Analysis of the Optical Response of Opaque Urban Envelope Materials: The Case of Madrid^†

Round 1

Reviewer 1 Report

In this manuscript, Pérez et al. perform an in-field optical and near-infrared characterization of several surface finishing materials for outdoor walls and urban pavements that are commonly found in the city of Madrid.

Buildings are more frequently studied for the indoor comfort that they provide, but their external surface finish serves also aesthetic purposes and contributes to the thermal comfort of pedestrians walking in the streets.

This study represents a first step to understand how these elements contribute to the visual appearance and solar absorptance of the urban environment. In this respect, this work focuses appropriately on commonly used materials instead of high-end or specialized ones. This will allow to better evaluate the potential improvement that one can achieve with future renovations. Additionally, the authors provide interesting insights on the effect of ageing under real use conditions, showing that soiling and weathering will typically increase the solar absorptance of several surface finish materials, but also possibly reduce it in the case of certain asphalt or cement pavements.

 

As a general remark on this manuscript, I think it would be interesting if the Authors could try to draw some quantitative insight on how the choice of certain pavement materials (weighted by their surface fraction over a certain section of a typical street) among those analyzed in this work could reduce the net amount of Watts of solar power deposited per unit area on the ground. A similar comment could be made on the expected solar energy balance envisioned for a given combination of common materials, before and after years of ageing.

Secondly, an aspect that could be mentioned either directly in this work or as an outlook, is the solar absorption of the vehicles that will be typically parked and driving along the roads. Also in this case, one can expect mixed effects as these metal bodies could suffer significant solar gains, but also shade large areas of the dark pavements.

Finally, I would ask the authors to comment further on the supposed mechanism(s) that are potentially responsible for the increased solar reflectance with ageing observed for the H12-H13 pair. A possible explanation is provided for the H16-H17 pair, related to the degradation of the binder, but no suggestions are proposed for the H12-H13 case. Looking at Figure 2, the visual appearance is quite different between these two surfaces, therefore I wonder if the only difference between these two materials is in terms of ageing, or if there are reasons to believe that the starting material composition was also different.

 

Additionally, I have the following minor remarks:

* Despite being very common, I suggest that the expanded form of the acronyms UHI and LCA are also reported on their first occurrence.

* At line 94, the authors mention "inefficient and deprived residential areas". What do "inefficient" and "deprived" refer to? Energy inefficient? Energy deprived? In what sense?

* For certain samples, both "brand new" and "aged" versions of the same material are considered. Does it mean that the "brand new" materials are unused specimens that are tested in as-purchased conditions, or were they still found in-field during the survey? In this case they would be probably "slightly used" (a few weeks or months after the installation?), compared to the aged ones (years? decades?). Some extra information about these qualitative definitions could be useful.

* I appreciate the effort of the authors to create a database and contribute to a future catalogue of experimental thermo-optical properties of opaque envelope materials. As a suggestion, the visibility and impact of such database could be greatly increased if the database is released on some open repository platform, and relying on non-proprietary service such as OpenStreetMaps for the geo-location of the materials.

* Check the notation of alphas at line 241 and line 322

* Check typo at line 330: this -> these

 

In conclusion, I think that this manuscript would make a nice addition to the targeted Special Issue and deserves publication on Infrastructures, provided that the previous remarks are addressed.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

In this paper authors present a work developed to measure/characterize the light refletance on most common coverings and opaque finish materials of ground and walls in Madrid, Spain, urban region. The work is valid and the aim very important. However the experiments, hopefully only the way it is presented in thos paper, needs improvement in order for the conclusions to have a significant value.

In order for a scientific work of this kind to be useful and meanningfull, anyone should be able to reproduce the experiment and for that the paper must describe it in a clear, complete and objective way.

It is not sufficiently explained how reflectance was measured. What light source was used? If sun light, the month, day and time of the measure? Whats' the baseline?. How the results are normalised?. What the incidence angle? What is the measurement angle. What kind of sensor head was used, point like, integration sphere,...? Was it measured specular reflectance, diffuse reflectance,total reflectance, angle resolved,...?

Table 1. Why data on B2 is missing? Authors mention "opto-thermal parameters". How infrared emmissivity was measured or calculated? 

What is the relevance of the information given on line 260 to 263?

Please take these questions and remarks in consideration when revising the paper (some spelling and grammar minor problems can also be easily corrected.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Authors haven taken into account the reviewer remarks. However they fail to show (if they realize it) the limitations of their study by not considering directionality issues. We strongly suggest the authors to model the physical process in a more compreensive way.