Geun Young Yun

Influence of Window Views on the Subjective Evaluation of Discomfort Glare

A window is an indispensable element in a building and acts as a view-giving component that keeps occupants in touch with the outside. This study investigated the potential effect of different window views on the subjective assessment of discomfort glare from a simulated window that rendered blank, natural and man-made views from far to close distances. Fortyeight subjects (24 men, 24 women) participated in the experiments. The experimental results confirmed that the subjective evaluation of discomfort glare can vary with the type of window views presented. The results also indicated that there were noticeable variations in the subjective assessments of discomfort glare over the same visual stimuli. A preliminary criterion for classification of subjects’ sensitivity to glare was illustrated and the difference for the ‘‘glare-sensitive’’ and ‘‘glareinsensitive’’ people was statistically significant. This study found that the psychological factor such as window views could be an important factor in the subjective evaluation of discomfort glare. Widely used glare evaluation formulas such as unified glare rating and daylight glare index would not consider psychological factors. Thus, the finding from this study would contribute to a more realistic evaluation of discomfort glare for future design of glare control systems.

The Effect of Seasons and Prevailing Environments on Adaptive Comfort Temperatures in Open Plan Offices

Creating comfortable indoor climates is one of fundamental functions of buildings and buildings use a large amount of energy to fulfill their function. Therefore, it is important to understand how and under what thermal environments, the occupants can achieve their comfort in their normal lives. This paper reports the results from a longitudinal field investigation, which has been conducted to reveal the comfort temperatures of occupants in open plan offices in summer, autumn and winter in Seoul, Korea and to identify the environmental factors that could affect comfort temperatures. The survey results confirm that comfort temperature would vary with seasons. This research provides the evidence to link the indoor and outdoor temperatures along with past thermal experience with comfort temperatures. An adaptive comfort model has been developed by this study for building occupants in Seoul, Korea based on the field investigation. Comparisons between the new adaptive comfort model and existing models have been also made. The establishment of an adaptive thermal comfort model for Seoul would have a significant impact on energy saving and for setting of thermal comfort standard for office buildings in Korea.

Performance Prediction by Modelling of a Light-pipe System used under the Climate Conditions of Korea

A light-pipe system can introduce daylight into the deeper building interiors, thus potentially displacing the requirement for electrical lighting. For the light-pipe system to be widely used in Korea, it is important to quantify its daylighting performance with due consideration regarding the effects imposed by the local climate conditions. This paper reports the development of a model to predict the daylighting performance of a light-pipe system used in Korea. This model study was based on the monitoring data obtained from a window-less space in which the light-pipe system was installed. The model can predict indoor illuminance distributions and daylight penetration factors as a function of outdoor illuminance, solar altitude and the amount of cloud present. Comparisons were made between the predicted and the monitored data obtained from the study; and also between predictions given by the developed model and other existing predictive models. The comparisons have provided validation of the newly developed model and that the predicted results were robust and reliable.

Evaluation of Daylighting Effectiveness and Energy Saving Potentials of Light-Pipe Systems in Buildings

A light pipe system is a simple daylighting device that allows the natural daylight to enter into interior spaces or underground spaces where access to windows or skylights is restricted. The use of a light pipe system can enhance illuminance without the use of artificial lighting and thus would reduce energy consumption significantly. This paper presents a performance prediction method of a light pipe system based on the amount of daylight admitted and energy saved by not needing electric lighting. The newly developed model was compared with the existing prediction model under the Korean climate conditions, to illustrate the reliability and robustness of the method. Energy saving potential due to the use of a light pipe system was determined with a due consideration of the different artificial lighting control methods (on and off control, two-step control, dimming control), demonstrating a possible saving in lighting energy usage of up to 30% in average. This study should encourage a wider application of light-pipe system in Korea especially in high rise buildings where day-lighting could be limiting; thus increasing the options for architectural design for building application.

