• Research Article

    Evaluation of Skin Temperature Response According to Foot Heater Type and Gender through Local Heating Experiments

    국부 난방 실험을 통한 발 히터 유형 및 남녀 성별에 따른 피부 온도 반응 평가

    Jae-Han Lim, Tamaskani Esfehankalateh Atefeh

    임재한, AtefehTamaskani Esfehankalateh

    Thermal comfort in indoor environments is crucial for occupant well-being, particularly when using personalized heating solutions such as foot heaters. This study … + READ MORE
    Thermal comfort in indoor environments is crucial for occupant well-being, particularly when using personalized heating solutions such as foot heaters. This study examined the effects of two types of foot heaters—Type A (foot warmer type) and Type B (Partition wall type)—on skin temperature across various body parts in both male and female participants. The objective was to explore skin temperature changes over time, focusing on differences between heater types, genders, and HVAC set points (22℃ and 26℃). Skin temperatures were measured at intervals of 0, 20, and 40 min at the back of the neck, fingers, feet, forehead, and wrist. The results indicated that both heater type and HVAC set point significantly influenced skin temperature. At 22℃, Type A heaters provided a stable warming effect on the feet, with women’s peak temperature reaching 26.7℃ at 20 min and men’s reaching 33.7℃. Type B heaters, while providing a more balanced warming effect across body parts, demonstrated greater variability. At 26℃, Type A heaters increased the back of the neck temperature to 34.8℃ for women and 35.2℃ for men at 40 min, indicating a stronger and more consistent effect compared to Type B. Gender differences were also observed, with men consistently exhibiting higher mean skin temperatures than women across all body parts and set points. Additionally, Type A heaters maintained a more consistent warming effect, suggesting their superiority for sustained thermal comfort. In contrast, Type B heaters resulted in greater variability, especially for the fingers and back of the neck. These findings underscore the importance of foot heater type, HVAC set point, and gender in designing personalized heating strategies that optimize thermal comfort. - COLLAPSE
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    28 February 2025

  • Research Article

    Durability Evaluation of Transparent Electrodes Based on Multilayer AZO/AgNW/AZO Structures

    다층 구조(AZO/AgNW/AZO) 기반의 투명전극 내구성 평가

    Hyeji Kim, Seunghee Cho, Joondong Kim

    김혜지, 조승희, 김준동

    Transparent conductive electrodes are essential components of modern optoelectronic devices that offer high visible transmittance and low electrical resistance. As next-generation electronic … + READ MORE
    Transparent conductive electrodes are essential components of modern optoelectronic devices that offer high visible transmittance and low electrical resistance. As next-generation electronic devices, such as displays, flexible electronics, and wearable devices, continue to evolve, the demand for transparent electrodes with excellent mechanical flexibility and thermal stability has grown significantly. In this study, we demonstrated high-performance transparent electrodes with AZO/AgNW/AZO multilayer structures on PET substrates and evaluated their potential for use in flexible and transparent photovoltaic devices. The combination of the superior flexibility and thermal stability of AZO with the excellent electrical conductivity of AgNWs enabled the development of highly durable electrodes. Bending and heating tests confirmed that the AZO layers protected the AgNW networks, maintaining a stable sheet resistance with less than 5.5% increase after 1000 bending cycles. Furthermore, the structures exhibited robust thermal stability, maintaining a sheet resistance of 12.9 Ω/□ at 210℃. These results indicate that the AZO/AgNW/AZO multilayer electrodes are highly durable and are suitable for flexible devices and high-durability applications. This suggests the potential of AZO/AgNW/AZO structures as transparent electrodes for flexible electronics and energy devices. - COLLAPSE
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    28 February 2025

  • Research Article

    Exploring the Potential of Urban Energy Usage Pattern Flattening through Building Usage Adjustment

    건물 용도 조정을 통한 도시 에너지 사용량 패턴 평탄화 가능성 검토

    Inseop Kim, Junwon Seo, Sungmin Lee, Hyunwoo Lim

    김인섭, 서준원, 이성민, 임현우

    Energy consumption in urban areas is rapidly increasing, and the variability of time-of-use energy demand is growing due to differing energy usage … + READ MORE
    Energy consumption in urban areas is rapidly increasing, and the variability of time-of-use energy demand is growing due to differing energy usage patterns among building types. This results in surges in peak-time electricity demand, threatening the stability of power grids. Therefore, flattening urban energy consumption is essential to enhance energy efficiency and reduce the strain on power grids. This study proposes a method to minimize the variability in time-of-use energy consumption by adjusting the proportions of building uses, focusing on Seohyeon-dong in Bundang-gu, Seongnam, South Korea. To achieve this, we analyzed the energy consumption patterns of various building types and applied the Harmony Search optimization algorithm to adjust the energy usage ratios for each building type, ultimately deriving optimal flattening results. The study results demonstrated a reduction in peak loads, with electricity consumption becoming more evenly distributed throughout the day. These results confirmed significant improvements in grid stability and overall energy efficiency in the region. Future research will aim to apply this optimization algorithm to a broader range of cities and building types to validate its effectiveness. Additionally, the study will explore strategies to maximize practical energy savings, contributing to long-term sustainability goals, including reducing greenhouse gas emissions and promoting the integration of renewable energy. - COLLAPSE
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    28 February 2025

