.5 times the minimum of the Dutch Building Code, was insufficient to stop the significant aerosol concentration rise over 30 min. Air cleaning alone with ACH = 1.39 h^-1 had a similar effect as ventilation alone. Simplified mathematical models were engaged to provide further insight into ventilation, air cleaning and deposition. It was shown that combining the above-mentioned ventilation and air cleaning can reduce aerosol particle concentrations with 80 to 90% , depending on aerosol size. This combination of existing ventilation supplemented with air cleaning is energy efficient and can also be applied for other indoor environments.

Keywords: Aerosol; Air purifier; Building ventilation; COVID-19; Fitness center; Sports club.

Fig. 1

Measurement set-up in stainless steel test room. Dimensions in mm.

Fig. 2

Plan view of fitness room 3 of Student Sports Center with indication of vertical screen that divides the room in two spaces of about equal volume. Left part is considered in this study. SB refers to vertical shield boards, also visible in Fig. 4, Fig. 5. Dimensions in mm.

Fig. 3

Position of ventilation inlets and outlets near the ceiling. Openings p4 to p8 apply for the half of the room used in this study.

Fig. 4

Measurement set-up in gym.

Fig. 5

Photo of (a) measurement set-up and (b) ongoing session with 35 test subjects.

Fig. 6

Aerosol particle concentrations at the end of every 5-min interval in the six 30-min measurement sessions.

Fig. 7

CO₂ concentrations at the end of every 5-min interval in the six 30-min measurement sessions.

Fig. 8

Calculated aerosol particle concentrations at the end of every 5-min interval in 60-min sessions for six scenarios: 1, 3′, 5′, 7, 8 and 9.

Fig. 9

Calculated asymptotic aerosol particle concentrations for six scenarios: 1, 3′, 5′, 7, 8 and 9, expressed as percentages compared to scenario 3’.