Jaesik Kang

Closed-cell phenolic foam (PF) insulation is widely assumed to exhibit monotonically increasing thermal conductivity after cutting, driven by progressive blowing agent release. This study reports a previously uncharacterized behavior: a consistent decrease–minimum–rebound pattern in the days to weeks after cutting, defined here as the transient thermal conductivity minimum (TTCM). Using n-pentane-blown PF foam, thermal conductivity and mass were tracked under standard (23 °C) and accelerated aging conditions (70 °C, 110 °C; slicing per KS M ISO 11561), complemented by gas chromatography–flame ionization detection (GC-FID), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FT-IR), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), and scanning electron microscopy (SEM). TTCM reductions of 3.8–16.7% were observed across all closed-cell specimens; a reference PF foam with cell-wall micro-perforations showed no TTCM, establishing intact closed-cell structure as a prerequisite. The mechanism is attributed to redistribution of dissolved n-pentane from the polymer matrix into the cell gas phase, thermodynamically favored by the proximity of n-pentane’s boiling point (36.07 °C) to the heat flow meter (HFM) hot plate temperature (33 °C). In the post-TTCM phase, thermal conductivity rises progressively as n-pentane is displaced by air; the rate of this rise is strongly dependent on diffusion path length. These results establish two mechanistically distinct aging stages and identify their respective governing factors.

Green remodeling projects for public buildings in South Korea aim to improve the energy performance of aging facilities, with a policy target of achieving at least 30% energy savings. Because the 30% saving rate functions as a key policy benchmark, it is necessary to identify why some projects achieve higher savings while others remain below the target. This requires a comparative analysis of energy-saving levels in relation to baseline energy-use composition and retrofit measure applications. This study analyzes the 1954 preliminary investigation and ECO2-OD-based assessment cases of public building green remodeling projects to examine energy-saving levels, baseline energy-use composition, end-use contributions, and retrofit measure applications. Pre- and post-retrofit primary energy demand for heating, cooling, domestic hot water, and lighting were used to calculate energy-saving rates. Based on the 30% policy target, the cases were classified into Low-saving, Target-achieving, High-saving, and Very-high-saving levels. The average energy-saving rate was 36.02%, but 39.61% of cases remained below the 30% target. Higher-saving groups showed greater baseline heating energy shares, increasing from 53.38% in the Low-saving group to 66.18% in the Very-high-saving group, suggesting an association between pre-retrofit energy-use structure and predicted retrofit potential under the ECO2-OD assessment framework. Heating was also the dominant contributor to total savings, with its contribution rising from 17.07 to 44.94 percentage points. Higher-saving cases tended to involve more comprehensive retrofit packages combining envelope, system, and lighting improvements. These findings suggest that energy-saving targets and retrofit strategies should consider baseline end-use energy composition and establish differentiated saving targets according to building characteristics, rather than relying only on uniform policy targets and average project performance.

Various studies on the envelope renovation of existing residential buildings have quantified energy savings effects across various climate conditions and building types yet have also reported discrepancies between predicted and actual energy savings performance. Given that identical technical improvements can yield substantially different actual outcomes depending on occupants’ behavioral adaptation patterns, renovation effect evaluation requires a multifaceted approach incorporating occupant behavioral changes. This case study empirically analyzed the effects of envelope renovation on occupants’ actual heating operation patterns. Envelope renovation effects applied to a 30-year-old apartment were analyzed by subdividing temperature conditions, with comparative evaluation using a non-renovated adjacent unit within the same building as a reference. While recognizing the inherent limitations of single-case analysis, this study presents a novel methodological framework for capturing subtle behavioral shifts through high-resolution temperature-specific analysis. Change-point models utilizing utility billing data were employed to analyze threshold temperature changes, and daily heating water-consumption estimation algorithms were applied to track heating pattern changes according to outdoor temperature variations. Results showed heating energy reduction despite more severe climate conditions post-renovation, with particularly pronounced savings under mild conditions. The upper limit of temperature ranges showing high heating dependency shifted downward from pre-renovation levels, improving to levels lower than the reference unit’s upper limit, demonstrating envelope performance enhancement effects. These results provide quantitative evidence that envelope improvements directly influence occupants’ heating decision-making criteria, though broader validation across multiple cases would strengthen these findings. This study quantifies envelope renovation effects not only in terms of energy savings, but also from the perspectives of occupant behavioral changes and comparison with reference units, presenting a novel evaluation methodology for effective energy efficiency improvements in aging buildings.

Green remodeling and retrofitting are effective strategies for enhancing the sustainability of existing buildings. While green remodeling involves significant structural modifications, green retrofitting typically focuses on improving energy efficiency and reducing environmental impact. However, easy-to-implement green retrofit technologies can be particularly valuable for low-income communities, offering a more affordable way to upgrade residences without extensive renovations. This paper analyzed the effectiveness of newly developed, easy-to-implement green retrofit technologies for windows in reducing heating energy use and greenhouse gas emissions. We conducted experiments using secondary glazing and windproof materials to enhance the thermal insulation and air-tightness performance of a residential building. Subsequently, we simulated the effectiveness of these green retrofit technologies under various conditions for residential buildings. In addition, we analyzed utility bills using data collected from residents. Our findings demonstrated an average reduction of 10–15% in heating energy consumption through the implementation of these green retrofit technologies for windows in older residential buildings.

