Steady versus dynamic exergy analysis of heating and cooling systems

It is well known that dynamic energy analyses of buildings and of heating and cooling systems are much more reliable than steady state ones. Therefore, the steady state approach is usually adopted only for first estimations of the energy demand/supply or for calculating the peak loads. In turn dynamic exergy analyses in the built environment are uncommon. A few examples can be found in literature, where a time varying outdoor temperature is adopted for the reference environment. However it may be argued that in this case exergy flows and then exergy indicators could be significantly time dependent, since temperature levels in building systems are very close to the reference temperature. Clearly more effort is needed to carry out a dynamic analysis, therefore the question arises on how different can be the results of a dynamic exergy analysis compared to a simple steady state one. If a significant difference is found, it is worth investigating how this is affected by the climatic context and by the kind of heating/cooling system. Therefore in this research both steady and dynamic approach are applied to evaluate the exergy performance of some heating and cooling systems in two representative Italian climates. The results of the two approaches are then compared and discussed.