Optimizing Energy Efficiency: Louver Systems for Sustainable Building Design

Abstract

As the global focus on sustainability intensifies, architects and engineers are increasingly seeking innovative passive strategies to improve building energy efficiency. Among these strategies, the strategic integration of louvers has garnered significant attention due to their potential to optimize building envelope performance and reduce energy consumption. Louvers effectively manage solar heat gain, mitigating the impact of extreme temperatures on indoor spaces. Consequently, louvers reduce the reliance on active HVAC systems, leading to notable energy savings and a decreased carbon footprint. This paper presents a comprehensive review of the role of louvers in enhancing building energy efficiency, highlighting their designs, efficiency, and improvement suggestions. Moreover, this review article addresses potential challenges related to louver design, such as balancing the trade-off between solar heat gain and daylighting and how to optimize louver configurations for specific building types. Approaches to overcome these challenges, including advanced modeling techniques and parametric design, are also explored to assist architects and designers in achieving the most energy-efficient outcomes.

1. Introduction

Global energy consumption comprises a wide range of activities, including industrial processes, transportation, residential usage, buildings, and commercial sectors [1,2,3]. As of now, global energy consumption stands at 445 EJ, reflecting a 15% increase over the last decade [4]. With continued population growth and economic development, energy demand has steadily risen and is projected to exceed 530 EJ by 2050 [4]. Among the major consumers, the industrial, building, and transportation sectors account for the largest share of electricity usage.

According to the World Energy Outlook, the building sector consumed approximately 120 EJ of energy in 2023 [4]. Electricity demand in buildings has grown significantly from 9637 TWh (2010) to 12,594 TWh (2021) and is expected to rise to 15,850 TWh by 2050 [5]. This rise is accompanied by a 4% increase in building energy demand and a 5% rise in CO₂ emissions since 2020 [6]. Approximately 37% of global operational energy and process-related CO₂ emissions are associated with the buildings and construction industry. Historically, fossil fuels have dominated the global energy mix, accounting for 80% of energy consumption in 2023 [4]. However, efforts are underway to reduce this dependence, with projections indicating a decline to 58% by 2050 under the STEPS scenario [4]. To address environmental concerns and promote sustainability, 560 GW of renewable energy capacity was added to the global energy mix in 2023 [4]. This shift reflects a growing emphasis on incorporating renewable energy alternatives to mitigate environmental impacts and ensure long-term sustainability [7,8].

Despite these advancements, governments, households, and businesses face challenges in investing in building decarbonization due to the unpredictability of global energy prices and rising interest rates. Reports suggest that the building and construction sector is not currently on track to achieve decarbonization by 2050. However, transitioning to a low-carbon economy is essential to achieving Sustainable Development Goals (SDGs) [9]. Energy supplied by renewable sources was documented at 74 EJ in 2021 and is expected to increase to 215 EJ by 2050 [5]. Monitoring and managing global energy consumption are crucial endeavors, as they play a pivotal role in shaping the world’s economic trajectory, environmental impact, and efforts to combat climate change. Sustainable practices, energy efficiency measures, and innovative technologies are essential for meeting future energy demands while minimizing adverse effects on the planet [10,11,12].

Energy Saving in Buildings

Energy in buildings can be optimized and saved using efficient lighting sources and appliances, onsite renewable production and use, improvements in existing building stock, and new buildings with high energy performance [13,14]. Combining renewable energy sources with energy-efficient practices is key to creating sustainable and eco-friendly buildings that meet their energy needs while minimizing environmental impact [15]. The importance of sunlight for the energy needs of a building cannot be overstated [16]. Sunlight, as a readily available and renewable energy source, plays a vital role in reducing a building’s reliance on conventional power grids [17,18]. Properly harnessing sunlight through strategically placed windows and solar panels can significantly contribute to passive heating, daylighting, and natural ventilation, thereby decreasing the demand for artificial lighting and cooling systems [19,20]. As a result, different research have been carried out focusing on relevant techniques [21], encompassing blinds [22,23], louvers [24,25], awnings [26], and light shelves [27]. Among these components, louver systems find extensive application in buildings due to their unique designs, exceptional efficiency, and high-performance capabilities [28]. In [29], a louver system reduced cooling energy consumption by 27% and achieved 80% energy saving in lighting requirements. Furthermore, the energy savings were also analyzed at 30%, 50%, 70%, and 100% opening of louvers.

2. Louvers in Buildings

Some common applications of louver systems in building design and architecture include sun shading, ventilation, daylighting, heating and cooling, privacy and security, rain and weather protection, aesthetic and architectural design, noise control, mechanical equipment screening, and sustainable building design. Overall, louver systems are versatile architectural features that serve both functional and aesthetic purposes in modern building design, contributing to energy efficiency, occupant comfort, and visual appeal. Figure 1 shows an adjustable louver to control blinds’ number, angle, and width for optimizing daylight and thermal comfort under diverse climatic conditions. The parameters affected the shading density, daylight transmission deep inside the building, and structural stability of the louver [30].

2.1. Illumination

2.1.1. Daylighting

Louver systems are designed to manage the direction, intensity, and distribution of daylight, enhancing the overall illumination while minimizing glare and heat gain. By harnessing daylight, buildings can reduce their dependence on artificial lighting during daylight hours, leading to significant energy savings and lower utility costs [31]. Incorporating louver systems for daylighting aligns with sustainable building practices, as it reduces the building’s environmental footprint by decreasing energy consumption and reliance on non-renewable resources. Furthermore, by carefully positioning louvers, glare from direct sunlight can be minimized, creating a more visually comfortable and productive environment for occupants [32]. Access to natural light has also been linked to improved mood, productivity, and overall well-being of occupants. Louver systems contribute to creating a more pleasant and health-supportive indoor environment. An innovative optical louver design was proposed to achieve better daylighting that also reduced the annual electrical energy cost as compared to the conventional blinds [24]. DF, DA, and UDI are the most widely used metrics to assess the daylight in a building. DF is the ratio of illuminance available inside the building over the illuminance available outside under the sky, as mentioned in Equation (1) [33]. A DF less than 2 required artificial lighting, while values of DF between 2 and 5 did not require any artificial lighting. When the DF was greater than 5, it caused visual discomfort and temperature issues [33]. UDI is preferred over DF and DA for more clarity and climate-based modeling because it contains hourly data of sun orientation [34,35].

Based on illuminance, daylight is divided into three categories: <100 lux, 100–2000 lux, and >2000 lux. Artificial lighting is required for an illuminance range of <100 lux, while 100–2000 lux is acceptable and does not require any artificial lighting. However, the illuminance >2000 lux creates thermal discomfort, necessitating cooling measures. UDI is based on an illuminance range of 100–2000 lux for the offices and buildings [34]. A computer-assisted simulation was performed by adjusting louver types and input parameters to improve DF up to 5% [33]. The results showed that daylight simulation assisted in improving the overall performance and helped to finalize the design in the early stages of building construction. Daylight simulation improved illuminance by 79.48%, 80%, and 146.26% in Sydney, Birmingham, and Jakarta, respectively [36]. Further, simulations were carried out to improve the daylight and energy savings using louver systems [37]. The simulation was carried out using Daysim and Trnsys simulation software to find out optimal angles for the louver. A unique design, split louver with parametric control, achieved illuminance of 150–700 lux in the month of June in Amman, Jordan [38]. To generate the weather data of Amman, an epw format was used with the help of Ladybug (plugin/toolkit) with Grasshopper software, and Honeybee (plugin/toolkit) was used to further connect the Daysim and Radiance software for daylighting simulations. The split louver improved illuminance in the front and back of the room compared to the conventional single louver.

Four different types of shading devices, such as venetian blinds, horizontal louvers, light shelves, and egg crates, were simulated to reduce energy consumption in South Korea [39]. The overhang-shaped louver and egg crate performed better than other shading devices to reduce cooling energy consumption by about 51% to 54%. Further, egg crate reduced the electric lighting energy consumption by 15%. An innovative kinetic louver system was used to improve daylighting and reduce energy consumption by reducing the electrical lighting consumption by about 99% compared to the ASHRAE 90.1 standard’s lighting profile [40]. In [41], the author improved the indoor daylight environment using electrochromic-applied kinetic louvers where LEED v4.1 daylight option 2 criteria was achieved for visible light transmission of 40–45%. In [42], a louver-based shading system was compared by investigating length, depth, and count in three different cities in Canada.

