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Outdoor Air Summary Report is 40% of the Outdoor Air setted?

asked 2016-09-27 16:18:04 -0500

updated 2020-01-27 18:46:34 -0500

Why Outdoor Air Flow in the Outdoor Air Summary Report is always 40% of the Outdoor Air setted?

I have a model with system Package Rooftop and the Outdoor Air System is setted for a minimum and a maximum of 153 cfm. Althought, when I calculate the flow in the Outdoor Air Summary Report (ACH x Zone Volume / 60), this is 63 cfm (40%) of I had setted in the Outdoor Air System. This occur in all systems of the model.

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Is your airloophvac or fan hard sized?

Julien Marrec gravatar image Julien Marrec  ( 2016-09-27 16:44:10 -0500 )edit

Hi @Julien Marrec. Thank's for your time. I only seted outdoor air flow hard sized, both in Air Loop as in Outdoor Air System. The fan is configured to autosized.

Geraldo Pithon gravatar image Geraldo Pithon  ( 2016-09-27 19:10:04 -0500 )edit
1

Are you hardsizing your supply air flow as well, in the OS:AirLoopHVAC?

gokul gravatar image gokul  ( 2016-09-28 09:39:39 -0500 )edit

@gokulram, the Design Supply Air Flow Rate is AutoSized, but the Desgin Outdoor Air Flow Rate is Hard Sized. I inserted a new figure in the question to represent this condition.

Geraldo Pithon gravatar image Geraldo Pithon  ( 2016-09-28 11:23:51 -0500 )edit

I am not sure how that is happening. I am guessing that it maybe the Supply Airflow that is limiting the Outdoor Airflow to that number. I would check the System Summary Report for the value of the Supply Airflow to this AirLoop, and see if it is higher than the outdoor air. If it's not, then the outdoor airflow will be limited by the maximum value of the supply air. Usually autosizing supply air should take care of this, but it is worth a check! Let me know if this helps.

gokul gravatar image gokul  ( 2016-09-28 12:38:20 -0500 )edit

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answered 2016-09-29 10:34:10 -0500

updated 2016-09-29 10:38:22 -0500

It looks like you have set both the min and max OA flow to 153 cfm, causing a constant OA flow whenever fresh air is needed. Since you have autosized the supply flow rate, there's a chance that EnergyPlus is calculating a supply flow less than your hard-sized OA flow. Check the Outdoor Air Summary report and the HVAC Sizing Summary report to see if this is the case.

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@Aaron Boranian thanks for your answer!! I think this is not the problem, because I ploted the Mechanical Ventilation and it is constant and equal to the input (see the new picture in the question) and the Supply flow is bigger than the Outdoor Air Flow in the HVAC Sizing Summary.

Geraldo Pithon gravatar image Geraldo Pithon  ( 2016-09-29 10:51:55 -0500 )edit

In the HVAC Sizing Summary, the OA Minimum Outdoor Air Flow Rate is different from calculated in Outdoor Air Summary and from the ploted.

Geraldo Pithon gravatar image Geraldo Pithon  ( 2016-09-29 10:54:25 -0500 )edit

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Asked: 2016-09-27 16:18:04 -0500

Seen: 152 times

Last updated: Sep 29 '16