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CFD analysis of Infiltration through cracks in Design Builder

asked 2018-05-06 07:56:26 -0600

Siva gravatar image

I am doing one project where I am modeling a Air conditioned room where I need to find out the infiltration rate through the crack areas because of the pressure differential existing between outside and inside...we would like to do CFD analysis and show the path of infiltration through windows...can that be possible in Design Builder?

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answered 2018-05-08 02:20:42 -0600

Dave gravatar image

I'm not 100% sure what you mean by "show the path of infiltration through windows". If you want to break this down to sub-component level, for example tracking infiltration through different parts of an opening such as the head, cill, mullions etc. then you can't do that. If you mean you want to calculate and see the infiltration rate through openings and its impact on space conditions then you can do that. You would set up a calculated natural ventilation simulation with the infiltration details specified (if you don't have data this could be an estimate using a crack template ranging from excellent (airtight) to very poor (leaky)) and run that to quantify the infiltration rate. You then select a time-step from the simulation results that represents the conditions of interest and input the simulation results as boundary conditions to the CFD calculation. You can transfer simulation data to populate the CFD starting/boundary conditions. As far as I recall the infiltration associated with a zone would be assigned to the relevant opening/s. Bear in mind that infiltration (as opposed to intentional ventilation) is likely to be small relative to the other convective/momentum forces in the zone from HVAC equipment etc. This process is shown in webinars and tutorials available on the DesignBuilder website, and the inputs associated with infiltration are detailed in the Help file. If you need further help you should contact the DesignBuilder Support Desk.

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Thank you very much. Here, the Scope of work is to determine the Infiltration due to window cracks....We would like to calculate infiltration rate (Ex filtration) through the spaces. Building is not yet installed. So, considering ASHRAE acceptable leakage values, we will do trail and error method to determine the crack that is suppose to be maintained during installation in order to term the building as ASHRAE tight building. We are generating indoor static pressures, external wind pressures and would like to see the infiltration effect through assumed crack areas.....

Siva gravatar image Siva  ( 2018-05-08 08:27:25 -0600 )edit

@Dave I am simulating the conditioned zone in Energy plus and once getting the infiltration values from energy plus, I would like to transfer it to Design builder and do the CFD analysis

When I am doing in Energy Plus, I can control the supply air flow rate by inputting the desired supply air flow rate. I do not know the pressure prevailing inside the room. I have return air flow rate. how can I represent return air flow rate in E+ without using the option of Pressure controller?...I want certain amount of air should enter and certian amount should leave. I want to model this situation in E+

Siva gravatar image Siva  ( 2018-05-11 16:57:32 -0600 )edit

Hi Siva, there are lots of possible ways to do this but it isn't appropriate for me to try to answer your detailed question here based on very little information (for example I don't even know whether you're using simple or detailed HVAC). Assuming you have a licence our tech support team will be able to help if you raise a ticket on the support desk. Alternatively you could start another thread on the forum asking the question you have raised here about fixing supply and extract air rates. Either way you'll need to provide more information.

Dave gravatar image Dave  ( 2018-05-14 01:44:54 -0600 )edit

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Asked: 2018-05-06 07:56:26 -0600

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Last updated: May 08 '18