Table 1. Summary of louver system studies: year, country, tools/methods, and key daylighting observations.

Year	Country	Simulation Tools	Experiment	Improvements (%)	Key Findings
1962 [44]	USA	Mathematical model	✕	-	Achieved a 50% light transmittance for north-facing and south-facing orientations Observed a low transmittance of 10% for east-facing buildings, which was unsatisfactory
2015 [45]	USA	Hybrid ray tracing	✓	-	Analyzed daylight glare probability and illuminance Used HDR cameras and calibrated photometers alongside simulations for data collection Glare equation could lead to inaccuracies in extreme brightness conditions, requiring adjustments
2016 [33]	Korea	Grasshopper, Rhinoceros, DIVA, NURBS	✕	5 (DF)	Improved performance incorporating genetic algorithm-based input parameters Galapagos optimization is less optimal for small datasets
2017 [46]	UK	Grasshopper, Radiance, DAYSIM, EnergyPlus,	✕	80 (Daylighting)	Compared the daylighting performance of parametric and conventional systems Limited energy savings in winter due to weak radiations
2017 [37]	Spain	SketchUp, DAYSIM, TRNSYS	✕	40 (UDI)	Reduced high solar gain for the south-oriented building Achieved UDI improvements at angles of −30°and 30°
2017 [47]	USA	Radiance, EnergyPlus	✕	43 (Daylighting)	Used synthetic and measured data to save lighting load Achieved optimum improvements at vertical angles of incidence from 18° to 35° Micro-structured prismatic louvers caused glare for seated positions looking directly at the window
2018 [48]	Chile, Canada, China, USA	Radiance, EnergyPlus SketchUp, Groundhog, WINDOW	✕	63 (Daylighting)	Improved energy saving by optimizing louver spacing High perforation rates caused glare in some locations Simulations were carried out in specific office locations; performance could vary in different climate conditions
2020 [49]	Israel	Radiance, DAYSIM, Rhinoceros, Grasshopper,	✕	51 (UDI)	Dynamic louver design increased illuminance compared to static louver Limited performance on specific window orientations and is influenced by seasonal variations
2020 [50]	Poland	De Luminae, SketchUp	✕	-	Improved daylighting in a fully glazed south-oriented façade located at 51° The impact of shading on thermal comfort, cooling, and heating loads was not discussed
2020 [51]	Taiwan	EnergyPlus	✕	-	Achieved better daylighting using roller shades Tested for south and west façade orientations, limiting their applicability in other orientations
2020 [52]	USA	EnergyPlus	✕	-	Improved daylighting using kinetic control strategy and multi-objective optimization technique In some cases, static louvers performed better compared to dynamic louvers, highlighting the need for context-specific optimization
2020 [53]	Indonesia	Radiance, DAYSIM, Rhinoceros, Grasshopper	✕	-	Thermal comfort should also be analyzed in addition to visual comfort for better adaptability Tested in tropical climate, findings may not be directly applicable to buildings in colder or temperate climates
2020 [54]	Egypt	Radiance, DAYSIM, Rhinoceros, Grasshopper	✕	90 (Daylighting)	Reflective slats improved floor illuminance to 300–500 lux Only tested for south-oriented office and hot arid climate, limiting its applicability
2021 [55]	UK	Radiance, Rhinoceros, Grasshopper, Ladybug, Honeybee	✓	-	Integrated simulations, Arduino, motors, and illuminance sensors, with prototypes tested at 1:20 and 1:1 scales, but under controlled conditions If sensors are miscalibrated or if there is error in the input data, the louver adjustments may not perform as expected
2021 [56]	Indonesia	EnergyPlus, Rhinoceros, Grasshopper, LadyBug, Honeybee	✕	16.78 (UDI)	L-shaped mini louvers improved UDI levels compared to overhangs These louvers can be easily retrofitted into both new and existing buildings, requiring minimal maintenance L-shaped aluminum louvers are lightweight, inexpensive, and widely available
2022 [36]	Australia, the UK, and Indonesia	EnergyPlus, Radiance	✕	79, 80, 146	Analyzed the effect of louver spacing and blade size using the MOO technique Daylighting improvements were a tradeoff between cooling energy reduction, requiring careful balancing.
2022 [38]	Jordan	Grasshopper, Radiance, DAYSIM, EnergyPlus, Ladybug, Honeybee	✕	-	Achieved illuminance of 150–750 lux using split louver with parametric control Maintained a glare-free ambiance
2022 [57]	Jordan	Grasshopper, Ladybug, and Honeybee	✕	50	Achieved a daylight uniformity of 0.6 Achieved UDI for 50% of the floor area in office hours Achieved UDI for 90% of the floor area at noon only
2022 [41]	Korea	Rhino 6′s, Grasshopper, Radiance	✕	75 (UDI)	Achieved UDI improvements using an electrochromic louver system Dependent on a mixed-humid climate and a visible light transmittance range of 20−70%, limiting the system’s practicality
2022 [58]	China	Radiance, EnergyPlus	✕	23 (UDI)	Achieved 23% and 68% improvements in UDI level and glare discomfort in comparison with double glazing Achieved a 29% improvement in UDI compared to the metal louvers
2023 [59]	China	Ladybug and Honeybee	✕	2.5 (UDI)	Tested on a west-facing school building in cold and severe cold regions Egg crate louvers were most effective in Beijing and Lanzhou, while horizontal louvers performed best in Urumqi
2023 [60]	Indonesia	Ant Colony Optimization (ACO) algorithm	✕	-	Achieved better indoor lighting by maintaining a distance of 0–18 cm between the window and louvers Conducted sensitivity tests on five design parameters: reflection coefficient, distance, depth, rotation angle, and number of louvers to improve daylighting
2023 [61]	Jordan	Grasshopper, Rhino, Radiance, Daysim, EnergyPlus	✕	90 (UDI)	Achieved a desirable UDI level at 90% of the workplace Achieved illuminance uniformity of 0.7 using PV-integrated split louvers
2023 [62]	USA	DIVA, Grasshopper	✕	14 (Daylight)	Designed a dynamic louver system for high-rise buildings Analyzed the system based on solar irradiance and daylighting as performance metrics
2024 [29]	South Korea	DIALUX evo, Rhinoceros	✕	80 (Daylight)	Improvements in daylighting and visual comfort. Reduced cooling energy consumption of 27% at 50% louvers opening
2024 [63]	China	EnergyPlus, Radiance, Grasshopper, Rhinoceros	✕	97 (UDI)	Achieved uniformity level of 0.6 Achieved a UDI level of 97% by optimizing slat angle
2024 [64]	USA	EnergyPlus, Rhino	✕	-	Achieved desirable illuminance level using PV-integrated louver system Illuminance level, DA, and visual comfort were used as performance metrics to improve illuminance
2024 [65]	Japan	-	✓	-	Control heat gain using slat angles Minor discrepancy in minute-by-minute predictions, especially when louvers open after a temperature drop
2024 [40]	Denmark	Rhinoceros, Honeybee, Grasshopper, and Ladybug	✕	99 (Daylighting)	Improve daylighting for South, East, and West orientations using kinetic louvers Reduction in electrical lighting energy usage from 14.22 to 0.2 kWh/m2 per year for south-facing
2024 [66]	USA	Rhinoceros, Honeybee, Grasshopper, and Ladybug	✕	75 (daylighting)	Enhance energy performance, particularly daylighting using prismatic-vertical louvers It caused overlit conditions near windows during some times of the year
2024 [67]	South Korea	Designbuilder, Revit and Twinmotion	✓	64	Achieved daylighting and electrical power generation efficiency of 64% using a PV-integrated automatic louver system Daylighting improvements caused a 6% increase in cooling loads

presents a comprehensive summary of studies conducted on louver systems from 1962 to 2024, highlighting advancements in daylighting performance. It includes information on the year and country of each study, the simulation tools or experimental methods used, and the key findings related to daylighting improvements. The data covers a wide range of simulation software, such as Grasshopper, Radiance, EnergyPlus, DAYSIM, and others, as well as experimental approaches involving physical prototypes and algorithms. Key observations include enhancements in daylighting metrics such as UDI, daylight factors, visual comfort, energy savings, and innovative louver designs, demonstrating their potential for improving indoor lighting and energy efficiency in diverse climatic and geographical contexts. Figure 2 illustrates reflective slats that adapt to the sun’s position throughout the day and year. The automated louver was simulated to determine the parameters for slat rotation and a full-system rotation [43].

