Round 1

Reviewer 1 Report

The submission addresses the impact of window ventilation on the air exchange rate in an elementary school classroom in Uruguay. From the CO2 measurements performed, calculations are then made on the impact on a possible risk of infection.

In general, this is an important and urgent issue. Unfortunately, the paper does not add much to the current state of knowledge. Regardless, it would be interesting and worth publishing real measurement data under real conditions in an elementary school in Uruguay. However, the data shown alone are not meaningful for this purpose, since the documentation lacks decisive boundary conditions. Nevertheless, the results of the ACH rates over time, the risk of infection and the reproduction numbers are of interest to the readership of AppSc. The article could be published after submission of the requested information.

Line 75: For the plausibility of the later measured values, it is helpful to know the actual number of students in the room.

Line 154: Please add comments about the following Questions to the paper. Why was the outdoor concentration not measured? What was the main flow direction during cross ventilation, west to east or east to west? The operating principles of CO2 meters lead to measurement deviations and offsets, these must be corrected/calibrated and discussed. 

Ventilation rate

In general: In the field of window ventilation there is a large number of publications that show the influence of important boundary conditions. Without these boundary conditions the measured values are hardly useful for other scientists. Important are among others wind speed, wind direction, outside and inside temperature, the height of the windows above the ground. Is there a chimney effect in the building, which supports the flow through the room. Please research the data for your measurement days and include them as boundary conditions.

Equation 14: How can the concentration Ceq can reach values of 350ppm? The CO₂ concentration of the outside air is presumed to be above 390ppm.

Line 259: It is said that the control tests were repeated several times. However, only the results for one test are shown in Table 2. If these are mean values, it is important to also show the individual test results to get an impression of the fluctuations from test to test and between September and October.

Daily measurements

The execution of the calculation must be documented clearly and comprehensibly. Is Ceq determined for each adjustment window individually, manually estimated as horizontal asymptote?

Line 312: Why is it that longer durations are associated with lower ventilation rates? Is it caused by the evaluation algorithm, or wether?

Figure 6: The meaning of all lines and circles in the diagram must be explained. It is unclear what the different bars and circles mean.

321: It is repeatedly argued that the cause of reduced ventilation behavior can be low outdoor temperatures. It would be helpful to have a chart that relates outdoor temperature to ACH and ventilation time. If a correlation can be shown, there is no need to speak in the subjunctive.

There is no reference to Figure 8.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript entitled « Quantitative Assessment of Natural Ventilation in an Elementary School Classroom in the Context of COVID-19 and its Impact in Airborne Transmission” Aims to measure and to propose simple correlations to evaluate the performance of the natural ventilation in a classroom. This topic is still of interest since the Covid-19 pandemic is still there.

The methodology is classical but robust and reliable, the results are clearly presented and allow a good overview of the performances that might be expected for the efficiency of natural ventilation. The correlation proposed are simple but seems to give reliable results. This article should be considered for publication. Those few elements should be discussed:

The main point that should be justified are:

-       The main drawback of this article is the fact that only one configuration of classroom has been investigated. How is it possible to extend those results to other surface, configuration …

 

-       What is the expected influence of atmospheric conditions (temperature difference in/outside, relative humidity…)?

 

-       the classical metrological standard to assess the repeatability and the dispersion of the results (3 measurement, 3 days, etc…) has not been applied. Is there a reason?

 

more globally,

-       it is assumed that CO2 is a tracer for human respiratory activities. However in the reality, Covid-19 is transmitted by aerosol. The behavior of aerosol is far from being as simple as simply gaseous renewal. Settling, Brownian motion, inertial, deposition and interception mecanismes,… strongly depending on particle size (which evolute with droplet drying dynamic…) is not considered when only CO2 is measured. This point should be at least discussed in the conclusion.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This paper assessed ventilation of a naturally ventilated Uruguayan primary school classroom by estimating ventilation rates and airborne transmission risk.

The paper addresses an important issue in school classrooms which has received wide attention recently due to the COVID 19 pandemic. The paper is well written, the methodology and conclusions are sound and the limitations are clearly articulated.

 I have some minor comments on the paper:

It is not clear what the outdoor weather conditions are though there was mention about cold weather. In order to explore the application of the findings to other locations, it is important to present the outside weather conditions for eg: air temperature during various seasons.

 Page 4 states that “As an adjustment alternative, we present a novel approach which is remarkably simple”. I am not sure how it can ne novel as equation 2 is not a new equation. This should be amended.

 Some of the recent papers relevant to this study could be reviewed and cited. Just one example below: 

Rajagopalan et al., 2021, Year long monitoring of indoor air quality and ventilation in school classrooms in Victoria, Australia, Architectural Science Review.

https://doi.org/10.1080/00038628.2021.1988892

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The corrections and additions substantially improve the article.