Energy Balance Data-Based Optimization of Louver Installation Angles for Different Regions in Korea

Abstract

A louver is a traditional environmental control device and passive architectural element based on an ecofriendly concept. Louvers are architectural elements that can be used to regulate natural lighting, thermal environment, and building energy use. To realize these integrated functionalities of louvers, they must be designed considering the climate and geographical characteristics of the target region. However, these aspects are typically not considered during building design in Korea, resulting in lovers being used as design elements with simple natural lighting control functions. Therefore, the objective of this study was to promote the integrated use of louvers by optimizing the louver angle according to the microclimate in Korea from the viewpoint of thermal energy use. We performed load and energy simulation planning and calculation and conducted optimization studies for the louver angle and range of motion for each region. The energy consumption in central and southern Korean regions was minimized when the angles of the fixed louvers were 45°–75° and 60°–90°, respectively. Kinetic louvers could enhance thermal energy management when installed at 30°–75° in spring, 135°–165° in summer, 75°–165° in autumn, and 45°–75° in winter. These findings can promote the realization of integrated functionalities of louvers from the perspective of indoor environment comfort based on the microclimates of the Korean regions.

1. Introduction

1.1. Background

More than 40% of the total building energy consumption pertains to maintaining the thermal comfort of indoor spaces. Most of the energy is consumed by building envelope components, such as windows and skylights, that have low insulation performances [1,2,3]. Therefore, these components must be optimized to maintain the indoor thermal environment sustainably [4]. Moreover, external environmental factors such as sunlight and airflow influence human comfort in indoor environments regarding lighting, indoor air quality, and noise [5,6]. Therefore, building envelopes must serve dual purposes of maintaining occupant comfort and optimizing energy use. Louvers, as solar inflow controllers and representative environmental control devices, have been traditionally used in combination with eaves [7]. Louvers are superior to several advanced windows in terms of visible light transmittance and solar heat gain coefficient. In terms of natural light, although high-efficiency windows can reduce the inflow of solar radiation, they do not perform light to penetrate the indoor space. Louvers can fulfill both these roles, and the reflected light can enhance the indoor atmosphere [8]. In addition, because high-efficiency windows are directly exposed to solar radiation, they serve as the primary solar energy shielding element. Thus, the indoor thermal environment may change dramatically with external solar radiation. In contrast, louvers can absorb solar energy before it reaches the window surface, thereby preventing significant changes in the indoor environment corresponding to changes in the external environment [9]. Additionally, louvers can serve as shading devices [10]. Overall, louvers are promising systems that can ensure occupant comfort by countering external factors.

Several researchers worldwide have attempted to analyze the roles of louvers from an integrated perspective. Louver properties such as the material, angle, thickness, and width have been optimized according to the country or region in which they must be installed [11,12,13,14]. Most of the relevant research in Korea has been focused on the specifications and installation methods of louvers considering the lighting energy consumption and natural lighting environment. For example, a hybrid system involving a solar panel and louver has been developed to realize various functionalities related to lighting [15,16]. Notably, research on the role of louvers in managing the thermal environment is limited, owing to which integrated functionalities cannot be achieved. Additionally, louvers must be designed considering the characteristics of the region in which they must be installed. To this end, microclimate analyses must be performed [17]. However, architects often neglect the significant effect of the environment and do not perform planning from an integrated perspective owing to the design complexity. Consequently, louvers are typically used as a simple design or decorative element, and their full potential cannot be exploited. Overall, it is necessary to consider the target region’s microclimate and identify the appropriate louver installation practices for different regions.

1.2. Goal and Scope

The optimal angle and operating range of louvers in each region in Korea were determined based on the thermal load balance data calculated using cooling and heating loads. The independent variables were the regional climate data of Korea, louver angle, and operating time, and the dependent variables were the thermal load balance data derived through simulations. Variables that could affect the energy simulation were set as control variables. Specifically, 2015 climate data, corresponding to the most recent base year for the EnergyPlus Weather (EPW) data collected for the Korean region, were used. The temporal range of the analyses, January, April, July, and October 2015, have typical seasonal climate characteristics. Referring to the standard space considered in the existing studies, the spatial range in this study was set as an office space for one or two occupants in a commercial building.

1.3. Research Steps

This research involved four key steps, as illustrated in Figure 1. First, the literature focusing on the outline, role, and scope of use of louvers was reviewed. The definitions and variables related to the building energy loads were clarified. The architectural factors and conditions that could affect the cooling and heating loads were identified, and the meaning and range of the thermal load balance were reviewed to examine its role as a dependent variable in the simulation.

Figure 1. Research flow.