$$DF={\displaystyle \frac{Inside illuminance}{Outside illuminance }}\times 100$$

(1)

2.1.2. Hybrid Lighting

Louver systems have been integrated with other daylight harvesting technologies, such as sensors and automated controls, to optimize the use of natural light throughout the day. These systems may adjust the angle of the louvers based on the position of the sun, time of day, and interior lighting needs. A sensor-based innovative design was proposed to improve the indoor light uniformity and energy savings (e.g., daylighting, heating, and cooling) up to 13.9% and 49.7%, respectively [28]. In New Cairo, prismatic panels and automated louvers were used to improve the daylight and visual comfort indoors [43]. The sunlight was reflected by prismatic louvers towards the ceiling and then redirected towards the floor to improve light distribution and comfort. The proposed system was tested using Grasshopper, Radiance software with the help of the Ladybug and Honeybee toolkit. An experiment was conducted using louvers integrated with LED dimming control in Jincheon-gun, Chungcheongbuk-do, Korea, to save lighting energy consumption of 85% [68]. In this experiment, concentrated louvers were used, which reflected the light towards the indoor setup with a reflectance of 90%. A sensor-based setup was used to dim the LED light intensity, which maintained 300 lux only instead of a constant lighting approach. In [69], a sensor-based horizontal louver system was designed to improve daylighting and energy savings for museum space in Poland. Figure 3 shows an experimental study on indoor illuminance and lighting energy-saving for a south-facing window with horizontal fixed louvers. Louvers with high reflective material having a reflectance of over 90% at an angle of 60° were tested [68].

2.2. Heating and Cooling

Energy consumption (e.g., heating, cooling, and lighting) and discomfort hours are quite important for the HVAC systems and optimized windows in high-rise buildings [70,71]. Excessive daylight can lead to higher indoor temperatures [72,73], which in turn increases the cooling load on air conditioning systems and results in elevated energy consumption and potentially higher utility bills. Furthermore, excessive daylight can create glare issues, making it uncomfortable for occupants and potentially hindering their productivity [74]. Louvers are strategically positioned to block or allow sunlight into a building [75]. During hot summer days, angled louvers can block direct sunlight from entering, reducing solar heat gain, and helping to keep the interior cooler [76]. In the winter, properly oriented louvers can allow sunlight to enter and contribute to passive solar heating, reducing the need for artificial heating.

A study was conducted in Sydney, Jakarta, and Birmingham, which showed the improvements in cooling energy consumption of 2.99%, 3.26%, and 28%, respectively, using the MOO technique [36]. The results showed that cooling energy consumption varies with the climate and energy requirements of a building. A louver-based system was proposed to find out the optimal angle, which saved the cooling demand of 68% [37]. The proposed system showed better improvements in cooling energy consumption at the north and south orientations at louvers angles of 60° and −60°, respectively. However, the system showed poor results for daylighting that increased the electrical load. Furthermore, the system achieved an equilibrium for the visual comfort, daylighting, and cooling demand at an angle of 30° and −30°. In Canada [42], a study was conducted to optimize and compare the performance of louver systems by changing the depth, count, and angles of the louver slats. Louvers were optimized by changing their angle to minimize the thermal energy consumption for different Korean regions [77]. In Australia, a case study was conducted, which saved building energy up to 38 MWh/annum with the help of open louvers [78]. A novel louver-based design was proposed to improve energy efficiency and thermal performance by analyzing different fin configurations with varying redirection louvers in domestic and transport air conditioning applications [79]. In [80], the TRNSYS and MATLAB-based simulation results showed solar heat gain of 17.7% in winter, which also saved 33.8% heating energy. A survey [81] is also conducted by the scholar of Greece to provide a review based on passive cooling strategies for the building envelopes. The authors concluded that mechanical ventilation systems with better heat recovery, cool-colored material, and green facades improved thermal performance and visual comfort. Furthermore, such cooling strategies could reduce urban heat by lowering peak temperatures. In Malaysia, a recent study focused on energy and thermal performance achieved superior results, with significant reductions in energy consumption and cooling load, alongside improved daylighting distribution and thermal comfort [82].

Table 2. Presenting Global studies on heating and cooling improvements using louvers: simulation tools, experimental methods, and key findings.

Year	Country	Simulation Tools	Experiment	Energy Savings	Key Findings
2001 [84]	Italy	TRNSYS	✕	-	Evaluated the effect of fixed horizontal louvers on south-facing windows in summer Analyzed the reduction in cooling load and overall annual energy consumption Need to incorporate dynamic control strategies and other louver designs to compare results for better generalizability
2010 [85]	UAE	IES-VR	✕	28.57, 30.31, and 34.02, respectively	Analyzed key variables included slat tilt angles, shading coefficients, and the location of light dimming sensors. Attained energy savings for the E, W, and S orientations showed varying percentages, respectively No analysis shown for cooler climates, where heating is required
2017 [46]	UK	RADIANC, DAYSIM	✕	80	The automatically-controlled louver system performed better in S and S-W orientation The system’s reliance on direct sunlight limits its effectiveness in regions with low winter solar radiation
2017 [37]	Spain	SketchUp, DAYSIM, and TRNSYS	✕	68	Recommended horizontal louvers for southwest facades and vertical louvers for east-facing facades Improved cooling but drastically reduced daylight exposure under certain conditions
2018 [48]	Chile, Canada, China, USA	Radiance, EnergyPlus SketchUp, Groundhog, WINDOW	✕	63	Improved energy savings at 120 mm louver spacing Energy savings were decreased by increasing the louver spacing Observed a trade-off between cooling efficiency and visual comfort
2020 [86]	Japan	CFD	✓	-	Louvers and windows are spaced at 1–2.8 m apart Experimental and simulation results were compared, revealing a temperature difference of less than 1° Assumptions of fully open windows and simulations in a humid subtropical climate (Kumagaya), limiting its adaptability
2020 [52]	USA	EnergyPlus	✕	-	Proposed multi-objective optimization technique for climate adaptive buildings Reduction in cooling load using radiation parameters No simulations were conducted for cold or mixed climates, which limits its generalizability
2021 [56]	Indonesia	EnergyPlus, Rhino, Grasshopper, LadyBug,	✕	18	Reduction in cooling load using L-shaped mini louvers for different orientations (E, W, N, S) Tested only for cooling needs in Jakarta’s tropical climate, limiting its applicability to heating demand and other climates
2023 [80]	China	TRNSYS, MATLAB	✕	33.8	Reduced heating energy consumptions by high solar heat gain The system’s performance is limited to winter conditions and heating energy only
2023 [59]	China	Ladybug	✕	2.5	Enhancement in thermal comfort using an external louver-based system for a west facing building setup Findings are based on non-air-conditioned buildings only; no analysis was conducted for HVAC setup.
2023 [87]	China	CFD	✕	-	Analyzed heat transfer pattern using vertical louver only, limiting its performance for other designs Optimized heat coefficients with the help of louver’s angle and width Used Wind Velocity (U10) standard, real time wind speed and direction could vary, affecting the result
2023 [88]	China	Numerical Analysis	✕	-	Optimized thermal performance and airflow by varying the louver’s inclination angle Achieved optimal performance at louvers angle of 90°
2023 [89]	Indonesia	THERB	✕	23	Improved annual energy savings and indoor temperature by optimizing louver’s area and insulation Combined solution performed better to reduce cooling demand
2023 [60]	Indonesia	Ant Colony Optimization (ACO) algorithm	✕	-	Proposed an Ant Colony Optimization algorithm to improve energy consumption in buildings Achieved energy savings in daylighting, heating, and cooling Limited to Jakarta, Indonesia only, results could vary in dynamic weather variations and unforeseen building behaviors
2023 [90]	China	CFD	✕	-	Fast prediction of glazing temperature Cavity heat transfer contributes 58−62% of solar heat
2023 [91]	China	Rhino, Grasshopper, Ladybug, and Honeybee plug-ins	✕	35	Fulfilled the energy demand of 46% by PV integration Reduced cooling load and thermal discomfort hours by 35% and 404, respectively
2024 [29]	South Korea	DIALUX evo and Rhino	✕	27	Achieved 27.02% total energy savings at 50% opening Higher louver openings improved the cooling, but modest overall savings
2024 [92]	Portugal	SEnergEd	✕	-	HVAC energy use varies by building type and climate. Recommended Tair optimization strategy for cooling Recommended PMV setpoints optimization for heating
2024 [93]	Japan	-	✓	9.3	Horizontal louvers achieved better energy savings compared to vertical louvers Adjustable PV-integrated louvers improved electricity generation
2024 [94]	China	CFD, COMSOL	✕	-	Compared the performance of louvers and circular hole covers to improve cooling Optimized louver angle and cover distance to reduce energy consumptions
2024 [64]	USA	Rhino	✕	-	Reduction in energy consumption in warm climates Maintained proper lighting levels using PV louvers
2024 [82]	Malaysia	Rhino, Grasshopper, Ladybug, Honeybee, and genetic algorithm	✕	26.2	Reduced cooling load using dynamic louvers integrated with a double-glazed façade Reduced thermal dissatisfaction by 28.72% Heating analysis is not conducted
2024 [67]	South Korea	Designbuilder, Revit, and Twinmotion	✓	64	Achieved accumulative electricity generation of 64% using PV-integrated louvers The system reduced heating energy, while daylighting louvers increased cooling loads by up to 6%

