Radiation analysis without epw weather file

I would like to conduct a radiation analysis using LadyBug. To do that I must input a sky matrix. To generate a sky matrix I need an .Epw weather file. I do not have a .epw file for my location but I do have the longitude/latitude location and I also have an hour by hour direct solar radiation values given in W/m^2. So I can generate a solar path and I know the direct radiation. I feel like this should be enough data to carry out a radiation analysis but I can't figure out how to do this be I am unsure how to generate a sky matrix from his data. I was thinking maybe I can create my own custom sky matrix? Or generate an .epw file (Although I have no clue on how to do either of these)?

Given the data that I have (direct solar radiation and location) how can I use the radiation analysis tool ?

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Replies to This Discussion

Permalink Reply by Omid Rashidi on March 12, 2017 at 1:56am

Hi Mike,

You can generate epw files with meteonorm.

best,

Omid

Permalink Reply by Mike Johnson on March 12, 2017 at 10:48pm

Omid, Thank you for providing that link. I'd like to avoid paying money for now, but I will play around with the demo version to see if I can use it. Thanks!

Permalink Reply by Sarith Subramaniam on March 12, 2017 at 6:26am

Hi Mike,

In addition to what Omid said, if you want to create a sky matrix from your data alone, you'd also need horizontal diffuse radiation values. The sky model used in Ladybug and Honeybee is based on Perez Skies. The sky matrix is created based on Reinhart patch subdivisions.

Below is a visualization of the Perez sky for a particular time and the sky-matrix corresponding to that.

The issue with using direct solar radiation only is that you won't be able to consider the effect of sky radiation in your simulation as shown below (the image on the right is sun-only):

Once you have the hourly data for direct-normal and diffuse horizontal radiation for the entire year, generating an epw(and then the wea) file from that isn't that difficult. We should be able to help you with that.

Permalink Reply by Mike Johnson on March 12, 2017 at 10:45pm

Ok great, thank you for the response.

So now I have 2 data columns - one for direct radiation (hour by hour for 1 year) and for diffuse radiation (also hour by hour for 1 year).

And then I have the location data.

I took a look at the link that Omid provided, but it seems as if it is paid software, which I want to avoid. Since I have all of the necessary data, I would like to make an epw file or a custom sky using the Ladybug/Honeybee components. Could you help me with this? Thank you!

Permalink Reply by Sarith Subramaniam on March 13, 2017 at 7:14am

Can you share the files here?

Permalink Reply by Mike Johnson on March 13, 2017 at 1:45pm

Yes absolutely!
Attached is the raw data: Direct solar radiation, diffuse radiation, ambient temperature, and location.

A couple things I would like to note:

I am only given a single days worth of data, so I am repeating the data day to day for 1 year. For my purposes, this is ok because my analysis period will only be a single day. The reason I repeated the data for 1 year is to maintain compatibility with the .epw format (from my understanding you need 1 years worth of data).
My Diffuse radiation values are estimated as 10% - 40% of the given direct radiation values. I figured this would be a reasonable approximation but perhaps there is a better way to produce an approximation.

Attachments:

weatherFile.xlsx, 248 KB

Permalink Reply by Sarith Subramaniam on March 13, 2017 at 4:38pm

So, here is a quick fix. The idea is to take an existing epw file and replace the desired datasets and location info. Below are some images as proof of concept. The first sun path contains data from the original epw file. The next one contains your dataset. The dataset to be replaced needs to be contained in a csv file as attached. You can replace more data from the original file by addiing additional columns in that CSV and assiging the correct column number in the grasshopper file. The ordering of columns in an EPW file is shown in the last image. For example, Direct-Normal rad is column -21 and Diff-Horz rad is -20. All of this will be clearer once you check the attached gh file.:

By the way, that theory about diffuse radiation being 10-40% of direct does not really hold. In a place like Seattle, one can expect to go without seeing the sun for extended periods of time and only see visible radiation from the sky.

(PS: I am sure there are probably more elegant ways to do this..I just wrote it this way to check if it was at all possible to do this with grasshopper).

Attachments:

weatherDataReplace.gh, 475 KB
weatherFile.csv, 134 KB

Permalink Reply by Sarith Subramaniam on March 13, 2017 at 4:43pm

Additional data that needs to be entered in the csv file is as per this:

Permalink Reply by Mike Johnson on March 14, 2017 at 12:42pm

Thank you, it worked! I was able to use your component successfully to change the .epw file by substituting in my data.

I then tried to feed the new EPW file into the following components: genCumulativeSkyMtx > selectSkyMtx > SkyDome for visualization. This required an Ladybug update, so i used the update component to update everything from 0.0.63 to 0.0.64. After the update I was able to see this:

which is over a 24 hour analysis period. (Look good?)

However, after I was able to obtain the sky matrix, the sun path component gave me an error : 1. Solution exception:global name '_solarOrStandardTime_' is not defined

I checked to make sure that _solarOrStandardTime was defined on the compnent (it is set to false).

Any ideas on what is going on?

Permalink Reply by Sarith Subramaniam on March 14, 2017 at 2:17pm

Is this happening with both the epw files ? If yes, it has to be a bug.

Permalink Reply by Mike Johnson on March 14, 2017 at 3:40pm

Just connected the original EPW file to the sun path component, and the error did not go away. So, possible bug. I am going to make sure I updated the components properly

Permalink Reply by Mike Johnson on March 14, 2017 at 3:44pm

it looks like the input variable on the gh component is "solarOrStandardTime_" but in the code it is "_solarOrStandardTime_" Maybe this could be the problem.

I looked at the old 0.0.63 component and the difference is that first underscore is not present on the variable. This could be the issue?