It can be seen that a case similar to that described above exists when the cold stream composite
enthalpy curve can overlap the hot stream curve at both ends. For this case, a critical value of ΔTmin
exists for which the cold utility duty is zero. Above this critical value, both utilities are required, but
below it, no cold utility is needed, and the hot utility duty remains constant, but heat must be added to
the system at both the hot and cold ends of the diagram