showcases a variety of studies that employed simulation tools such as TRNSYS, IES-VR, RADIANCE, DAYSIM, and SketchUp to assess how louver systems influence energy performance. The findings from these studies indicate energy savings ranging from 17.7% to 80%, influenced by factors such as the building’s orientation and design features. These outcomes underscore the significant role shading devices play in enhancing thermal efficiency and lowering energy usage. Figure 4 shows horizontal and vertical louvers for a double-skin façade office building. The horizontal and vertical blades were placed near the outer layer at right angles and 45 degrees, respectively, for better performance [83].

2.3. Ventilation

Louvers are adjusted to allow or restrict airflow into a building. During hot weather, opening the louvers allows fresh air to enter and promotes natural ventilation, helping to cool down the interior without relying solely on air-conditioning systems. In colder weather, louvers can be closed or adjusted to reduce heat loss, thus improving energy efficiency. A wind-tunnel test was conducted in a factor building to assess ventilation [95]. In [96], soffit louvers were used to stop the intrusion of wind-driven force in hip and gable roof buildings. The University of Southampton has conducted an experiment for cross-ventilation, which examined various louver openings, including the center, lower, and upper sections, and compared scenarios with and without louvers. Results indicated that the highest flow rate occurred at the upper part of the façade, while the maximum air exchange efficiency (AEE) of 45% was achieved with the louvers opened at the center [97]. The natural airflow was increased, and simulations were conducted to analyze the louver system using CFD techniques [83]. Horizontal louvers showed better results and were preferred over the vertical louvers.

In one study, [98], a windcatcher-louver system was designed to improve natural ventilation. The highest wind speed was achieved to optimize the angle of attack (8°) of the airfoil. The natural airflow increased up to 14% by optimizing the louver’s angle at 45° [99]. A case study has shown improvements in heating energy only. On the other hand, airflow and ventilation reduce infection using semi-shaded openings along with external louvers, resulting in an infection rate of 26.17% [100]. A recent study was conducted in Portugal to assess the HVAC energy needs using SEnergEd software for the residential and commercial buildings [92]. The energy demands of cooling and heating were observed with the different climate changes. Various studies have explored ventilation performance using a mix of experimental setups and simulation tools as shown in

Table 3. Summary of Global Investigations on Ventilation Improvements Using Software and Hardware Configurations.

Year	Country	Simulation Tools	Experiment	Improvements (%)	Key Findings
2005 [101]	Italy	TRNSYS, LOOPDA	✕	8	Utilized the stack effect for ventilation to prevent overheating, particularly in summer Reduced cooling energy demand by 8% through nighttime ventilation Tested in a Mediterranean climate (Cavaso del Tomba, Italy), limiting the findings of the double-skin façade system, which may vary in hotter or colder climates
2008 [95]	Republic of Korea	✕	✓	-	Improved ventilation by setting the outer louver at 90° and the inner louver angle at −70° Real time factors such as wind direction, velocity, and outdoor conditions vary dynamically and were not fully analyzed in the wind tunnel test
2017 [96]	USA	✕	✓	-	Used Soffit louvers for hip and gable roof buildings Closed vents affected the net mean and peak pressure coefficients
2019 [97]	England	CFD, RANS turbulence models; RNG, SST, RSM	✓	45	Achieved higher volume flow rate with the louver openings at the upper side Obtained AEE of 45% with the louver openings at the center Valid for isothermal conditions only, and the impact of heat or temperature-driven ventilation was not addressed
2020 [83]	Iran	CFD, Google Assistant, Amazon Alexa, or Apple Siri	✕	-	Natural air flow and ventilation increased in a five-story office building Horizontal louvers showed better results compared to vertical louvers
2020 [98]	Korea	CFD, Star-CCM+	✕	-	Achieved the highest wind speed at an 8° angle of attack using windcatcher-louvers Enhanced indoor air quality by reducing the fine particle concentration by 37.5% Limited wind directions (0° and 90°)
2020 [102]	Jordan	CFD	✕	96.6	Ventilation system met the standard (CO concentration < 50 ppm, ACH > 2.7) IAQ results showed a maximum deviation of 1.5 ppm, with an error of 3.4%
2021 [99]	Australia	CFD	✕	14	Airflow increased around 14% at a louver angle of 45° Focused on solar altitude angles, while other factors such as wind direction, building orientation, and internal thermal loads were not considered
2022 [100]	China	CFD	✕	-	Improvements in energy saving for heating only Louvers showed a decrease in airflow and ventilation Increased infection risk by 26.17% due to shading
2022 [103]	China	CFD	✓	-	Enhanced the indoor air quality by fully opening slats Windward louvers preferred over leeward ones
2022 [104]	Malaysia	CFD	✕	53.4	Optimization of louver angle and position for ventilation Achieved a high AEE of 53.4% at a louver angle of 15° Achieved a low AEE of 20% at a louver angle of 0°
2023 [88]	China	Numerical Analysis	✕	6.25	Achieved ventilation rate from −16.45% to 6.25%. Showed better improvements at a louver angle of 90°
2023 [90]	China	CFD	✓	-	Fast prediction of ventilation and heat The proposed theoretical model could replace time-consuming simulations
2023 [105]	Iran	Simulation	✕	-	Vertical louvers showed maximum AEE at low wind speeds (1 m/s), and louver angle of 15° Horizontal louvers showed maximum AEE at higher wind speeds (2–3 m/s), and louvers had an angle of 15°
2024 [106]	USA	Large Eddy	✓	-	Cut paper (kirigami) design was preferred for adaptive ventilation, offering an alternative to traditional louvers Idealized box models and controlled wind tunnels may not capture the full range of variable outdoor conditions, limiting their scope and adaptability
2024 [92]	Portugal	SEnergEd	✕	-	Showed improvements in ventilation and thermal energy PMV and Tair set points affected the ventilation efficiency Mediterranean climate zones may not be directly applicable to regions with extreme climates (either very hot or cold)

. Different simulation methods included software such as TRNSYS, CFD with advanced turbulence models (e.g., RNG, SST, RSM), and Star-CCM+, as well as virtual assistants such as Google Assistant. Experimental approaches involved wind-tunnel tests, rain impact studies, and practical investigations conducted at institutions such as the University of Southampton. Figure 5 shows the geometry of the louver and boundary conditions around the building to perform velocity and heat transfer simulation on the building façade and louver surfaces [71].

