This study evaluates the energy performance of a liquid desiccant and indirect/direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS) for application in a commercial passenger ship. The LD-IDECOAS consists of an LD system and an indirect and direct evaporative cooler (IEC and DEC, respectively) for dehumidification, and it provides for sensible and adiabatic cooling of the process air. The proposed system used seawater as the cooling source and the engine waste heat recovery (WHR) system as the heating source. The organic Rankine cycle (ORC) regression model from existing literature was adapted as a WHR system to evaluate the thermal efficiency of using waste heat. For estimating the energy performance of the LD-IDECOAS, an energy simulation was conducted for two cabins. The area of each cabin was 177.6 ft2 (16.5 m2). The required thermal load of the passenger cabins was estimated according to ISO-7547 standards considering typical operating conditions. Additionally, the energy consumption of the LD-IDECOAS was determined by using a commercial equation solver program. The energy performance of the proposed system was then compared with that of the air conditioning system of a conventional commercial passenger ship (e.g., CAV), which used absorption chillers, for estimating the energy saving potential of the proposed system.