[esp-r] airflow network, problems with component type 20/25

[Christian Anker Hviid]

Hello ESP-r community

I am modelling a passive ventilation system with the air flow facility in
ESP-r. In my system I have a heat exchanger with the characteristics dP =
5.6e-3 x m + 4.8e-5 x m^2
This calls for a quadratic flow component type 20 or 25 to model the heat
exchanger in my system.
However using any of the two causes this error message:

Please check (in the following order) that:
 - each node has some flow path to a boundary pressure and
 - iteration convergence control is not too strict
Day xx Month xx Hour xx: 100 iterations; flow solution failed

Using power law components (e.g. 10, 15 or 17) does not generate this error
message and I can't find the iteration convergence control (for integrated
simulations). What am I doing wrong?
I am using esp-r version 11.2 from learnix.

Christian Hviid