2.4. PV Integrated Louvers

For PV-based renewable energy systems, PV [107], floating PV [108], CPV [109,110], and CSP [111] are widely used to meet energy needs. PV integrated louver systems combine two important functions in building design: PV electricity generation and sun-shading through louver structures [112]. These innovative systems offer a dual-purpose solution that maximizes the benefits of solar energy while enhancing the building’s energy efficiency and occupant comfort [113]. PV integrated louver systems incorporate solar panels into the design of louver structures. These solar panels capture sunlight and convert it into electricity, which is used to power the building’s electrical systems, reducing reliance on conventional grid power and lowering utility costs.

The PV-integrated louver system helped with electricity production, passive cooling, and lowering carbon footprints [114,115]. To predict PV output, work plane illuminance, and daylight glare index, an ANN model was used to save energy up to 1.88 kWh. Further, a case study using a naturally ventilated double PV window was conducted in China, which generated 18,917 kWh of electricity [116]. A sun-tracked PV-integrated shading design was presented, which achieved 50% more electricity generation in comparison with the static PV-integrated building envelope [117]. However, it also provided 115% of the energy demand in temperate and arid climates for an office room. A PV-louvered window design [118] was proposed, which enhanced the daylight time up to 85%. Further, it also increased the electricity revenue due to the production of electrical energy using sunlight. A novel PV-integrated double-glazed façade system [119] was tested that saved 25% of energy. In [93], a PV-integrated horizontal louver system has shown an improvement of 9.3%, while vertical louvers were less effective by producing only 7.3% of electrical energy. Seventeen various sites in the USA were analyzed using PV-integrated building envelopes to predict the illuminance and heating and cooling load. The proposed design saved energy, which was a sustainable building strategy for a south-facing building envelope [64]. Recent research [120] added a value to existing literature, which proposed a design to maximize the energy generation on a building façade using PV panels. In [61], the transparent PV-integrated louver system was used to improve daylighting by testing PV glass transmittances of 30%, 50%, and 70%. To reduce daylight glare, PV glass transmittances of 30% and 50% were used. Furthermore, a semi-transparent PV window was used to optimize the energy consumption and thermal comfort hours [121], which showed improvements of 65.7% and 5%, respectively. In one study, [67], a servo motor-based control strategy was used to optimize the performance of a PV integrated louver system, which showed 65% power generation performance. The proposed study suggested 2-axis and 3-axis louver systems to enhance the louver’s performance. A case study conducted in Zhengzhou, China, demonstrated a 35% reduction in cooling load and energy generation, meeting 46% of the total energy requirements of the test room [91]. The integration of PV louvers in buildings has significantly demonstrated energy saving as well as energy generation by optimizing indoor illumination and ventilation. Figure 6 shows three different types of PV-based façade shading systems. Maximum array power per module was calculated to compare the performance of each shading system. A horizontal louver system having a vertical cell orientation produced higher power. For the vertical louver system, the horizontal cell gave higher power. For the diamond pattern louver system, the −45° cell produced higher power than other orientations [122].

3. Louver Designs

A louver system consists of adjustable slats, allowing for precise control over the amount of sunlight entering the building. This system enables occupants to optimize natural lighting while preventing excessive heat gain during hot periods, promoting a more energy-efficient and comfortable indoor environment. By integrating sunlight and a louver system, buildings can enhance their sustainability, reduce energy consumption, and contribute positively to the overall green building movement. Louver systems can add an aesthetic touch to building facades while serving a functional purpose. The patterns created by louver arrangements can be architecturally pleasing, enhancing the overall design. There are different classifications of louver systems based on shapes, angles, and objectives [28,33,123]. Figure 7 illustrates four different shading devices_ horizontal louvers, vertical louvers, egg crate shading, and baffle shading_ to study thermal comfort in the interior. The design variables for each louver system were parameterized through the Grasshopper software. The study concluded that fixed louvers significantly performed well for both thermal comfort and daylighting [59].

3.1. Vertical Louver

The vertical louver systems consist of vertical slats without any snow load. However, the view is not much clearer as compared to the horizontal louver systems. They have been classified as vertical fin and overhanging vertical fins.

Table 4. Vertical louver designs depicting performance metrics, orientations, and angles across various applications.

Year	Country	Slat Angle	Orientation	Key Findings
1962 [44]	USA	-	N	Vertical louvers performed better for buildings facing north Achieved transmittance >50%
1962 [44]	USA	-	E/W	Resulted in transmittance <10% if avoiding sunlight Not a recommended orientation (E/W) for window installation
2010 [124]	Jordan	0°, 45°	S	Vertical louvers performed better compared to horizontal louvers Regression analysis was used to correlate the shading device positions with lighting levels and achieved better results at 0° Findings may not apply universally to other climates except Mediterranean climate (Amman, Jordan)
2010 [125]	Portugal	10°−90°, with a difference of 10°.	E, W	Preferred vertical louvers for E-W facades Limited to single zone building model, which may not fully capture the complexities of multi-zone or larger buildings
2010 [85]	UAE	−80°, −60°, −40°, −20°, 0°, 20°, 40°, 60°, 80°	E, W	Preferred dynamic louver system over static louver system Vertical louvers at 20° achieved energy savings of 26% and 25.97% for E and W orientations, receptively
2017 [46]	UK	15°	S, S-W	Compared and preferred parametric control-based louvers over aluminum-based vertical louvers Spacing and depth of 15 cm for each vertical louver is maintained
2017 [37]	Spain	−60°, −30°, 0°, 30°, 60°	E	Louver length and spacing of 1 m and 0.5 m were chosen, respectively Preferred vertical louvers in the east façade Dynamic louvers were not considered, limiting the scope of the findings
2020 [49]	Israel	-	N-W, N-W, and S-W	Improvements in daylighting by 7.62% Showed better improvements in the N-W orientations Preferred dynamic louvers compared to static louvers
2020 [83]	Iran	0°	-	Increased airflow and heat transfer rate Preferred horizontal louvers compared to vertical louvers
2020 [50]	Poland	15°, 30°, 45°, 60°	S	Achieved improvements in visual comfort and UDI level De Luminae and SketchUp simulation tools were used
2023 [87]	China	-	-	Analyzed the heat transfer coefficients Deployed Newton’s cooling equation and CFD simulation
2023 [105]	Iran	15°, 30°, 45°	-	Vertical louvers showed maximum AEE at low wind speeds (1 m/s), and louver angle of 15° Horizontal louvers showed maximum AEE at higher wind speeds (2–3 m/s), and louvers had an angle of 15°
2024 [93]	Japan	-	-	Showed improvements of 7.3% in electricity production using PV-integrated vertical louvers PV-integrated horizontal louvers showed better results
2024 [66]	USA	-	-	Achieved daylighting improvements of 75% for east-facing using a prismatic-vertical louver system Despite its benefits, the system led to overlit areas near the windows

outlines how different countries have applied vertical louver systems to improve building performance. In the USA [44], louvers with transmittance higher than 50% were used effectively, while orientations facing east or west showed less than 10% transmittance, which is not ideal for window installation. In Jordan [124], horizontal and vertical louvers were tested at an angle of 0° and 45°, and vertical louvers were preferred over horizontal ones for south-facing buildings. In Portugal [125], a case study was conducted to explore the impact of slat angles (10–90°) on energy savings in various regions. The UAE favored dynamic louvers at a wide range of angles, as opposed to static ones. In the UK [46], parametric control was the choice for improving daylight in office spaces. In [37], louvers were adjusted to a length of 1 m and a spacing of 0.5 m. Louver angles of 60° and −60° achieved better reductions in cooling energy demand facing north- and south, respectively, but enhanced the use of electrical lighting energy due to poor daylight at these specific orientations. A study in Israel [49] achieved the highest UDI levels with fixed, movable, and automated designs. In Iran, horizontal and vertical louvers were used to enhance natural airflow and heat transfer rate [83]. Horizontal louvers achieved a high ventilation rate. In Poland, authors have focused on visual comfort and UDI levels in vertical shading systems. A case study was conducted in Japan that demonstrated a 7.3% and 9.3% increase in electricity production with a vertical and horizontal louver system [93]. Horizontal louvers were preferred over vertical louvers. Despite having shadows on the louvers, optimum spacing was maintained to achieve the improvements in electricity generation.

