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Fresh Air Deficit error


Mick Loney

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I'm modelling a number of diesel machines driving a tunnel ventilated by a forcing fan and ductwork.  I get the error message "Fresh Air Deficit" x 5 when I try to run the model.  The error persists even if I reduce the utilisation factor for the machines to 10%.  The error isnt being caused by excessive DPM levels, or by excessive temperature.  I assume its because the total flow available in the road is less than the total engine power x 0.06m3/s?  How does the software assign this error?  Is there a reason that the first 2 vehicles in the flow dont have the error but the last 5 do?

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Hi Mick, thanks for your message. 

When you run a Diesel Simulation, Ventsim is now keeping track of the use of fresh air by the diesel machines and is showing the Fresh Air Deficit warning when a diesel machine is hit by air which has been used up upstream by other machines. In this way it checking the 0.06 (m3/s)/kW requirement locally at each airway. This warning is independent of simulated DPM levels or temperatures. 

The first 2 vehicles in your road are receiving the fresh air so don't see the warning. Downstream the fresh air is used up by the upstream vehicles and the warning appears on the later vehicles. You can switch to the Diesel | Air Surplus property to see the air being used up. If a Diesel machine is placed in an airway that has negative Air Surplus, then the warning appears. 

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You mentioned that the Utilisation Factor is having no effect. This is because the calculation of the fresh air usage ignores the Utilisation Factor and is based on the rated engine power of the diesel machine as, by our understanding, this is how the flow requirement is assessed. 

This is a fairly new feature and we'd be interested in any feedback or suggestions you have about it. 

 

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