  • Research Article

    All Transparent Heater Based On Metal Oxide

    금속 산화물 기반의 완전 투명 히터

    Seunghee Cho, Hyeji Kim, Junghyun Lee, Seonghwan Yun, Joondong Kim

    조승희, 김혜지, 이정현, 윤성환, 김준동

    In this study, a transparent heater based on metal oxides was developed. Although conventional heaters have been studied to improve transparency, their … + READ MORE
    In this study, a transparent heater based on metal oxides was developed. Although conventional heaters have been studied to improve transparency, their electrodes typically employ metallic materials that inherently possess opaque characteristics. To address this limitation, a functional electrode with an oxide/metal/oxide (OMO) structure was introduced for transparent electrodes to realize an all-transparent heater design. This structure maintained the excellent conductivity of silver (Ag) while achieving high transparency through indium-tin-oxide (ITO). The heating layer used ITO, similar to conventional transparent heaters, thereby maintaining an overall transparent structure. The ITO heating layer exhibited an excellent low sheet resistance of approximately 10 Ω/□, and the OMO electrode structure exhibited a low sheet resistance of approximately 2.5 Ω/□. Owing to this superior conductivity, the heater could reach a high heating temperature of approximately 220°C at an applied voltage of 7 V. In contrast to conventional Ag metal electrodes, this OMO electrode design implemented a multilayer structure combining Ag and ITO for the electrodes, satisfying the requirements of both transparency and conductivity. The multilayer structure was designed to maintain high transparency without compromising the performance, enabling the realization of transparent electrodes with excellent properties. The heater demonstrated an electrode transparency of approximately 67% and a heating layer transparency of 87%, significantly enhancing the overall transparency compared with conventional heaters. This transparent heater is expected to be applied in various next-generation transparent electronic devices such as smart windows and transparent displays. - COLLAPSE
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    28 February 2025

  • Research Article

    Research on Indoor Environment Refinement using the Complementary Color Relationship of BIPV Solar Modules

    BIPV 태양광모듈의 보색관계를 활용한 실내환경 개선연구

    Hyunyoung Lee, Juyeon Kim

    이현영, 김주연

    Perovskite solar cells and Dye-Sensitized Solar Cells (DSSCs), which have emerged as promising technologies worldwide, are increasingly recognized as next-generation Building Integrated … + READ MORE
    Perovskite solar cells and Dye-Sensitized Solar Cells (DSSCs), which have emerged as promising technologies worldwide, are increasingly recognized as next-generation Building Integrated Photovoltaic (BIPV) solutions. These technologies can enable transparent or translucent designs by leveraging their light transmission properties. However, the inherent light transmittance and color characteristics of perovskite and DSSC modules significantly influence the comfort and emotional stability of indoor environments. These factors are crucial when designing both solar modules and buildings. This study investigated BIPV modules with specific colors to improve the surface reflection and chromaticity characteristics of the transmitted light, using the unique color contrast relationships of the modules. We measured, compared, and analyzed the transmitted light chromaticity coordinates of photovoltaic modules coated with complementary colors, in contrast to traditional photovoltaic modules. The analysis revealed that the chromaticity coordinates of the coated modules improved by more than 10% compared to uncoated modules. Furthermore, the indoor environment exhibited a refinement effect of over 10%. Based on these findings, we propose a design guideline for incorporating complementary colors into photovoltaic modules, accounting for various module sizes and light transmittance levels. This study aims to establish a principle for designing pleasant indoor environments using solar modules, while enhancing the potential of BIPV technology to maximize both energy efficiency and user satisfaction. - COLLAPSE
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    28 February 2025

  • Research Article

    Review of DC String Design Problem for Solar Power Generation

    태양광발전 DC 스트링 설계 문제 고찰

    sukwhan Ko, woogyun Shin, youngchul Ju, hyemi Hwang, jinseok Lee, hongjun Ju, youngseop Ahn