3.2. Horizontal Louver

The horizontal louver systems provide free air movement with horizontal slats. They provide a clear view, unlike vertical louver systems. However, the snow load is experienced in horizontal louver systems. Further, they have been classified as horizontal single blades, overhang horizontal louvers, and overhand multiple blades. In [37], 68% energy was saved with the help of a horizontal louver system. A study was conducted to assess the performance of daylight, which showed that the illuminance level was decreased at louvers angles of 15° and 30° [126]. Furthermore, the horizontal louvers design has provided better daylighting with a slat angle of 0°. Different geometrical designs of ceilings were optimized to enhance the daylight performance.

Table 5. Horizontal louver designs highlighting slat angles, orientations, and energy performance across countries.

Year	Country	Design	Slat Angle	Orientation	Key Findings
1962 [44]	USA	Flat	0°	S	Horizontal louvers are most effective for south-facing facades Tilt angle, aperture sizes, and the solar position were optimized to analyze the transmittance
2001 [84]	Italy	Flat/external	0°, 30°, 45°, 60°, and 90°	S	Reduction in cooling load for summers, while allowing some passive solar gain in winter Not fully applicable to tropical, desert, or extreme cold climates, where different shading strategies were required
2009 [126]	UK	Flat/external	0°	-	Louvers integrated with curved and chamfered ceilings significantly improved daylighting Other geometries such as arched ceilings or dynamic ceiling systems were not explored
2010 [124]	Jordan	Flat/external	0°, 45°	S	Vertical louvers reduced energy consumption by 40% compared to no shading Tested on south-facing facades, limiting their applicability to buildings with different orientations
2010 [125]	Portugal	Flat/external	10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90°	S	Preferred horizontal louvers for south facades Limited to single zone building model, which may not fully capture the complexities of multi-zone or larger buildings
2010 [85]	UAE	Flat/external	−80°, −60°, −40°, −20°, 0°, 20°, 40°, 60°, 80°	S	Dynamic louver design was preferred Energy saving of 31.28% at −20 for S orientation Highest energy saving of 34.02% at south orientation using dynamic louvers
2016 [33]	Korea	External	-	S	Preferred horizontal louvers over vertical louvers Higher weight for input parameters
2017 [37]	Spain	Flat/external	0°	S	Preferred horizontal louvers for south orientation Reduced cooling energy demand of 68%
2019 [127]	Chile, Canada, USA	Curved/External	30°, 45°, 60°	-	Improved energy savings and visual comfort Fixed louvers with a 60° title angle performed best for the W-facing building A limitation of this study is the exclusion of a hybrid control setup, as fixed louvers outperformed dynamic systems in certain cases
2020 [49]	Israel	External	-	N-W, W, and W, respectively	Horizontal louvers achieved 1–2% higher UDI levels compared to diagonal louvers under certain conditions Heating and cooling were not considered, and the results are based on a Mediterranean climate, limiting broader applicability
2020 [83]	Iran	Flat	0°	-	Increased airflow and heat transfer rate Horizontal louvers showed better results
2021 [69]	Poland	Flat	60°	S-W	Saved 1215 h/yr of artificial lighting Limited to horizontal louvers; other shading strategies are not tested Roof aspects and ceiling geometry were not considered
2022 [58]	China	-	7°	-	Combined system achieved better daylight distribution compared to metal louvers No assessment conducted for thermal analysis and energy efficiency
2023 [105]	Iran	Flat	15°, 30°, 45°	-	Horizontal louvers achieved better results at 15° In-depth daylighting and thermal analysis were not considered
2024 [63]	China	Flat	0°	E, S-E, S, S-W, and W-oriented	Horizontal louvers showed less energy savings as compared to trapezoid louvers Achieved a daylighting uniformity of 0.6
2024 [68]	Korea	Flat	0°	-	Louver’s upper slat optimized at 0° horizontal Not analyzed the effect of the summer season on energy savings
2024 [92]	Portugal	External, fixed	0°	-	Energy needs were observed for different climate conditions using fixed horizontal louvers Simulations are based on hypothetical scenarios, so real-world variables might differ
2024 [93]	Japan	-	-	-	PV-integrated horizontal louvers enhanced electricity production by 9.3% Preferred horizontal compared to vertical louvers The analysis is conducted in a specific climate (Japan), and the results may not be directly applicable to buildings in other regions

presents horizontal louver designs, highlighting key parameters such as slat angles, orientations, and energy performance outcomes across different countries.

3.3. Innovative Louvers

There are distinct architectural elements (e.g., egg crate, diagonal louvers, trapezoids, overhangs, and baffle louvers) commonly utilized in building design to control light, airflow, and privacy. The egg crate design [39] features a grid-like pattern resembling the structure of an egg carton, characterized by a series of square or rectangular openings. This configuration effectively diffuses and distributes light while maintaining a degree of privacy. Diagonal louvers [49], on the other hand, are slanted elements that can be adjusted to control the angle and intensity of sunlight entering a space. Their adjustable nature allows for dynamic modulation of natural light throughout the day, reducing glare and minimizing heat gain. Overhang louvers are horizontal projections that extend outward from a building’s facade. They serve as a shading device, effectively blocking direct sunlight from entering a space during peak daylight hours, which aids in maintaining a comfortable and energy-efficient interior environment. Each of these architectural features represents a thoughtful approach to balancing the interplay between natural elements and the built environment, enhancing both aesthetic appeal and functional performance in architectural design. A trapezoid louver system was tested under different orientations [63], which saved energy and showed better results in comparison with the horizontal, vertical, diagonal, and egg crate louver systems. A novel design [128] was presented, which consisted of a vertical greening shading device using climbing plants. It was compared with the louver system, and the proposed design achieved a 2.6° lower temperature. In [56], an L-shaped louver system was tested in different orientations (E, W, N, S) in Jakarta, which improved the daylighting and energy savings with a payback year < 1.

4. Louver System Control

4.1. Fixed Control

A fixed louver system consists of non-adjustable angled slats or blades that are permanently set in a fixed position. These louvers are designed to provide a consistent and predetermined level of shading and daylighting. Fixed louvers are often positioned at a specific angle to allow a certain amount of natural light to enter the building while minimizing direct sunlight and excessive heat. They are commonly used in building facades and windows to control daylighting and improve energy efficiency, as given in

Table 6. Performance of fixed control louvers for sustainable building energy performance.

Year	Country	Slat Angle	Orientations	Key Findings
2001 [84]	Italy	0°, 30°, 45°, 60°, and 90°	S	Improvements in thermal performance using fixed horizontal louvers with varying slat lengths and tilt angles Dynamic control strategies integrated with other louver designs (e.g., vertical, egg crate) were not tested
2009 [126]	UK	0°	-	Daylight performance was improved by modifying the ceiling geometry
2010 [85]	UAE	−20°, 20°	S, E/W	Dynamic louvers were preferred instead of static louvers
2020 [49]	Israel	-	S, S-E, E, N-E, N, NW, W, and SW, respectively.	UDI levels of 35.73, 33.83, 36.65, 37.78, 39.49, 41.27, 39.47, and 39.58 were achieved, respectively, using horizontal design Horizontal louvers performed best in the N, N-W, W, and S-W orientations
2020 [49]	Israel	-	S, S-E, E, N-E, N, N-W, W, and S-W, respectively.	UDI levels of 35.65, 35.04, 36.79, 37.21, 38.64, 39.94, 37.58, and 37.70 were achieved, respectively, using vertical design Vertical louvers performed lower than diagonal and horizontal louvers
2023 [59]	China	-	W	The proposed shading system improved thermal comfort by a factor of 1.5–2.5
2024 [63]	China	45°	-	A UDI level of 92 and a DA of 67 were achieved
2024 [92]	Portugal	0°	-	A novel louver system was designed to improve energy requirements

.

4.2. Moveable Control

Moveable louver systems, also known as adjustable or operable louvers, consist of slats or blades that can be adjusted or moved to control the amount of daylight, natural ventilation, and solar heat entering a building [99], as discussed in

Table 7. Performance of moveable louvers with different orientations.

