[Bldg-sim] IES CFD Modeling Issue: Reverse Flow through Diffusers

Brain, Joshua JBrain at Vanderweil.com
Fri Jan 11 05:44:22 PST 2008



I am using IES to conduct a CFD model on a long and narrow room (283ft
by 60ft) with three large ducts (square 4ft by 4ft) running along the
ceiling (280ft long, 28ft off the floor). I have 18 diffusers equally
spaced along each of the three 280ft ducts for a total of 54. Each
diffuser has a CFM of 1110, an area of 3.75 sf, and a discharge velocity
of 300 fpm. There is a single return grill at one end of the building. 


My problem is: when I look at the velocity vectors in the MicroFlo
Viewer some of the diffusers have the air flowing backwards or into the
diffuser, not flowing out as it is supposed to. This occurs across all
three duct lengths at the same diffuser location. 


Has anyone else run into this and have they resolved the issue?  IES
took my model and made changes to it only to find that they could not
fix it. 


Thank you in advance for any advice, 



Joshua Brain

Mechanical Group 

R.G. Vanderweil Engineers, LLP 

274 Summer Street     Boston, MA  02210 

Tel: (617) 423-7423 

Fax: (617) 423-7401 

Direct: (617) 956-4565 





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