• Journal of the Korean Solar Energy Society
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• v.36 no.3
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• pp.33-43
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• 2016

Daylight is an important factor which influences building energy efficiency and visual comfort for occupants. It is important to predict precise sky luminance at the early stages of design to reduce light energy in the building. This study predicted sky luminance distributions of standard sky model(CIE overcast sky, CIE clear sky) that was provided from the CIE(Commission internationale de $l^{\prime}{\acute{e}}clairage$). Afterward, result of sky luminance was compared and verified with simulation value of Radiance program. From the CIE overcast sky, zenith and horizon ratio is about 3:1. From the CIE clear sky, luminance value gets most high value around the sun. On the other hand, luminance value is the lowest in the opposite direction of the sun when angle is $90^{\circ}$ between the sun and sky element. As a result of comparing the calculation results with Radiance program, sky luminance prediction error rate is 0.4~1.3% when it is CIE overcast sky. Also, sky luminance prediction error rate is 0.3~1.5% when it is CIE clear sky. When compared with the results of radiance simulation, it was evaluated as fairly accurate.

• Journal of the Korean Solar Energy Society
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• v.30 no.5
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• pp.100-106
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• 2010

The purpose of this study is to predict the effective sky temperature on Osan City during the summer. The north latitude, east longitude of Osan City is $37^{\circ}06'$ and $127^{\circ}02'$. The altitude from the sea level is 48m. Empirical relations of the effective sky temperature suggested by Duffie and Beckman are compared on clear days. For the effective sky temperature prediction, data measured by the Korea Meteorological Administration is used as an input to the Bliss model. Both Hottel and Krondratyev model are used to calculate the water vapor emissivity. The results using Hottel's model match well with the empirical relation proposed by Bliss. The results show maximum, minimum, and average values depending on water vapor emissivity model. The maximum deviation is about 10K and is due to total emissivity model.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.282-285
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• 2007

Satellite observed brightness temperature simulation using a radiative transfer model (here after, RTM) is useful for various fields, for example sensor design and channel selection by using theoretically calculated radiance data, development of satellite data processing algorithm and algorithm parameter determination before launch. This study is focused on elaborating the simulation procedure, and analyzing of difference between observed and modelled clear sky brightness temperatures. For the CMDPS (COMS Meteorological Data Processing System) development, the simulated clear sky brightness temperatures are used to determine whether the corresponding pixels are cloud-contaminated in cloud mask algorithm as a reference data. Also it provides important information for calibrating satellite observed radiances. Meanwhile, simulated brightness temperatures of COMS channels plan to be used for assessing the CMDPS performance test. For these applications, the RTM requires fast calculation and high accuracy. The simulated clear sky brightness temperatures are compared with those of MTSAT-1R observation to assess the model performance and the quality of the observation. The results show that there is good agreement in the ocean mostly, while in the land disagreement is partially found due to surface characteristics such as land surface temperature, surface vegetation, terrain effect, and so on.

• KIEAE Journal
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• v.17 no.3
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• pp.35-44
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• 2017

Purpose: This study questioned the efficiency of daylight factor as a daylight adequacy and investigated a method of how to complement its weakness by considering a direct sunlight component under a clear sky condition. Method: The Snowdon visitor centre cafe was chosen as a case study building and various techniques such as BRE formula, BRE sky protractor, Pilkington dot diagram and mock-upscale model under the artificial sky simulator were used to analyse and compare daylight factor values. An analysis of direct sunlight component under the clear sky condition was carried out by Climate Consultant 5.5, sun path diagram, and the artificial sky simulator. Result: The result of daylight factor analysis differed by the adopted techniques and it was also contradictory to the results on a direct sunlight penetration. The result not only showed the limitation of daylight factor as a metric but also suggested an improvement by combining it with direct sunlight analysis. The techniques used in this study had a merit of being applied in the early design stage and thus be beneficial to many design professions in order for early daylight performance analysis.

• KIEAE Journal
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• v.9 no.5
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• pp.105-113
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• 2009

Daylighting provides the opportunity for both energy savings and improved visual comfort. An accurate estimation of the amount of daylight entering a building is the key step for daylight designing. This research aims to assess comparative daylighting performance of four different configurations of fenestration in case of unilateral windows and their variation under clear and overcast sky conditions. The selected window openings in this study were single punched, double punched, multiple punched and clerestory, and the area was same for each type of window. The experiment was designed for an office space using 1/10 scale model. Daylighting performance was evaluated by measuring the illuminance on work-plane height using Agilent data logger and photometric sensor Li-Cor. Thecomputer program ECOTECT was also used to simulate the pattern of interior illuminance distribution. Clerestory window showed the best performance in term of both illuminance level and distribution in the experiment. Multiple punched window provided more uniform illuminance distribution than single punched window. Lowest daylighting performance in the experiment was shown by double punched window.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.33 no.5
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• pp.415-426
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• 2015

Solar radiation under a clear sky is a important factor in the process by which meteorological satellite images are converted into solar radiation maps, and the quality of estimations depends on the accuracy of clear sky models. Therefore, it is important to select models appropriate to the purpose of the study and the study area. In this instance, complex models were applied using Linke turbidity, including ESRA, Dumortier, and MODTRAN, in addition to simple models such as Bourges and PdBV, which consider only the solar elevation angles. The presence of cloud was identified using the Communication, Ocean, and Meteorological Satellite and the Meteorological imager (COMS MI), and reference data were then selected. In order to calculate the accuracy of the clear sky models, the concepts of RMSE and MBE were applied. The results show that Bourges and PdBV produced low RMSE values, while PdBV had relatively steady RMSE values. Also, simple models tend to underestimate global solar irradiation during spring and early summer. Conversely, in the winter season, complex methods often overestimate irradiation. In future work, the cause of overestimation and other factors will be analyzed and the clear sky models will be adjusted in order to make them suitable for the Korean Peninsula.

