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    Topic review

    External Horizontal Fixed Shading Devices

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    Definition

    Solar protection is a passive strategy that directly influences thermal and visual comfort as well as heating, cooling, and lighting energy consumption of buildings. Using shading devices can produce some conflicts, such as the contradiction between winter requirements, summer comfort, and luminous comfort. This is why the shading device choice is a necessary issue for building design, especially in a hot and dry climate. Optimal solar protection must provide a maximum protection during the overheating period while permitting solar radiation penetration during the winter.

    1. Studies on Shading Devices

    Many researchers have studied the effect of shading devices on thermal comfort, especially in a cold climate; Datta conducted a study for four different cities in Italy [1]and Tzempelikos et al. [2][3]performed an experimental study of the indoor thermal environment with different types of shading devices under Montreal climatic conditions in winter. Other studies were carried out in hot climate regions to evaluate fixed shading devices [4][5] and dynamic ones [6].
    Certain studies focused on shading devices’ effect on indoor factors; Dubois evaluated the daylight quality of shading devices [7]. Wong et al. studied the effect of external shading devices on daylighting penetration [8]. Freewan et al. [9] investigated the impact of ceiling geometries on the performance of louvers using two performance indicators: the illuminance level and its distribution uniformity. Datta[1] and Bessoudo et al. [3] evaluated the shading devices’ effect on the thermal performance of building.
    Several studies focused on energy consumption. Kim et al.[10] studied the external shading device effect in terms of energy savings for heating and cooling. Al Touma and Ouahrani [5] [11] conducted a study on shading and daylighting controls energy savings in offices with fully glazed façades in hot climates. Ossen et al. [12] studied the impact of solar shading geometry on building energy use in hot humid climates. Palmero-Marrero and Oliveira [13] studied the effect of louver shading devices on building energy requirements.
    Cillari et al. [14] analyzed the effects of the integration of different passive systems’ energy demand for cooling and heating and showed that fixed shadings led only to 1.28% energy saving in cooling and an increase in energy demand for heating by 0.46%. Hammad [10] demonstrated that the optimal static angle is -20° (i.e., 70° to the vertical) that resulted in a 31.36% reduction in energy consumption, which is about 34.02 for the dynamic facade.
    Other studies explored both the luminous and thermal effect [15] [4][16][17]. Alzoubi et al.[18] assessed vertical and horizontal shading devices’ performance in terms of daylighting and consumption; Vera et al. [19] focused on the optimization process of a shading device composed of curved and perforated fixed louvers, considering the visual comfort and energy consumption criteria. Kim [20] performed a series of simulations and measurements to evaluate the daylighting, energy and view performance of shading devices. Nielsen et al [21] studied the daylight and energy saving potential of automated dynamic solar shading in office buildings.
    Settino et al. [22] performed a multi-objective analysis of fixed external solar shading systems with the aim of minimizing the energy consumption for heating, cooling and artificial lighting, while ensuring the visual comfort of the occupants, showing that the use of an optimal shading configuration allows a reduction in the annual energy consumption of up to 42%.

    2. Design Parameters

    2.1. The Ratio Between Slats Vertical Distance and Their Width s/l

    Datta [1] studied three values of s/l (1, 2 and 0.92). Ouahrani and Al Touma [11] found that, for south orientation, a slat separation-to-width ratio of less than one (s/l< 1) saves between 27.6% and 35.0% of the space total energy demand, eliminates glare visual discomfort, and
    reduces CO2 emissions.

    2.2. The Spacing Between the Slats:

    Oliveira [13] conducted a study of shading devices with a spacing of 0.23 m and 0.26 m depending on latitude. Hammad [6] from the United Arab Emirates set the spacing at 0.3 m and Alzoubi [18] from Jordan studied the case of spacing of 0.5 m; in both studies, the ratio s/l was equal to one, i.e., the vertical shading angle was 45. In the United Kingdom, Freewan [9] fixed the s/l ratio to the same value, and spacing between the slats was fixed at 0.05 m.

    2.3. The Tilted Angle:

    In a previous study [15], the effect of three tilted angles (60°, 90°, and 120°) on luminous and thermal conditions within spaces in hot climates was investigated. Hammad [6] and Alzoubi [18] both show that the total annual energy consumption and lighting level changes in correlation with the tilted angle of slats. Al Touma and Ouahrani [5] studied the impact of two tilted angles (45° and 90°) for north and south orientations. It was found that a tilted angle of 45° reduces energy demand by 7.7% and 18.6% for south and north-oriented offices, respectively; however, a tilted angle of 90 leads to 9.1% and 20.6% energy savings.

    3. Conclusion

    Shading devices could significantly reduce energy used for cooling and lighting by reducing air temperature and controlling illuminance without glare. However, they have a negative impact on heating loads because they reduce useful solar gains during the winter.
    Most studies considered the Vertical Shading Angle (VSA) as a variable parameter, which changes according to the spacing between slats and their width, which means that shading either is not optimal during the overheating period or there is no sunshine in cold periods.

