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Peer review report 1 on “Modeling short wave solar radiation flux in a trench water harvesting system”
Agricultural and Forest Meteorology 217 (2016) 248
Contents lists available at ScienceDirect
Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet
Peer Review Report
Peer review report 1 on “Modeling short wave solar radiation flux in a trench water harvesting system”
Original Submission Recommendation
3.
Minor Revision 4. Comments to Author: This paper presents a model for irradiance on the bottom of rectangular trenches intended for micro-catchment water harvesting. The the study is certainly suitable for Agricultural and Forest Meteorology. The model is validated with experimental data, the results are convincing and the conclusion that the optimal trench water orientation depends on the time of the year when the rainfall occurs, is interesting. I raise two points here. First: although it is possible to follow the derivation of the equations, it takes considerable effort because references to equation numbers are not correct. Second: multiple scattering has not been taken into account in the model. The diffuse illumination on the trench walls is not only due to the visible part of the sky (Section 2.3.2), but there is also a contribution reflected by the opposite wall. If the sky is clear, the opposite wall is sunlit, and the albedo of the wall is 20%, then the contributions from the sky and the opposite wall could be in the same order of magnitude. Neglecting the multiple scattering could explain the underestimate of the irradiance in the deepest trench (see line 196, ‘..indicating some minor inaccuracy in the models computation, probably of the reflected radiation’). It is useful to show at least with one example whether neglecting this component is justified. Detailed comments: 1. The derivation of Eqs 8 and 19 are not so easy to follow because references to equation numbers are incorrect in Lines 97, 99, 106, 135, and 142. This needs to be corrected. 2. One limitation of the model that has not been addressed in the paper is that it does not consider multiple reflections. Multiple reflectance may enhance the diffuse irradiance on the walls. This will probably not affect the main conclusions of the paper, but it could perhaps explain the underestimate of irradiance at
DOI of published article: http://dx.doi.org/10.1016/j.agrformet.2016.02.014. http://dx.doi.org/10.1016/j.agrformet.2016.11.068 0168-1923/
5. 6. 7. 8. 9. 10. 11.
12. 13.
the bottom of the 60-cm deep trench close to the walls in the morning. In the derivation of Equation 8, and equation saying that dS = R2ˆ sin(psi)d alpha d psi is missing. Also (capital) R is undefined but I guess it is small ‘r’. Line 46, ‘The first step. . .’ this sentence is grammatically incorrect, probably ‘in’ was meant to be ‘is’ Line 74, ‘angel’ should be ‘angle’ Equation 3. I did not find the definition of AZI. Equation 3: Following the definitions in Figure 2, one gets to Theta = pi+NOR-Phi, not the equation given here. Line 139: ‘fraction of skies’ -> ‘fraction of the sky’ Line 144: It would be helpful to mention that gamma i is defined in Figure 8. Line 235, Sentence Which case are you referring to?’ is odd. Line 254, The E-W direction is discussed in terms of aspect (Line 250: ‘a trench with aspect of 0.25’ etc), while the N-S direction is discussed in terms of depth (‘In the 1.5 m deep trench’). For consistency it might be better to use only ‘aspect’. Figure 6. The figure caption does not make it clear what we see in left and the right figure. Figure 11, Depth 60 cm, 28/7/14, what could have caused the large discrepancy between model and measurement in the afternoon at 8 cm from the southern wall?
First revision Recommendation Accept Comments to the author The authors have addressed all the earlier comments well. There is still one issue with the equation numbers. There are two Equations 4. The equations starting line 94 should be incremented. With the incremented numbers, the references to equation numbers in the text are correct. Anonymous Available online 2 December 2016
Contents lists available at ScienceDirect
Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet
Peer Review Report
Peer review report 1 on “Modeling short wave solar radiation flux in a trench water harvesting system”
Original Submission Recommendation
3.
Minor Revision 4. Comments to Author: This paper presents a model for irradiance on the bottom of rectangular trenches intended for micro-catchment water harvesting. The the study is certainly suitable for Agricultural and Forest Meteorology. The model is validated with experimental data, the results are convincing and the conclusion that the optimal trench water orientation depends on the time of the year when the rainfall occurs, is interesting. I raise two points here. First: although it is possible to follow the derivation of the equations, it takes considerable effort because references to equation numbers are not correct. Second: multiple scattering has not been taken into account in the model. The diffuse illumination on the trench walls is not only due to the visible part of the sky (Section 2.3.2), but there is also a contribution reflected by the opposite wall. If the sky is clear, the opposite wall is sunlit, and the albedo of the wall is 20%, then the contributions from the sky and the opposite wall could be in the same order of magnitude. Neglecting the multiple scattering could explain the underestimate of the irradiance in the deepest trench (see line 196, ‘..indicating some minor inaccuracy in the models computation, probably of the reflected radiation’). It is useful to show at least with one example whether neglecting this component is justified. Detailed comments: 1. The derivation of Eqs 8 and 19 are not so easy to follow because references to equation numbers are incorrect in Lines 97, 99, 106, 135, and 142. This needs to be corrected. 2. One limitation of the model that has not been addressed in the paper is that it does not consider multiple reflections. Multiple reflectance may enhance the diffuse irradiance on the walls. This will probably not affect the main conclusions of the paper, but it could perhaps explain the underestimate of irradiance at
DOI of published article: http://dx.doi.org/10.1016/j.agrformet.2016.02.014. http://dx.doi.org/10.1016/j.agrformet.2016.11.068 0168-1923/
5. 6. 7. 8. 9. 10. 11.
12. 13.
the bottom of the 60-cm deep trench close to the walls in the morning. In the derivation of Equation 8, and equation saying that dS = R2ˆ sin(psi)d alpha d psi is missing. Also (capital) R is undefined but I guess it is small ‘r’. Line 46, ‘The first step. . .’ this sentence is grammatically incorrect, probably ‘in’ was meant to be ‘is’ Line 74, ‘angel’ should be ‘angle’ Equation 3. I did not find the definition of AZI. Equation 3: Following the definitions in Figure 2, one gets to Theta = pi+NOR-Phi, not the equation given here. Line 139: ‘fraction of skies’ -> ‘fraction of the sky’ Line 144: It would be helpful to mention that gamma i is defined in Figure 8. Line 235, Sentence Which case are you referring to?’ is odd. Line 254, The E-W direction is discussed in terms of aspect (Line 250: ‘a trench with aspect of 0.25’ etc), while the N-S direction is discussed in terms of depth (‘In the 1.5 m deep trench’). For consistency it might be better to use only ‘aspect’. Figure 6. The figure caption does not make it clear what we see in left and the right figure. Figure 11, Depth 60 cm, 28/7/14, what could have caused the large discrepancy between model and measurement in the afternoon at 8 cm from the southern wall?
First revision Recommendation Accept Comments to the author The authors have addressed all the earlier comments well. There is still one issue with the equation numbers. There are two Equations 4. The equations starting line 94 should be incremented. With the incremented numbers, the references to equation numbers in the text are correct. Anonymous Available online 2 December 2016