Hot Climate Double Facades: A Focus on Solar Avoidance

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An overview of the adaptation of double facade systems for iconic buildings in the Gulf Region through the adaptation of the traditional mashrabiya screen.

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  • Good afternoon. My name is Terri Meyer Boake and I am a professor of architecture at the University of Waterloo. My apologies for being unable to travel here to present in person. However I did not wish to submit a paper without making a point to share some additional insights, images and information that lie beyond the limits of the paper.
  • The construction of double façade envelope systems has continued to increase and persist in spite of the lack of conclusive hard data to prove the energy benefits. This may be due in part to an architectural infatuation with tectonics and appearance, a desire to believe in the technological/environmental benefits of the system and an appreciation of many practical benefits that may not be readily quantifiable but are nonetheless easily understood.
  • Early double façade research that I conducted with a group of masters students in the early 2000s into the developing typologies of double façade envelope systems tended to reveal a function based grouping into three clear types. the Buffer Façade (where the indoor and outdoor air do not mix and the façade acts as an environmental buffer); the extract-air façade (where the stack effect in the double façade is used to remove hot used air from the interior) and the twin face system (where the second skin is used to permit controlled infiltration of exterior air to the interior). We also identified the “hybrid” type that did not fall into any of these categories but that typically used the exterior skin as a very large, usually continuous, shading element. Where the first three types used two skins that were comprised of glass and separated by an air corridor of varying size the hybrid system tended to be constructed with an inner enclosure that consisted of a relatively typical curtain wall system and the exterior skin consisted of a shading screen.
  • Early double façades tended to be constructed in temperate and then colder climatesValue was sought for their ability to provide additional insulation and to slow heat transferThe cavity was seen as a great place to locate the shading system as the blinds could be protected from snow, ice and wind. The use of a very complete shading system in snowy climates has been difficult without this added protection that can prevent mechanical and material failures.The virtual exterior location of the shades placed them in a position where they could be of greatest benefit in preventing unwanted solar gain in the summer.The shades could be deployed or retracted due to the high range of seasonal variation in temperature in colder climates. Permanent shades that would block the sun over the entire envelope were not desired.
  • This presentation/paper focuses on recent developments in the adaptation and application of double façades in hot climates.Given that hot climates need not respond so such extreme swings of temperature and seasonal changes, hot climates have focused performance criteria towards their biggest concern,SOLAR AVOIDANCEMany hot climate façades that are being constructed in the Gulf Region are beginning to incorporate external shading devices into their designs. Pictured here is a building that sits at the base of the BurjKhalifa.
  • Although the tightly clustered towers of Dubai, with their small floor plates may seem extraordinarily dense to the Western eye, the density succeeds in providing shading of the streets as well as for large portions of the exposed façades to also be shaded.High sun angles also make it easier to incorporate shading devices as the required length of projection is minimized.
  • This climate chart extracted from Climate Consultant 5.4 for Abu Dhabi, UAE demonstrates the type of climate that is fairly typical of many cities in the Gulf Region. The temperature range is normally well above the comfort zone.There is a large amount of direct normal radiation to avert throughout the year. The temperatures rarely dip low enough to warrant needing the solar radiation for passive heating.The humidity levels are also high.
  • One of the biggest ongoing issues with double façade systems is the lack of hard evidence to support their use. A focus on solar avoidance makes it easier to quantify the benefits.Shading devices are more easily incorporated into current energy modeling software.Accuracy is good.If A/C can be downsized, there is benefit.Issues with embodied energy, maintenance and related costs will continue to be problematic.
  • Where Western society is unaccustomed to an obscured view, many of the cultures that inhabit the Gulf Region have long used screen devices to achieve shading and privacy. This screen device, known as a mashrabiya has been incorporated into many contemporary buildings in the region including Masdar City, designed by Foster + Partners with Arup.
  • In the instance of Masdar City the heavy nature of the screen is being used to satisfy a number of functions that include the privacy screen, a shaded balcony and shaded recesses for clear vision glass. Although atypical of temperate climate double façades, the system creates a second skin outside of the primary enclosure system.
  • A contemporized version of the mashrabiya screen device is used to create the character of the New Souk in Abu Dhabi, also designed by Foster + Partners.
  • Screens are also used throughout the interior of the Souk as spatial divisions, demonstrating a widespread cultural acceptance for the use of the screen as well as acceptance for its impact on vision and views.
