Hot climate Double facades

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“Specializations” of the general double façade (buffer, twin face or extract-air)reflect climate-focused considerations that have evolved and can be seen in recent hot climate projects. This has resulted in either a hybrid approach to the façade or in simplification of a more complex, traditional approach, elaborates, Professor Terri Meyer Boake, School of Architecture at University of Waterloo, Canada.

In extremely hot climates, the design strategy has focused on the strength of a double façade approach to achieve solar avoidance. Frequently, the shading system has become the outer layer of the hybrid double façade system, eliminating the more usual extra curtain wall layer. This new typology is emerging as a specific hot climate double façade type. Also, in hot climate applications operable louvers are not positioned in unsealedair corridors to avoid accumulation of dust and fine sand that results in cleaning problems. Interior blinds continue to be chosen to assist in shading & glare control and provide occupant control. twinface or extract-air)reflect climate-focused considerations thathaveevolved and can beseen in recent hot climate projects. This has resulted in either a hybrid approach to the façade or in simplification of a more complex,traditional approach, elaborates, Professor Terri Meyer Boake, School of Architectureat University of Waterloo, Canada.

As, natural ventilation is not commonly utilized in many high-rise commercial buildings even in extremely hot climates,to address the same, the twin face system can provide effective natural ventilation. The strategies that offset the path of the flow of air, mitigate the effect of wind gusts and transfer of urban noise into the interior spaces – a common problem arising from direct openings in the envelope. The offset of air flow also diminishes issues of pollutants in the air if the system is fitted with closable dampers for use during peak traffic hours or weather events.

The double façade provides protection to solar shading devices which would otherwise be exposed to weather elements like wind, rain, snow and ice allowing flexibility in the design and deployment of operable louvers and shading systems. This helps to reduce the cleaning requirements and wear and tear on mechanical components, thereby offering durability and longevity.

Double façade applications in UAE
The climate of the United Arab Emirates and Qataris unusual and extreme for a desert climate as it is also extremely humid. The high humidity combined with extreme levels of sand particulates due to the windy desert conditions make condensation a concern.

The highly chilled glazing surfaces that result from highlevels of air-conditioning come into contact with outsidetemperatures in the range of 45oC with humidity in therange of 80%. If the U-values of the glazing units is high,the dew point can be reached on the outer surface. This causes blowing sand to adhere to the buildings. As freshwater is not to be found and the desalination of sea water isthe primary source of water, the cleaning and maintenance of buildings is of great alarm and cost.

The projects here show a very clear adaptation of the double façade envelope. One approach is the exchanging of the outer glazing layer for a ventilated mashrabiya-like screen element. The cultural tradition and acceptance of the screen has reinforced its modernized use in the emergent double façade typology. The other approach maintains the glazed characteristics of the typology, concentrating on creating a buffer to slow heat transfer. In this 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.

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