On the Performance of Diffuse Ceiling Ventilation in Classrooms: A Pre-Occupancy Study at a School in Southern Sweden

Round 1

Reviewer 1 Report

I have carefully read this paper entitled “on the Performance of Diffuse Ceiling Ventilation in Classrooms: A Pre-Occupancy Study at A School in Southern Sweden". As a result, I have miner revision for this interesting work before publication.

1-      Rewrite the novelty statement at the end of the introduction section.

2-      Change the capital letter of the preposition in the title

3-      The manuscript needs English correction.

 

 

Author Response

Reviewer 1

Dear Reviewer,

Thank you very much for making time to review our manuscript and providing useful comments to help improve the quality of our study. We have tried our best to address the comments, of which we have incorporated some suggested changes (see tracked changes) and have explained others that we have not included in the revised version of the manuscript.

We have provided responses to your comments below.

Thank you, and we hope the revisions meet your expectations.

/Authors

Comments:

I have carefully read this paper entitled “on the Performance of Diffuse Ceiling Ventilation in Classrooms: A Pre-Occupancy Study at A School in Southern Sweden". As a result, I have miner revision for this interesting work before publication.

 

Comment 1-      Rewrite the novelty statement at the end of the introduction section.

Reply: We have rewritten the novelty. The main take away from the study is that DCV can be implemented with the existing systems without a lot of structural and operational changes. Only reconfiguring the air supply from room diffuser into the plenum (removing room diffusers and instead supplying air in the plenum) and maintaining control setpoints in existing, DCV can easily be implemented. Thus, there is minimal costs in changing existing MV to DCV systems.   

Comment 2-      Change the capital letter of the preposition in the title

Reply: Revised, thanks!

Comment 3-      The manuscript needs English correction.

Reply: Corrected accordingly, thanks!

Reviewer 2 Report

Introduction: The authors correctly presents the challenges that DCV presents. The introduction needs to be integrated with references to experimental and numerical studies on DCV with ceiling plenum and sound absorbing panels, especially for whats concerns the different available alternative of ventilation air inlet.

 

Materials and Methods. The configuration of air inlet through gaps between panels and structure was adopted. Can the author mention why this configuration was chosen? Other possible configurations are porous panels and perforated panels. Did they author perform a deeper literature search on the pro and cons of these configurations?

 

167. the lamps had no influence on the airflow distribution. Can the authors explain better? Did the authors take into account the heat the lamps produce? From the Figure they look like neon tube, which can represent a non-negligible heat source for the plenum.

 

The instrumentation of the room is thoroughly explained and the choice of sensors seems to be adequate. 

 

188. How are the TCs on the surfaces installed? Are they shielded?

 

Figure 2. It could be beneficial to add quotes to give an idea of the distances.

 

219. The font is slightly different. If the authors wants to remark a difference with the rest of the text, this difference should be increased.

 

Air change efficiency and index are expressed in a clear fashion.

 

Acoustic measurements. Did the author perform measurements with both systems on and off? This is important in order to assess the eventual impact of the airflow on the sound absorbing power of the panels. In literature, some authors who conducted numerical research have referred to this as a necessary measurement.

 

Results. It would be interesting to have a contour representation of the temperature distribution on the area of the room, chosing one or two horizontal planes.

 

Figure 5 must be improved, especially in the description of the reported axes. 

Some minor comments:

43. the sentence could be expressed in a clearer fashion

60. MV can be described in a more efficient way.

155. double space between words

170. Figure 1 needs to be improved

237. typo: flowe pattern

325. typo: installation

Author Response

Dear Reviewer,

Thank you very much for making time to review our manuscript and providing useful comments to help improve the quality of our study. We have tried our best to address the comments, of which we have incorporated some suggested changes (see tracked changes) and have explained others that we have not included in the revised version of the manuscript.

We have provided responses to your comments below.

Thank you, and we hope the revisions meet your expectations.

 

Comments 1:

Introduction: The authors correctly present the challenges that DCV presents. The introduction needs to be integrated with references to experimental and numerical studies on DCV with ceiling plenum and sound absorbing panels, especially for whats concerns the different available alternative of ventilation air inlet.

