A numerical analysis of double skin facades in summer

Dual skin facade is an architectural concept originally intended for office buildings and indeed considered and implemented extensively. The façade to the building actually is a skin، but consist of two layers (the internal and external) which could be out of different glass types، they are separated by in-between air-gap and it is capable of air ventilation. The external skin protects the building not only against the climate hazards، but also can reduce noise pollutions significantly. The residents could take advantage of adjustable windows regardless of the element types such as wind and gust، the adverse effect of direct sunlight (glare)، the environmental pollutions، and so on. Shading mechanisms allow the inner rooms of the building to benefit from an indirect sunlight while reducing the load on HVAC in cooling downthe building in summers. Dual skin facades function as a heat conserver in cold climates in a way that stores the radiated energy in the air-gap whose temperature is almost made equal to the one of the temperature inside the building. In addition to providing the needed light within، indeed the external glass of the dual skin systems is capable of absorbing the light and storing heat in the winter، also induces natural ventilations in the summer to reduce the same sun light related heat. This is how the dual skin system helps in reduction of the heating and air conditioning load also with the internal air quality. Tolerance of the temperature above 24 degree Celsius in the buildings without natural air condition such as closed HVAC is difficult. While in buildings with natural air conditions the temperatures of even above 27 degree Celsius is pleasant. This reduces the energy consumption in the building. Therefore in this paper while studying the methods of using this system in hot arid climates، for the purpose of taking advantage، analysis and optimization of natural ventilation of double skin facade as one of the most important factor in hot and dry climates are considered. The layers to dual skin façade include the External Skin، the Internal Skin، and the air-gap in between the two. The External Skin (Façade): Generally it is a singular toughened glass، and the external skin could bemade completely out of it. The Internal Skin (Façade): They are thermal insulating double pane glasses and could be made completely out of glass. Varieties of solar glasses could be applied. The in-between the Two Glasses Air-gap: The air-gap could be ventilated completely natural or mechanical. The air-gap width varies anything from 20cm to 2 meters thick، and it could be effective when applied as a support. The windows are users accessed to allow ventilation; also the shading could be consolidated and controlled by an automated system within the air-gap. Plans for the Direction of Air Current There are three suggested air ventilation plans in construction of a façade: To ventilate inward (Type A): The air tends to drift away from within the building to the air-gap، and the fresh air to the facility is replaced from outside. The air in the A type flows outward from the rooms، enters the air-gap and continues to move passing above the rollers to the awnings. In some designs، the air is guided out or through the duct is returned to central heating or A/C systems of the building. Ventilation Combo (Type B & C): The air is guided outward through the air-gap or vice versa. In cold climates، the B & C types can have a pre heating effect on the air before it enters the rooms. The ventilation system of A، B، & C are mechanical and they could be implemented in conjunction with the HVAC system of the building. The air is ventilated out of the building (Type D): The fresh air from outside is guided inward through the air-gap and then it is ventilated outside. The D type as a breather to the dual skin façade is implemented along with natural ventilation mechanism. The system may allow the fresh air inward through open windows and when closed may function as a thermal insulator providing a suitable thermal stability. With reference to the conducted research and with consideration to the contributing parameters، the numerical analysis of natural ventilation in dual skin façades is as follows: In order to achieve the most optimum performance of the dual skin façades in hot and arid climate considering the suggested specifications، for natural ventilation in the said type of climate، a dual skin façade sample is designed. The numerical analysis of the sample design generated by GAMBIT and FLUENT with which the numerical analysis of the dual skin façade is conducted. The intended case study is an imaginary 3 story high building in which there is a single room allocated to each floor. The allocated air-gap size of the dual skin façade is 50cm. There is a window to each floor allocated to both the inner and the outer skin with variable dimensions of 0. 6، 0. 4، and 1. 0 meters. The current case study is analyzed in hot and dry climate of Kerman city located on 38 ’17 ○30” N. Latitude and 3 ’5 ○57” E. Longitude. As a result، the numerical output of this software show that the two-shelled buildings help to taking advantage of natural ventilation and improve indoor air quality and it will be more effective in order to reduce the use of air conditioning systems and to achieve a comfortable temperature. Dual skin façades are utilized in office building a lot and looking back at the conducted research and considering numerous applications of the said façades is ever more advantages for using the elements such as weather، and specifically implementation of natural ventilation in balancing the in-building temperature، also a significant reduction in the use HVAC in the buildings; therefore، here is the model of choice recommended the best for hot and arid climate in residential buildings too