KIEAE Journal

Shading device is an important building component to prevent direct insolation from the outside, decrease heating and cooling loads, and make comfort indoor environment by controlling natural lights and air flows. The type of the device is various for those reasons, and there are own characteristics depending on the operation mechanism that makes possible to get energy consumption down. [4]Table 1 shows the comparison between the fixed shading devices and the motorized kinetic components.

Category		Mechanism	Characteristics
Fixed	Horizontal		- Prevents the insolation at the time with the highest temperature - Suitable for the south direction
	Vertical		- Prevents the low Sun in the early morning or the late evening - Suitable for either the east or the west direction
Kinetic	Horizontal		- Controls the amount of insolation by length of horizontal louvers
	Vertical		- Controls the amount of insolation by movement of vertical louvers

The light shelf system has two major functions; it can reflect light deeper into interior space and block the direct light as well. When the reflected light on light shelf comes into the deeper interior space, the lighting energy will be decreased during a day time. Moreover, the solar radiation will be blocked by the light shelf as a shading device. These two functions are deeply related to the use of energy. [5]

For this reason, this proposed device is considered as a promising and practical skill. But this device is significantly affected by the altitude and motion of the sun, so it may have a limitation about the range of use. Accordingly, the purpose of this study aims at suggesting a kinetic light shelf makes the functions to be formed according to the altitude of the sun.

Fig. 1  
Concept and function of the light shelf

In order to the function shown on Fig. 1, the position of the sun should be located between 11 AM and 1 PM (See Fig. 2). This is because the light generated from the higher altitude of the sun can be reflected by light shelf. But when the sun set down into the ground, this function of light shelf will become dwindle. [6] And the sunlight that penetrate window will have an impact on the indoor environment.

Fig. 2  
Performance section of light shelf

The most important feature of the kinetic light shelf unit is possible to adjust in the altitude of the sun. When the sun is located between a and b including meridian transit altitude (lower-left corner), the kinetic light shelf unit works as a light shelf. Through this a to b course, indoor space can get the natural light reflected by surface of the light shelf.

The surface of the shelf is covered with high reflectance material. And when the sun is located between b and c (red part, lower-left corner), the kinetic light shelf unit operates as a vertical louver to block out the direct light. Two types of the function are shown on Fig. 3 which represents the changing course from horizontal (light shelf) to vertical (louver). Like this, the kinetic light shelf unit can be changed light shelf into vertical louver and it works to fit in each situation. [7]

Fig. 3  
Exemplar prototype of the kinetic light shelf unit

This unit should meet the requirements for both fundamental mechanisms accordingly to execute expected performance successfully. First, a light shelf needs the appropriate width and the reflectance. To calculate the width of the shelf, the extension line should be considered from bottom of the window up to the position of the sun in summer. The angle decided by two elements is normally set as 20 to 25 degrees. And the light shelf is placed above the eye-level. In case of a vertical louver, it can be rotated to any direction for blocking direct sunlight from the east or the west side.

Fig. 4  
Overall system configuration

This section is to discuss the procedure of selecting simulation tools to analyze the sustainability of the suggested façade system on the basis of comparative investigations.

EnergyPlus, first of all, provides a precise way to analyze indoor and/or exterior environmental factors in detail. But, this tool also has disadvantages that data input process requires complicated professional skills, additional modeling tool and converter are needed since its interface doesn't allow to make a target model for itself, and the analysis process takes long relatively. [8] Project Vasari uses DOE-2 analysis engine provided by the Department of

Energy in the U. S., and produces pretty exact simulation results by loading the parameters defined in the ASHRAE (Standard supported by American Society of Heating, Refrigerating and Air-conditioning Engineers). In addition, this tool can easily be linked with Green Building Studio (GBS) and provides a well-organized analysis report about the energy performance. But, this method also has a shortcoming that analyses for specific time periods are not easy, because it takes a given broad range for input parameters instead of the modifiable input by users. [9]

Ecotect is being developed by Autodesk. This simulator can predict results for environmental settings simply and make data individually per experiment. This program also can estimate various elements such as radiation from the sun, natural lighting, air flow, heating, shade and shadow, building heating and cooling load, and so on, from the pre-design phase to the design development process for designers. The weather tool and the solar tool are also provided by Ecotect, and make possible to interpret weather situation and solar movement for the loaded building model. Analysis data generated by this tool can easily be exported to various formats for interlocking with more applications. [10]

For this study, Ecotect and GBS are selected for simulation to compare indoor environment and energy efficiency of the target buildings.