Year	Country	Angle	Orientation	Key Findings
2020 [49]	Israel	-	S, S-E, E, N-E, N, N-W, W, and S-W, respectively	UDI levels of 37.33, 34.19, 36.67, 37.81, 40.23, 41.75, 41.93, and 41.30 were achieved, respectively using horizontal design.
2020 [49]	Israel	-	S, S-E, E, N-E, N, N-W, W, and S-W, respectively.	UDI levels of 37.20, 35.87, 36.82, 37.21, 38.64, 40.54, 38.84, and 39.76 were achieved, respectively, using vertical louver design.

. These louvers are often manually operated but can also be motorized for easier control and convenience. Occupants can adjust the angle of the louvers to optimize natural light while minimizing glare and heat gain.

4.3. Automated Control

A hybrid louver system combines elements of both fixed and moveable louvers to provide a versatile daylighting solution. Typically, this involves installing fixed louvers with movable sections or panels integrated within the system. The fixed louvers provide a consistent shading effect, while the moveable sections allow for adaptability and finer control over daylight levels.

Table 8. Building louvers with automatic control mechanisms to enhance energy efficiency and daylighting performance.

Year	Country	Control method	Building	Key Findings
2010 [85]	UAE	Sensor-based	Office	A dynamic louver system was proposed and compared with sensor-based dimming light techniques
2017 [47]	USA	Prismatic	Office	The proposed system achieved energy savings of 43% and was tested at different louvers angles
2020 [49]	Israel	Simple control	Office	UDI increased up to 51% in N-W orientation
2020 [43]	Egypt	Parametric	Virtual room	A case study in New Cairo to improve daylighting
2020 [51]	Taiwan	Sensor-based	Office	Radiance-based strategy is used to optimize the daylighting and glare control
2020 [52]	USA	Parametric	Office	Climate adaptive envelope achieved less cooling load and better daylighting in hot and humid climates
2020 [53]	Indonesia	Parametric	Office	The proposed study enhanced daylighting performance and was tested in a south orientation
2020 [54]	Egypt	Parametric	Office	This study was conducted in an office room in New Cairo that used an automatic louver system
2021 [55]	UK	Parametric	Office	Illuminance of 300–500 lux was achieved.
2021 [69]	Poland	Sensor-based	Museum	An energy savings of 118 kWh/yr was achieved
2022 [38]	Jordan	Parametric	Office	Split louvers were used to improve daylighting
2022 [57]	Jordan	Parametric slat angle	Office	The proposed system used a slat angle to parametrically control the louvers
2023 [61]	Jordan	Parametric	Office	Transparent PV panels were used to enhance energy generation and improve daylighting
2023 [121]	China	Rule-based strategy	Office	Semi-transparent PV windows were used to improve thermal comfort hours (up to 5%) and energy savings of 65% (W orientation)
2023 [91]	China	Parametric	Office	The proposed louver system effectively reduced the cooling load of a west-facing building
2023 [62]	USA	Parametric	Office	Louvers were tested at different angles to achieve the optimum results
2023 [130]	China	Parametric	Office	Photovoltaic louvers and prismatic design achieved 22.8% energy savings
2024 [68]	Korea	Sensor-based	Office	Daylighting was improved using sensor-based LED dimming control of the louver system
2024 [65]	Japan	Sensor-based	Office	The slat angle, opening, and closing of a louver system are managed by a solar collector, having very less error
2024 [40]	Denmark	Parametric	Office	The proposed louver-based system improved visual comfort and electrical lighting energy utilization
2024 [66]	USA	Sensor-based	Office	An Arduino microcontroller was used to test the performance of vertical louvers
2024 [67]	South Korea	Sensor-based	Office	An illuminometer, thermocouple, servo motor, controller, and energy sensors were used to control the louvers

provides a summary of automatic louver control methods applied across different buildings and countries. It includes various control techniques such as dynamic systems with sensor-based controls, simple controls, and parametric controls, implemented in office, residential, and other types of buildings. The remarks highlight the impact of these control methods on energy efficiency, daylighting, and overall building performance. Parametric control in louvers is a dynamic control strategy that adjusts the orientation, tilt angle, or position of the louvers based on various parameters, such as the solar position, time of day, season, occupants, and weather conditions. A parametric control-based louver system behaves differently depending on the presence or absence of occupants. When no occupants were present, the parametric louvers redirected sunlight to the PV module for electricity generation. In the presence of occupants, the louvers adjusted to secure the necessary illuminance for lighting [67]. Figure 8 shows a flowchart to optimize visual comfort and energy efficiency using multi-objective optimization for an external shading device. The optimal design reduced the discomfort glare by 49% to 53% and the annual load by 100 kWh [129]. Figure 9 illustrates a sensor-based dynamic louver system that integrates real time outdoor conditions to optimize indoor daylighting, heating, cooling, and overall energy management [85]. The dynamic system effectively reduced both lighting and cooling loads.

5. Materials

The choice of material for louvers significantly impacts their durability, performance, and maintenance needs. Each material used in louver systems—aluminum, plastic, glass, and wood—offers distinct advantages and considerations for improving building energy efficiency. Aluminum with insulating cores provides a robust solution with high durability and low maintenance. It is frequently used in both residential and commercial applications. The natural oxide layer on aluminum provides excellent protection against rust and degradation, and its low density makes handling and installation easier. Additionally, aluminum can be easily fabricated into various shapes and finishes through processes such as powder-coating or anodizing.

While plastic louvers offer cost-effective, lightweight options with customizable insulation. Glass louvers with low-E coatings or double glazing contribute to thermal performance and natural lighting, albeit at a higher cost and with greater maintenance needs. Wooden louvers provide natural insulation and aesthetic appeal but require regular upkeep to maintain their performance. The choice of material depends on various factors, including the building’s design requirements, environmental conditions, budget, and desired energy efficiency outcomes, as presented in

Table 9. Different louver materials and their impact on durability, performance, and energy efficiency.

Year	Country	Material	Reflectance	PV-Integrated	Key Findings
2017 [46]	UK	Mirror	75%	✕	Mirrored louvers enhanced daylight deep inside the office room Electrochromic window maintaining desired illuminance levels
2017 [119]	China	Glass	-	✓	PV blinds enhanced energy efficiency and maintained indoor visual comfort Lowered the solar heat gain and reduced indoor cooling power consumption
2020 [83]	Iran	Glass for windows and plastic for louvers	-	✕	Horizontal louvers provided higher temperatures. Vertical louvers maintained lower temperatures while providing weaker airflow
2020 [49]	Israel	Diffused metal	0.175	✕	Dynamically adjusted louver of diffuse metal increased UDI by 51% Horizontal louvers performed better than vertical and diagonal louvers
2022 [41]	Korea	Electrochromic (smart glass)	20−70%	✕	Maximized performance by dividing the electrochromic louvers into 10–15 parts Achieved LEED criteria at visible light transmittance of 40–45%
2023 [61]	Jordan	Glass	50−70%	✓	Significantly enhanced daylight distribution and improved uniformity to 70% PV glass having transmittance of 30–50% reduced glare
2024 [29]	South Korea	Aluminum	90%	✕	Aluminum louvers with high reflectance boosted indoor illumination Highest cooling energy savings at 30% louver opening
2024 [67]	South Korea	Aluminum	90%	✓	Integrated louver and PV modules achieved an efficiency of 64% Limited efficiency due to 1-axis louver

. By carefully selecting and applying the appropriate material, building owners and designers can effectively enhance energy performance and achieve sustainable building goals. Figure 10 shows the split louver for balance distribution of daylight in the interior using different shapes of upper section slats and controlling the orientation of the lower section slats [61].

6. Results and Discussion

The results emphasize the versatility and efficiency of various louver systems in optimizing energy performance across diverse climates and building types, as discussed in

Table 10. Overview of energy savings and performance improvements across different building types and climates.

