https://doi.org/10.6110/KJACR.2026.38.6.293

Yu Jin Kim ; Sun Ik Na ; Sangmu Bae ; Beomjoon Lee

With the rise of Zero Energy Buildings (ZEBs), energy performance simulation has become essential for evaluating building designs in their early stages. However, in ECO2, key input variables like infiltration rates often depend on empirical values or conventional assumptions, limiting the reliability of these simulations. To overcome this challenge, this study develops a theoretical model that predicts stack-driven infiltration in high-rise residential buildings using the Residential Thermal Draft Coefficient (RTDC). When tested on a real building, the model demonstrated strong accuracy in predicting infiltration rates, achieving average errors of 15.58% for CV(RMSE) and 6.144% for NMBE when compared to multi-zone airflow simulation results. Additionally, using the predicted infiltration values, ECO2 showed an energy demand reduction of 11 kWh/m² compared to results derived from the ZEB pre-certification infiltration standard. These findings suggest that the RTDC-based infiltration model can accurately predict energy patterns in high-rise residential buildings and has potential for direct integration into building energy simulations.

https://doi.org/10.6110/KJACR.2026.38.6.307

Yongjin Choi ; Joon Ahn ; Young Soo Chang

This paper reviews the development trends of Thermal Energy Storage (TES), focusing on Carnot batteries as a key solution for addressing both grid variability and carbon reduction. A Carnot battery stores surplus electricity as heat using electric heaters or high-temperature heat pumps, and later reconverts the stored heat back into electricity through a steam turbine when needed. From a retrofit perspective, replacing a coal boiler with TES and integrating it with existing steam turbines allows for the reuse of transmission and balance-of-plant assets, providing a capital-efficient pathway to long-duration, dispatchable capacity. As a result, Carnot batteries are gaining attention as a viable option for large-scale, long-duration storage and for repurposing stranded coal assets. Government-led demonstrations and policy support are advancing in Germany, the United States, and Korea, with multiple pilot projects reported in Europe and the U.S. Building on these developments, this paper examines the market prospects and policy needs for Carnot battery TES, synthesizes current retrofit design approaches, and outlines future directions necessary for practical deployment at fossil fuel plants.

https://doi.org/10.6110/KJACR.2026.38.6.313

Soowon Chae ; Yujin Nam

Power-to-Heat (P2H) systems represent an effective solution for utilizing surplus renewable electricity to satisfy thermal energy needs while also improving grid flexibility and stability. This study involved the development and demonstration of a pilot-scale P2H system at the Western Agricultural Technology Center on Jeju Island, South Korea, where frequent renewable energy curtailments occur due to high levels of renewable energy integration. During the spring season, thermal charging and heating operations were carried out using excess electricity from renewable sources. In the thermal charging phase, 2,757.1 kWh of electricity was used to produce 7,724 kWh of thermal energy, achieving a coefficient of performance (COP) of 2.8. The heating operation successfully maintained an indoor temperature of 19-21℃, which is ideal for crop cultivation, thereby confirming the system's suitability for agricultural heating. These results demonstrate that the P2H system can not only alleviate renewable energy curtailment and enhance the operational flexibility of the power grid but also provide a sustainable solution for thermal energy supply in agriculture. Additionally, the findings suggest that widespread adoption of P2H systems could significantly contribute to regional energy transitions and improve renewable energy utilization in isolated grid areas like Jeju Island.

https://doi.org/10.6110/KJACR.2026.38.6.323

Jinkyun Cho

This study examines the thermal stratification characteristics of a water-based thermal energy storage (TES) tank under various charging directions and flow rate conditions. A lab-scale TES system was designed using Froude similarity, based on a prototype intended for integration with a 1000RT heat pump system. We conducted experiments and CFD simulations using a 2-D axisymmetric model (Ansys Fluent) to validate thermal behavior and assess stratification performance. Charging tests were performed for both top-to-bottom and bottom-to-top configurations at flow rates of 127 LPM and 215 LPM. The results indicated that top charging effectively maintained a distinct thermocline region, with a Richardson number up to five times higher than that of bottom charging, demonstrating stronger stratification. While increased flow rates accelerated charging, they also weakened stratification due to enhanced momentum effects. The discharging tests confirmed that the outlet temperature remained stable at 43℃ for the designed discharging duration before beginning to decrease. These findings underscore the importance of inlet design and flow control in enhancing TES tank performance and sustaining thermal stratification.

https://doi.org/10.6110/KJACR.2026.38.6.337

Joon Ahn ; Sumin Kim ; Hyun Jung Kim ; Yujin Nam ; Kwang Ho Lee ; Jae-Weon Jeong ; Honghyun Cho

This study introduces a physics-based co-simulation framework designed to evaluate the differential-pressure control performance of HVAC systems in nuclear fuel cycle facilities. These facilities handle radioactive materials under stringent confinement requirements, making it crucial to maintain negative pressure gradients between different zones for safety. Since experimental testing under degraded or abnormal conditions is not feasible, a simulation-based verification approach was adopted. In this framework, the building envelope and ventilation zoning were modeled using EnergyPlus, while major HVAC components?such as fans, dampers, filters, and ducts?were represented with the Modelica Buildings Library, relying on physics-based formulations. The two domains were integrated through a functional mock-up interface (FMI), facilitating comprehensive analysis of thermal loads and dynamic airflow responses. The Modelica fan model demonstrated strong correlation with theoretical affinity laws, achieving an R² value above 0.99 for airflow, static pressure, and power consumption. The coupled Modelica-EnergyPlus simulation successfully reproduced the intended pressure cascade, with calculated pressure differences in the hot-cell zones (-334 to -149 Pa) satisfying the design criteria. These findings indicate that the proposed framework offers a reliable and safe method to assess HVAC performance in safety-critical nuclear facilities and lays the groundwork for future research on fault prediction, degradation assessment, and control optimization.