A new TRNSYS type for thermosiphon flat-plate solar thermal collectors

This paper presents a new TRNSYS Type (called Type 99) for the energy assessment of thermosiphon Flat-Plate solar thermal Collectors (FPCs) for water heating. The accuracy of such new type is higher than the one of the standard type (Type 45) available in the TRNSYS library, since the density and specific heat of water is considered variable with the related temperature. The results of a suitable experimental campaign are also presented for different commercial FPCs system layouts, Figure 1. Specifically, by such measurements the developed Type 99 was successfully validated (a very good agreement between the simulation and experimental results was achieved). By such new Type 99 a suitable Design of Experiment (DoE) analysis was carried out with the aim to assess the design and operating parameters mostly affecting the energy and economic performance of two commercial FPCs. Specifically, collector water pipes diameters, slope, storage tank volume, and thermal insulation thickness were investigated. The analysis was carried out for suitable case studies referred to residential Domestic Hot Water (DHW) production applications and to three different European weather zones (Freiburg, Naples and Larnaca). For such case studies an optimization procedure was also carried out by varying the same design and operating parameters for two different objective functions: best energy behaviour (maximum PES); best economic performance (minimum SPB, maximum NPV). Interesting novel design criteria and encouraging economic results were obtained.