This study investigates the energy performance improvement in an aging public healthcare center in South Korea through a comprehensive “Green Remodeling” project. The building, originally constructed in 2001 before the establishment of national energy-saving standards, exhibited substandard insulation performance in its walls, roof, floors, and windows. The remodeling was designed to meet the highest current energy-saving criteria, incorporating advanced insulation techniques and energy-efficient systems. The remodeling process achieved a significant improvement in heating efficiency, with the ECO2 simulation predicting a 50% reduction in energy consumption. However, actual post-remodeling savings were approximately 10%, influenced by factors such as varying occupancy patterns and construction challenges. Despite these obstacles, the project demonstrated the effectiveness of targeted energy-saving measures in enhancing the overall performance of the building. This research underscores the importance of green remodeling as a viable strategy for improving energy efficiency in aging buildings, particularly in the context of South Korea’s carbon reduction goals. This study provides practical insights into the design and implementation of energy-saving technologies, offering a model that can be adapted for similar projects in other contexts.

This study analyzed the effect of indoor lighting energy reduction using a daylight-concentrating indoor louver system, which is a renewable energy equipment item. Daylight-concentrating indoor louver systems enhance indoor lighting by directing natural light, entering through windows, into the room via louvers. This study demonstrates significant lighting energy savings through the use of LED-linked dimming control, particularly during the transitional season, achieving an 85.65% reduction in power consumption. In contrast, the winter season showed higher cumulative power consumption due to reduced natural light availability, with a three-day average consumption of 1128.22 W compared to 836.60 W in the transitional season, representing a 25.85% increase. The illuminance distribution analysis revealed that, while winter had higher illuminance at 1 m from the window, the transitional season recorded higher values at 3 m and 5 m, indicating more effective natural light penetration. The solar altitude during the transitional season facilitated even light distribution through daylighting louvers. These findings confirm the substantial energy savings and improved illuminance distribution achieved with daylighting louvers and LED dimming control, with notable efficiency during the transitional season. Consequently, daylight-concentrating indoor louvers are confirmed to be effective in reducing indoor electric lighting energy consumption.

The building energy efficiency grade of old buildings in Korea is rated according to criteria of building energy performance calculated by the ECO2 energy simulation program. To evaluate this performance, ECO2 input data are required, which influence both the intermediate decision process and final calculation results. However, the required input data collection of old buildings for ECO2 simulation is not as simple as expected, and is more difficult than that for new buildings because of many unrecorded changes and updates after the original construction. In these aspects, certification assessment documents for old public buildings are not suitable for preparing input data for ECO2 and usually do not reflect the actual status and condition of buildings from either passive or active perspectives. Therefore, in this study, an ECO2 building energy simulation was performed for 41 old public buildings to examine how input data differences from on-site audits can induce differences in both the simulation process and results. The error range of the primary energy consumption for grades extended from 0 to 231.9 kWh/m 2 ․ yr, depending on whether on-site audit results are considered or not. Because of the long operation period of old public buildings, the initial design plan and current operation status have changed significantly, and our suggestion is that the confirmation step for collecting input data for old public buildings must be a prerequisite and an essential aspect for on-site investigation based on ECO2 simulation.

International standards for vacuum insulation panels (VIPs) include an accelerated test method and a minimum quality standard for evaluating their long-term thermal performance after 25 years. The accelerated test method consists of various tests according to the characteristics of the core material and requires six months (180 days) at minimum. Herein, we propose an accelerated method for determining the long-term thermal performance of fumed-silica VIPs by shortening the required time and simplifying the procedure. Highly accelerated conditions (80 °C and 70% Relative humidity (RH)) were set for the evaluation method, using the maximum temperature (80 °C) cited in international standards and compared with the accelerated test method under accelerated conditions (50 °C and 70% RH). The inner-pressure increase rate of the VIP samples after conditioning for approximately 70 days was similar to that after conditioning for 180 days under highly accelerated and accelerated conditions, respectively. In addition, the estimated long-term thermal conductivities of the fumed-silica VIP were derived as 0.0076 and 0.0054 W/m·K under highly accelerated and accelerated conditions, respectively. These accelerated methods can be used to produce fumed-silica VIPs with similar long-term thermal conductivities. Therefore, the accelerated test method for long-term thermal performance using the highly accelerated conditions can be evaluated using a test that involves conditioning the sample for approximately 70 days under 80 °C and 70% RH.

Most of the existing buildings in Korea, constructed before the insulation standards for parts were strengthened, are requested by an act to improve the building energy performance grade. In this study, five old public buildings were examined to evaluate their energy efficiency rating using an in-situ analysis of each old public building. Energy efficiency measures were derived to achieve the zero-energy level of the buildings' energy performance based on the energy consumption analysis results using ECO2 and the actual building status survey. It is expected that all buildings to be analyzed will be able to achieve ZEB 5th grade when applying the appropriate remodeling measures considering the characteristics of each building. To effectively reduce greenhouse gas emissions, energy-intensive buildings need to be selected as the target of the green remodeling project as a top priority. In the case of buildings with a 1++ grade, current energy efficiency is excellent to date. Therefore, it is necessary to improve the overall building performance by improving the lack of partial performance.