Uncertainty analysis of various CO2-Based tracer-gas methods for estimating seasonal ventilation rates in classrooms with different mechanical systems

Reducing the transmission of SARS-CoV-2 through indoor air is the key challenge of the COVID-19 pandemic. Crowded indoor environments, such as schools, represent possible hotspots for virus transmission since the basic non-pharmaceutical mitigation measures applied so far (e.g. social distancing) do not eliminate the airborne transmission mode. There is widespread consensus that improved ventilation is needed to minimize the transmission potential of airborne viruses in schools, whether through mechanical systems or ad-hoc manual airing procedures in naturally ventilated buildings. However, there remains significant uncertainty surrounding exactly what ventilation rates are required, and how to best achieve these targets with limited time and resources. This paper uses a mass balance approach to quantify the ability of both mechanical ventilation and ad-hoc airing procedures to mitigate airborne transmission risk in the classroom environment. For naturally-ventilated classrooms, we propose a novel feedback control strategy using CO 2 concentrations to continuously monitor and adjust the airing procedure. Our case studies show how such procedures can be applied in the real world to support the reopening of schools during the pandemic. Our results also show the inadequacy of relying on absolute CO 2 concentration thresholds as the sole indicator of airborne transmission risk.

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“…eq. (7) ), the primary uncertainty of this calculation is likely the exhaled CO 2 emission rate uncertainty [ 80 , 81 ].…”

Section: Resultsmentioning

confidence: 99%

Ventilation procedures to minimize the airborne transmission of viruses in classrooms

Stabile

Pacitto

Mikszewski

et al. 2021

Building and Environment

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“…Indeed, the CO 2 measurement uncertainty could represent a secondary contribution to the AER back-calculation through the eq. 7, in fact, the uncertainty of the exhaled CO 2 emission rate could mainly affect the AER uncertainties [73,74].…”

Section: Resultsmentioning

confidence: 99%

Ventilation procedures to minimize the airborne transmission of viruses at schools

Stabile

Pacitto

Mikszewski

et al. 2021

Preprint

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Reducing the transmission of SARS-CoV-2 through indoor air is the key challenge of the COVID-19 pandemic. Crowded indoor environments, such as schools, represent possible hotspots for virus transmission since the basic non-pharmaceutical mitigation measures applied so far (e.g. social distancing) do not eliminate the airborne transmission mode. There is widespread consensus that improved ventilation is needed to minimize the transmission potential of airborne viruses in schools, whether through mechanical systems or ad-hoc manual airing procedures in naturally ventilated buildings. However, there remains significant uncertainty surrounding exactly what ventilation rates are required, and how to best achieve these targets with limited time and resources. This paper uses a mass balance approach to quantify the ability of both mechanical ventilation and ad-hoc airing procedures to mitigate airborne transmission risk in the classroom environment. For naturally-ventilated classrooms, we propose a novel feedback control strategy using CO2 concentrations to continuously monitor and adjust the airing procedure. Our case studies show how such procedures can be applied in the real world to support the reopening of schools during the pandemic. Our results also show the inadequacy of relying on absolute CO2 concentration thresholds as the sole indicator of airborne transmission risk.

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“…Ventilation rate was calculated separately for each experimental session by measuring the rate of decay of the concentration of metabolic CO 2 after each subject left the sleeping capsule 32–34 assuming that VR did not change whether the subjects were present or absent in the capsule; the rate of decay of CO 2 was used to estimate air change rate (ACH). Figure 4 shows an example of the measurements of CO 2 under two experimental conditions (T24P800 and T24P1700); the time periods used for estimating CER and ACH using the decay of CO 2 32–34 are indicated. The ACH was used to derive VR using the volume of the part of the capsule in which the subjects had been sleeping.…”

Section: Methodsmentioning

confidence: 99%

Emission rate of carbon dioxide while sleeping

et al. 2021

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Humans emit carbon dioxide (CO2) as a product of their metabolism. Its concentration in buildings is used as a marker of ventilation rate (VR) and degree of mixing of supply air, and indoor air quality (IAQ). The CO2 emission rate (CER) may be used to estimate the ventilation rate. Many studies have measured CERs from subjects who were awake but little data are available from sleeping subjects and the present publication was intended to reduce this gap in knowledge. Seven females (29 ± 5 years old; BMI: 22.2 ± 0.8 kg/m2) and four males (27 ± 1 years old; BMI: 20.5 ± 1.5 kg/m2) slept for four consecutive nights in a specially constructed capsule at two temperatures (24 and 28°C) and two VRs that maintained CO2 levels at ca. 800 ppm and 1700 ppm simulating sleeping conditions reported in the literature. The order of exposure was balanced, and the first night was for adaptation. Their physiological responses, including heart rate, pNN50, core body temperature, and skin temperature, were measured as well as sleep quality, and subjective responses were collected each evening and morning. Measured steady‐state CO2 concentrations during sleep were used to estimate CERs with a mass‐balance equation. The average CER was 11.0 ± 1.4 L/h per person and was 8% higher for males than for females (P < 0.05). Increasing the temperature or decreasing IAQ by decreasing VR had no effects on measured CERs and caused no observable differences in physiological responses. We also calculated CERs for sleeping subjects using the published data on sleep energy expenditure (SEE) and Respiratory Quotient (RQ), and our measured CERs confirmed both these calculations and the CERs predicted using the equations provided by ASHRAE Standard 62.1, ASHRAE Handbook, and ASTM D6245‐18. The present results provide a valuable and helpful reference for the design and control of bedroom ventilation but require confirmation and extension to other age groups and populations.

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Uncertainty analysis of various CO2-Based tracer-gas methods for estimating seasonal ventilation rates in classrooms with different mechanical systems

Cited by 45 publications

References 21 publications

Ventilation procedures to minimize the airborne transmission of viruses in classrooms

Ventilation procedures to minimize the airborne transmission of viruses in classrooms

Ventilation procedures to minimize the airborne transmission of viruses at schools

Emission rate of carbon dioxide while sleeping

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