Analysis of Particulate and Microbiological Filtration Performance of Air Handling Unit Filters in a Low-Energy Office Building over 12 Months

Round 1

Reviewer 1 Report

Comments to submission: Buildings-1854451

Title: Analysis of particulate and microbiological filtration performance of air handling unit filters in a low-energy office building over 12 months

This manuscript investigated the evolution of filtration efficiency in an AHU 12 fitted with bag filters, installed to treat office air in a low-energy building, over a 12-month period. This work reported that the particulate and microbial filtration efficiencies measured were almost identical. However, the results need more in-depth analysis and discussion. In a whole, the paper needs major revision before acceptance for publication.

My detailed comments are as follows:

1. The academic innovation of this study should be clearly addressed.
2. In 2.3, the culture temperature and time are usually adopted to incubate fungi. As for incubating bacteria, 3 to 7 days may be too long. Besides, the temperature may not be suitable enough for incubating bacteria compared to 37 ℃.
3. In 3.3, the real pictures of cultured colonies on dishes should be provided as the proof for the data displayed in Figure 3 and 4.
4. Through the whole study, the concentrations of particles and bioaerosols were sampled monthly. I wonder if the day you chose could just represent the average level of the entire month. The microbial components carried on the particles from the outside can change apparently in a day and a month.
5. In Figure 3 and 4, was there only one sample of each point? Actually, based on impactor sampling as you adopted, the difference between samples in one period can be very large. However, the error bars in Figure 3 and 4 were even smaller than that of Figure 6 and 7, which were particle concentrations. On the other hand, if there was only one bioaerosol sample each month, the result may be inaccurate.
6. In 3.4.1, it is not obvious that the pressure drop showed a linear increase as you reported in Figure 5. A fitting curve may be better. Besides, you should provide a reasonable explanation for the pressure drop decrease in June and July. It was against your conclusion. You could find a similar reference in Tian et al.’s “Electrostatically assisted air coarse filtration for energy efficient ambient particles removal: Long-term performance in real environment and influencing factors” (https://doi.org/10.1016/j.buildenv.2019.106348).
7. In Figure 8, 10 and 11, it is recommended that you adjust the horizontal ordinate incase the left part of the graphs were blank. Besides, Figure 9 seems lost.
8. In 3.5, the PCR data like reads and OTUs should be provided as a proof. What’s more, the original data and PCR method can be added in Supplementary Materials.
9. There was “5. Conclusion” following Section 3.5. Section 4 seemed lost. You should be careful.
10. In conclusion part, the main point you concluded was “Direct measurement of particulate efficiency could be a good indicator of filtration efficiency in filters for cultivable microbial aerosols”. However, it seems a common sense now. Many researches about bioaerosol filtration have applied this result. Therefore, this point can hardly support the innovation of this study. I hope you could pick up other points and rewrite the conclusion part.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Thank you for submitting the author's research results to the journal.

My review opinion is as follows.

I think it is necessary to add a literature review related to the subject of this study.

It is necessary to present the floor plan of the target building.

Figure 1. It is recommended to add pictures of ERV and measuring equipment in addition to the schematic diagram.

Table 2 It is recommended to indicate the performance resolution of the measuring instrument.

Equation number (4) was duplicated

In the explanation of the formula, it is necessary to indicate the unit of the physical quantity.

Check ‘ccma’ in figure 3, 4.

Check the numbering of tables.

The content of the conclusion is insufficient compared to the amount of research content. On page 2, the purpose of the study was presented in four ways. In conclusion, it is necessary to quantitatively summarize the results for these four purposes.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This is an important piece of work where the authors study the efficiency of an air handling unit in an office. The authors should provide more discussion and insights into the manuscript. Further, there are several sections throughout the manuscript where the language could be improved. The authors also should check the manuscript for grammatical errors. Here are some comments which if addressed could improve the scientific rigour of the manuscript.

Abstract: Some of the key quantifiable findings of the study should be mentioned in the abstract. Percentage decrease in filtration efficiency over time or typical bioaersosol concentration in indoor and outdoor air or insights into the particle size distribution could be mentioned in the abstract.

Introduction: The authors should define the term ‘low-energy’ buildings in the introduction section of the manuscript.

Line 61: What do authors mean by ‘low-energy building standard’? The authors should discuss these standards in the text and provide some reference. How do they compare with ASHRAE standards? The authors should also comment about the national IAQ or building standards applicable in France. This can either be discussed in the introduction or later in the results and discussion.

Line 80: It would be useful for the readers to know about the dimensions of the room. 2450 m3/h is provided as the flow rate of the AHU. Can the authors also provide the air exchange rate in the room?

Figure 1 can be improved. Use of engineering schematic for denoting components of the AHU is advised. The legend can be more descriptive. The dimensions of the AHU can be provided in the figure. Also use arrow to denote the direction of the flow within the AHU units. It is not clear from the figure that ‘Each compartment contains two four-bag filters’. Heating battery is not labelled in the figure.

Line 104: It would be useful to know the sampling duration for the TEOM instrument. It is later mentioned in Table 2 that continuous measurement were used for the instrument, however here it is also mentioned that an oscillating microbalance was in place. Is this gravimetric measurement? What was the sampling resolution of the instrument?

Table 1: Need to be re-done. Unless the authors describe the utility of these media in their experimental methodology, this table seems redundant. This can go into the supplementary information or as brief text in the methodology section.

Table 2: This is a good table and the authors could describe it right at the beginning of the methodology text.

Line 144: The term VOAS is not defined. Further, the authors should cross-check and make sure all the terms in the equation are properly defined in the text.

Results:

Table 3 is redundant as this data is already provided in Figure 2. The authors can discuss the findings from the table in the text.

Table 4: Instead of this table can the authors provide a realtime particulate matter data for each measurement location. Location of the measurement could be mentioned in the caption for ease to the readers. The present table 4 values can be discussed in the text.

Line 217: It would be interesting to see the particle size distribution data for all the measured locations. Also, the corresponding bio-aerosol measurements can be provided. I suggest having a figure of particle size distribution for all the measurement points.

The authors should compare the particle size distribution data with bioaerosol measurements.

 with other bioaeorosol studies such as

Pahari, A.K., Dasgupta, D., Patil, R.S. and Mukherji, S., 2016. Emission of bacterial bioaerosols from a composting facility in Maharashtra, India. Waste management, 53, pp.22-31.

Conclusions needs to be re-written with keeping in mind the major takeaways from the findings and how it can be used in future studies.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

It is sorry that the authors almost did not revise the manuscript according to the comments. They just explained why they did not make the revision. 

Thus, I keep my suggestion that this version is not suitable for publication.

Author Response

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Author Response File: Author Response.docx