Study of Low-Temperature Heat Accumulation in Sensible and Latent Thermal Energy Storage Systems for Greenhouse Applications

The main objective of this study is to determine the energy efficiency of a sensible heat storage system employing a dense crushed stone bed in a vertical heat exchange channel, as well as a latent heat storage system using a phase change material based on paraffin T3, intended for greenhouse applications. To achieve this objective, several tasks were performed, including analytical and experimental investigation of heat transfer processes in thermal energy storage system elements using a greenhouse model, analysis of the temporal variation of temperature profiles and solar radiation intensity, and a comparative evaluation of the energy efficiency of phase change heat storage materials, represented by modified paraffin, and capacitive heat storage systems, represented by crushed stone. The most significant results demonstrate that the derived analytical relationships for calculating working medium temperatures adequately describe the physical process of heat accumulation when experimental heat transfer coefficients are considered. Heat exchange between the dense crushed stone bed and the water flow occurs with high intensity, with an average heat transfer coefficient of α = 80 W/(m²·K). The emissivity of the surface of paraffin-filled heat storage tubes was determined to be εp = 0.65. The significance of the results lies in defining conditions for efficient application of thermal energy storage systems in greenhouse practice. For thermal stabilization of the internal greenhouse volume, the use of modified paraffin T3 is recommended, as its heat storage efficiency is 7.5–9.3 times higher than that of a dense crushed stone bed.