This study categorizes national renewable heat policies into regulatory, subsidy-based, and hybrid schemes, and compares the structures and mechanisms of 8 countries. Regulatory models rely on mandates such as bans on fossil-fuel heating and renewable supply obligations; subsidy-based schemes provide financial support for certified technologies. Hybrid systems combine tools like carbon taxes, district heating mandates, and public funding to enhance both policy acceptance and enforcement, with variations shaped by national climates and institutional traditions. Based on this analysis, performance-based incentives, boiler replacement programs, and region-specific policy mixes are recommended for Korea. Replacing one million gas-heated households annually with heat pumps could reduce emissions by approximately 50 MtCO₂eq by 2040, offering both quantitative and strategic guidance for national policy development.

The supply air set-point temperature (SAST) is a critical parameter in economizer control that determines the free cooling range. This study aimed to evaluate the potential for cooling energy savings resulting from changes in the SAST and to determine its optimal setting. To achieve this, a parametric analysis was conducted using EnergyPlus, in which seven simulation cases were classified based on varying SAST. The simulation results were analyzed in terms of free cooling range, indoor thermal environment, and energy usage during the economizer operating periods. The findings revealed that increasing the SAST extended the free cooling period, thereby reducing cooling energy consumption, whereas decreasing the SAST shortened the free cooling period and increased cumulative OA intake. Among all cases, setting the SAST to 17℃ (Case #6) yielded the greatest energy savings, reducing total energy usage by approximately 34.7% compared to the Base Case, while maintaining acceptable indoor temperature and relative humidity levels. These results confirm that appropriate SAST can simultaneously improve cooling energy performance and ensure indoor thermal comfort. Furthermore, the optimal SAST should be adjusted according to climatic conditions and building operational characteristics to maximize energy performance.

This study aims to quantitatively evaluate the heating and cooling energy demand of mid-rise timber buildings and determines the optimal capacity of renewable energy systems to achieve Zero Energy Building(ZEB) certification. A dynamic simulation model was developed that integrated the thermal properties of timber and the operational characteristics of office buildings. As the simulation results, the annual heating and cooling energy demands were 14.7 kWh/m²·yr and 55.3 kWh/m²·yr, respectively. Moreover, the annual average coefficient of performance was 4.38 for the heat pump and 3.47 for the overall system. In the baseline configuration with a 10 m² photovoltaic(PV) system, the energy self-sufficiency ratio remained below 20%, which is insufficient to satisfy the minimum requirement for ZEB certification. However, doubling the PV installation area increased the self-sufficiency ratio to 21.3%, satisfying the criteria for ZEB.

Numerical simulations were conducted to examine the effects of diffuser geometry and tank aspect ratio on thermocline characteristics in a stratified thermal storage tank. Increasing the diffuser height from 10 mm to 40 mm enlarged the thermocline thickness from 57.2 mm to 77.5 mm, corresponding to an increase of approximately 35.4%, whereas increasing the diffuser diameter from 100 mm to 400 mm caused only a slight increase from 61.8 mm to 65.8 mm (about 6.5%). A higher Froude number consistently reduced the thermocline thickness ratio, producing a sharper interface between hot and cold layers. Increasing the tank aspect ratio from 0.5 to 4 reduced the thermocline thickness ratio from 8.44 to 3.27, while the Richardson number decreased from 2.67×10⁶ to 6.69×10⁵. Although Ri decreased, it remained greater than unity, indicating that buoyancy effects were still dominant and contributed to maintaining stratification.

This study analyzed energy consumption changes pre and post-green remodeling (GR) in a senior citizens' center located in Seoul. The building's energy performance was evaluated across three phases: Case-A (2019-2021 baseline), Case-B (2022 pre-GR), and Case-C (2024 post-GR). During the baseline period (2019-2021), the building consumed an average of 48.2 MWh annually due to poor insulation, inadequate air-tightness, and outdated HVAC systems, resulting in a Level 6 energy performance rating. Following external insulation improvements in 2022 (Case-B), annual energy consumption decreased to 32.6 MWh, representing a 32.4% reduction and improving the building's energy performance to Level 4. After comprehensive green remodeling in 2024 (Case-C), energy consumption further declined to 19.4 MWh, achieving a 40.5% reduction compared to Case-B and a 66.0% reduction compared to the baseline period. Post-GR energy distribution showed city gas accounting for 79.6% (15.4 MWh) and electricity for 20.4% (3.9 MWh) of total consumption. Compared to pre-GR (Case-B), gas usage decreased by 46.8% while electricity usage increased by 10.3%. Monthly analysis revealed consistent reductions in city gas consumption following both external insulation and green remodeling interventions, while electricity consumption remained relatively stable between Case-A and Case-B phases. These findings demonstrate the significant energy efficiency improvements achievable through green remodeling and provide valuable baseline data for similar building GR projects.