Second-Law Analysis to Improve the Energy Efficiency of Environmental Control Unit

This paper presents a second-law of thermodynamics analysis to quantify the exergy destruction in each component of an Environmental Control Unit (ECU) for military applications. The analysis is also used to identify the potential contribution from each component to improve the overall energy efficiency of the system. Three ECUs were investigated experimentally at high ambient temperature conditions to demonstrate the feasibility of the model presented herein. The investigated ECUs have capacities of 1.5 (5.3 kW), 3 (10.6 kW), and 5 (17.6 kW) tons of refrigeration (RT). The results indicate that the largest potential to improve exergetic efficiency of each unit resides in the compressor. This is followed in order by the evaporator and the condenser in the case of 1.5 RT and 3 RT units, whereas for the 5 RT unit, relatively high irreversibility is associated with the evaporator when compared to the compressor. The second law analysis may help to focus on the components with higher exergy destruction and quantify the extent to which modifying such components can increase the exergetic efficiency of any ECU operating in high ambient temperature environments.