Second, energy simulation planning and calculation were performed. The control variables and conditions for the simulation were set. An algorithm focused on energy consumption calculation was formulated to calculate the thermal load balance data. Specifically, the physical and spatial characteristics, such as the standard and physical properties of the space to be analyzed, programs, schedules, and space occupancy, were defined. The energy simulation algorithm was implemented using the Rhino 6 Grasshopper Tool.

Third, the calculated data were divided into annual data and those in specific periods. The angles with the lowest and highest energy consumption were determined as the optimal and worst louver angles for each region.

Lastly, the optimal angle and range of motion for fixed and kinetic louvers for each region were presented considering different seasons.

2. Literature Review

2.1. Louver

A louver is defined as a window blind or shutter in which angled plates are arranged at regular intervals on the outer surface of windows and doors [18]. The light-blocking parts of louvers are angled to prevent direct sunlight from entering the space without interfering with the airflow. In this context, louvers can be considered passive devices to create an indoor environment that is comfortable for the occupants and architectural elements that enhance the indoor light environment and thermal environment [19]. As shown in Figure 2, louvers can enhance the indoor light environment in the daytime. Because indirect light is guided into deep space, the illuminance of the indoor space becomes homogeneous. In addition, the inflow of excessive solar radiation can be prevented to maintain a comfortable thermal environment [20]. From the design viewpoint, louvers can impart visual effects, such as the repeatability of a member, expression of color and texture of a material, and continuity through a change in arrangement. In other words, louvers are diverse architectural design elements with aesthetic and practical purposes [20].

Figure 2. Environmental effectiveness of louvers.

Louvers can be divided into vertical and horizontal types according to the arrangement of the slats. Moreover, they can be categorized as overhanging, fin, and grid types according to the configuration [21]. Furthermore, kinetic louvers have been developed that can be autonomously driven through a mechanical device. Depending on the characteristics of the target region, louvers can be used to generate renewable energy while protecting the occupants from external environmental factors such as sunlight and wind [22].

2.2. Building Energy Load

Building energy load refers to the amount of energy that must be supplied or removed to maintain a comfortable environment for occupants regarding external conditions that change according to geographical and climatic conditions. The energy loads can be divided into typical and additional loads. Typical energy loads are associated with the building construction, openings, seepage and leakage, human body heat, and equipment heat. Additional loads include external loads, system loads, and thermal loads associated with equipment, such as ducts and blowers, in addition to the indoor load factor [23].

Among the building energy loads, the amount of energy that must be additionally supplied or removed to maintain the indoor temperature is defined as the heating and cooling load, respectively. As shown in Figure 3, most of the typical energy load factors influence the heating and cooling loads [24]. The value introduced by substituting positive and negative numbers for the heating and cooling loads is defined as the thermal load balance. This value depends on the season. Large positive and negative values mean that the proportion of energy required for heating and cooling the space is high, corresponding to winter and summer, respectively. A value closer to 0 means lower energy required for cooling and heating; thus, the thermal load balance approaches zero in spring and autumn [25].

Figure 3. Factors influencing the calculation of heating and cooling loads.

Louvers form a part of the typical energy load as an architectural element installed on building facades. As louvers affect the inflow of sunlight, their characteristics influence the heating and cooling loads. To clarify the influence of louvers on the thermal environment, Palmero-Marrero and Oliveira calculated the heating and cooling loads for buildings in summer and winter in Mexico, Cairo, Lisbon, Madrid, and London using TRNSYS. The data were used to explore the influence of the indoor thermal environment when louvers were installed on the east, south, and west sides of the building. The results indicated that the louvers’ specifications, such as the target region, installation angle, and installation location influenced the thermal comfort conditions and energy use [26].

Furthermore, Lin et al. analyzed the summer energy performance of a double skin facade (DSF) composed of glass louvers, accounting for China’s continental climate and indoor ventilation conditions. The DSF could achieve thermal energy savings of 11.9% and 5% on a summer day and night, respectively. Using these results, the authors presented a configuration plan and operation strategy for DSFs [27].

Li et al. examined the reduction in thermal energy consumption resulting from using phase change material (PCM) louvers. The energy consumption of buildings in Anda, China, with or without Sunspace windows and with or without PCM louvers, was compared. Annual energy savings of 22.73% were achieved using Sunspace skins instead of general skin, and additional energy savings of up to 5.27% could be achieved by applying PCM louvers to the Sunspace skin [28].

2.3. Results

According to the abovementioned studies, louvers directly influence natural lighting, indoor thermal environment, and building energy use. The building energy consumption can be reduced by optimizing the louver design, such as the configuration, size, and installation location. Specifically, the optimal installation angles of the louver in each region can be determined based on the cooling and heating loads. Therefore, in this study, a comparative analysis was performed for the energy required for cooling and heating in cases involving different types of louvers for a given building in different regions.

