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This study discusses the preparation and thermophysical characterization of microencapsulated stearyl alcohol (SA) for thermal energy storage and heat transportation applications. The developed microcapsules consist of SA, an organic phase change material (PCM) core material, and melamine formaldehyde (MF) shell material. The PCM microcapsules have been synthesized using sodium dodecyl sulfate as a surfactant using an in-situ polymerization technique and subjected to various thermal and structural characterization techniques. The results revealed that prepared microencapsulated PCM (MPCM) with 0.25 g of surfactant and 5 g of PCM exhibits better morphological structure with an average diameter of 4.7 µm. The onset melting point and latent heat were estimated as 42 °C and 137.7 Jg−1, respectively. The highest encapsulation ratio of 51.9 % and 52.3 % were observed for the core to the shell ratio of 5:8.4. The MPCMs are thermally stable and the decomposition temperature of the MPCM was higher than the pure PCM. The developed MPCM shows good chemical stability and no leakage during the phase change process. The obtained results elucidate the suitability of the developed MPCM in thermal energy storage applications.

Direct-expansion solar-assisted heat pumps (DX-SAHP) are increasingly used in heating applications owing to their high efficiency. In this study, the energy performance of a DX-SAHP for a distributed thermal prosumer in a thermal network was investigated. A thermal network for supplying hot water, established in the eco-friendly energy town of Jincheon, was selected as the test site, and a daycare center was selected as the pilot building. A control logic for serving produced thermal energy to the thermal network was developed as an operation of thermal prosumer. Experiments were conducted during the cooling and heating seasons, and the results of three operation cases showed that the proposed prosumer operation can transfer the thermal energy within the thermal network. The daily load of domestic hot water was approximately 50–100 kWh, and the daily coefficient of performance of the DX-SAHP ranged from 2.0 to 5.0. The coefficient of performance of the DX-SAHP was found to be strongly dependent on the outdoor air temperature, solar irradiation, and outlet water temperature. During the operation, the DX-SAHP contributed to achieving over 66% savings in the operating energy compared with a conventional electric heater.

The utilization of renewable energy sources have gained significant attention in recent years for greenhouse that consumed lots of cooling and heating energy. This study investigated a solar thermal and seasonal thermal-based renewable energy convergence system. This system consists of a solar thermal system, tank- and borehole-type seasonal thermal energy storage, multi-source (i.e., air and water) heat pumps, and ground-source heat pumps. The detailed control logic of the proposed system was implemented, and the system was constructed in a test greenhouse at the Purme Yeoju Farm in South Korea. During the cooling season, the multi-source heat pumps were operated as air-source heat pumps, which showed a coefficient of performance (COP) only 0.5 less than that of the ground source heat pump. The efficiency of the solar thermal system was determined to be 36.6% throughout the investigation period, and the heat storage efficiency of the tank-type seasonal thermal energy storage was 75.7%. Consequently, the proposed system showed a COP of 2.9 during the heating season. The proposed system shows that over 70% of the operating energy can be saved, which is unachievable when using conventional electric heaters.