Thermal energy transfer processes are important problems to be solved in the field of engineering. In this field, heat exchangers are one of the most used equipment in the industry. The present investigation was carried out in an operating hydrogen sulfide cooler system, with the objective of determining the overall heat transfer coefficients by two methods, applying the passive experimentation procedure. With the Logarithmic Mean Temperature Difference (LMTD)

method, values ranging from 11.1 to 73.3 W/(m² ·K) were obtained, compared to 11.0 to 58.9 W/(m² ·K) when applying the Effectiveness-Number of Transfer Units (ε-NTU) method. Although the results obtained were similar, for the thermal evaluation of the chiller system studied, it was recommended to employ the LMTD approach, used by most researchers.