singlezone_commercial_hydronic: Unbalanced flow rates supply and exhaust fan

[mariuseb]

For the testcase "singlezone_commercial_hydronic": the supply and exhaust fans have unbalanced flow rates, despite the presence of a balancing connection in the infiltration model. A plot of 7 days of operation (first 7 days of the year) that documents the issue is attached.

[EttoreZ]

@mariuseb Thank you Marius. I will take a look.