Empirical and Numerical Analysis of an Opaque Ventilated Facade with Windows Openings under Mediterranean Climate Conditions

Round 1

Reviewer 1 Report

The presented manuscript sets out to investigate the behaviour of an opaque ventilated façade with windows through experimental and numerical analyses. The experimental campaign is thoroughly described and results are shown for three different seasons and two different ventilate façade configurations (both with the cavity opened and closed). The numerical simulations were performed by means of a FEM tool, and a validation process was carried out with respect to the data gathered during the experimental campaign. With the validated model, further analysis were performed considered the ventilated façade, in particular the assessment of the potential yearly energy savings with respect to a standard, non ventilated façade.

In the abstract, the main novelty highlighted is that the presented paper investigates an opaque ventilated façade with a window, with 3D implications scarcely explored in literature. However, the importance of taking into account the window (seen merely as an obstacle to airflow, with no thermal implications) was not assessed: it could have been expected, for example, a comparison between a 2D and a 3D simulation, in order to quantify the assessment error due to not considering the window, as authors state occurs in the majority of cases.

The introduction is quite poor and not well organized. Many papers regarding opaque ventilated façades that are present in literature and are in line with the presented topic are not cited in the work. Just to cite few:

• Environmentally friendly opaque ventilated façade for wall retrofit: One year of in-field analysis in Mediterranean climate, De Masi et al., 2021
• An experimental sensitivity analysis on the summer thermal performance of an Opaque Ventilated Façade, Fantucci et al., 2020
• Methodology used to investigate the energy savings of opaque ventilated façades in residential buildings in Brazil, Maciel et al., 2021
• Sensitivity study of an opaque ventilated façade in the winter season in different climate zones in Spain, Lopez at al., 2015

In the Introduction, as well as in other sections of the paper, there are repeated sentences (e.g. from line 101 to 106).

The experimental setup is well described.

The modeling setup is very long, confusing and does not add much to the overall paper: many basics building physics equations are presented along with concepts which should not be detailed in a journal paper, being matter of well known physics principles.

Results include too many plots, many avoidable, redundant or simply not useful. In many cases plots are hard to read and difficult to compare: for example, Figure 9 presents an unusual representation of solar radiation plotted in the same y-axis as the ambient temperature; Figure 10 a) and b) are meant to be compared by the reader, but the scales of the neither of the two y-axes are not the same.

The model validation is presented merely as a comparison between the measured results and the simulation results in terms of temperatures (surprisingly not air velocities). Graphs are not well readable also in this section.

The analysis of energy saving section is well described and clear, although it seems out of the scope of the paper and not novel.

In the conclusions, authors list a number of findings: first, they state that the OVF behavior is three dimensional, which does not seem surprising; moreover, no comparison between a 3D and a 2D model were performed, demonstrating the impossibility or the big errors done by simplifying the OVF façade with a window using a 2D model. Then, it is stated that the OVF acts as a barrier between external and internal conditions; this facts are largely discussed and stated in literature. The other findings regard the façade performance, especially in comparison with the non ventilated one. These, again, are largely discussed in literature and were not the outcomes expected by reading the title and the abstract of the paper.

Concluding, this paper presents single portions of the work that yield a good potential (the experimental campaign, the FEM model, ecc), but which do not lead to novel conclusions.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

• The authors performed excellent work on the OVF, studied the thermal behavior both experimentally and numerically.
• Highlight various protocols used for measured and analyzed data
• The effects of shading of test cell have been considered in the study, which helps in reducing the uncertainty in analysis.
• The thermal performance of the individual materials performs differently, compare to an envelope assemblage, the dynamic thermal performance of the envelopes should be having been considered.
• Why the effects of hygrothermal material properties have not been considered in the study?
• Table 4: Have you considered the accuracy / tolerance of sensor used for measuring the data in validation of numerical model?
• Line 278: Appendix is missing
• Line 688: The reference is missing
• Did you considered the temperature dependent thermal conductivity of the materials in the numerical model?

Author Response

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Reviewer 3 Report

Report on the manuscript “Empirical and numerical analysis of an opaque ventilated facade with windows openings under Mediterranean climate conditions”. Carlos-Antonio Domínguez-Torres, Ángel L. León-Rodríguez , Rafael Suárez , Antonio Domínguez-Delgado.

This paper deals with the mathematical modelling and numerical simulation of opaque ventilated façade (OVF) in Mediterranean areas. The experimental study is carried out in a building located at Seville (Spain). The mathematical model solved is based on Navier-Stokes equations with a Bousinesq formulation for buoyancy, and k-e model for the consideration of turbulence. The model is mainly solved in 3D, although some comparisons are performed with a 2D model. Numerical results are given using the software FreeFem++ combined with the characteristic method for time discretization. Results of the numerical simulation show a good agreement with experimental data.

1. Is this study focused in new buildings or is it possible to apply it also to old buildings? Would this be too expensive or even unaffordable?
2. Concerning the window that is incorporated to the façade, is it possible to consider in this model PV Windows in order to generate electricity?
3. The authors carry out also 2D simulations and conclude that the errors are much higher than in the 3D case. Concerning the computation time, is there a big difference between the 2D and the 3D case? Could the authors introduce some hint related to CPU time?
4. Why the authors choose P2 elements for velocity computation but P1 for pressure and temperature? Why different types of elements are chosen?
5. It seems that the mesh considered is regular. Is it possible to introduce a non-structured mesh to be refined where needed?
6. Is the code parallelized?
7. Could this methodology be applied to other regions in Europe, with different climatic features?

 

 

Minor:

• In line 677 a number of a figure is missing (it is written??).

 

Author Response

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Author Response File: Author Response.pdf