• Energy Research

Building integrated photovoltaic (BIPV) modules with color-cover glasses have been developed to overcome design limitations in building applications. Although several current studies have presented informative outcomes through experimental analysis, understanding the long-term operating performance of color BIPV modules is still insufficient, especially when considering the transmittance features of the color-cover glass. Therefore, this study evaluates the operational performance of color BIPV modules based on comparative analysis under outdoor experimental conditions. A typical BIPV module (i.e., a non-color BIPV module) and color BIPV modules are used for this comparative analysis. The transmittance characteristics of general low-iron tempered glass (LTG) and LTG with the color coating are considered to evaluate the effect of performance degradation according to the transmittance reduction by the color coating. The thickness differences of the coating layer make different color patterns of gray, blue, and orange. In addition, the color modules are installed on the inclined (30°) and the vertical (90°) plane to assess power performance on different angle positions. Compared to the ratio of transmittance reduction (RTR) by the color coating and the percentage of efficiency reduction (RER) by the color-cover glass, the RER is less than the RTR. The RER of operational efficiency for blue and orange modules is similar to the RER in STC. Still, the RER of the gray module’s operational efficiency is about 5% greater than RER in STC. , the voltage and current characteristics for the gray module using operational data are analyzed to investigate the effect of color differences on the power efficiency. Based on the result, it was confirmed that the active efficiency reduction of the gray module is expected from the decrease in the current.

Heated glass can be applied to improve windows’ condensation resistance and indoor thermal comfort in buildings. Although this applied technology has advantages, there are still some concerns in practical applications, such as additional energy consumption and control issues. This study evaluates the effectiveness of a heated window heating (HWH) system in terms of thermal comfort and heating energy performance (HEP). The simulation-based analysis is performed to evaluate the effectiveness of the HWH using a residential building model and to compare it with radiant floor heating (RFH) and hybrid heating (HH) systems (i.e., combined HWH and RFH). This study also investigates the peak and cumulative heating loads using HWH systems with various scenarios of control methods and setpoint temperature. The predicted mean vote (PMV) is used as an indoor thermal comfort index. The ratio of cumulative thermal comfort time to the entire heating period is calculated. The results show that HWH and HH can reduce the heating load by up to 65.60% and 50.95%, respectively, compared to RFH. In addition, the times of thermal comfort can be increased by 12.55% and 6.98% with HWH and HH, respectively. However, considering the social practices of South Korea, HH is more suitable than HWH. Further investigations for HH show that a surface setpoint of 26 °C is proper, considering both heating demands and thermal comfort. In addition, the setpoint temperature should be determined considering HEP and the thermal comfort for HWH, and the optimal setpoint temperature was suggested under specific conditions.

Abstract Useful thermal bridge performance indicators (ITBs) of existing buildings may differ from calculated thermal bridge performance derived theoretically due to actual construction conditions, such as irregular shapes and aging. To fill this gap practically, a more realistic quantitative evaluation of thermal bridge on-site needs to be considered to identify thermal behaviors throughout exterior walls and thus improve the overall insulation performance of buildings. In this study, a case study is conducted using an infrared thermal imaging method to evaluate the thermal bridge of an existing building practically. The study's main purpose is to review the thermal bridge performance indicators measured by the steady-state model under field conditions in terms of convergence and uncertainty. Bayesian Markov Chain Monte Carlo (MCMC) is used to examine the validity of the results by deriving evaluation results in the form of distribution, including uncertainty. After the measurement was completed, an analysis of the results was conducted. As a result of measurement for 3 days, it was found that the thermal bridge part had 1.221 times more heat loss than the non-thermal bridge part, which showed a 6.7% deviation from the numerical method. However, the uncertainty was 0.225 (18.4%, CI 95%), a large figure. This is due to the influence of field conditions and shows the limitations of the steady-state measurement model. Regarding the convergence of the results, the measurement results were found to converge continuously as the measurement time increased. This suggests that valid results can be obtained in the field if the measurement is performed for a sufficient time, even with a thermal bridge measurement method assuming a steady-state.