  • There are two primary types of double façade systems in use in the Gulf Region at this point in time.The first type are that employ a shading screen (mashrabiya) as the exterior face coupled with a high performance curtain wall system as the interior layer of the façade, in which A second layer of glass is not used to provide the outer layer.The layers tend to be separated by a wide air corridor to provide access for cleaning.The exterior shading layer is either fixed or responsive.The shading layer must be very durable to withstand exposure to the elements as well as cleaning.
  • The second type are those that use a more traditional approach (buffer, twin-face or extract-air) where the exterior layer is glazed and whereThe air corridor is usually wide enough to allow cleaning access without interfering in the interior spaces.The air corridor is used to buffer the temperature extremes.The air corridor may or may not form part of the cooling system.The shading devices are not normally positioned in this cavity if it is not sealed.
  • The Al Bahar Towers in Abu DhabiAedas Architects w/ ArupPrivate client, Islamic bankMashrabiya type double façade on south, east and west portionsNorth façade left open due to minimized solar issues and to allow for a primary view to the city beyondResponsive system that opens and closes according to solar path
  • The mashrabiya at Al Bahar Towers is comprised of a series of semi-transparent PTFE umbrella-like components that open and close in response to the sun’s path. Each of the two towers includes over 1,000 individual shading devices that are controlled via the building management system to create an intelligent second façade. This view shows the screen in its fully closed mode.
  • Where the previous exterior image might have the screen appear very solid, the transparency of the PTFE screen can be easily seen in this interior image. The cultural traditions of this region make this level of obscured vision acceptable given the benefits in terms of the reduction of heat from the sun.
  • The façade system will be cleaned via suspended access between the layers which have been set approximately 2 meters apart. This will be labor intensive as the nature of the PTFE screen and its protective Teflon coating system will not allow for power washing. A gentler method is required that will include brushing and wiping of the screens with a damp cloth to remove the build-up of particulates.
  • As can be seen by this construction image, the issue of the build up of sand on the system will be a critical maintenance issue. Low cost labour in this region makes the maintenance of this system possible where it would be prohibitively expensive in other regions.
  • The view at the left is looking through one of the exterior atriums that are situated sporadically between the mashrabiya and the curtain wall of the office. The view at the right is towards the north in the Sheikh’s entertainment space on the top floor where clear glazing and screen are both in play in the space.
  • According to Aedas each unit is comprised of a series of stretched PTFE (polytetrafluoroethylene) panels and is driven by a linear actuator that will progressively open and close once per day in response to a pre-programmed sequence that has been calculated to prevent direct sunlight from striking the façade and to limit direct solar gain to a maximum of 400 watts per linear meter. The entire installation is protected by a variety of sensors that will open the units in the event of overcast conditions or high winds. The benefits of this system include: reduced glare, improved daylight penetration, less reliance on artificial lighting, and over 50% reduction in solar gain, which results in a projected reduction of CO2 emissions by 1,750 tonnes per year.
  • O14 is a hybrid system that uses a double façade system to simultaneously provide an exterior structural diagrid-like support system and shading. The Business Bay location has the tower situated adjacent to a body of water which increases the exposure of the tower to the sun and limits shading from adjacent buildings.
  • This drawing of the unrolled exoskeleton shows a different contemporized variation on the mashrabiya screen.
  • The project is quite intriguing in its use of the exterior reinforced concrete structure with the core to provide a very clear and open, column-free plan. The floor to ceiling glazing is located approximately 1 meter away from the exterior wall to allow for cleaning access.
  • The variation in the sizes of the openings in the screen is used to block sun as well as to preserve some of the views into Business Bay. The white finish on the concrete allows for a high degree of reflectance of light to the interior.
  • This construction detail shows that at this point the exterior frame is 900mm away from the glazed wall. Rolling blinds are discreetly housed on the interior of the glass, above visual line of the curved ceiling to maintain very clear sightlines when these are not in use.
  • The Doha Tower by Ateliers Jean Nouvel, located in Doha, Qatar also uses a hybrid double façade arrangement. In this instance the mashrabiya screen creates a very complete second skin and encloses the entire building. Except at the entrance, no large expanses of vision glass are maintained. Instead the density of the screen is varied according to the solar orientation of the building.
  • The exterior skin of the Doha Tower is fixed or non responsive. It is instead composed of four “butterfly” aluminum elements of different scales to evoke the geometric complexity of the Islamic mashrabiya while serving as protection from the sun. The pattern varies according to the orientation and respective needs for solar protection: 25% towards the north, 40% towards the south, 60% on the east and west. The variation in opacity of the aluminum screen addresses the variation in solar avoidance required on the façade orientations. Due to the round shape of the tower, some shading is required on the “north” façade as it will receive sunlight in the early morning and late afternoon hours.
