Numerical investigation on the optimization of solar hot water heating systems

This study compares two different calculation procedures for the part of domestic hot water (DHW) production heat energy demand filled by a solar heat collector system: the first procedure is based on the UNI TS 11300-4 regulatory model, that uses UNI 10349 regulation climate data according to the calculation method set by UNI/TR 11328; the second one, on the other hand, in a dynamic regime, was implemented with the TRNSYS retail programming code, using Meteotest station climate data. Specifically, the values of the systems solar production, combined with monthly and yearly solar fractions, were compared with three Italian locations: Bologna, Milan and Rome. Comparing the irradiation values on the surfaces calculated with UNI/TR 11328, to the values obtained by TRNSYS software, and those subsequently measured by Meteonorm7 retail software, a systematic over-estimate of the regulatory values is detected. The analysis of the production values and solar fraction obtained in the two methods demonstrates how dynamic simulation leads to less abundant and more realistic results than the stationary regime method, confirming the overestimated evaluation of the regulatory calculation. This study focused on the need to review and correct the regulatory method currently in effect in Italy for renewable energy source system energy evaluations, preferring the dynamic regime method over the stationary one. This leads to the need to correct and standardise the calculation method for climate values to create a complete and accurate map of the Italian climate data to make energy evaluations that best represent real conditions.