Using the ASTMC1340 convection algorithm in E+

asked 2025-08-06 13:42:28 -0500

updated 2025-08-07 03:23:48 -0500

Hi all,

I’m trying to model a ventilated roof cavity, completely unconditioned, with a few openings (but tbc where and how big etc). Right now I’m testing a few different infiltration rates to see how the cavity temperature changes. But I’d also like account for the internal convection coefficient, which will change as a function of the air movement. I’m trying out the ASTMC1340 algorithm which should be a function of air speed (among others), but I can't figure out how to change this air speed parameter...

I'm currently trying

ZoneAirVelocity,
      Room1,
      0.2;

... but this doesn't seem to work. Any ideas?

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Comments

@Jroberts what simulation tool are you using? Please mention it in the title or body of your post, as well as add a tag so that others can provide better help.

Aaron Boranian's avatar Aaron Boranian  ( 2025-08-06 16:44:38 -0500 )edit

Sorry Aaron, first time here, I've clarified I'm using E+

Jroberts's avatar Jroberts  ( 2025-08-07 03:24:37 -0500 )edit

@Jroberts thanks for updating your post!

Can you upload your model to Google Drive, Dropbox, etc. and then share a URL for others to download? That would help others provide better solutions.

Aaron Boranian's avatar Aaron Boranian  ( 2025-08-07 11:10:15 -0500 )edit

I figured out the answer from the E+ source code. E+ calculates the velocity based as the air change rate multiplied by the cube root of the volume of the thermal zone

Jroberts's avatar Jroberts  ( 2025-08-07 11:32:03 -0500 )edit
1

@Jroberts nice! Glad that you found a solution. You can "self-answer" your own question by creating a solution post below, which lets others know that the solution works. Plus, other users can up-vote your solution and give you karma points.

Aaron Boranian's avatar Aaron Boranian  ( 2025-08-07 14:11:51 -0500 )edit