Monitoring and Evaluation of a Light-pipe System used in Korea

The use of natural lighting has the potential for improving both the energy efficiency and indoor environmental quality in buildings. A light-pipe system can bring natural light to spaces that would otherwise not be able to benefit from the advantages of daylight penetration. This paper presents the monitoring results of a light-pipe system that was installed in a windowless space of a building located in Korea. Indoor illuminance distributions and concurrent outdoor illuminance were monitored at a 1 s interval over a period from April 2009 to May 2009. The results demonstrated the effects caused by the amount of clouds, solar altitudes and external total illuminances; on both the daylighting performance of the light-pipe system and the indoor illuminance distributions of the space. The findings of this study indicated that the light-pipe system could be an effective tool particularly for introducing daylight indoors, even under overcast sky conditions in Korea. Introduction Daylight within buildings is fundamental to human wellbeing and health. Daylight closely matches human visual response and supplies good colour rendering. A study found that most survey participants preferred daylighting to artificial lighting due to psychological and health benefits [1]. Heschong and Mahone [2] showed that an increase in the level of daylight resulted in an increase in the test scores of elementary school children. The low level of daylight in buildings was associated with seasonal affective disorder [3]. It is important for occupants to be exposed to the high level of daylight in order to entrain the circadian system that influences all parts of the human body and brain, because the spectral distribution of daylight is similar to the spectral sensitivity of the human circadian system [4]. A light-pipe system is an advanced daylighting device that introduces natural light into deeper building interiors where sunlight cannot reach due to inappropriate building design and a lack of properly designed windows. Although the light-pipe system has been used in America, Canada, and the UK [5], only a few companies provide light-pipe systems in Korea. It is, therefore, important to evaluate carefully the daylighting performance of a light-pipe for its widespread use in Korea. Several studies investigated the daylighting performance of light-pipes through field measurements and SAGE Publications 2010 Los Angeles, London, New Delhi and Singapore DOI: 10.1177/1420326X09358007 Accessible online at http://ibe.sagepub.com Figure 1 appears in colour online Jeong Tai Kim, Department of Architectural Engineering, Kyung Hee University, Yougin 446-701, Republic of Korea. Tel. þ82 31 2012539, Fax þ82 31 206 2109, E-Mail jtkim@khu.ac.kr laboratory experiment [6–8]. Oakley et al. [6] demonstrated that light-pipes employed under the climate conditions of the UK were useful devices to transport daylight into buildings. Al-Marwaee and Carter [7] found that light-pipe systems could provide 25–50% of the workplane illuminance of the 13 surveyed buildings using the lightpipe system and thus, reduced lighting energy consumption. Paroncini et al. [8] reported the internal illuminance distribution of a windowless test room with a light-pipe system and evaluated the seasonal effects of the light-pipe system used in Italy. The findings of the above studies were based on the measured data that were directly influenced by their respective local climate conditions. The aims of this study are: to investigate the daylighting performance of a light-pipe system used under the climate conditions of Korea, to evaluate the potential of the lightpipe system as a device that would bring daylight indoors and to investigate the effects of the local climate conditions on the performance of the light-pipe system. Another research to develop and validate methods for prediction of performance has been carried out in parallel and this would contribute to future design and application of light systems to be used in Korea [9]. Data Acquisition and Analysis Experimental Room An experimental room was built on the roof of the S apartment located in Yongin, Korea (Figure 1). The test room was a windowless space and was 6m long and 6m wide with a height of 4m. The reflectance values for four sides and the ceiling of the room were 0.64 and the floor was covered with tiles with a reflectance of 0.53. Light-pipe System A straight light-pipe manufactured by SIT Inc. (Seoul, South Korea). was installed in the centre of the roof of the test room (Figure 1). The cylindrical light-pipe was 1.32m long with a diameter of 0.65m, giving an aspect ratio of 2.03. A highly reflective aluminium film was coated to the inside of the pipe, which had a reflectance of 0.99. The top of the light-pipe was fitted with a clear acrylic dome and a flat polycarbonate diffuser was attached to the lower opening of the light-pipe. The light-pipe was 4m from the floor to the bottom of the diffuser. Measurement Themonitoring periodwas fromApril 22, 2008 toMay 5, 2008. LI 201SA illuminance sensors were used to measure internal and external illuminance levels (sensor measurement range: 0–150,000 lux). The sensors were positioned horizontally on the steel bars located on the floor. Figure 2 shows the positions of the internal sensors. The external and internal illuminance data were measured at 1 s interval and the mean values of the data over a period of 5min were used for analysis. Data for the values of their sky clearness index were equal to or higher than 1 were not used in this study in order to guarantee the reliability of the analysis. Fig. 1. Images of an experimental facility and a light-pipe. 130 Indoor Built Environ 2010;19:129–136 Yun et al. Statistical Analysis We performed linear regression analysis to show the relationships between internal and external illuminance levels and local climate factors. F-statistic was used for the overall test of the regression model and t-statistic for the test of individual regression coefficients [10]. Significant differences between different sky conditions were illustrated by analysis of variance (ANOVA) analysis. Analysis of covariance (ANCOVA) analysis was carried out in order to determine the significance of the difference between regression models used under different sky conditions. The coefficient of determinant (R) was used to measure the overall fit of the regression models.The use of natural lighting has the potential for improving both the energy efficiency and indoor environmental quality in buildings. A light-pipe system can bring natural light to spaces that would otherwise not be able to benefit from the advantages of daylight penetration. This paper presents the monitoring results of a light-pipe system that was installed in a window-less space of a building located in Korea. Indoor illuminance distributions and concurrent outdoor illuminance were monitored at a 1 s interval over a period from April 2009 to May 2009. The results demonstrated the effects caused by the amount of clouds, solar altitudes and external total illuminances; on both the daylighting performance of the light-pipe system and the indoor illuminance distributions of the space. The findings of this study indicated that the light-pipe system could be an effective tool particularly for introducing daylight indoors, even under overcast sky conditions in Korea.