3. Planning and Calculation for Thermal Load Balance Simulations

3.1. Outline

The objective of the simulation was to determine the optimal installation and operation angle of louvers for each region in Korea (taking into account the microclimate in different regions), with optimality defined in terms of the cooling and heating loads. Therefore, the same indoor space was considered in each target site. Overall, the energy consumption for each type of louver applied in the same space in different regions with different climate data was calculated. Table 1 lists the steps in the simulation.

Table 1. Simulation process flow.

Step	Content
01	space definition with universal specifications
02	setting of fixed and independent variables
03	introduction of EnergyPlus energy simulation function
04	calculation of cooling and heating energy consumption
05	processing and recording of hourly thermal load balance data

The algorithm’s results were expected to reflect changes in energy consumption with changes in the weather conditions and resulting cooling and heating requirements. The thermal load balance data accounted for cooling by external shadows in summer and heating by the influx of solar radiation in winter. Therefore, the actual energy required to create a comfortable indoor thermal environment could be determined, which was especially necessary to calculate the corresponding values for spring and autumn. Therefore, thermal load balance data were analyzed in this study.

In the algorithm, nine of the 10 influencing factors (excluding regional climate data) shown in Figure 3 were set as the control variables. Regional climate data were set as an independent variable to clarify the influence of the microclimate of a region on the indoor thermal environment. The geographical setting involved a flat area with a slope of zero, which is most commonly perceived as a building structure. Because the heating, ventilation, and air conditioning (HVAC) system may operate differently in each season according to the amount of energy required to induce a certain indoor thermal environment, no HVAC system was assumed to be installed on the site.

Rhino 6 Grasshopper was used to implement the space to be analyzed. Because Grasshopper has a parametric modeling function, various numerical data, including the angle of the louver, could be used as parameters. In general, using parameterized angle data can promote the automation of environmental analysis and labeling of output data. The environment analysis was conducted using the Ladybug Series among the plug-ins available in Grasshopper. Notably, the Ladybug Series can integrate various stand-alone programs such as EnergyPlus engine, OpenStudio, Radiance, Daysim, OpenFoam, BlueCFD, Therm, and Windows. In addition, the Ladybug Series is easy to work with because the environment analysis engine can be used without running a separate program in the modeling framework.

3.2. Set Conditions

3.2.1. Spatial and Material Conditions

Regarding the work of Kim et al. [29], the space to be analyzed had a width, depth, and height of 6000 mm, 4500 mm, and 2700 mm, respectively. The elevation had a front glass window structure over the curtain wall, with 99% of the walls on the south side made of glass. A louver with opaque material was implemented on the front part of the elevation, and an opaque frame was attached to the outer surface of the louver to block the inflow of sunlight from the side. The louver was defined to be of the horizontal type, referring to the work of Datta [30], Jang and Chen [31], and Fang et al. [32]. The union of all areas of light-blocking parts implemented in the louver was the same as the area of the south side. The final analysis space is shown in Figure 4.

Figure 4. Shape and dimensions of the analysis space.

Two types of louvers were considered: fixed and kinetic, considering the transitional situation at present in Korea, which involves the use of both types of louvers. Specifically, in small-scale buildings, fixed louvers are typically used as design elements.

The physical properties of the walls, floors, and roofs of the 4A climate zone presented in “ASHRAE 189.1 Standard for the Design of High-Performance Green Buildings: Except Low-Rise Residential Buildings” were used to define the material properties. Clear glass (3 mm) was applied to the window, and the louver involved a 50 mm wood board made by laminating G05 25 mm wood. The material properties are presented in Table 2 below.

Table 2. Material of each component in the analysis space.

Component	Construction	Material
Wall	ASHRAE 189.1-2009 Extwall Climate Zone 4	1 in. Stucco
		8 in. Concrete HW
		U-Factor 0.0432 Insulation
		½ in. Gypsum
Floor	ASHRAE 90.1-2004 Floor Climate Zone 1–5	½ in. Gypsum
		AtticFloor NonRes Insulation-5.18
		½ in. Gypsum
Roof	ASHRAE 189.1-2009 ExtRoof Climate Zone 2–5	Roof Membrane
		Roof Insulation [21]
		Metal Decking
Window	Clear Glass	3 mm Clear Glass
Louver	Wood Louver	G05 25 mm Wood
		G05 25 mm Wood

The target region was selected by considering the site geography, climatic universality, and specificity from climate data of 22 regions in Korea surveyed by the Passive House Institute of Korea (PHIKO). The weather data of three islands and two mountainous areas among the 22 areas were excluded because of the unique climatic characteristics. Next, the target areas were selected, focusing on six out of 17 areas classified as metropolitan regions: Seoul, Incheon, Daejeon, Gwangju, Busan, and Daegu, which were considered to have regional representativeness and universality. To reflect the microclimate differences and geographic characteristics, such as the latitude and longitude across regions, four additional regions, Suwon, Pohang, Andong, and Gangneung, were added to the target areas. Accordingly, 10 regions were finally selected for analysis, as indicated in Table 3 and Figure 5.

