Comparison of the Thermal Performance of a Solar Heating System with Open and Closed Solid Sorption Storage

Abstract

The aim of this paper is to compare two solar heating systems with different solid sorption storage concepts; an open storage concept with material transport and external reactor and a closed sorption storage concept with the material reservoir as reactor. Both storage concepts are part of system concepts that have been investigated during national projects for a period of more than 3 years each. A TRNSYS model has been developed for each concept and the corresponding mathematical model is described. An emphasis is given on the model simplifications and thus its up- and downscaling possibilities. TRNSYS simulation studies were performed using similar boundary conditions. Hence the simulation results can be compared directly, thus the advantages and disadvantages of both concepts under investigation can be elaborated and assessed.TRNSYS simulations have been performed for each system concept using the properties of two different thermochemical storage materials (TCM). It is shown that the type of TCM has a significant influence on the systems fractional thermal energy savings. Using silica gel as TCM, both system concepts’ performances are only slightly better compared to a standard water-filled storage tank of the same size. The TCM zeolite 13 XBF, a binder free 13 X zeolite, leads to significantly better fractional thermal energy savings. Although the two systems under investigation behave differently, the fractional thermal energy savings are similar. High solar thermal fractions up to a complete solar coverage can be achieved for both storage concepts with moderate collector array and store sizes.