Ideal cooling (ideal=true):
Boundary has fixed temperature T_amb.
Cooling by linear heat transition (ideal=false):
Boundary has one common variable temperature T.
T is determined by the difference between heat inflow at the heat-port and outflow=G*(T-T_amb) towards ambient, according to a given heat capacity C.
The time-average equation
der(q) = (Q_flow - q)/tcstis equivalent to the heat equation
C*der(T) = Q_flow - G*(T - T_amb)at constant ambient temperature. The correspondence is
tcst = C/G q = G*(T - T_amb)