Daylight analysis and grid dimensions

[sercas12]

Hi I’m Sergio Castellano,

I’m trying to evaluate daylight factor inside a photovoltaic greenhouse (a plastic film greenhouse partially covered with opaque photovoltaic panels). My purpose is to compare computational results with data gathered by some luxmeters installed at 1800mm from the ground inside and outside the greenhouse. In Ecotect DF was calculated in the analysis grid whose dimension was defined by means of the “auto-fit grid to object” type to fit “within” (grid dimensions 53000x9500x6600mm). I divided the grid in 32x10x2 cells.

The problem is that changing the height of the grid (I used H=6600mm, H=3500mm, H=2500mm, H=2000mm) results on reference plane at 1800mm from the ground change too.

The same happens performing Solar Access Analysis – Shading Overshadowing and sunlight hours. I don’t understand what is wrong.

Thank you in advance and best regards

Sergio Castellano

[Pennetier1]

Hello sercas12, 

I think I understand your issue.  You are calculating DF on the grid @ 18000 mm but then when you want to compare to another grid at another level (6600, 3500, 2500 or 2000 mm), then you lose your previous calculations.

There are a couple of solutions to this issue:

1. You can save each grid for each elevation by going to the Grid Management button of the Analysis Grid control panel > Save as a .grd file (such as "1800.GRD") after each calculation.  You can then import your grids by going to the File menu > IMport > Model / Analysis Data > your .GRD file.

2. You can do the same steps as above but instead of saving as .GRD, you click on the "Manage Grid Data" tab and export your calculation as a .txt file.  This as the advantage to allow you to re-import all of your separate .txt files on a single Analysis Grid - you will still have to save that final grid as a .GRD file though.

3. Perhaps the easiest solution is for you to run the calculation on the 3D Analysis Grid. When running your calculation, select "Use Full 3D Extent of the Analysis Grid".  The calculation will take longer, but once it is done, you will be able to move your grid in all axis.  You can set the correct "Offset" to match one of your grid elevation.

I hope that makes sense.

Let me know if you have more questions on this topic, otherwise please accept as a solution so that others can benefit from this information.

Cheers,

[sercas12]

Thank you very much for your quick answer,
I performed calculation on the 3D Analysis Grid selecting "Use Full 3D
Extent of the Analysis Grid".

The problem was that changing the height of the 3D grid (6600, 3500, 2500,
2000 mm) using "grid size" in "grid management" and performing each time a
new calculation, changed also the results on the grid @ 1800 from the
groud. I expected to have the same (or almost the same) results. Please
find attached the file with different results @ 1800mm.

I hope I was more clear in my explanation

Thank you

Sergio

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[Pennetier1]

Hello sercas12, 

I did not see any attachment to your post.

I have created a quick and simple model to illustrate my idea about the 3D grid.

Create the grid on your greenhouse floor as you usually do.

Once in the grid management, set the Z Start position to 1800 and Grid Size to 4800.  I set the Number of Z cells to 12 for this one.

Run the calculations using the 3D grid extent.

Under the Snap Settings (the Magnet looking logo on your snap toolbar), enter 100.

Use the Offset sliding scale in the Analysis Grid control panel to move your grid from 1800 mm to 6600 mm in steps of 100 mm.

This might be the easiest thing for you to do for your analysis.

Let me know if that works.

Let me know if you have more questions on this topic, otherwise please accept as a solution so that others can benefit from this information.

Cheers,

[sercas12]

I performed a first Analysis  following your suggestions:

Once in the grid management, Z Start position to 1800 and Grid Size to 4800. I Ran the calculations using the 3D grid extent.

I used the Offset sliding scale in the Analysis Grid control panel to move my grid from 1800 mm to 6600 mm in steps of 100 mm.

It worked correctly.

Afterwards I performed a second Analysis changing the grid Z side:

In the grid management I set the Z Start position to 1800 and Grid Size to 1000. I Run the calculations using the 3D grid extent and with the same parameters of the previous.

I used the Offset sliding scale in the Analysis Grid control panel to move the grid from 1800 mm to 2800 mm in steps of 100 mm.

The problem is that results of two analysis @ 1800 are different (completly different) !! while I expected the same, it seems that results are affected by the grid size.

I performed other analysis changing the Z grid size and results @ 1800 were each time different.

Sorry for my insistence but I'm not understanding where the problem is.

Thank you

Sergio

PS the file was .docx, attached the file with the right extension

[Pennetier1]

Hello Sergio, 

I am sorry this is still not working for you.  I do not know why this happens since tests on the model I have sent you (changing the size of the grid in the Z axis) keeps similar results.

Please send me your .eco model so I can have a better look at your issue - you will have to zip it first and attach to the post.

Cheers,

[sercas12]

please find attache the "PV greenhouse" model.

Thank you in advance

[Pennetier1 · Accepted solution]

Hello sercas12, 

I have had a go at your model.  A couple of things:

1. Whn doing DF in Ecotect, you typically want an enclosed thermal zone on its own, rather than just various zones used for different objects as you have it in your model.  I understand you imported a 3DS file.  I have created a simple zone based on the general geometry and ran some calculation with the PV on the roof.  The reason for this is that Ecotect uses the surface normals of the zone, as well as some calculation that helps it determine if the light comes from the outside (as in outside of the zone).  This does not affect other analyses such as radiation, or even daylighting if using Radiance.

2. I still haven't been able to reproduce your issue.  I have used the model I am attaching here.  After I ran the calculation on the grid, I changed the Z height of the grid and ran the calc again.  For both models the results were the same on the 1800 mm plane.

So this got me wonder if you mean that the grid colour looks different or the numbers themselves?  If the color looks different, it is simply a matter of re-adjusting the scale by clicking on the "Fit Scale" button, next to the Maximum range input in the Analysis Grid control panel.  For both models, my average DF was identical on the 1800 mm plane, even though one had an Z extent of 4800 mm and the other was 2000 mm.

Let me know how things go on this model.

Best,

[sercas12]

The model you attached me works correctly ! probably something was wrong in my model, I'll try to semplify it considering, when possible a confinated volume as a unique thermal zone. In any case it works so now I have a good starting point to find the problem.

Thak you very much for your help.

sergio  castellano