Since there are no specified guidelines about detail levels of building models for performance evaluation, Level Of Development (LOD) 100 suggested by American Institute of Architects (AIA) has been used for modeling in this study. LOD 100 is known as an equivalent level of the conceptual design in Korea that volume of the building mass and the building type are defined and overall modeling process is established with fundamental building parameters such as area, height, volume, place, axis and so on. [11] In addition, this detail level determines not only a type of the project procurement as suggested by Integrated Project Delivery (IPD) and an initial step for design process with Building Information Modeling (BIM) as well; The AIA documentation, E202TM-2008, includes all the steps of the IPD design process and their detail levels towards BIM. [12]

This study has utilized LOD 100, because the target for the performance evaluation is not for building equipment and utilities, but for building façade as an architectural component. [13] Then, building performance focused on environmental and energy factors would be reviewed with a few alternatives of building skins chosen from both general curtain walls and kinetic façade components for comparison.

Fig. 5  
Building model for simulation on LOD 100

Simulation data can be categorized with four types such as general/fixed horizontal, general/fixed vertical, kinetic horizontal and kinetic vertical, and this study performs analyses for insolation, illuminance, radiation, and heating & cooling loads for each of those. [14] The fundamental simulation settings are described in Table 2.

Category	Contents
Unit Size	Four unit set (1 unit=W: 12,000mm, D: 7,000mm, H: 3,200mm)
Opening Size	W: 11,600mm, H: 2,000mm
Indoor Reflection Rate	Ceiling : 74.99%, Wall : 55%, Floor : 25.1%
Weather Data	Gwangju (Latitude: 35.1°N, Longitude: 126.8°E)
Orientation	South
Comparative Models for Simulations
Fixed Horizontal (F-H)		Fixed Vertical (F-V)
Kinetic Horizontal (K-H) - Controlling the length of the louver every hour		Kinetic Vertical (K-V) - Controlling the angle of the louver every hour

Simulation analyses for four different types performed in this study include the effectiveness from the Sun, such as insolation, illuminance, radiation, and heating & cooling loads. The step-by-step simulations has measured the amount of energy gained through windows to conclude the insolation and the radiation first, and then monthly energy consumptions to maintain the indoor comfort have been examined for heating and cooling requirements. The simulation results have been summarized in Table 3 through Table 5.

Two models have been made to perform comparative analyses for the performance of the proposed unit. The one has the suggested kinetic light shelf unit on the front of the façade. And the other has an ordinary window module without any installation. The same simulation processes have been performed for those models.

Category	Contents
Model Specification	W:12,000mm D:7,000mm H:3,200mm
Opening Size	W: 11,600mm, H: 2,000mm
Indoor Reflection Rate	Ceiling : 74.99%, Wall : 55%, Floor : 25.1%
Light Shelf	Reflectance:80% Width : 600mm
Weather data	Gwangju (Latitude: 35.1°N, Longitude: 126.8°E)
Orientation	Southward
External Illumination	8000 lux (overcast)
Simulation Results
	Basic		Kinetic
Model Information
Daylight Rate
	10.50%		8.33%
Solar Radiation
	799,150 Wh/m2		650,530 Wh/m2

Simulation results shown on Table 6 indicate that the model installed with the kinetic light shelf unit has better capabilities of controlling indoor environment than the basic formation in aspects of both daylight rate and solar radiation. More specifically, it will be able to find more concrete information when comparing the amount of energy consumption in various conditions as monthly, seasonal and annual usages; this part remains as a future study.