How to get Wind Factor for Pedestrian Wind Comfort Tool

grasshopper butterfly
1

Hi,

I would like to run the Pedestrian Wind Comfort Tool but I don’t know where to get the Wind Factor values. I have run an Outdoor Airflow Analysis using butterfly, is there something within there that gives me the Wind Factor?

Best,
Elizabeth

2

Hi @ELeriche

Wind factor values are non dimensional values produced always for a height of interest. What we usually do to calculate them is sample wind velocity values from our simulation at a certain height, say 1.5m from the ground, and then divide that to the wind velocity our wind tunnel would have at 1.5m.

The second number is quite easy to calculate using the Ladybug_Wind Speed Calculator component where you give the velocity you used in BF for the ‘windspeed_tenMeters’ value and the height you want to calculate velocity for (remember to use logarithmic profile).

Dividing those numbers should do the trick. However the pedestrian comfort calculator takes yearly values so this means you’d need more wind directions to generate enough data. If you only have the one, and still want to try this despite having quite a bit of error, multiply the wind velocity in your EPW by these wind factors you calculated above.

Kind regards,
Theodore.

1 Like
3

Hi Theodore @TheodorosGalanos ,

Thank you for your reply, this is a great help. What would be the best method to conduct an analysis in a particular season of the year?In particular we are looking at the winter months for this analysis as it is a cold climate and the wind will have a big effect on the pedestrian wind comfort.

Right now I am thinking of getting the wind speed results from the Ladybud_Wind Speed Calculator from November to December and running the cfd for multiple (thinking 6) directions using these values and then calculating the wind factor and plugging that into the pedestrian comfort. Is there a better method to going about this?

Thanks,
Elizabeth

4

Hi @ELeriche,

That is pretty much the approach yes. If you want to do a specific study then a good start is the wind rose component. Visualize your winds for the period and/or time during the day you want and see what the dominant winds are. Then choose some or all of them and run the corresponding CFD. That will give you one wind factor for each point, in each direction.

Using those should get you the result you want. I would run the CFD first and then start with one point trying to get to a wind velocity schedule based on your wind factors, then replicate that to all points in the mesh.

Kind regards,
Theodore.