Radon Progeny - Bug?

[Roy Moreby]

Hi Ventsim

There appears to be a error in the calculation of radon progeny concentrations with time.

I have run this on version 5 and 6 and get the same error

Attached is a graph  showing the theoretical growth of radon progeny per 1,000Bq/m3 Rn (1Bq/l Rn)

 

The maximum radon progeny concentration is about 5.6uJ/m3 after about 200minutes

This also gives you the equilibrium factor i.e. about EQF= 1 at 200 minutes. Slightly different if you include decay of Rn gas

I have tested this by putting 25,000Bq/s into 25m3/s in a 5m x 5m airway i.e. 1.0m/s - see model attached

I have then used different airway lengths to test the radon progeny concentrations e.g. 60m = 1min

The results show an ever increasing radon progeny concentration with time - see attached table

When I plot the Ventsim results with time against the theoretical values (Bateman Equations) I get the following. This indicates a divergence of theoretical v Ventsim after about 70mins.

This is a significant difference in air passing through old workings or cave piles. Could you take a look at this please

Thanks

 

Roy

 

 

 

 

 

 

 

 

 

Radon Test.vsm

[Martin Griffith]

Hi Roy, as discussed via email, the calculation Ventsim is relying on to calculate this is not correct for residence times longer than about 70 minutes. Thank you for bringing this to our attention. 

We've redone the calculation ourselves, so that it is correct for all residence times. This will appear in a new version soon. 

[Martin Griffith]

This is now out in Ventsim DESIGN version 6.0.1.7. The new Radon Simulation method calculates correct radon progeny levels for long residence times (>70 minutes).