Hyun-Jung Choi

The expansion of zero-energy building requirements has intensified the interest in Building Integrated Photovoltaic (BIPV) systems as a solution to the limited installation space for renewable energy sources in urban environments. BIPV systems serve both as building envelope elements and power generators. Partial shading from surrounding buildings and structures often causes significant power losses in these systems. Module Level Power Electronics (MLPE), such as power optimizers, can reduce these power losses by optimizing individual module performance; however, conventional products designed for standard photovoltaic (PV) modules are limited when applied to BIPV modules. These limitations occur because BIPV modules have lower electrical specifications owing to custom designs that meet the architectural requirements of various sizes and colors. This study develops a power optimizer specifically for BIPV modules to mitigate power loss, featuring hardware improvements with a buck converter for low-voltage operation and firmware enhancements for optimized shadow detection and Maximum Power Point Tracking (MPPT) control. Comparative experiments were conducted under various shading conditions (10%, 25%, 50%, and 75%) on vertically installed BIPV modules. Results indicate that the developed power optimizer improved performance under high shading conditions, demonstrating reduced power loss by 12.1% compared to that of conventional products under 75% shading. These findings confirm that the developed power optimizer can maintain power generation under partial shading in urban environments, thereby facilitating the adoption of zero-energy buildings through enhanced BIPV system reliability.

To combat climate change and achieve global carbon neutrality, photovoltaic (PV) systems have been widely used in the building sector, particularly in zero-energy buildings. In urban areas, space constraints make building-integrated photovoltaic (BIPV) systems appealing, as they combine building materials with power generation and are designed with aesthetics in mind. However, BIPV systems are often affected by partial shading from surrounding structures. Moreover, unlike general PV modules, BIPV modules are custom-designed, resulting in poor electrical specifications. To address these challenges, this study developed a new prototype power optimizer for the module-level power electronics used in BIPV systems. The performance of BIPV systems was evaluated without a power optimizer, with a conventional power optimizer, and with the new prototype power optimizer through simulations and experiments under different shading conditions. Compared with the non-optimized system, power optimizers effectively alleviated shading loss and significantly increased the power efficiency, and the prototype power optimizer achieved a 2.8-fold average improvement in efficiency. This confirms the optimizer function in enabling shaded and non-shaded modules to operate independently at maximum power. Although further research is needed, these optimizers can improve BIPV performance and promote zero-energy buildings.

A building-integrated photovoltaic (BIPV) system produces power using photovoltaic (PV) modules as building exterior materials, whose architectural performance serves the same functions as those of existing building materials. Most relevant studies targeted general PV modules used in the building-mounted and -attached types. This study aims to integrate the building elevation-type BIPV system and exterior materials to secure both exterior material performance and PV electrical performance by embedding a power optimization device in an integrated system of BIPV modules and exterior materials. Thus, the advantages of economy, safety, aesthetics, and ease of maintenance can be achieved. In this study, experiments were conducted on elevation-type BIPV modules with and without a power optimizer, that is, a DC/DC converter, under various shade conditions, and the power loss rate of the BIPV system was analyzed. The power optimizer-equipped BIPV system was experimentally observed to have a PV power-loss rate approximately 2–3 times lower than that of the BIPV system without a power optimizer when the shade ratio of one module was approximately 10–75%. This exterior material-integrated BIPV-specific power optimization device reduces dependence on fossil fuels for power production and improves energy sustainability, contributing to the spread of zero-energy buildings and carbon neutrality.

In response to the international demand for reducing greenhouse gas emissions, the South Korean government officially declared a plan to achieve carbon neutrality by 2050 through the 88.1% reduction in greenhouse gas emissions compared to 2018 levels. The building sector, which accounts for 7% (24.6% when including indirect emissions) of the country's total greenhouse gas emissions in 2018, was compared to the policies of major countries on energy efficiency for old buildings and policies for supporting energy performance improvements for old public buildings. As a result, the following improvement directions were derived: 1. the need for quantitative goal-setting, 2. establishment of management strategies for project participants, 3. verification of energy performance after completion, 4. improvement of understanding among non-experts (residents, local government officials), and 5. expansion of accessibility for non-experts to activate policies. In the future, we need to investigate the latest policies of various countries to utilize them as basic data for the effective operation of South Korea's public building green modeling projects.

The Korean government is implementing a 2050 carbon neutrality initiative to handle the climate crisis; furthermore, is striving to reduce building energy consumption through zero-energy building construction for new buildings and green remodeling projects for existing buildings. The latter is primarily based on the diagnosis of the thermal performance of the existing building envelope, and this diagnosis can lead to the development of rational energy-saving improvement measures. However, in practice the thermal insulation performance value of the envelope is derived based on the calculation values on the blueprint or the legally required thermal transmittance at the time of completion, which is used for building energy analysis. In this study, the thermal transmittance of the wall was measured based on on-site diagnosis using the ISO 6946:2017 "Building components and building elements-Thermal resistance and thermal transmittance-Calculation methods". The results were compared with those obtained from the calculation method to be utilized as a basis for analyzing the rational effects of green remodeling.

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.

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.

The indoor environment is a crucial part of the built environment where our daily time is mostly spent. It is governed not only by indoor activities, but also affected by interconnected activities such as door opening, walking and routine tasks throughout the inside and outside of buildings and houses. Pollutant control is one of the major concerns for maintaining a sustainable indoor environment, and finding the source of pollutants is a relatively hard part of that task. Pollutants are emitted from various sources, transformed by sunlight, react with vapor in ozone and are transported into cities and from country to country. Due to these reasons, there has been high demand to monitor the transportation of particulate matters and improve air quality. The monitoring of pollutants and identification of their type and concentration enables us to track and control their generation and consequently discover reliable suitable mitigation measures to control air quality at regulated levels by contaminant source removal. However, the monitoring of pollutants, especially particulate matter generation and its transportation, is still not fully operated in atmospheric air due to its open nature and meteorological factors. Even though indoor air is relatively easier to monitor and control than outdoor air in the aspect of specific volume and contaminant source, meteorological parameters still need to be considered because indoor air is not fully separated from outdoor air flow and contaminants’ transportation. In this study, an optical approach using a spectral sensor was attempted to reveal the feasibility of wavelength and chromaticity values of reflected light from specific particles. From the analysis of reflected light of various particulate matters according to different liquid additives, parameter studies were performed to investigate which experimental conditions can contribute to the enhanced selective sensing of particulate matter. Five different particulate matters such as household dust, soil, talc powder, gypsum powder and yellow pine tree pollen were utilized. White samples were selectively identified by the peak at 720 nm for talc and 433 nm and 690 nm in wavelength for gypsum under chemical additives. Other grey household dust and yellowish soil and pine tree pollen revealed a distinct chromaticity x, y coordinates shift in vector within the maximum range from (0.22, 0.19) to (0.55, 0.48). Applicable approaches to assist current particle matter sensors and improve the selective sensing were suggested.