Question about the quality of wind data within DOE epw files

A bit off topic.

I'm in the midst of a pedestrian comfort study and I'm currently analyzing wind velocities on 12 orientations. To do that I need an average velocity over the year for each of the orientations (0, 30, 60, ..).

I use a simple definition with native components to extract this information from the epw file. However, I run into some 'trouble'.

There seem to be a lot of 0 values in the wind velocities. Most of these 0 values seem to be associated with the 0 direction (north direction is common in this weather file, i.e. Singapore, but I doubt it is so many 0s).

I then proceeded to cull all the hours with 0 wind velocity and did the averaging over all the remaining hours (around 7100 for this weather file). However, I still get a bit of odd results that don't coincide with other data I have for the area. For example, average wind velocity in the north seems to be 1.12m/s while officially Singapore reports 2.1m/s. More discrepancies arise in the frequencies of the wind directions (the hours of each direction per year divided by total hours) from publically available data.

Anyways, I don't want to tire you with so many specifics. The question to the forum is if anyone has used .epw files to collect wind data before and if we believe they are dependable for such calculations? If not, do you have any idea on where I could find open wind data of good quality?

Thank you very much in advance.

Kind regards,

Theodore.

P.S.: Will be adding the definition once I'm in the office, even though it is quite straightforward.

Replies are closed for this discussion.

Replies to This Discussion

Permalink Reply by Abraham Yezioro on February 14, 2016 at 4:08am

Theodoros,

This is an interesting one.

First of all, without knowing how is the weather in Singapore, i don't agree and like annual averages for wind considerations. Yo can't bring together winter and summer (for instance) into the same calculation for the average. You should know, at least, what is going on in winter, summer, or any other period of time.

Second, you are right about your fears of the reliability of the weather files. But, unless you have a local station, there is not much you can do about this. Unfortunately this is a big constrain and limitation. The best is to have the station at your plot. Any other data you have will be an approximation to your site.

Third, this is a wish for the wind analysis components. I wish to get the main first and second directions and their average velocities (in just 2 numbers and directions).

-A.

Permalink Reply by Mauricio Aguilar Cardenas on February 14, 2016 at 10:51am

You can find daily mean and max values for singapore here, you can even download csv data which makes life much easier:

http://www.weather.gov.sg/climate-historical-daily/

As Abraham said, best thing would be a station near your plot and detailed data, but "you can't always get what you want...but..sometimes...you get what you need".

Hope this helps.

regards,

Mauricio

Permalink Reply by amedeo scofone on April 25, 2016 at 4:33am

hi Theodoros,

Usually in wind data (at least here in the UK) when you have wind coming from north it is 360 deg and not 0. the wind direction 0 usually indicates calm, no wind condition that does no relate to the wind coming from north.

I would suggest you to put a condition in you formulas that when wind speed is 0 and direction 0 it goes on a 13th category.

I hoppe this helps.

Best,

Permalink Reply by Theodoros Galanos on April 25, 2016 at 10:09pm

Hi Amedeo,

Since the original post I have realized that indeed and have filtered out the results. It has brought the frequencies to the expected number for each orientation.

The other mismatch of average velocities was my mistake. Apparently Singapore is unique in the way the average their velocites (@15m), which is different than what EPW files do (@10m).

Thanks!

Kind regards,

Theodore.

Permalink Reply by Mostapha Sadeghipour Roudsari on April 25, 2016 at 9:29am

Ladybug windrose does already filter the hours with 0 wind speed. That's why it generates a separate circle for calm hours.

Permalink Reply by Theodoros Galanos on April 25, 2016 at 10:10pm

Hi Mostapha,

Do you think it is easy to incorporate average wind velocity calculations to the windrose? That is if that isn't there already :)

I can imagine the component cutting the rose into as many segments the user requires, and spiting out average velocities for each segment.

Kind regards,

Theodore.

Permalink Reply by Mostapha Sadeghipour Roudsari on April 26, 2016 at 6:53am

It's not there but it's pretty doable. Let's add it to Ladybug's github.

Permalink Reply by amedeo scofone on April 26, 2016 at 9:16am

I developed a definition that gives you % of frequencies based on the beaufort scale and season, Is that something you might be interested in?

Permalink Reply by Theodoros Galanos on April 26, 2016 at 10:00am

Hi Amedeo,

That would be very interesting definition. It would be nice if you wanna share. It would be very helpful for single point pedestrian wind comfort assessment.

However, for assessment of even the smallest grid the files produced by the current workflow we are testing will be way too large for GH lists. I think python coding will be needed. That said, that code is quite simple and doable (if I knew how). At the moment, my solution is working in R, which handles big data quite well. I will share my R code/process here in the morning (again a very simple code), in case it helps this.

Kind regards,

Theodore.

Permalink Reply by amedeo scofone on April 26, 2016 at 10:31am

Theodoros,

It is still a WIP but I hope it helps, sometime the wind roses are a bit funny.

Sadly i don't know python so it is based on gh components

Ranges are <3,3,4,5,6 and >6 in order to correlate wind speeds with the lawson criteria which is the pedestrian wind comfort mostly used in the UK.

Best,

Attachments:

Beaufort scale Ranges.gh, 756 KB

Permalink Reply by Theodoros Galanos on April 26, 2016 at 11:15pm

Thank you very much for sharing Amadeo!

Will give this a try and see the limits of native GH components in relation to how long can the lists imported be.

Kind regards,

Theodore.

Permalink Reply by Mostapha Sadeghipour Roudsari on April 27, 2016 at 7:37am

Hi Amedeo,

I couldn't get the file to work as I wasn't sure what is the excel data to be imported. I definitely think it's quite useful to map comfort on top of values. How do you use this? Do you map the values on top of the wind-rose or do you calculate percentages?

I'm going to re-write wind-rose component soon and I can include this feature in the component. What about mapping the values as an annualHourlyData?

Mostapha