A Field Survey of Occupancy and Air-Conditioner Use Patterns in Open Plan Offices

This paper reports the survey results from a field monitoring study of office occupancy and air-conditioner use pattern of an office building in Seoul, Korea, from 20 July to 29 September 2009. The survey has an aim to reveal the relationship between the indoor environment conditions and occupancy; and the use patterns of air-conditioners and energy consumption in offices. The results showed that the average occupied time of the investigated offices was 15.48 h per day for normal weekdays, which was longer than expected occupancy schedules assumed for offices for the design prediction of building energy consumption. This study also presents the hourly profiles of air-conditioner use and evaluates the effect of longer occupancy period on energy consumption for air cooling in open-plan offices in Korea. The findings of this study could contribute to inform building energy simulation based on realistic office occupancy profile provided by the survey, which would therefore inform better operation of air-condi...This paper reports the survey results from a field monitoring study of office occupancy and air-conditioner use pattern of an office building in Seoul, Korea, from 20 July to 29 September 2009. The survey has an aim to reveal the relationship between the indoor environment conditions and occupancy; and the use patterns of air-conditioners and energy consumption in offices. The results showed that the average occupied time of the investigated offices was 15.48 h per day for normal weekdays, which was longer than expected occupancy schedules assumed for offices for the design prediction of building energy consumption. This study also presents the hourly profiles of air-conditioner use and evaluates the effect of longer occupancy period on energy consumption for air cooling in open-plan offices in Korea. The findings of this study could contribute to inform building energy simulation based on realistic office occupancy profile provided by the survey, which would therefore inform better operation of air-conditioners and more efficient use of energy in building management.

Prediction of Discomfort Glares from Windows: Influence of the Subjective Evaluation of Window Views

Lighting in buildings can exert a large influence on the comfort, well-being, and health of occupants. A window plays a major role in providing both natural lighting in buildings and a view out, so that occupants can keep in touch with the external environment. Thus, it is essential to understand what the visual requirements are to meet occupants’ needs and how window views could affect those requirements. This study aims to reveal occupant perception on window views and to identify its effects on the assessment of glare from windows. This paper presents the results from the experiment conducted in a chamber with a simulated window, which can render various window views and luminance conditions. Forty-eight subjects participated in the experiment. The results show the evidence that the glare sensation of occupants could vary with the occupant’s perception on window views under the same luminous conditions. A discomfort glare index that predicts a subjective discomfort glare as a function of background and window luminances, position index, and perception on window views, has been developed by this study. A comparison between the developed and existing glare prediction models was discussed in this paper.

Bond strength of steel deformed rebars embedded in artificial lightweight aggregate concrete

The recycling of industrial waste such as bottom ash from furnaces is an important issue in construction industry, since it enables reduction in construction cost and has beneficial effect on the environment. In this study, we have investigated the bond characteristics of steel deformed bars embedded in artificial lightweight aggregate concrete which is manufactured from bottom ash. A pullout test was performed on 144 lightweight aggregate concrete specimens to measure the bond strengths. In this test, the parameters included the compressive strength of the concrete and embedment length of rebar. The pullout load vs. slip responses and modes of failure of the specimens were identified during the test. A bond strength equation for lightweight concrete is formulated by performing a regression analysis on the test results and compared with the predictions by the existing equations such as ACI 408, Orangun’s, and Darwin’s. The comparison shows that the existing bond strength equations cannot be directly applied to the design of lightweight concrete structures and the proposed equation is able to provide a more accurate estimation of the bond strength of lightweight concrete than the existing equations.

Energy-Saving Potential of LED Lighting Systems

Light emitting diode (LED) with its long lifetime of up 100,000 h has been receiving keen interest as there has been a rapid increase in luminous efficacy of LED recently. One interesting feature of LED is that its spectral power distributions can be easily controllable by regulating electric circuits to LED. Therefore, the same colour from LED can have quite different spectral power distribution due to metamerism. This is important as spectral power distribution is a key factor that can affect human circadian rhythm and subjective responses to changes with different spectral power distribution under the same illuminance level. The study aims to explore the energy saving potentials of LED lighting system by modulating spectral power distributions. The wavelength controllable LED system was developed in the previous study and was used in this study. Dynamic building simulations were carried out in order to quantify the total energy use including energy demands for lighting, cooling and heating indoors. Our study indicates that subjects would tend to feel brighter under red-colour emphasizing spectral power distribution, as compared to their perception under blue-colour. Also, simulation results indicate that total energy consumption can be reduced by 38% by changing spectral power distribution without sacrificing subjects’ visual comfort.

Thermal and Non-Thermal Stimuli for the Use of Windows in Offices

Windows in a building is an essential element in creating comfortable, energy-efficient and healthy indoor environment. However, the actual performance of a building depends highly on the ways of using the windows by occupants. An understanding of window use patterns is thus of importance in the design and evaluation of buildings. This study aims to extend the understanding of window control behaviour by occupants in offices. A field campaign has been conducted from March 12, 2010, to January 31, 2011, in four offices, located in Suwon, South Korea, to demonstrate the close link between carbon dioxide concentrations, prevailing internal and external temperatures, occupancy schedules and window control patterns; and to predict window use as a function of thermal and non-thermal stimuli. The research reveals that there could be large and significant seasonal effects on window control patterns, which provided main stimuli for the use of windows in spring, summer, autumn and winter. Finally, the influences of different window control patterns on indoor thermal environment and air quality have been analysed in detail.