Unbalanced airflow in a space

asked 2021-09-11 16:18:46 -0600

updated 2022-02-08 09:15:15 -0600

Hi, everyone! So it appears to me that my energy modelling software does not allow for modelling unbalanced airflow in a space (i.e. exhaust rate is higher than supply or vice versa). What are some workarounds people use to account for energy use in unbalanced airflow situations? I imagine one can model a system with a correct supply airflow and account for additional (or reduced) exhaust rate later in exceptional calculations. Can someone describe this in more detail? My main interest is energy modelling as per 90.1 for LEED. I use DesignBuilder but I am mostly interested in a universal solution.

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answered 2021-09-12 05:25:05 -0600

Jim Dirkes
3564 ●27 ●16

Energyplus DOES allow modeling unbalanced airflow - though it complains in the error messages. DesignBuilder allows this, too (at least it has in the past) If you want to get rid of the error messages, add one of the E+ "transfer" objects via DesignBuilder's "additional IDF" option at simulation time

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Thank you for the reply. I can't quite get what you mean by "add one of the E+ "transfer" objects via DesignBuilder's "additional IDF" option at simulation time". What are a transfer object and additional IDF option at simulation time? Where can I read more about this?

Kirill Fedtsov ( 2021-09-12 05:42:52 -0600 )edit

In DB, follow the menus: Simulation, Options, Include IDF Data. The Help file for this is:https://designbuilder.co.uk/helpv7.0/#Advanced_Calculation_Options.htm Note that the "included" IDF must be placed in a specific folder, which is noted on the Help article.

The E+ objects are: ZoneMixing and ZoneCrossMixing (sorry to have gotten the names wrong!)

Jim Dirkes ( 2021-09-12 08:10:00 -0600 )edit

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answered 2021-09-12 04:25:15 -0600

Dave
1627 ●16 ●4

I don't believe your statement that "my energy modelling software does not allow for modelling unbalanced airflow in a space (i.e. exhaust rate is higher than supply or vice versa)" is correct. I would advise you raise a ticket on DesignBuilder's support desk (https://support.designbuilder.co.uk/) with relevant model details and they will provide guidance.

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I already did that and they replied with the following: "No, there isn't any way to model unbalanced flow from the AHU directly. The way to have unbalanced flow is by adding an exhaust fan air component in the same HVAC zone." So adding an exhaust fan is a workaround and I am wondering about which methods do people use to setup such a system. For example, I have a space with 100 l/s supply air and 50 l/s exhaust air.

Kirill Fedtsov ( 2021-09-12 05:38:18 -0600 )edit

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