Insulation materials used for buildings are broadly classified as organic insulation materials or inorganic insulation materials. Foam gas is used for producing organic insulation materials. The thermal conductivity of foam gas is generally lower than that of air. As a result, foam gas is discharged over time and replaced by outside air that has relatively less thermal resistance. The gas composition ratio in air bubbles inside the insulation materials changes rapidly, causing the performance degradation of insulation materials. Such performance degradation can be classified into different stages. Stage 1 appears to have a duration of 5 years, and Stage 2 takes a period of over 10 years. In this study, two insulation materials that are most frequently used in South Korea were analyzed, focusing on the changes thermal resistance for the period of over 5000 days. The measurement result indicated that the thermal resistance of expanded polystyrene fell below the KS performance standards after about 80–150 days from its production date. After about 5000 days, its thermal resistance decreased by 25.7 % to 42.7 % in comparison with the initial thermal resistance. In the case of rigid polyurethane, a pattern of rapid performance degradation appeared about 100 days post-production, and the thermal resistance fell below the KS performance standards after about 1000 days. The thermal resistance decreased by 22.5 % to 27.4 % in comparison with the initial thermal resistance after about 5000 days.

Foam insulation materials are widely used in the construction industry due to their low thermal conductivity attributable to their microstructures and their low-conductivity blowing agents and affordability. In this study, we evaluate how the thermal performance of foam insulation materials used for the exterior walls of buildings, viz., extruded polystyrene (XPS), polyisocyanurate (PIR), and phenolic foam (PF), age over the life cycle of a building. To compare the aging of thermal performance during the life cycle of a building, each material was tested at 70 and 110 °C and with slicing acceleration according to EN and ISO standards. The thermal conductivity of each foam insulation material was measured using a heat flow meter at an operating temperature of 23 °C and converted into thermal resistance values. Different foam insulation materials have different aging procedures according to material-specific EN standards, while ISO 11561 applies the same procedure to all material classifications. Upon comparing the aged values according to ISO and EN standards to the initial values, the analysis showed a change rate of 23 to 26% in PIR and 18 to 20% in PF. In XPS, a rate of change of 10 to 23.8% was calculated. Our results indicated that the slicing acceleration induced a thermal resistance reduction rate about three times faster than aging at 70 °C. However, the long-term changed thermal resistance values of the foam insulation material applied via the calculating procedure specified in the ISO and EN standards were similar.

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.

Two experiments were executed to examine the slice accelerated test method, suggested in ISO 11561 “Ageing of thermal insulation materials—Determination of the long-term change in thermal resistance of closed-cell plastics (accelerated laboratory test methods)” and to observe the changes in the thermal performance of insulation material over time by the real-time ageing process. The accelerated test method was conducted for 120 consecutive days using 10 mm thick-sliced specimens, which were sampled from a 50 mm thick plate body. The real-time ageing process was performed for 5000 consecutive days under constant temperature and relative humidity conditions as of 20 ± 5 °C and 50 ± 5% without any slicing. Degradation of thermal performance was shown to be stabilized at around 38 to 41% down from the initial values, which were correspondent with the approximately 10 days after the initial time. The real-time ageing process revealed similar degradation levels at around 130 days after the starting point. Converting the results using the scaling method specified in ISO 11561, the change was found in the range of 37 to 41% for the thermal resistance after 25 years and of 30 to 38% for the 25-year-average thermal resistance, respectively. Within the 10% error range, both the accelerated method and real-time ageing resulted in a similar level of degradation. Consequently, it was our observation that the slice accelerated test was quite enough to predict the practical degradation of insulation materials with at least 90% of accuracy under the specified time duration, temperature and thickness satisfactions.

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.