Table 3. Latitudes and longitudes of target regions.

Code	Name	Latitude	Longitude	Code	Name	Latitude	Longitude
A	Seoul	37.56	126.95	F	Busan	35.1	129.01
B	Incheon	37.46	126.61	G	Daegu	35.88	128.61
C	Suwon	37.26	126.98	H	Pohang	36.01	129.36
D	Daejeon	36.36	127.36	I	Andong	36.56	128.7
E	Gwangju	35.16	126.88	J	Gangneung	37.75	128.88

(Unit: degrees, °).

Figure 5. Selected analysis target regions.

3.2.2. Temporal Conditions

According to the “American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) Climate Zones”, Korea lies in the warm and humid (4A) climate zone and has four distinct seasons. Therefore, the optimal installation and operational characteristics of the louvers for all four seasons were determined. To this end, hourly thermal load balance data for January, April, July, and October were considered, as they reflected the general characteristics of the four seasons in Korea.

The year of analysis was 2015, corresponding to the period in which the climate data for each region were most recently updated. In addition, because the analysis space was a general office, the analysis period was 10 h, from 09:00 to 18:00, in accordance with Korea’s legal working hours. It was assumed that during the lunch period (included in the analysis period), the facility operation did not change to maintain the indoor environment.

3.2.3. Building Program, Schedule, and Load

The analysis space was a “closed office” with 1 or 2 occupants, a default type provided by the EnergyPlus engine. The ASHRAE standard schedule of heating and cooling temperatures, lighting time, and equipment usage time was applied to this office space.

Moreover, values related to typical loads, such as the equipment heat load, ventilation levels, and occupancy, were set. The analysis space was set as an office equipped with a variety of equipment, with an occupancy of one. Indoor lighting was based on LEDs. The infiltration rate corresponded to a high-performance passive house. No HVAC system was implemented to evaluate the changes in the cooling and heating energy resulting from the louver. Table 4 summarizes the set parameters.

Table 4. Target region characteristics.

Load Type	Description	Value
equipment load per area	office filled with computers and appliances	15 W/m2
infiltration rate per area	tight Building	0.14 cfm/sf facade @ 75 Pa
lighting density per area	LED lamps	3 W/m2
number of people per area	lightly occupied	0.02 ppl/m2
ventilation per area	laboratory level	0.0025 m3/s
ventilation per person	minimum level	0.001 m3/s

3.2.4. Variables

The control, independent, and dependent variables were set as described in Section 3.2. The independent variables included the regional climate data, louver angle type, and analysis time. Ten analysis target areas with different regional climate data (Section 3.2.1) were selected among the 22 regional climate data provided by Ladybug EPWmap. Thirteen louver installation angles were set by dividing the movable range of 0° to 180° into 15° intervals. The values of 0° and 180° (completely shielded windows) were excluded from the analysis. Therefore, a total of 11 installation angles were considered.

The dependent variables were the thermal load balance data. All variables that affected the energy use, such as geographical characteristics and the direction of windows, were classified as control variables with fixed values.

3.3. Results

All aspects related to the energy analysis, such as time, space, and physical properties, were reviewed. Additionally, thermal load balance data for each season were calculated for different types of louver and microclimate characteristics. Specifically, 132,000 values of the hourly thermal load balance data were calculated for the complete region, and all hourly data were processed into daily data. These daily data were classified again by region and finally summed into seasonal and annual data. Accordingly, 550 regional data points were processed and recorded in the data sheet format shown in Figure 6.

Figure 6. Thermal load balance data sheet.

4. Simulation Data Analysis and Louver Angle Optimization

4.1. Optimized Louver Angle in Different Seasons

The monthly and annual data were summed up by substituting the absolute values for the daily thermal load balance data. Negative and positive values correspond to cooling and heating energy consumption, respectively. The optimal louver angle was determined considering the total thermal energy consumption in the space. Specifically, a comparative analysis was performed by summing up the absolute values of the thermal load balance data for each region to be analyzed. Maximum and minimum value of simulation results in the table of Section 4 were respectively expressed in red and green.

As shown in Table 5, the regional minimum thermal energy consumption for the spring season was 46.09148 kWh, corresponding to louver angles of 30°–60°. The maximum energy consumption corresponded to a louver angle of 165° in all regions except C and E. In the C and E regions, the highest energy consumption corresponded to a louver angle of 30°. In other words, in the spring season, it was preferable for the louver to be aligned parallel to the direction of the inflow of sunlight. In regions C and E, the energy consumption was highly sensitive to the change in the louver angle. Therefore, in the spring season, it was necessary to vary the louver angle in these regions between 30° and 60°.

