Art Montemayor concentrated his right comments on the STHE shell side pressure drop, the most difficult to calculate with a degree of accuracy.
Also on the tube side of HE, pressure losses include inlet and outlet nozzles, as for the inlet and outlet of tubes, both generally taken for liquids to be 1 and 0.5 velocity heads, for sudden contractions and sudden expansions, respectively, (Perry et al. Chemical Engineers' Handbook).