Year	Type	Energy Savings/Improvements	Illuminance/Heat/Ventilation	Building	Climate
2001 [84]	Fixed, horizontal	70	Cooling	Office	Hot-summer Mediterranean
2005 [101]	External and internal	12	Ventilation	Factory	Mediterranean
2008 [95]	External, Internal	60	Ventilation	Factory	Temperate
2010 [124]	Vertical	39.8	Illuminance	Office	Subtropical arid
2010 [85]	External, dynamic, horizontal, vertical	34.02, 30.31, 28.57	Illuminance	Office	Arid desert
2016 [33]	Horizontal	5	Illuminance	Office	Dry-winter humid continental
2017 [37]	External, Horizontal, Vertical	68	Cooling	Office	Mediterranean
2017 [47]	Vertical	39–43	Daylighting	Office	Warm-summer Mediterranean
2018 [48]	External	63	Illuminance and cooling	Office	Continental semiarid, tropical, humid subtropical
2020 [49]	External, dynamic, horizontal, vertical, and diagonal	51	Illuminance	Office	Mediterranean
2020 [98]	External, horizontal, vertical	37.5	Ventilation	Office	Temperate
2020 [83]	Internal, external, horizontal, and vertical	-	Ventilation	Office	Hot and arid
2021 [99]	External, movable	14	Ventilation	Office	Semi-arid, temperate
2021 [56]	External	18	Illuminance and cooling	Office	Tropical
2021 [69]	Horizontal, automatic	30.2	Illuminance	Museum	Moderate
2022 [38]	Parametric control	100	Illuminance	Virtual office	Subtropical arid
2022 [104]	-	53.4	Ventilation	Office	Tropical
2023 [59]	External	2.6	Illuminance and thermal	School office	Severe cold and cold
2023 [89]	External	23	Cooling	Residential	Tropical
2023 [61]	PV-integrated and retro-shaped	90	Illuminance	Office	Arid, desert, Mediterranean
2023 [121]	PV-integrated	65.7	Illuminance, heating, and cooling	Office	Humid subtropical
2023 [91]	Parametric	46	Illuminance, heating, and cooling	Office	Humid subtropical
2024 [29]	Curved	27	Illuminance and cooling	Office	Mid-Latitude
2024 [63]	Trapezoid	44	Illuminance	Office	Subarctic and tropical
2024 [68]	External, horizontal	85	Illuminance	Office	Humid continental
2024 [92]	External, horizontal, and fixed.	-	HVAC	Residential & commercial	Temperate Mediterranean
2024 [93]	Vertical, horizontal	7.3, 9.3	Heating and cooling	Office	Subarctic-subtropical
2024 [64]	PV-integrated, external	-	Illuminance, heating, and cooling	Office	ASHRAE
2024 [40]	Parametric, Kinetic	99	Illuminance	Office	Temperate
2024 [67]	Automatic, Sensor-based	65	Illuminance, heating, and cooling	Office	Humid temperate

. Fixed horizontal louvers showed exceptional cooling performance, achieving up to 70% energy savings in hot-summer Mediterranean offices. Both internal and external systems improved ventilation by 12–60% in factory settings, depending on the climate. Vertical and dynamic designs demonstrated strong illuminance control, with improvements up to 39.8% in subtropical arid regions and 34.02% in arid deserts.

Advanced configurations, such as PV-integrated and parametric controlled louvers, achieved remarkable results, with illuminance improvements reaching 100% in subtropical arid climates and 90% in arid and Mediterranean regions. External and horizontal systems contributed significantly to both cooling and illuminance in offices, while trapezoid and curved designs enhanced energy efficiency in mid-latitude and subarctic regions. Dynamic and automatic louvers proved effective in museums and virtual office settings, optimizing both daylighting and thermal comfort. The study highlights how tailored louver designs, including vertical, horizontal, PV-integrated, and trapezoidal shapes, can address specific building energy needs while adapting to diverse climatic conditions.

Louver systems also have certain limitations that can influence their performance and practicality. Advanced systems, such as automated or dynamic louvers, often entail high installation and operational costs, along with the need for regular maintenance to prevent mechanical failures or wear and tear, particularly in external applications. Designing optimal configurations for specific climates and building types can be complex, requiring sophisticated modeling tools and expertise. Additionally, in extreme climates, louvers alone may not provide sufficient thermal regulation, necessitating supplementary active systems such as HVAC. Material selection is another critical factor, as durability varies—wood may deteriorate in humid conditions, while metal systems could exacerbate heat transfer if not adequately insulated. Fixed louvers also lack adaptability to changing weather conditions or sun angles, reducing their efficiency, while automated systems may rely on sensors prone to malfunction or requiring frequent calibration. Moreover, louvers can present aesthetic or structural challenges, potentially conflicting with architectural styles or local codes, and their energy-saving potential often involves trade-offs with natural daylighting, which can increase dependence on artificial lighting. These challenges highlight the need for innovative designs, advanced materials, and adaptable control mechanisms to maximize the benefits of louver systems in sustainable building practices.

7. Conclusions

This study underscores the vital role of louvers in promoting sustainable building design by enhancing energy efficiency and minimizing environmental impact. It examined various louver control methods, including fixed, movable, and automatic systems, alongside design configurations such as vertical, horizontal, and egg crate styles for varying climate conditions, from subtropical to arid regions. The analysis of their performance across different orientations highlighted their effectiveness in optimizing daylighting, ventilation, heating, and cooling, contributing to significant energy savings.

The studies on louver designs and orientations conducted across various countries from 1962 to 2024 highlighted the critical influence of design parameters, such as slat angles (ranging from −90° to 80°), orientations (e.g., south, east, west, and southeast-facing facades), and louver configurations on achieving energy efficiency, visual comfort, and airflow improvements. Various studies were found to optimize performance based on climatic conditions and building orientations where horizontal louvers, typically installed in equatorial or temperate regions, were most effective in reducing solar heat gain and glare for buildings with high solar altitudes, such as those with south-facing facades. Addition of automated design could significantly improve their performance for dynamic climates. Other louver designs were orientation-dependent to reduce glare and thermal discomfort.

Various control strategies for louvers were evaluated alongside these design configurations, highlighting their unique advantages and limitations. Fixed louvers, while providing basic shading, were constrained by their static nature and inability to adapt to changing environmental conditions, and they produced glare and heat when poorly integrated with buildings. In contrast, moveable louvers offered enhanced flexibility, improved daylighting, and moderate energy savings, proving effective across diverse orientations and climates, especially in office settings. However, automatic louvers, including parametric, PV-integrated, and dynamic systems, significantly outperformed traditional fixed control strategy and designs in energy savings, daylight optimization, and adaptability. Parametrically controlled louvers demonstrated exceptional flexibility by adjusting slat angles based on solar conditions, as seen in studies reporting enhanced daylighting and reduced cooling loads. PV-integrated louvers added an energy generation feature, which also maintained the thermal and visual comfort. Dynamic louvers, such as sensor-based and climate-adaptive systems, further improved energy efficiency by optimizing shading and ventilation in real time, effectively addressing diverse climatic and building demands. The optical design of louvers should be carefully designed for providing uniform illumination deep inside buildings. In addition, efficient coating materials having reflection, refraction, absorption, and scattering properties can increase efficiency by providing high illuminance, low glare, and low heat penetration inside buildings without blocking views.

The study explored the adaptability of louvers in diverse building types and climates, emphasizing the impact of material selection on durability, performance, and maintenance. By addressing design challenges and employing advanced modeling techniques, this review offers valuable guidance for optimizing louver configurations to achieve superior energy efficiency and sustainability. Incorporating dynamic and sensor-based louvers capable of adjusting in real time to changing solar angles and weather conditions will foster a more responsive indoor environment. Additionally, facade designs should consider hybrid louver systems—combining horizontal, vertical, and diagonal elements—to optimize solar control across various orientations. Materials with high thermal resistance and durability should be employed to generate renewable energy while maintaining shading and thermal comfort. By aligning louver innovations with regional climatic demands and sustainable building practices, future construction can achieve significant energy savings, enhanced comfort, and reduced environmental impact.

In summary, this study offers a comprehensive review of louver performance across different climates and various architectural building types. Future research should focus on evaluating simulated louver designs through practical implementations. Additionally, integrating louvers into the façade design offers challenges, such as design complexity, climate dependency, building orientation, sizing, and cost, which need to be investigated considering diverse approach, local conditions, and building requirements. To find the effectiveness of integrating PV with louvers, adaptive designs for various louver types need to be experimented with for sustainable development. Future research should explore advanced louver designs considering AI-based control methods for optimizing performance using weather, energy demand, and illumination data. The aforementioned research needs for optimizing louvers will have an impact on sustainable building design.