Abstract The concept of zero-energy buildings is gaining much interest, and its technical feasibilities have been demonstrated for sustainable development. Although several case studies present how effectively zero-energy performance can be achieved, there is still a lack of data understanding adopting different combined passive and active systems for zero-energy performance. In response to this gap, this study introduces new integrated systematic approaches of enabling all-electric zero-energy performance and presents these features and operating performance for each part of energy consumption contributors based on measured data over two years. Structural insulation panels, vacuum glazing with heated glass were applied as passive techniques. An air-source heat pump and package air conditioner were used for heating and cooling systems, respectively. In addition to the passive and active systems, building-integrated solar thermal and roof-integrated photovoltaic (RIPV) systems were installed to offset all the remaining energy in the house. The energy use intensity of the house was 77.98 kWh/m2·yr; heating and domestic hot water had the highest consumption. To save cooling consumption, exterior electric venetian blinds and natural ventilation were used to cut down energy consumption. The house consumed 7,368.95 kWh/yr and produced 11,439.68 kWh/yr through the RIPV, the annual RIPV surplus accounting for 35.58 % of the annual energy production. The results from this case study provide a comprehensive overview of the feasibility of different combined technologies and insights into proper design strategies to improve the performance of zero-energy houses and buildings from another point of view.

The performance of the Operable Building Integrated Photovoltaic (OBIPV) system applied to the building envelope to reduce the building energy consumption varies significantly depending on the operation method and influence of the surrounding environment. Therefore, optimization through performance monitoring is necessary to maximize power generation of the system. This study used temperature-corrected normalized efficiency (NE*) to evaluate the power generation performance of the operation methods and predict that of the OBIPV system based upon the measured data. It was confirmed that power generation performance decreased when the photovoltaic (PV) operation angle changed, the system remaining the same. A decrease in power generation performance due to partial shading from an overhang was also observed. As a result of the power generation prediction for two months using NE*, the error of the measured values was found to be less than 3%. In addition, with or without any partial shading of the OBIPV system, its performance degradation was predicted with an annual electricity generation decrease by 36 kWh/yr (6.5%). Therefore, NE* can be used as an indicator for evaluating the power generation performance of PV systems, and to predict generation performance considering partial shading.

This study presents the influence of multi-skin façade (MSF) design with photovoltaic (PV) systems on the thermal behaviors and power generation potential when installed on the entire southern façade of an office building model. This study considers various flexible changes in MSF system design based on geometrical concepts. For the simulation model development, this study uses the medium-sized prototype office building model, developed based on the ASHRAE 90.1-2019. A total of 24 different patterns are created based on a pyramid configuration: triangular pyramid (TP) and rectangular pyramid (RP). Changing the tilt angle for PV integrated surfaces is the main method used to compare the power generation efficiency of different MSF configurations. Results from this analysis indicate that the proposed PV-integrated MSF system with generated patterns tends to reduce cooling and heating demands. The system also presents increased PV power generation performance compared to vertically installed PV systems (i.e., the base case). The designed pattern has the highest performance in the RP configuration, 49.4% and 46.6% higher than the base case when compared based on energy yield and energy yield per unit area parameter, respectively. Increasing the cavity depth and installing the PV-integrated roof surface angle to coincide with the local latitude can achieve efficient power generation for the TP configuration, provided that only one unit is required for a pattern. As for the RP configuration, reducing the cavity depth and combining the number of units (up to nine units) on the pattern surface can achieve the best-performing power generation, while the heating and cooling demands of the perimeter zone are not significantly impacted. The results show the influence of geometrical design aspects of MSF systems on energy efficiency and the potential to generate energy from PV systems. This study is a part of developing an energy-efficient design method for multi-skin façade systems for commercial buildings.

Energy loss through windows can be high relatively compared to other opaque surfaces because insulation performance of fenestration parts is lower in the building envelope. Electrically heated window systems are used to improve the indoor environment, prevent condensation, and increase building energy efficiency. The purpose of this study is to analyze the thermal behaviors of a heated window under a field experiment condition. Experiments were conducted during the winter season (i.e., January and February) with the energy-efficient house that residents occupy. To collect measured data from the experimental house, temperature and heat flux meter sensors were used for the analysis of heat flow patterns. Such measured data were used to calculate heat gain ratios and compare temperature and dew point distribution profiles of heated windows with input power values under the changed condition in the operating temperature of the heated glazing. Results from this study indicated that the input average heat gain ratio was analyzed to be 75.2% in the south-facing and 83.8% in the north-facing at nighttime. Additionally, compared to January, reducing the operating temperature of the heated glazing by 3 °C decreased the input energy in February by 44% and 41% for the south-facing and north-facing windows, respectively. Through such field measurement study, various interesting results that could not be found in controlled laboratory chamber conditions were captured, indicating that the necessity of establishing various control strategies should be considered for the development and commercialization of heated windows.