  • While the screen may appear quite dense from the exterior, the interior view shows the amount of sunlight that still enters the space. Additional blinds are provided on the interior to cut out glare and penetration when needed.
  • These construction details illustrate the layering effect of the screen elements to achieve an increase in density.
  • The system relies on contemporary precision cutting methods in combination with the selection of solid aluminum plate to achieve a durable element that is easier to maintain than other finishes.
  • The fixed mashrabiya screen is situated more than a meter from the high performance curtain wall.This is to allow for cleaning access to the space.The metal grating at each floor provides additional shading for the glass.
  • This view inside the air corridor and looking out gives a good appreciation for the density and texture of the exterior skin. The diamond grating of the walkway allows for air circulation up the façade which is essential to prevent the entrapment of hot air at each level. Night lighting is also located in this space.
  • It might be very surprising to most, but the sustainable agenda was very high on the priority list in the design of Capital Gate in Abu Dhabi, according to Jeff Schofield, formerly of RMJM and one of the designers of the furthest backward leaning structure in the world. It was recognized that the reduction in solar gain provided by the double façade system would be of great benefit to the building. For this reason the designers used two distinct types of systems that worked with the specific conditions of the project that resulted from the offset of spaces from the vertical elevator core.
  • The upper hotel portion of the building uses a modified extract-air arrangement. Interior air from the guest rooms is recycled into the façade cavity. Here it creates an insulating buffer between the cool interior and the extremely hot exterior. The air is filtered, reconditioned and reused in the rooms rather than replaced with outside air. There are operable glazing units on the exterior of the double façade wall to allow fresh air intake at those times of year when it is feasible. No operable units are installed in the glazing layer of the guest rooms. It would be difficult to control user input by transient guests that would not understand or appreciate the operation of the system.
  • A diamond shaped prefabricated curtain wall system is attached to the structural steel diagrid of the tower and forms the outside layer. The interior layer uses a less expensive rectilinear glazing system. There are no shading devices used in the cavity. Traditional blinds are included in the guest rooms. The cavity width is sufficient to provide access for cleaning.
  • The lower office floors are protected by a large metal mesh canopy called “the splash” which starts at the entry level as a sun shade over the car drop-off area and climbs the façade, terminating at the projecting pool level provided at the 19th floor. The mesh is supported on an Architecturally Exposed Structural Steel Frame and is 90% open. The mesh allows for air circulation while blocking approximately 30% of the solar radiation from striking the curtain wall of the office spaces.
  • The application at Capital Gate is innovative in that the screen transforms from a shading system for the office floors to become a shading canopy for the passenger drop-off area. As can be seen, this interpretation of the mashrabiya screen makes no use of traditional patterning.
  • This close view of the underside of the canopy system provides a better view of the mesh with an indication of its density and transparency.
  • Façade maintenance strategies were well considered for Capital Gate. A good understanding of the tendency for the build-up of sand and grit on the building, which would be exacerbated by its backwards lean and highly exposed location were understood. Cleaning is managed through the use of abseiling, a method of suspending the maintenance crew from ropes to access the building for cleaning.
  • The double façade system used on the Cleveland Clinic in Abu Dhabi, designed by HDR Architecture, differs from others in the region in that it is not designed to focus on the provision of shading and uses a variation of a buffer and extract-air double façade system. The facility has been designed to LEEDTM Gold principles and the designers feel that this particular double façade application to be the first ever used in a hospital.
  • This view of the Cleveland Clinic, taken during its construction in 2012, demonstrates the extensive use of this double façade application on the project. The double façade cavity is open from the bottom to the top and creates a stack or “lung” effect, allowing the building to “breathe.” The process works by placing the mechanical floor at the bottom of the hospital tower, exhausting cool air previously used within the hospital from the bottom of the tower to the stack between the double curtain wall which warms and rises by chimney effect through to the roof. This exhaust creates a protective buffer between outside air and the interior of the building. The air inside the building is cooled in a tripartite approach using sea water, heat reclamation, and used cool air exhausted through the 1.5 meter wide air corridor space.
  • This image shows the installation of the layers of the double façade. The interior layer is a fairly standard sealed rectilinear curtain wall system. The tubular steel diagrid that supports the exterior layer of glazing is supported by arms that are connected back to the building structure. Grated walkways span between the arms to provide access to the cavity for cleaning and flow through ventilation to support the stack effect. The exterior diamond shaped glazing layer is connected to a cable system that is used to further subdivide the larger structural diamonds.
