Modelling of room with exhaust ventilation
 

Hello,

I am modelling a room with exhaust ventilation system, with an extraction fan. I know the cross-section of the air outlet (50 x 60 mm) that if exposed to a pressure jump of 80 Pa will cause a flowrate of 135 m3/h. I first simulated the problem with a pressure inlet BC (with 0 gauge pressure as it takes air from the atmospheric pressure) along with exhaust fan and a pressure jump of 80 Pa (I used a positive value). I used tried all k-e models with SIMPLE p-v coupling, PRESTO! for pressure solver and second order upwind schemes for all variables in steady state regime. During the simulation, I had reversed flow faces on both inlet and outlet with 26 % and 49 % of their respective areas. I then used first order upwind for Momentum equation and I was able to get rid of the reversed flow at the inlet only. Moreover, when I checked the mass flowrate at the inlet, it was considerably lower than the target 135 m3/h.

I finally used as BC: inlet vent and mass flow outlet with the impose 135 m3/h (or 0.45 kg/s) using the same schemes as before and the solution was very smotth with small residuals (all below 10^-4). However, when I checked the static pressure at the outlet, it was -168 Pa.

Hence my question, since I know the fan exhaust flowrate, can I direclty use it with the 'Mass flowrate outlet' BC instead of having the 'exhaust fan' BC and will this affect my end resullts?

PS: the inlet and outlet locations are very far from each others.

Thank you in advance!