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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.

This study investigates the economic benefits of solar thermal and seasonal thermal energy storage based on a renewable energy conversion system for greenhouses. The proposed system consists of solar collectors, seasonal thermal energy storage, hybrid-source heat pumps, and ground-source heat pumps. The heat generated from the proposed system was stored in two types of seasonal thermal energy storage and supplied to the greenhouse using Purme Yeoju Farm in South Korea for experimental analysis. Based on the experimental data gathered over a heating system, the economic benefits of operating cost savings and carbon trading with the greenhouse gas emission reduction of the proposed system were investigated by comparing to a conventional heating season using oil and electric boilers. From October 2021 to March 2022, approximately 38.4% of the total 482 MWh of heat was supplied either directly or indirectly through the solar system. In addition, the coefficient of the performance of the entire proposed system was calculated to be 2.28. Both the operating cost savings and greenhouse gas emission reductions of the proposed system showed over 73% and 82% compared with those of conventional systems.

To effectively analyze building energy, it is important to utilize the environmental data that influence building energy consumption. This study analyzed outdoor and indoor data collected from buildings to find out the conditions of rooms that had a significant effect on heating and cooling energy consumption. To examine the conditions of the rooms in each building, the energy consumption importance priority was derived using the Gini importance of the random forest algorithm on external and internal environmental data. The conditions that had a significant effect on energy consumption were analyzed to be: (i) conditions related to the building design—wall, floor, and window area ratio, the window-to-wall ratio (WWR), the window-to-floor area ratio (WFR), and the azimuth, and (ii) the internal conditions of the building—the illuminance, occupancy density, plug load, and frequency of room utilization. The room conditions derived through analysis were considered in each sample, and the final influential building energy consumption factors were derived by using them in a decision tree as being the WFR, window area ratio, floor area ratio, wall area ratio, and frequency of use. Furthermore, four room types were classified by combining the room conditions obtained from the key factor classifications derived in this study.

This study evaluated the energy saving potential of renewable energy generation systems based on integrated solar energy in an urban environment. The solar city concept was implemented using photovoltaic (PV) and solar thermal systems. As a case study, the Sejong national pilot smart city in South Korea was selected to evaluate the renewable energy penetration rate. For evaluating the proposed renewable energy systems, the electrical and thermal loads of the smart city were estimated using field measurement data. Then, the renewable energy penetration rate of the city was evaluated. The HomerPro software was used to analyze the PV generation and operating energy consumption of the natural gas (NG) generator with a district heating network. The thermal load-supporting potential of the solar thermal system was estimated using the TRNSYS software. The results showed that the proposed urban integrated renewable energy system could meet over 30% of the renewable energy penetration rate and the levelized cost of energy and total net present cost was 7% lower than the base case system (i.e., NG generator). The proposed system also exhibited 38% less CO2 emissions than the base case system.

Due to the wide-spread use of photovoltaic (PV) systems, interest regarding economic benefit and energy-sharing from surplus electricity has been raised. In this study, decentralized thermal and electric convergence energy prosumers for an energy-sharing community are proposed. For the convergence energy system, a simultaneous heating and cooling heat pump (SHCHP) system integrated with a thermal network is proposed, and the energy performance and operating energy savings of the proposed system were investigated. A smart village located in the Busan Eco Delta Smart City was selected as a case study for the simulation analysis. Experimental data of the heat pump system were used to analyze the SHCHP. The analysis results showed that the proposed system could provide over 53% and 86% of the load cover and supply cover factors, respectively. The proposed system can earn economic benefits, such as energy trading from the surplus electricity of PV systems and thermal energy produced by an SHCHP, more than 30.5 times those of conventional air-source heat pump systems. These benefits mainly originate that a conventional system can trade the surplus electricity from a PV system but the proposed system can trade produced thermal energy from SHCHPs and the surplus electricity from PV systems.

The demand for district heating and cooling systems in block units with a heat pump that utilizes various unused energy sources for energy supply has been increasing. This study investigated experimentally the ground source heat pump (GSHP) and sewage water source heat pump (SWSHP) facilities used in block cooling and heating networks. Then, a heat pump performance prediction model was derived for utilization in future designs. Operational data for heating and cooling energy supply from an experimental site were investigated for the period between 2018 and 2020. During the cooling season, the coefficient of performance (COP) of the GSHP was approximately 4.1, and that of the SWSHP was approximately 2.9. The cooling performance of the SWSHP gradually decreased because of the fouling. The COP of the GSHP and SWSHP during the heating season was approximately 3.6 and 3.4, respectively. The results also demonstrated that, if fouling in the SWSHP can be prevented or reduced, the acquired COP can be similar to that of the GSHP. The derived prediction model serves as a good reference for engineers who require information on the performance of field operations.

District cooling and heating methods that can utilize highly efficient heat pumps and various unused new and renewable types of energy are required to achieve low carbon emissions and zero energy usage in buildings and community units. The technical requirements for the implementation of decentralized thermal networks and heat trading are increasing, both for thermal networks in new buildings and for those remodeled based on existing centralized thermal networks. In this study, a conventional centralized thermal network was implemented as a decentralized thermal network and the possibility of heat prosumers feeding thermal networks was demonstrated experimentally. A real-scale plant was constructed by employing unused thermal energy facilities as prosumers in a school and childcare center based on the existing small-scale block heating and cooling thermal network. The decentralized thermal network and heat prosumer concepts were proven through operation experiments performed on the constructed system in summer and winter. An economic benefit can be achieved by increasing the peak power cost. The experimental results also showed that the proposed bi-directional heat trading reduced carbon emissions by 12.7% compared with conventional centralized thermal systems.