Table 5. Total thermal energy consumption in spring.

Category	Region
	A	B	C	D	E	F	G	H	I	J
Value Without the Louver	165.82	231.5	209.74	290.81	138.56	211.19	190.55	190.55	241.92	289.76
Minimum Angle	30°	30°	60°	45°	60°	30°	45°	45°	30°	45°
Minimum Value	116.20	72.74	71.97	70.46	85.78	46.09	80.32	62.89	121.59	148.00
Maximum Angle	165°	165°	30°	165°	30°	165°	165°	165°	165°	165°
Maximum Value	169.98	178.29	107.29	118.96	140.84	86.87	101.36	106.60	191.03	179.35

(Unit: kWh).

As shown in Table 6, the minimum angle for all regions in summer was 165°, and the energy consumption was 309.51–676.68 kWh. The highest energy consumption corresponded to a louver angle of 75°–90°. Specifically, the maximum energy consumption was 395.28–803.36 kWh, 85.77–144.13 kWh higher than the minimum value. In other words, more sunlight was blocked in the case of an obtuse angle with the sunlight direction instead of an acute angle. Therefore, in summer, it was preferable for the louver to form an obtuse angle with the sunlight-inflow trajectory.

Table 6. Total thermal energy consumption in summer.

Category	Region
	A	B	C	D	E	F	G	H	I	J
Value Without the Louver	557.88	495.85	909.01	741.68	878.8	844.16	827.24	812.92	822.12	710.18
Minimum Angle	165°	165°	165°	165°	165°	165°	165°	165°	165°	165°
Minimum Value	318.82	309.51	676.68	483.16	633.35	579.04	587.32	590.71	554.68	464.31
Maximum Angle Type	75°	90°	75°	75°	75°	90°	75°	75°	75°	75°
Maximum Value	427.59	395.28	803.36	616.44	777.48	702.15	716.72	697.09	685.70	567.74

(Unit: kWh).

As shown in Table 7, the minimum energy consumption in autumn was 41.81–72.24 kWh. However, the optimal angle varied across locations. For regions A, B, C, and D, located in central Korea, the minimum energy consumption was observed at an angle of 90°. In contrast, for regions E, F, G, and H, located in southern Korea, the minimum energy consumption was observed at an angle of 165°. In other words, the louver must be designed considering the differences in the characteristics of southern and central Korean regions.

Table 7. Total thermal energy consumption in autumn.

Category	Region
	A	B	C	D	E	F	G	H	I	J
Value Without the Louver	129.89	215.57	186.11	216.2	309.97	378.85	221.32	213.65	153.42	315.56
Minimum Angle	90°	90°	90°	90°	165°	165°	165°	165°	75°	165°
Minimum Value	41.81	45.40	57.50	70.16	46.16	64.84	56.00	43.29	52.68	72.24
Maximum Angle	45°	45°	45°	45°	45°	45°	45°	45°	45°	45°
Maximum Value	105.63	143.74	142.43	155.63	208.73	280.85	158.28	158.43	102.13	261.92

(Unit: kWh).

Nevertheless, the louver angle with the maximum energy requirement was 45° for all regions. The maximum energy consumption was 102.13–280.85 kWh, 49.45–216.01 kWh higher than the minimum value. These results highlighted that in autumn in Korea, the louvers must be optimized considering the differences in the characteristics of southern and central Korean regions because of the more intense summer in the southern region.

As shown in Table 8, the minimum energy consumption in winter was 172.01–367.5 kWh, corresponding to an optimal louver angle of 60°. The maximum energy consumption was 536.52–769.05 kWh, corresponding to the louver angle of 165°. In the case of winter, seasonal characteristics must be emphasized over regional differences associated with geography and microclimate differences. Moreover, energy consumption could be reduced by increasing the angle to promote the inflow of daylight into the indoor space through light reflection.

Table 8. Total thermal energy consumption in winter.

Category	Region
	A	B	C	D	E	F	G	H	I	J
Value Without the Louver	542.47	382.71	502.3	488.06	395.09	297.89	355.58	290.96	406.82	476.15
Minimum Angle	60°	60°	60°	60°	60°	60°	60°	60°	60°	60°
Minimum Value	367.50	252.03	331.31	337.78	287.02	186.46	226.55	172.01	260.31	342.48
Maximum Angle	165°	165°	165°	165°	165°	165°	165°	165°	165°	165°
Maximum Value	769.05	712.01	754.38	762.82	603.97	536.52	608.43	537.06	679.85	642.28

(Unit: kWh).

