Discrepancy between hand calc and CONTAM -- flow from ambient

[Joe Roberts]

Hi all,

I'm trying to double check the results I got from my CONTAM model. I have the ambient at -4C and zone temperature at 20C. I have an external door (closed) defined by the flow coefficient 0.0025 m3/s/Pa^n and flow exponent 0.6. 

According to my results, the dp on the flow path is 55.2113 Pa, so I would expect a flow rate of 0.0025 * 55.2113^0.6 = 0.0277 m3/s.

... but according to CONTAM, the flow rate is 0.06 sm3/s. Even if I adjust for the difference in density this is still a way off.

Moreover, I don't understand why the pressure difference is reported as 55.2113 Pa, because the Pambt is -217.966 Pa and the Pg in the zone is -57.9929 Pa, so should dp not be around 159 Pa???

I have attached screenshots and my model - in this example I was referring to ExtDoor-CIBSE-A and zone G-BOHNorth on the Ground floor.

Thank you!

[Dols, William Stuart (Fed)]

There is a multiplier of 2 on the flow path.

Pressure also varies with elevation by Rho * g * h.

 

See attached spreadsheet.

 

- Stuart

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[Joe Roberts]

Thanks Stuart, should have spotted that x2!

Joe