Reply: Thank you for your comment. Since we are not performing a laboratory study but a field study, we have avoided diving deep in the literature to discuss different methods and air diffusion with DCV to simplify the manuscript and make it readable. We earlier provided review papers that had a comprehensive discussion on DCV. However, following the reviewer’s comment, we have expanded paragraph 5 in the introduction to highlight experimental and numerical studies and the paragraph, and if the readers are interested to read more, they can refer to the cited literature. The ne statement includes the following statement:

“Apart from reduced risk of draft and low fan energy use, Zhang et al. [32] explained that DCV is economical due to the low cost of ductwork and requirement for no room diffusers. An additional benefit of DCV is the use of suspended ceilings tiles made of panels with sound-absorbing properties. Due to the characteristics of the panels, they can be adapted as noise dampers as well as airflow devices without any design or physical changes [33]. Therefore, acoustic ceiling tiles can be used which increases the performance in office environments and learning in classrooms as the system dumps/limits the low frequency noise within the plenum as opposed to traditional ventilation systems (normally silencers are installed to reduce the noise) [24]. Three types are DCV panels are discussed in literature, and these differ on specifications of pressure drop across the false ceiling and consequently the airflow characteristics in the ventilated room, see [3], [34]. Experimental and numerical studies have explored DCV [32], [33], [35], [36], while other studies have explored integration of other building technologies and strategies, to enhance building ventilation performance [37]– [40]. Overall, DCV has several benefits over conventional duct-based ventilation. A common thread in literature is that overall DCV systems are typically smaller, use less energy and create more uniform indoor environmental conditions [3], [41].”

 

Comment 2:

Materials and Methods. The configuration of air inlet through gaps between panels and structure was adopted. Can the author mention why this configuration was chosen? Other possible configurations are porous panels and perforated panels. Did they author perform a deeper literature search on the pro and cons of these configurations?

Reply: Thank you for the comment, As stated the school was recently renovated and the school management and the contractor had decided on the choice of the ceiling tiles to use. They based their decisions on previous studies and projects the company that manufactures the ceiling tiles had in Denmark on DCV. Our job was to assess and evaluate the performance of DCV in this school since the only thing that was changed was how to distribute air in the room. Yes, we did the literature dive and have provided review studies that summaries DCV quite well.

 Comment 3:

167. the lamps had no influence on the airflow distribution. Can the authors explain better? Did the authors consider the heat the lamps produce? From the Figure they look like neon tube, which can represent a non-negligible heat source for the plenum.

Reply: The reviewer refers to paragraph 2 in section 2.1. Here the authors are talking about the plenum structural setup and whether it had any influence on the airflow and ventilation performance in the plenum and classroom. The focus is on service ducts, fire water pipes, and cables for electricical lights and sensors. And the laps that are used in the classrooms are LED lamps. An earlier analysis (1) on the flow structure in the ceiling showed no/little influence of plenum structures on airflow distribution. If anything, the influence was on boundary walls.

(1) A. Kabanshi, E. Linden, T.-C. C. Ogbuagu, D. MacCutcheon, and T. Persson, “Plenum airflow distribution and its influence on the performance of a diffuse ceiling ventilation,” E3S Web Conf., vol. 356, p. 01026, 2022, doi: 10.1051/e3sconf/202235601026.

 Comment 4:

The instrumentation of the room is thoroughly explained and the choice of sensors seems to be adequate.

Reply: Thank you!

Comment 5:

188. How are the TCs on the surfaces installed? Are they shielded?

Reply: Yes, the surface TCs were shielded by covering them with gray ventilation tape to remove the effect of air temperature on the measurements.

Comment 6:

Figure 2. It could be beneficial to add quotes to give an idea of the distances.

Reply: Since we had a lot of measurement points, and the measurement region is restricted about 60 cm from all the surfaces. It would be cumbersome to give description of the locations of the sensors. Therefore, we went for a qualitative representation as shown in the Figure. We would like to maintain the qualitative representation of the measurement points since we have tried to estimate it according to the scale.

 Comment 7:

219. The font is slightly different. If the authors want to remark a difference with the rest of the text, this difference should be increased.

Reply: Noted and corrected.

Comment 8:

Air change efficiency and index are expressed in a clear fashion.

Reply: Thank you!

 

Comment 9:

Acoustic measurements. Did the author perform measurements with both systems on and off? This is important in order to assess the eventual impact of the airflow on the sound absorbing power of the panels. In literature, some authors who conducted numerical research have referred to this as a necessary measurement.

