In the technical field the energy balances are derived from the 1st thermodynamic law, which covers merely the instantaneous quantitative aspects of heat flows. In terms of energy conservation law these balances are expressed in the form of constant sums of exergy and anergy. And that is why they cannot, or can only to a very limited extent, be used to define the transformation of part of the energy (exergy) to the less valuable energy (anergy). Using the 2nd thermodynamic law we have a chance to trace the energy transformation through entropy, a quality indicator of every heat process and an accompanying symptom of process irreversibility. The plate air-to-air heat exchanger, whose exergy analysis is in the spotlight of our interest, operates, in terms of the laws above, in irreversible changes, while the change of entropy induced by the heat flows depends on the construction and surface of the heat exchange areas. The article analyses the influence of air inlet temperatures on the thermal exergy efficiencies of the heat exchanger and the heat loss exergy. Assessment is based on extensive measurements of the temperature, humidity and flow rate of the heated and cooled air in the plate heat exchanger. Both ...
