Should LMTD be used in calculating heat load?

[kwisatz_haderach]

Sorry if this question is basic. I'm reading Pressure vessel design manual by dennis moss and in "chapter 6: related equipment" he used LMTD to calculate the heat load/heat required, but shouldn't actual temperature difference be used which gives the actual heat energy to be given to the process fluid. LMTD will be less than actual temperature difference isn't it? Is he wrong or am i missing something?
Thanks in advance.

 

[IRstuff]

LMTD is typically used where the temperature difference is not a constant value, where it varies across the breadth or length of the heat transfer interface.

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