AFN Simulation Control Azimuth Angle

asked 2025-04-18 13:43:01 -0500

Fred

11 ●3

updated 2025-05-06 17:37:17 -0500

Aaron Boranian

14385 ●90 ●25 http://bigladdersoftware.com/

Hello there, This might be a silly newby question, but I have a doubt about AFN: Simulation Control-Azimuth Angle of Long Axis of Building. Suposing my Buildin is 15 degrees from north, my AFN Angle of Long Axis of Building should be equaly 15deg. Now suposing my Buildin is -15 degrees from north (witch means 345deg in the Building North Axis object) what should be my correct AFN Angle of Long, since E+ in that object does not accept negative or higher than 180 deg values? Thanks in advance

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answered 2025-04-22 17:59:16 -0500

Jamie Sullivan
326 ●11 ●5

The trick here is that the AFN angle of long axis parameter is not asking you which way north is (at least not directly). Rather, it is there to rotate an imaginary rectangular building in order to carry out the simple pressure coefficient calculations. If we imagine a rectangle being rotated, then while one end might be pointing -15 degrees north, the other end will be pointing 165 degrees south (180-15). Editing the diagram in the InputOutput reference, it would look something like this:

quick edit of the AFN footprint diagram in the InputOutput reference

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Thanks for the answer, I was getting there, In fact I reviewed my ancient trigonométric class notes and got a trigo aproach. We are working here in the 2o quadrant where the bearing is 180 minus azimuth. For the 1o quadrant (the original fig 1.114) bearing equals azimuth. Posting a pic on that.

Fred ( 2025-04-24 14:02:28 -0500 )edit

@Fred you should have enough karma points now to post a photo. Please edit your original post to add an image.

Aaron Boranian ( 2025-04-24 16:02:09 -0500 )edit

I appreciate it!

Fred ( 2025-04-26 10:04:06 -0500 )edit

Whilst the EnergyPlus AFN is powerful, it is renowned for being difficult and time-consuming to use directly within EnergyPlus. I've known several EnergyPlus experts that avoided using it for that reason. They then tried it within DesignBuilder, which handles the complexity 'behind the scenes' and were amazed at how much easier they found AFN modelling. So you might want to try DesignBuilder with the "calculated natural option" selected and see how much faster and easier it is for yourself.

Dave ( 2025-04-27 06:46:13 -0500 )edit

Thanks for the comment, Dave. I'd love to use DB except for its price here, which is absolutely out of question, compared to an app that's free......

Fred ( 2025-05-05 08:10:22 -0500 )edit

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answered 2025-04-25 13:22:15 -0500

Fred

11 ●3

updated 2025-04-25 13:22:41 -0500

I reviewed my ancient trigonométric class notes and got a trigo aproach. We are working here in the 2o quadrant where the bearing is 180 minus azimuth. For the 1o quadrant (the original fig 1.114) bearing equals azimuth. image description