abstract
Seasonal heat storage systems are important for the integration of large-scale solar thermal systems into district heating networks, as they bridge the temporal mismatch between summer heat supply and winter heat demand. This paper answers the question of how earth basin storage systems can be modeled and analyzed as seasonal heat storage systems in the TRNSYS simulation software.
Two validated TRNSYS models, Type 342 and Type 1535+1301, are compared and their suitability for representing thermal behavior is evaluated. The models differ fundamentally in their geometric representation. Type 342 represents the storage tank as a cylinder, while Type 1535+1301 models a conical geometry. Based on the 60,000 m³ reference storage tank in Dronninglund, Denmark, temperature profiles, heat losses, and ground temperatures are analyzed over five years of operation.
The results show that Type 1535+1301 calculates 83 % higher heat losses than Type 342, which simplifies the storage as a cylinder, due to its realistic representation of the conical geometry. The parameter variations show that steep slope angles (84°) reduce losses by 30 % compared to shallow angles (12°), and that a tenfold increase in storage volume reduces specific heat losses by 42 %. This study identifies the key differences between the two modeling approaches and the influence of geometric parameters.