    고석환, 신우균, 주영철, 황혜미, 이진석, 주홍진, 안영섭

    The use of string inverters in photovoltaic power plant construction has been rapidly increasing due to reduced installation costs and improved system … + READ MORE
    The use of string inverters in photovoltaic power plant construction has been rapidly increasing due to reduced installation costs and improved system utilization compared to central inverters. However, with the application of string inverters, the length of DC string lines increases, leading to greater line resistance losses and overall system losses. In this study, we measured the degradation in output performance under standard test conditions (STC) as the DC string length increased. The results showed that for a 4 mm2 line with a length of 100 m, the resistance was 0.42 Ω, resulting in a 10% loss in output compared to initial performance. This maximum power point tracking (MPPT) loss can be referred to as system loss. Additionally, a module-level testbed was constructed to collect and analyze data. that the analysis confirmed that resistance loss is proportional to the product of the square of the current flowing through the line and the resistance value. It was also observed that systems with higher resistance exhibited greater system losses, as demonstrated in experiments conducted under STC. Furthermore, when applying string inverters, it is essential to establish design criteria regarding line resistance and length. Analysis using data from irradiation levels above 700 W/m2 revealed significant system losses in systems with a resistance of 2 Ω. - COLLAPSE
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    28 February 2025

  • Research Article

    Estimation of Variability in Internal Rate of Return for Korea Offshore Wind Projects with Financing Conditions

    국내 해상풍력사업의 프로젝트 파이낸싱 조건에 따른 내부수익률 변동성 추정

    Keon-Woo Lee, Kyung-Nam Ko

    이건우, 고경남

    An investigation into the variation in revenue based on project financing conditions was conducted for 20 offshore wind projects in Korea permitted … + READ MORE
    An investigation into the variation in revenue based on project financing conditions was conducted for 20 offshore wind projects in Korea permitted by the government. Capital Expenditures (CapExs) and Operational Expenditures (OpExs) for these projects were estimated using data from a government commission and a report by the U.S. National Renewable Energy Laboratory. Wind speed distribution estimates for Korean territorial waters were used to calculate the annual energy production (AEP), leading to the determination of the capacity factor (CF), assuming the installation of 18 reference 15 MW wind turbines from the International Energy Agency (IEA) at the 20 project sites. Next, financial assumptions were established to compute the Internal Rate of Return (IRR), considering interest rates of 4.5%, 5.5%, and 6.5%, loan periods of 12, 15, and 18 years, and debt levels of 50%, 60%, 70%, 80%, and 90%. The results showed that equity IRR increased with a higher percent of debt, but the variability in IRR also grew, indicating higher financial risk. As the loan period lengthened, interest payments increased, leading to a reduction in taxes for the projects. - COLLAPSE
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    28 February 2025

  • Research Article

    Wavelength-dependent Light Control Transparent FIlm of Oxide/Metal/Oxide/Metal/Oxide Structures for Infrared Shielding Utilization

    Oxide/Metal/Oxide/Metal/Oxide 구조의 파장 제어 투명 필름을 이용한 적외선 차폐 활용

    Minwoo Hong, Younggwang Lee, Junghyun Lee, Chanhyuk Choi, Joondong Kim

    홍민우, 이영광, 이정현, 최찬혁, 김준동

    Light control can provide practical improvements in regard to energy utilization. Light scattering is the interaction of light with a medium that … + READ MORE
    Light control can provide practical improvements in regard to energy utilization. Light scattering is the interaction of light with a medium that spontaneously enables the uniform diffusion of sunlight and improves heat and light management efficiency. In this study, we have developed functionally transparent films capable of controlling light. These films were composed of alternating layers of metal (M) and oxide (O) in the form of oxide/metal/oxide (OMO) and oxide/metal/oxide/metal/oxide (OMOMO) structures that exhibited high visible transmittance and infrared reflectance. The films of the OMO and OMOMO structures efficiently tuned the light to filter long-wavelength heat radiation and pass through the visible light range, providing superior heat shielding performance. The OMO film provided higher optical transmittance (>72%) than the OMOMO film at a wavelength of 550 nm with effective infrared (IR) blocking. Meanwhile, the OMOMO film enhanced the IR reflection effect by 30% compared to that with the OMO film. The addition of a metal-oxide layer to the OMO structure generates multiple instances of light refraction and reflection according to Bragg’s law and multiple thin-film structures, thus leading to increased reflectance in the near-infrared range. These light-scattering films can be applied in smart windows and agricultural greenhouses, contributing to energy savings. Beyond the energy aspect, it suggests potential applications in regard to military technology by providing capabilities for evading infrared detection and camouflage effects. - COLLAPSE
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    28 February 2025
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