Proceedings of the International scientific and practical conference ―Israel Ukraine Forum of Science and Innovation‖ (April 27-29, 2026) / Publisher website: www.naukainfo.com. – Tel Aviv, Israel, 2026. - 262 p.

78 The aim of this study is to investigate the operational characteristics of low- grade thermal energy storage systems based on a packed bed of crushed stone and a modified paraffin T3 PCM under greenhouse conditions. An experimental setup was developed in the form of a model greenhouse constructed from acrylic glass. The system incorporated two types of thermal storage elements: a vertical heat exchange channel filled with a dense packed bed of crushed stone, and polymer tubes filled with modified paraffin T3. In the crushed stone system, water served as the heat transfer fluid. During daytime, it was heated by solar radiation in pipes located beneath the greenhouse roof and subsequently supplied to the upper section of the heat exchange channel. To reduce the melting temperature of the paraffin, petroleum jelly oil and glycerin were added, resulting in a phase transition temperature in the range of 34–35.5 °C, which is well suited for greenhouse thermal regulation. During the experiments, the following parameters were continuously monitored: water temperature in the circulation loop, temperature distribution of the crushed stone along the height of the channel, paraffin temperature, air temperature inside the greenhouse and in the ambient environment, as well as solar irradiance. Data acquisition was performed using an automated system based on Arduino Mega 2560 R3, ESP32, and Raspberry Pi 5, with a sampling interval of 10 seconds, ensuring high temporal resolution of the measurements. The results demonstrated that the air temperature inside the greenhouse model strongly depends on solar radiation intensity, reaching 42–45 °C during daytime, while the ambient temperature did not exceed 24 °C. It was found that heat exchange between water and the packed bed of crushed stone is sufficiently intensive, with an average interfacial heat transfer coefficient of α = 80 W/(m²·K), which significantly exceeds typical values observed in air-based heat transfer systems. Thermal calculations showed that the specific heat storage capacity of the crushed stone ranged from 18.4 to 22.8 kJ/kg. In contrast, the modified paraffin exhibited a much higher storage capacity of up to 171.2 kJ/kg under similar conditions, which is approximately 7.5–9.3 times greater than that of the crushed