  • The shading system in this case is not positioned in the cavity but rather on the interior for easy occupant control. The double façade system is expected to reduce the cooling costs of the patient tower building by approximately 33% due to a reduction in the cooling loads.
  • The examples provided show a very clear adaptation of the double façade envelope system to address the avoidance of solar radiation in the hot climate of the Gulf Region. Two primary types of façade systems have been developed to respond to the climate: one that has exchanged the outer glazing layer for a ventilated mashrabiya-like screen element and one that maintains the glazed characteristics of the typology and concentrates on creating a buffer to slow heat loss. In the latter type the operable shading devices have been moved to the building interior to provide occupant control and remove them from potential degradation due to airborne dust and sand. Although no performance data is available to substantiate the projected savings to the cooling loads of the projects, the adapted mashrabiya system, as it is based on the known benefits of a vernacular type in the region, affords confidence in its performance as a credible shading system. The full benefits and performance of the modified buffer system will likely not be known.
  • Thank you very much for your attention. If the high tech Q&A system fails to function, please feel free to contact me by email for more discussion!
  • Hot Climate Double Facades: A Focus on Solar Avoidance

    1. 1. HOT CLIMATE DOUBLE FAÇADES: AVOIDING SOLAR GAIN TERRI MEYER BOAKE, PROFESSOR SCHOOL OF ARCHITECTURE, UNIVERSITY OF WATERLOO, CANADA
    2. 2. Introduction The construction of double façade envelope systems has continued to increase and persist in spite of the lack of conclusive hard data to prove the energy benefits. This may be due in part to • an architectural infatuation with tectonics and appearance, • a desire to believe in the technological/environmental benefits of the system and • an appreciation of many practical benefits that may not be readily quantifiable but are nonetheless easily understood.
    3. 3. Early research into double façade types Buffer Façade Extract-air Façade Twin Face Façade
    4. 4. Typical Placement of Shading - Early double façades tended to be constructed in temperate and then colder climates - Value was sought for their ability to provide additional insulation and slow heat transfer - The cavity was seen as a great place to locate the shading system as it could be protected from snow, ice and wind - The virtual exterior location of the shades placed them in a position where they could be of greatest benefit in preventing unwanted solar gain in the summer. CCBR, University of Toronto, Canada
    5. 5. Hot Climate Issues This presentation/paper focuses on recent developments in the adaptation and application of double façades in hot climates. Given that hot climates need not respond so such extreme swings of temperature and seasonal changes, hot climates have focused performance criteria towards their biggest concern, SOLAR AVOIDANCE
    6. 6. Bioclimatic design strategies Although the tightly clustered towers of Dubai, with their small floor plates may seem extraordinarily dense to the Western eye, the density succeeds in providing shading of the streets as well as for large portions of the exposed façades to also be shaded. High sun angles also make it easier to incorporate shading devices as the required length of projection is minimized. Marina Bay, Dubai, UAE
    7. 7. Taken using Climate Consultant 5.4 Typical Climatic Conditions in the Gulf Region
    8. 8. Economic justification A focus on solar avoidance makes it easier to quantify the benefits. Shading devices are more easily incorporated into current energy modeling software. Accuracy is good. If A/C can be downsized, there is benefit. Issues with embodied energy, maintenance and related costs will continue to be problematic. Al Bahar Towers, Abu Dhabi Aedas Architects w/Arup
    9. 9. Humidity + Dust One of the most difficult environmental issues in the Gulf Region that must be addressed is the combination of high humidity and dust. This construction image of Capital Gate in Abu Dhabi demonstrates the severity of façade cleaning issues. Capital Gate, Abu Dhabi, RMJM Architects There is no fresh water available so all water must be desalinated. This is very costly and impacts the frequency of cleaning operations.
    10. 10. Mashrabiya - A Culturally Acceptable Screen Masdar City, Foster + Partners, Abu Dhabi, UAE
    11. 11. Masdar City Masdar City, Foster + Partners, Abu Dhabi, UAE
    12. 12. A Modernized Screen The Souk, Foster + Partners, Abu Dhabi, UAE
    13. 13. The prevalence of screens The Souk, Foster + Partners, Abu Dhabi, UAE
    14. 14. Doha Tower, Qatar Ateliers Jean Nouvel © Ateliers Jean Nouvel, CSCEC The Hybrid-based type 1. Those that employ a shading screen (mashrabiya) as the exterior face coupled with a high performance curtain wall system as the interior layer of the façade, in which • A second layer of glass is not used to provide the outer layer. • The layers tend to be separated by a wide air corridor to provide access for cleaning. • The exterior shading layer is either fixed or responsive. • The shading layer must be very durable to withstand exposure to the elements as well as cleaning.