4.2. Optimized Louver Angle Considering Annual Energy Consumption

In analyzing the annual energy consumption, the louver installation angle was evaluated considering the collected seasonal data instead of the actual annual energy. This method was implemented to perform a comparative analysis of the optimal installation angle for each season, considering the extreme seasonal characteristics.

As shown in Table 9, the minimum energy consumption in regions A, B, C, D, and H, located in central Korea, was 975.57 kWh, 822.14 kWh, 1286 kWh, 1136.25 kWh, and 1144.69 kWh, respectively, corresponding to an angle of 60°. The corresponding values for southern regions E, F, G, I, and J were 1259.12 kWh, 1080.53 kWh, 1110.7 kWh, 1024.49 kWh, and 1214.41 kWh, respectively, pertaining to an angle of 75°. Therefore, the optimal louver angles for the central and southern regions were 60° and 75°, respectively.

Table 9. Annual total thermal energy consumption.

Category	Region
	A	B	C	D	E	F	G	H	I	J
Value Without the Louver	1396.1	1325.6	1807.2	1736.8	1722.4	1732.1	1594.7	1508.1	1624.3	1791.7
Minimum Angle	60°	60°	60°	60°	75°	75°	75°	75°	60°	75°
Minimum Value	975.6	822.1	1286.0	1136.3	1259.1	1080.5	1110.7	1024.5	1144.7	1214.4
Maximum Angle	150°	150°	135°	135°	30°	135°	135°	135°	135°	15°
Maximum Value	1325.6	1234.9	1612.5	1451.8	1458.3	1305.8	1372.7	1296.1	1497.8	1393.9

(Unit: kWh).

The worst louver angles were 165°, 150°, 30°, or 15°, depending on the region. Regions A and B exhibited the highest energy consumption (1326.61 kWh and 1247.58 kWh, respectively) at an angle of 165°. The highest energy consumption values for regions C, D, F, G, H, and I (1619.83 kWh, 1459.05 kWh, 1310.7 kWh, 1377.76 kWh, and 1508.58 kWh, respectively) were observed for an angle of 150°. Overall, energy use in Korea increased when the louver was installed parallel to the wall.

4.3. Optimization of the Louver Installation and Operation Angle

4.3.1. Fixed Louver

The rank of optimal angle provided in Section 4.3 was expressed in the order of red, blue, and bold style according to the ranking. Because a fixed louver does not have any mechanism to adjust the angle, it cannot actively respond to changes in the climate. Therefore, the range of installation angles for the fixed louvers was obtained (Table 10), considering the top 3 annual minimum energy consumption values for different regions. Note that in the following text, the angles correspond to the lowest, second-lowest, and third-lowest energy consumption values. The optimal fixed-louver installation angles for central regions A, B, C, D, and I were 60°, 75°, and 45°. Although region J was classified as a central region, the optimal angles were 75°, 90°, and 60°, similar to those of region F, which lies in southern Korea. This phenomenon occurs because of the similar climatic zones of region J and the southern regions. In other words, the optimal louver angle must be determined considering both geographical and climatic characteristics. Except for F, the optimal angles for the southern regions were 75°, 60°, and 90°.

Table 10. Ranks of optimized installation angles for a fixed louver.

Type	Region
	A	B	C	D	E	F	G	H	I	J
15°	7	7	9	9	10	8	8	7	7	11
30°	5	5	5	5	11	6	5	5	5	8
45°	3	3	3	3	5	4	4	4	3	5
60°	1	1	1	1	2	3	2	2	1	3
75°	2	2	2	2	1	1	1	1	2	1
90°	4	4	4	4	3	2	3	3	4	2
105°	6	6	6	6	4	5	6	6	6	4
120°	8	8	8	8	9	9	9	9	8	7
135°	9	9	10	10	8	10	10	10	10	9
150°	10	10	11	11	7	11	11	11	11	10
165°	11	11	7	7	6	7	7	8	9	6

These results highlighted that for fixed louvers, it was preferable to gradually narrow the installation angle in the direction forming an acute angle with the sun inflow angle as the latitude increased. However, regardless of the geographical characteristics, in cases in which the climatic conditions were different from those of the surrounding area, the angle of installation required widening again. Therefore, louvers can optimize energy use if installed considering the climatic characteristics and latitude/longitude of the region.

4.3.2. Kinetic Louver

The orientations of kinetic louvers can be transformed by mechanical devices to respond to seasonal changes. The seasonally variable ranges for such louvers were determined by extracting the lowest, second-lowest, and third-lowest minimum energy consumption values, as shown in Table 11. The movable range for the kinetic louver in the spring season was 30°–75°, with minor variations across regions. In regions B, D, and I (central Korea), the louver angle continuously varied between 30° to 60°. For region C, the minimum energy consumption was observed in the 45°–75° range, similar to that for regions E, G, H, and J. The louver angle with the minimum energy consumption for regions A and F was discontinuous: 30°–45° and 75°. In other words, the energy use could be minimized only when the kinetic louver was operated in the movable range of 30° to 45° in regions A and F.

