[e22rico]

Hello, I have ran a few different HVAC simulation models with the inclusion of S2S radiation model, and with air density as "incompressible-ideal-gas".



I am using the following UDF to calculate age of air.

#include "udf.h"
DEFINE_DIFFUSIVITY(mean_age_diff, c, t, i)
 {
return C_R(c,t)*2.88e-05+C_MU_EFF(c,t)/0.7;
}

DEFINE_SOURCE(mean_age_source, c, t, dS, eqn)
{
dS[eqn]=0;
return C_R(c,t);
}

I run the uds in transient after my models have converged with all other equations turned off. It converges perfectly for one of my models which was run with a constant density instead of "incompressible-ideal-gas". Otherwise it diverges. The age of air (volume average) jumps between really high positive and negative numbers.



Any idea on how to calculate it for the incompressible-ideal-gas cases?