Demonstrates that is not only possible but necessary to relate system irreversibility, exergy destruction, and entropy generation numerically as well as conceptually. The relationships are evident, if reservoir temperature differentials are considered. Demonstrates that component irreversibilities can, and must, be consistent with system irreversibility. Using effective reservoir (entropic average) temperatures in second-law analysis of thermal systems accounts for reservoir temperature variations, enables numerical and conceptual relationships between systems irreversibility, exergy destruction, and entropy generation, and ensures consistency between system and component irreversibilities.

KEYWORDS: exergy, entropy, temperature, fluids, heat balance, variable temperature, thermal capacity, calculating, thermodynamics, performance, heat exchangers, heat pumps, comparing, compressors, condensers, evaporators.