On board the ships, vapour compression technologies are the most suitable ones. Seen the significant amount of energy used for cooling perishables during voyages, energy efficiency gains more importance. In present times, marine refrigeration is dominated by HFCs, a key role being played by R134a. Despite that R134a is a potent greenhouse gas, marine refrigeration systems using this refrigerant are subject of energy consumption improvement. In this paper it is performed a first and second laws based analysis under the influence of sea water temperature. This analysis is very important in the case of the direct use of sea water as a coolant in refrigeration condensers on board—especially in the context of global warming. It is investigated the effect of condensation temperature (sea water temperature) on the Coefficient of Performance, work input, heat rejection in the condenser, total exergy destruction and exergy efficiency. One of the most significant findings to emerge from this study is that high sea water temperatures accelerate work consumption and total exergy destruction - with negative impact on energy efficiency of the system.