• KIEAE Journal
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• v.3 no.1
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• pp.21-29
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• 2003

Scale model measurements should be conducted under an actual sky or in a simulated sky where conditions can be held constant. A number of successful attempts have been made to develop artificial sky domes with man-made sun emulators. With reference to formerly-developed examples, sky simulator facility has recently been activated in oder to provide desirable sky conditions for teaching and studies. The structure is a 6m-diameter dome and promises to set various condition for energy related and lighting research activities. The sky dome is also equipped a heliodon, the tilt table, to facilitate additive direct sun impact under clear skies. Shading studies, using scale models with the heliodon, reveal how a building's design blocks or permits light's passage to the interior; solar access studies, and tests of the reflection and transmittance characteristics of new daylighting technologies. The design and construction specification and the initial operating experience with a building configuration are reported.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.12-16
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• 2002

The clear sky radiative forcings of aerosols were evaluated over East Asia. We first investigated optical characteristics of aerosol using sky radiation measurements. An algorithm of Nakajima et al. (1996) is used for retrieving aerosol parameters such as optical thickness, ${\AA}$ngstr$\"{O}$m exponent, single scattering albedo, and size distribution from sky-radiation measurements, which then can be used for examining spatial and temporal variations of aerosol. Obtaining aerosol radiative forcing at TOA and surface, a radiative transfer model is used with inputs of obtained aerosol parameters and GMS-5 satellite-based cloud optical properties. Results show that there is a good agreement of simulated downwelling radiative flux at the surface with observation within 10 W m$^{-2}$ rms errors under the clear sky condition. However, a relatively large difference up to 40 W m$^{-2}$ rms error is found under the cloudy sky condition. The computed aerosol radiative forcing at the surface shows downward flux changes ranging from -100 to -170 W m$^{-2}$ per unit aerosol optical thickness at 0.7 $\mu$m. The different values of aerosol radiative forcing among the stations is mainly due to the differences in single scattering albedo ($\omega$$_{0.7}$) and asymmetric parameter (g$_1$) related to the geographical and seasonal variations.

• Journal of the Korean Solar Energy Society
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• v.23 no.3
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• pp.63-71
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• 2003

According to the recent report, the lighting energy consumption of commercial buildings reaches to $30%\sim40%$ of the total energy consumption. It is more than that of cooling & heating energy consumption and it is the major target of energy-saving policy. It is obvious that they are interested in natural lighting device such as Light-shelf for the purpose of raising the lighting energy-saving efficiency. In most of highly developed countries, a thorough study on Light-shelf makes it possible to propose a practical plan while at home there leaves much to be desired to study a guiding principle of optimum plan in spite of its efficiency based on experiments using scale4 model and analysis of simulation. Aiming at making an optimum plan of Light-shelf suitable for the domestic situation, this study is worked by experiments using light-shelf and analysis of variables using illumination program. The experiments is to analyse the efficiency of Light-shelf on condition of the sky and the analysis is to make the simulation using illumination program. This study is composed of 1) the analysis of light with some variables such as presence of light-shelf and degree of angle using 1/2 scaled model 2) making the simulation using Lightscape, illumination program, In brief, concerning presence of light-shelf, it causes little difference in its efficiency in the overcast sky, whereas it decreases an illuminance of window side and provides inner side with the light, which decreases the ratio of the maximum to the minimum inner illuminance and makes the inner of illuminance to range evenly in the clear sky. On degree of angle, as the daylight increases in proportion of degree of angle, the ratio of the maximum to the minimum inner illuminance decreases, which makes it possible to increase the proportion of inner daylight.

• Journal of the Korean housing association
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• v.12 no.2
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• pp.191-198
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• 2001

The aim of this research was to examine the thermal performance of the flat roof in proportion to various directional changes, the results of which were drawn from the miniature model experiment. In this process, various thermal environmental factors were measured and compared with one another to research their aspects of changes. The brief results of this research are as follows: 1) The indoor temperature and load per hour in proportion to directional changes shows the same degree of changes. As for the results of the clear-sky and cloudy-sky experiments, both of them generally appear advantageous in the order of S, $S-30^{\cire}C$-E, $S-30^{\cire}C$-W, $S-60^{\cire}C$-W, E, $S-60^{\cire}C$-E, despite slight differences in the indoor temperature and load per hour in proportion to directional changes. 2) As for the total load of degree day per direction of the clear-sky and cloudy-sky experiments, both of them shows their advantageous results in the order of S, $S-30^{\cire}C$-E, $S-30^{\cire}C$-W, $S-60^{\cire}C$-W, E, $S-60^{\cire}C$-E, despite minor differences in their loads. 3) As for the peak load of degree hour, while the clear-sky experiment shows its advantage in the order of $S-30^{\cire}C$-E, S, $-30^{\cire}C$-W, $S-60^{\cire}C$-W, E, $S-60^{\cire}C$-E, the cloudy-sky experiment does so in the order of S, $S-30^{\cire}C$-E, $S-30^{\cire}C$-W, E, $S-60^{\cire}C$-W, $S-60^{\cire}C$-E.