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Manually specified airflow is "ignored"

asked 2022-10-20 10:57:50 -0500

Jim Dirkes
3424 ●25 ●15

updated 2022-10-20 15:53:42 -0500

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13830 ●76 ●24 http://bigladdersoftware.com/

I'm scratching my head! I've specified a very simple, electric heating-only system with heat exchanger to be constantly at 6.6m3/s (14,000 cfm). The IDF confirms this value in several locations. (AirLoopHVAC, HeatExchanger:AirtoAir:SensibleandLatent, Fan:Constantvolume)

When I run the simulation, however, and examine the output, the airflow shows a constant 4.6m3/s (~9,800 cfm).

If I change the inputs to 9.9m3/s (21,000cfm), the results stay at 4.63m3/s.

This makes no sense to me, since I think I've manually specified everything associated with airflow... Insights will be very much appreciated.

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Can you attach your IDF via e.g. Google Drive or Dropbox? I doubt anyone can help without more information.

shorowit ( 2022-10-20 18:13:29 -0500 )edit

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answered 2022-10-21 08:13:19 -0500

Jim Dirkes
3424 ●25 ●15

I was reminded of something I "learned" several months ago by Shaun Wang at DesignBuilder: If I autosize AirDistributionUnits (ADU), but hard size the fan airflow... the hard sized fan airflow is ignored whenever the autosized ADUs need a smaller total.

Manually sizing the ADUs corrects that problem.

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Asked: 2022-10-20 10:57:50 -0500

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Last updated: Oct 21 '22

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