WUFI

Hello

I haven't managed to find out which model WUFI 2D uses to calculate the wind-dependent heat transfer coefficient. How is it done?

Best regards
Pär Johansson

Hello Pär,
that is not yet included in the 2D online help. I copy it for you from the Wufi 1D help file:

If you have activated the option "wind-dependent", WUFI determines the heat transfer coefficient as follows, in dependence of the format of the selected climate file:

TRY and IWC format:

If the inclination of the component is greater than 10° and the surface of the component is facing away from the mean wind direction (i.e. leeward conditions):

a = 0.33 * v_wind + 4.5 + 6.5 [W/m²K].

Else (windward conditions):

a = 1.6 * v_wind + 4.5 + 6.5 [W/m²K].

4.5 W/m²K is the convective heat transfer coefficient for v_wind = 0 m/s and 6.5 W/m²K ist the radiative component.



DAT format:

Same method as with TRY, but DAT files may also indicate variable wind (wind direction "999"). In this case, the average of leeward and windward conditions is used.

WET format:

Instead of a general mean wind direction, the WET format offers detailed information about the frequency of different wind directions during the hourly measurement interval.

If the inclination of the component is less than 10° (i.e. permanent windward conditions):

a = 1.6 * v_wind + 4.5 + 6.5 [W/m²K].

Else:

a = weight_windward * (1.6 * v_wind + 4.5 + 6.5) +
weight_leeward * (0.33 * v_wind + 4.5 + 6.5) [W/m²K].

The weighting factor weight_windward is the sum of the components of the measured wind directions perpendicular to the component surface and weighted according to their duration.
Weight_leeward is (1 - weight_windward).

4.5 W/m²K is the convective heat transfer coefficient for v_wind = 0 m/s and 6.5 W/m²K ist the radiative component.

WAC and WBC Format:

Same method as with TRY if the file contains wind direction and wind speed (scalar or vectorial). Otherwise, no wind-dependent heat transfer coefficient can be determined, and WUFI simply uses the value in the text box.

KLI format:

This format does not contain any information about wind speed or direction, so that no wind-dependent heat transfer coefficient can be determined, and WUFI simply uses the value in the text box.

Hope that answers your question,
Christian

Indeed, that helped.

Thank you very much for your fast response!

/Pär