Table 11. Ranks of optimized installation angles for a kinetic louver in spring.

Type	Region
	A	B	C	D	E	F	G	H	I	J
15°	7	4	9	5	10	6	8	6	6	9
30°	1	1	11	2	11	1	10	2	1	10
45°	2	2	2	1	3	2	1	1	2	1
60°	4	3	1	3	1	5	2	3	3	2
75°	3	5	3	4	2	3	3	4	4	3
90°	5	6	4	6	4	4	4	5	5	4
105°	6	7	5	7	6	7	5	7	7	5
120°	8	8	6	8	9	8	6	8	8	6
135°	9	9	7	9	8	9	7	9	9	7
150°	10	10	8	10	7	10	9	10	10	8
165°	11	11	10	11	5	11	11	11	11	11

Overall, the angle could continuously vary in a 30° range in all regions except A and F, for which the movable range was 15°. Therefore, in regions A and F in spring, the kinetic louver must be operated with limited variations.

As shown in Table 12, in summer, the kinetic louver exhibited the lowest energy consumption at angles of 135°–165° or 150°–165°. The energy consumption was low for angles of 15° in all areas except A and D. In other words, in summer, the louvers must primarily be used for providing shade. The energy consumption could be reduced by maximizing the angle with the sunlight inflow angle. All regions except A and D corresponded to a variable range of 15°, because in summer the seasonal characteristics more significantly influenced the indoor environment than the microclimate and geographical characteristics. Therefore, in summer, the thermal environment can be efficiently managed by operating the kinetic louver in the direction parallel to the wall.

Table 12. Ranks of optimized installation angles for a kinetic louver in summer.

Type	Region
	A	B	C	D	E	F	G	H	I	J
15°	4	2	3	4	3	2	3	2	3	4
30°	9	8	8	8	6	7	8	7	9	10
45°	6	5	5	6	8	4	6	4	5	5
60°	8	6	9	9	9	6	9	6	8	7
75°	11	9	11	11	11	9	11	10	11	11
90°	10	11	10	10	10	11	10	11	10	9
105°	7	10	7	7	7	10	7	9	7	8
120°	5	7	6	5	5	8	5	8	6	6
135°	3	4	4	3	4	5	4	5	4	3
150°	2	3	2	2	2	3	2	3	2	2
165°	1	1	1	1	1	1	1	1	1	1

As shown in Table 13, the movable range of the louvers varied the most according to the geographic and climatic characteristics of the target regions in autumn, compared with those in the other seasons. The optimal movable ranges across regions were 75°–105°, 90°–120°, 90°–105°, 135°–165°, and 150°–165°. The A, C, D, and I regions’ optimal movable range was 60° to 105°. The E, F, G, and H regions’ movable range was between 135° and 165°. Notably, the influence of the summer season decreased more rapidly in the central region, and the movable range regressed to that in spring. In contrast, southern regions or regions with similar climatic zones still had a strong influence in summer, and thus, the movable range in these regions was limited. Therefore, in autumn, the ranges of the kinetic louver must be differently set in central and southern regions considering the geographical characteristics.

Table 13. Ranks of optimized installation angles for a kinetic louver in autumn.

Type	Region
	A	B	C	D	E	F	G	H	I	J
15°	6	8	6	8	7	7	7	7	5	6
30°	10	10	10	10	10	10	10	10	10	9
45°	11	11	11	11	11	11	11	11	11	11
60°	5	9	9	9	9	9	9	9	8	10
75°	2	7	7	7	8	8	8	8	1	8
90°	1	1	1	1	6	6	2	5	2	7
105°	3	6	2	2	5	5	6	6	3	5
120°	4	5	3	5	4	4	5	4	4	4
135°	7	4	4	4	3	3	4	3	6	3
150°	8	3	5	3	2	2	3	2	7	2
165°	9	2	8	6	1	1	1	1	9	1

As shown in Table 14, the minimal energy consumption in winter was observed at louver angles of 75°, 60°, and 45° in all regions. These angles promoted the inflow of sunlight and reflected light into the room, enabling effective exploitation of solar energy. In the winter season, seasonal characteristics exerted a greater influence than geographic and climatic conditions, unlike in summer. Therefore, in winter, the louver must be operated parallel to the angle of incidence to avoid impeding the sunlight entering the space.

Table 14. Ranks of optimized installation angles for a kinetic louver in winter.

