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The employing of recuperative heat exchangers in the utilization of the secondary ventilation air heat in stables aims at lowering the consumption of fuel for heating, and improving the stable's microclimate, along with heat comfort of the animals and protecting external structures against deterioration. Whether or not these results will be achieved depends above all on the construction of the heat exchanger and of the heat exchange surfaces.In the technical field the energy balances are derived from the 1 st 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), or in other words, the so-called energy losses conditioned by the irreversibility of processes. Using the 2 nd 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.An overview on the utilization of a physical model of entropy change in various technical fields is given in the BEJAN's paper (1996). The EGM (Entropy generation minimization) model, when applied to heat exchangers, expresses the change of total entropy S gen as a sum of partial changes of entropies evoked by heat exchange S gen,ΔT and fluid friction S gen,Δp . The ratio of the change of entropy in the real design S gen to the change of entropy in an optimal design, in which the entropy change reaches its minimum S gen,min , is called the entropy change coefficient N S . This method, which is well suited for finding out how close the design comes to the ideal alternative under given conditions, was published by BEJAN (1978).The SEKULIC paper (1990) mentions an equation for entropy change as a function of temperature and pressure differences. In case of an air-to-air heat exchanger the influence of the pressure difference is later ignored, while a new coefficient, HERN (heat exchanger reversibility norm), is introduced to describe the quality of the energy transfer. This coefficient considers a reversible process as a limiting case and the real irreversible processes as less favourable alternatives. The author assumes that there exist such shapes and dimensions of heat exchanges surfaces, for which the increase of entropy will be minimal.Another article (DE JONG et al. 1997) presents a simplified method for evaluating air-to-air heat exchangers. In principle, it is based on previous papers dealing with the generation of entropy in an irreversible process, yet the solut...

The current thermal properties of building external structures including openings are supposed to suppress effects of draft to thermal comfort. But is it true expectation? The subject of the paper is the analysis of airflow around the window in three types of heating systems with predominant radiant as heat transfer. The analysis is based on experiments in the climatic cabin representing the room of a low-energy family house. To obtain the relevant data, a series of particle image laser velocimetry measurements were performed to visualize and quantify the airflow in the investigated area. The paper present results of the thermal comfort of the inhabitants of the room, which prove that with the influence of draft it is necessary to count on modern energy-saving buildings. They prove that old well-known rules about the position of the heating surface apply to the most cooled constructions and bring interesting conclusions about underfloor heating.