    The entry is from 10.3390/buildings11080348

    References

    1. Gouri Datta; Effect of fixed horizontal louver shading devices on thermal perfomance of building by TRNSYS simulation. Renewable Energy 2001, 23, 497-507, 10.1016/s0960-1481(00)00131-2.
    2. Athanasios Tzempelikos; Andreas K. Athienitis; The impact of shading design and control on building cooling and lighting demand. Solar Energy 2007, 81, 369-382, 10.1016/j.solener.2006.06.015.
    3. M. Bessoudo; Athanasios Tzempelikos; A.K. Athienitis; R. Zmeureanu; Indoor thermal environmental conditions near glazed facades with shading devices – Part I: Experiments and building thermal model. Building and Environment 2010, 45, 2506-2516, 10.1016/j.buildenv.2010.05.013.
    4. Ahmed A.Y. Freewan; Impact of external shading devices on thermal and daylighting performance of offices in hot climate regions. Solar Energy 2014, 102, 14-30, 10.1016/j.solener.2014.01.009.
    5. Albert Al Touma; Djamel Ouahrani; Shading and day-lighting controls energy savings in offices with fully-Glazed façades in hot climates. Energy and Buildings 2017, 151, 263-274, 10.1016/j.enbuild.2017.06.058.
    6. Fawwaz Hammad; Bassam Abu-Hijleh; The energy savings potential of using dynamic external louvers in an office building. Energy and Buildings 2010, 42, 1888-1895, 10.1016/j.enbuild.2010.05.024.
    7. Marie-Claude Dubois; Shading devices and daylight quality: an evaluation based on simple performance indicators. Lighting Research & Technology 2003, 35, 61-74, 10.1191/1477153503li062oa.
    8. Wong; Agustinus Djoko Istiadji; Effect of external shading devices on daylighting penetration in residential buildings. Lighting Research & Technology 2004, 36, 317-333, 10.1191/1365782804li126oa.
    9. Ahmed A. Freewan; Li Shao; Saffa Riffat; Interactions between louvers and ceiling geometry for maximum daylighting performance. Renewable Energy 2009, 34, 223-232, 10.1016/j.renene.2008.03.019.
    10. Gon Kim; Hong Soo Lim; Tae Sub Lim; Laura Schaefer; Jeong Tai Kim; Comparative advantage of an exterior shading device in thermal performance for residential buildings. Energy and Buildings 2012, 46, 105-111, 10.1016/j.enbuild.2011.10.040.
    11. Djamel Ouahrani; Albert Al Touma; Selection of slat separation-to-width ratio of brise-soleil shading considering energy savings, CO2 emissions and visual comfort – a case study in Qatar. Energy and Buildings 2017, 165, 440-450, 10.1016/j.enbuild.2017.12.053.
    12. Ossen, D.R.; Ahmad, M.H.; Madros, N.H. Impact of solar shading geometry on building energy use in hot humid climates withspecial reference to Malaysia. In Proceedings of the NSEB2005—SUS-TAINABLE SYMBIOSIS, National Seminar on Energy in Buildings, Shah Alam, Malaysia, 10–11 May 2005.
    13. Ana Palmero; Armando Oliveira; Effect of louver shading devices on building energy requirements. Applied Energy 2010, 87, 2040-2049, 10.1016/j.apenergy.2009.11.020.
    14. Giacomo Cillari; Fabio Fantozzi; Alessandro Franco; Passive Solar Solutions for Buildings: Criteria and Guidelines for a Synergistic Design. Applied Sciences 2021, 11, 376, 10.3390/app11010376.
    15. Magri, S.; Ait Haddou, H.; Boussoualim, A. Luminous and thermal effect of slat angle solar protection in hot climates. In Proceedings of the International Conference on Environment and Renewable Energy, Vienna, Austria, 20–21 May 2015.
    16. Tzempelikos, A.; Roy, M. A Simulation Design Study for the Facade Renovation. In Proceedings of the Canadian Solar Buildings Conference 2004, Montreal, QC, USA, 20–24 August 2004.
    17. Mathieu David; M. Donn; F. Garde; A. Lenoir; Assessment of the thermal and visual efficiency of solar shades. Building and Environment 2011, 46, 1489-1496, 10.1016/j.buildenv.2011.01.022.
    18. Hussain H. Alzoubi; Amneh H. Al-Zoubi; Assessment of building façade performance in terms of daylighting and the associated energy consumption in architectural spaces: Vertical and horizontal shading devices for southern exposure facades. Energy Conversion and Management 2010, 51, 1592-1599, 10.1016/j.enconman.2009.08.039.
    19. Sergio Vera; Daniel Uribe; Waldo Bustamante; German Molina; Optimization of a fixed exterior complex fenestration system considering visual comfort and energy performance criteria. Building and Environment 2017, 113, 163-174, 10.1016/j.buildenv.2016.07.027.
    20. Jeong Tai Kim; Gon Kim; Advanced External Shading Device to Maximize Visual and View Performance. Indoor and Built Environment 2010, 19, 65-72, 10.1177/1420326x09358001.
    21. Martin Vraa Nielsen; Svend Svendsen; Lotte Bjerregaard Jensen; Quantifying the potential of automated dynamic solar shading in office buildings through integrated simulations of energy and daylight. Solar Energy 2011, 85, 757-768, 10.1016/j.solener.2011.01.010.
    22. Jessica Settino; Cristina Carpino; Stefania Perrella; Natale Arcuri; Multi-Objective Analysis of a Fixed Solar Shading System in Different Climatic Areas. Energies 2020, 13, 3249, 10.3390/en13123249.
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