    15. 15. Traditional-based types Capital Gate, Abu Dhabi, RMJM Architects 2. Those that use a more traditional approach (buffer, twin-face or extractair) where the exterior layer is glazed and where • The air corridor is usually wide enough to allow cleaning access without interfering in the interior spaces. • The air corridor is used to buffer the temperature extremes. • The air corridor may or may not form part of the cooling system. • The shading devices are not normally positioned in this cavity if it is not sealed.
    16. 16. Al Bahar Towers The Al Bahar Towers in Abu Dhabi Aedas Architects w/ Arup • Private client, Islamic bank • Mashrabiya type double façade on south, east and west portions • North façade left open due to minimized solar issues and to allow for a primary view to the city beyond • Responsive system that opens and closes according to solar path
    17. 17. Façade fully closed
    18. 18. View through the PTFE screen
    19. 19. View up air corridor
    20. 20. Space required for physical access for cleaning
    21. 21. Views from the interior looking out
    22. 22. Façade during testing showing fully open
    23. 23. O-14, Dubai O-14, Dubai UAE RUR Architecture Located in the Business Bay area of Dubai, this iconic tower has significant exposure to the sun and is not located in a dense tower grouping. Its exterior shading element is highly unusual in that it is • Made from reinforced concrete • Acts as an external structural support for the building • Acts also as a shading device Images and drawings courtesy RUR Architecture
    24. 24. Variation on the mashrabiya
    25. 25. Structure as the exterior layer
    26. 26. Preservation of views
    27. 27. Construction detail
    28. 28. Doha Tower, Qatar Doha Tower, Doha, Qatar Ateliers Jean Nouvel © Ateliers Jean Nouvel, CSCEC The mashrabiya screen element forms a complete second façade for the building without any large view openings
    29. 29. © Ateliers Jean Nouvel, CSCEC Variation in density
    30. 30. © Ateliers Jean Nouvel, CSCEC A bright interior
    31. 31. © Ateliers Jean Nouvel Construction details of the screen
    32. 32. © Ateliers Jean Nouvel Details of the mashrabiya screen
    33. 33. Sectional view The fixed mashrabiya screen is situated more than a meter from the high performance curtain wall. This is to allow for cleaning access to the space. The metal grating at each floor provides additional shading for the glass. © Ateliers Jean Nouvel
    34. 34. Inside the air corridor
    35. 35. Capital Gate, Abu Dhabi Capital Gate, Abu Dhabi RMJM Architects © Jeff Schofield, ADNEC • Iconic freestanding structure • Sustainable agenda high on the priority list • Traditional double façade on the upper, hotel portion of the tower • Screen layer exterior skin on the lower, office portion of the structure
    36. 36. © Jeff Schofield, ADNEC Modified extract-air façade
    37. 37. © Jeff Schofield, ADNEC Two glazing systems A diamond shaped prefabricated curtain wall system is attached to the structural steel diagrid of the tower and forms the outside layer. The interior layer uses a less expensive rectilinear glazing system. No shading devices in the cavity.
    38. 38. © Jeff Schofield, ADNEC Exterior shading screen for office floors
    39. 39. © Jeff Schofield, ADNEC The “Splash” shading screen
    40. 40. Metal mesh and support system
    41. 41. © Jeff Schofield, ADNEC Façade maintenance
    42. 42. Cleveland Clinic Cleveland Clinic, Abu Dhabi, UAE HDR Architecture • Very large scale traditional glazed double façade system • Covers almost 100% of the hospital exterior • Assists in achieving LEEDTM Gold • Does NOT focus on solar avoidance • Designed to reduce costs of conditioning the air
    43. 43. Construction view 2012
    44. 44. Prefabricated elements The system is constructed from prefabricated elements. There is some economy achieved in time and cost through prefabrication and the uniform application of the system around the building.
    45. 45. A layered system
    46. 46. Double façades in the Gulf Region Iconic Architecture…. Sorry, no performance data.
    47. 47. Thank you! For more detailed information on these buildings, please look up “Diagrid Structures” written by me, published by Birkhäuser. http://www.amazon.com/Diagrid-Structures-SystemsConnections-Details/dp/3038215643 Terri Meyer Boake tboake@uwaterloo.ca www.tboake.com

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