The UWG failed to run with low temperatures

Hi there,
I am encountering issues while running the Urban Weather Generator (UWG) simulation. After investigating, I discovered that the simulation fails on days when the temperature in the EPW file is lower than approximately -24°C. By replacing the EPW file with one containing higher temperatures, the simulation runs without any interruptions. I understand that the chosen region is characterized by extremely cold conditions, but I would like to know if there is a solution to this issue. Below is the error code I encountered:

  1. Solution exception:The UWG failed to run:
    UWG model simulation failed.
    Got canyon temperature at -23.246093420283643 C. Something obviously went wrong (
    Traceback (most recent call last):
    File “C:\Users\62667\ladybug_tools\python\lib\site-packages\uwg\cli\”, line 50, in simulate_json_model
    File “C:\Users\62667\ladybug_tools\python\lib\site-packages\uwg\”, line 1354, in simulate
    self.forc, self.geoParam)
    File “C:\Users\62667\ladybug_tools\python\lib\site-packages\uwg\”, line 288, in UCModel
    ‘wrong (’.format(self.canTemp - 273.15))
    Exception: Got canyon temperature at -23.246093420283643 C. Something obviously went wrong (
    Any help or suggestions on how to resolve this problem would be greatly appreciated. Thank you!

Hi @XINYUXU - this is probably an error checking code from the UWG Matlab code (i.e. the version that I worked on back in 2016) that should have been removed. At the time, I was dealing with numerical convergence issues so had added a check but I probably forgot to remove it and it probably just got copied to the Python version of it. At the time, I was working with warmer weather files so this was an arbitrary value as a quick & dirty way to check when the solution failed to converge.

@chris @SaeranVasanthakumar

1 Like

Thanks for your response. I’m using Dragonfly v1.60 with built-in UWG, but the issue persists. This interruption prevents a full EPW file from morphing.I’m still experiencing this problem.

As a quick fix for your own set up, use a text editor to open the file ““C:\Users\62667\ladybug_tools\python\lib\site-packages\uwg\”” and edit the values in line 286 to a different value. The problem is the ‘self.canTemp < 250’ part as the lower threshold so either use something lower like 200 or comment out the section altogether.

Note for @chris & @SaeranVasanthakumar:
If I remember correctly, this checking is not really necessary at this point anymore as the canyon temperature calculation was changed to an implicit step.

Thanks for your help. I’ll work on resolving the issue. If I have more questions, I’ll reach out.

Thanks for making us aware of this, @josephyang , and for reporting the issue, @XINYUXU .

I loosened the check to accept temperatures down to -73C, which should accommodate some of the coldest recorded temperatures on Earth:

The fix should be available with the LB Versioner component in a couple of hours or so.