Type	Region
	A	B	C	D	E	F	G	H	I	J
15°	8	8	8	8	8	8	8	8	8	8
30°	5	5	5	5	5	5	5	5	5	5
45°	3	3	3	3	3	3	3	3	3	3
60°	1	1	1	1	1	1	1	1	1	1
75°	2	2	2	2	2	2	2	2	2	2
90°	4	4	4	4	4	4	4	4	4	4
105°	6	6	6	6	6	6	6	6	6	6
120°	7	7	7	7	7	7	7	7	7	7
135°	9	9	9	9	9	9	9	9	9	9
150°	10	10	10	10	10	10	10	10	10	10
165°	11	11	11	11	11	11	11	11	11	11

4.4. Results

The optimal louver installation angle and movable range were determined by comparing the thermal load balance data. The optimal installation angle for a fixed louver in central and southern Korea was 60° and 75°, respectively. For a kinetic louver in central and southern Korea, the lowest energy consumption corresponded to movable ranges of 45° to 75° and 60° to 90°, respectively. Because the kinetic louver could respond to seasonal changes, the mobile range was calculated for each season. In spring, the minimum energy consumption corresponded to angles of 30°–75° for all regions. In summer, the optimal angles were 135°–165° or 15°, corresponding to extreme values. In autumn, the optimal angles were diverse: 75°–105°, 90°–120°, and 135°–165°, owing to the dominant influence of the regional microclimate. In winter, the optimal angles had low values (45°–75°).

Below Table 15 compared the seasonal and annual energy consumption rate between installed optimal angle louver and non-installed. And, the maximum and minimum values were expressed in red and green, such as the table written in Section 4.1 and Section 4.2. It shows that the introduction of louvers can help achieve annual energy savings of at least 25.7% in all areas, compared with the cases in which a louver is not installed. In region F, energy benefits can be obtained year-round by installing louvers, although the effectiveness of louvers is limited in region I. Compared with the cases without louvers, energy savings of 14.04%, 25.56%, 65.66%, and more than 27.35% can be achieved in spring, summer, autumn, and winter, respectively. In winter, the indoor solar light input area is reduced by the louver installation, leading to an increased energy consumption of 4.67–19.05% in different regions. Moreover, the installation of louvers in winter did not enhance the thermal environment. These findings can help designers set appropriate installation and operation angles of louvers considering the thermal energy use and microclimate to promote the realization of integrated functionalities of louvers. Nevertheless, the disadvantages of introducing louvers in winter must be carefully considered in the application stage.

Table 15. Annual and seasonal energy savings in cases without louvers and with optimal louvers.

Category	Region
	A	B	C	D	E	F	G	H	I	J
Spring	14.04	24.45	58.05	50.12	51.43	46.09	46.42	53.88	23.14	30.79
Summer	42.85	37.58	25.56	34.86	27.93	31.41	29.00	27.33	32.53	34.62
Autumn	67.81	78.94	69.10	67.55	85.11	82.89	74.70	79.74	65.66	77.11
Winter	−4.67	−19.05	−6.20	−11.79	−16.78	−18.21	−12.42	−14.41	−13.12	−9.42
Annual	28.55	30.94	27.30	28.41	28.48	32.74	28.53	29.53	25.70	29.22

(Unit: %).

5. Conclusions

Energy simulations were performed to promote the integrated use of louvers from the viewpoint of thermal energy management. Cooling and heating energy data were calculated for different louver installation angles. The optimal louver angles and range of operation for different regions in Korea were determined considering the minimum energy consumption by reflecting the geographic and microclimate characteristics of the central and southern regions. The results highlighted that the introduction of louvers could help achieve annual energy savings of 25.7% in all regions in Korea, demonstrating the effectiveness of optimal louvers. Because the results were obtained considering the microclimate characteristics, they can be readily used by architects to promote the integrated use of louvers, for instance, by establishing local louver installation guidelines. Moreover, because the proposed technique is based on EPW data, the optimal louver angle in terms of energy consumption can be determined for all regions for which the local climate data can be collected and recorded.

This study involves the following limitations: Because this study was focused on thermal energy management, among the complex roles of louvers, the louver angle was not optimized in terms of the light environment or ventilation. Therefore, the findings cannot be extended for the louver-based optimization of the overall environment. Future research can be focused on exploring the environmental control ability of louvers in terms of natural lighting, lighting energy consumption, thermal environment, and ventilation environment.

In addition, fixed values were set for the parameters in the thermal environment analysis, such as the topographical structure, elevation direction of buildings, and materials of louvers, which are typically variable. It is thus necessary to optimize louvers in scenarios involving diverse independent variables.

Moreover, Korea has yet to implement energy scenarios in accordance with the United Nations Sustainable Development Goals (UN SDGs). The present research can be extended to establish Korea’s unique energy scenarios.