Reply: We performed several acoustic measurements focusing on room acoustics (which are reported in the study) and the noise energy level from the ventilation system. We did not see the need to compare the differences between “when the ventilation is running” and “when it was not running” since it was a field study, and our interest was to assess the difference between two classrooms when in operation. We agree with the reviewer that performing the acoustic measurements both with the system on and off is a necessary measurement particularly so in experimental setups and during system design. Since this is a field study, our interest was what differences exists when the system is in operation. In this case both MV and DCV are running on the same air handling unit and fan. From the room acoustic measurements ( and also since the classrooms are on the same floor, same building and similar characteristics), we can expect that the sound level or acoustic measurements will be similar between the rooms when the ventilation system is running and when it is not running.

Comment 10:

Results. It would be interesting to have a contour representation of the temperature distribution on the area of the room, chosing one or two horizontal planes.

Reply: We opted not to include a contour representation of the temperature distribution because we would not get more meaningful results other than what we have in Fig 3. From Fig 3 we see that the room temperature distribution is quite homogeneous and varies by less than 0.5 °C to the room mean value. Unlike the velocity profiles which show a scatter, temperature is close to the mean. Therefore providing a contour plot will not give any more meaningful information other than what is given in Figure 3.

Comment 11:

Figure 5 must be improved, especially in the description of the reported axes.

Reply: Noted and we have added a description in the Figure caption.

ome minor comments:

43. the sentence could be expressed in a clearer fashion.

Reply: Noted and rephrased. Ventilation facilitates controlling and conditioning of supply indoor air and its distribution in the buildings/rooms. At the same time, ventilation works to remove indoor contaminants, e.g., heat, CO2 (Carbon dioxide), VOCs (volatile organic compounds), and other particulate matter among other things [8], [9].

60. MV can be described in a more efficient way.

Reply: Thank you. We have revised the description and hope this is clear and efficient.

155. double space between words

Reply: Noted and corrected.

170. Figure 1 needs to be improved

Reply: Not clear what the reviewer means specifically on what needs to be improved about Figure 1..

237. typo: flowe pattern

Reply: noted and corrected

325. typo: installation

Reply: noted and corrected

Reviewer 3 Report

This is an interesting paper that covers a ventilation air ditribution system that works slightly better than mixing ventilation. I have written my comments below:

Page 2 Line 70

Here the authors are describing a stratified ventilation system but there is no mentioning of a ventilation system that is heavily classified as stratified ventilation and that is impinging jet ventilation. Can the authors maybe write a small section with references to that system also maybe?

Page 4 Line 177

"60 W incandescent lamps were distributed in the classroom and 176 a 100 W was used for the teacher (See Figure 1A)."

 This line is referencing Figure 1A in relation to heat loads that has been set in the room. I think the correct reference to figure should be Figure 2.

 

Page 7 Line 253

"classroom has opposed"

should be “classroom as opposed”

Also if possible please doublecheck the English language in the paper.

Author Response

Dear Reviewer,

Thank you very much for making time to review our manuscript and providing useful comments to help improve the quality of our study. We have tried our best to address the comments, of which we have incorporated some suggested changes (see tracked changes) and have explained others that we have not included in the revised version of the manuscript.

We have provided responses to your comments below.

Thank you, and we hope the revisions meet your expectations.

 Comments:

This is an interesting paper that covers a ventilation air ditribution system that works slightly better than mixing ventilation. I have written my comments below:

Comment 1: Page 2 Line 70

Here the authors are describing a stratified ventilation system but there is no mentioning of a ventilation system that is heavily classified as stratified ventilation and that is impinging jet ventilation. Can the authors maybe write a small section with references to that system also maybe?

Reply: Thank you for the comment. We have discussed displacement ventilation as a classical type of stratified ventilation, since (1) its commonly used alongside underfloor air distribution in high occupancy spaces, (2) Impinging jet is undeveloped and not commonly used in high occupancy spaces although there is a surge of interest in the technology. Overall, displacement ventilation has been discussed since it’s a traditional and well-developed type of stratified ventilation system. Therefore, to simplify the study and to make it readable (not verbose), we have opted not to include discussing different types of ventilation systems.

Comment 2: Page 4 Line 177

"60 W incandescent lamps were distributed in the classroom and 176 a 100 W was used for the teacher (See Figure 1A)." This line is referencing Figure 1A in relation to heat loads that has been set in the room. I think the correct reference to figure should be Figure 2.

Reply: Thank you so much, its noted and corrected.

 Comment 3: Page 7 Line 253 "classroom has opposed" should be “classroom as opposed”

Reply: Noted and corrected. Thank you!

Comment 4: Also, if possible please doublecheck the English language in the paper.

Reply: Noted and spellchecked. Thank you!