• Vol 11, No 2 (2020)
  • Architecture

The Effects of Building Glass Façade Geometry on Wind Infiltration and Heating and Cooling Energy Consumption

Amiraslan Darvish, Seyed Rahman Eghbali, Golsa Eghbali, Yousef Gorji Mahlabani

Corresponding email: Amiraslandarvish@gmail.com


Cite this article as:
Darvish, A., Eghbali, S.R., Eghbali, G., Mahlabani, Y.G., 2020. The Effects of Building Glass Façade Geometry on Wind Infiltration and Heating and Cooling Energy Consumption. International Journal of Technology. Volume 11(2), pp. 235-247
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Amiraslan Darvish Department of Architecture and Urban Development, Imam Khomeini International University, Qazvin, Iran
Seyed Rahman Eghbali Department of Architecture and Urban Development, Imam Khomeini International University, Qazvin, Iran
Golsa Eghbali Department of Architecture Engineering, University of Zanjan, Zanjan, Iran
Yousef Gorji Mahlabani Department of Architecture and Urban Development, Imam Khomeini International University, Qazvin, Iran
Email to Corresponding Author

Abstract
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The control of energy loss through building envelopes has always been a passive design solution for architecture and improvements in space quality. A significant factor is the control of infiltration through the geometry of the glass façades of buildings. The uncontrolled input air flow from the outside into an interior space is known as infiltration. The main infiltration factor is the pressure difference between a building’s interior and exterior. This difference might result from the interaction of the wind with the façade. Other possible causes are the stack effect and mechanical ventilation. There is a fundamental question about the effects of the outer glass shell geometry on wind infiltration and building energy consumption. The purpose of this study was to investigate the geometries of building façades with glass materials in different climates and to measure wind infiltration. Consequently, building energy simulations were performed to calculate the infiltration rates in building shells with different geometries. Four forms were simulated, and the effects of the wind infiltration-induced air exchange on heating and cooling energy consumption were evaluated in four climates in Iran. The results indicate that convex geometry reduces the wind pressure in the outer shell and the air exchange rate resulting from the infiltration; thus, heating and cooling energy consumption is reduced.

Energy consumption; External geometry; Infiltration; Simulation; Wind pressure

Introduction

The building sector is responsible for approximately 40% of the world’s total annual energy consumption (Omer, 2008). This situation has therefore raised the need for sustainable designs for reducing energy consumption in buildings (Pacheco et al., 2012; Russ et al., 2018; Yusuf et al., 2018). The sustainable development principles in the built environment have encouraged researchers to focus on more efficient building envelopes (Hong et al., 2019). A principal constituent of building envelopes, façades play a vital role in protecting indoor environments and controlling the interactions between outdoor and indoor spaces (Ghaffarianhoseini et al., 2016). Conventional façades can lead to poor natural ventilation, low daylight levels, thermal discomfort, and increased energy consumption (Yin et al., 2012; Luo et al., 2016). With the modern movement in architecture, vast glazed façades were introduced to improve the aesthetics of architecture.  Now, many high-rise buildings around the world have fully glazed façades or large areas of glazing. Infiltration  through  glazed  façades  plays  a  significant  role  in  energy  loads  and, consequently, energy demands and costs (Chen et al., 2012; Younes, et al., 2012).

Infiltration is unintended leakage, such as the flow of outdoor air through cracks in a building (ASHRAE, 1997). The main reason is the difference between the pressure inside the building and the pressure on its façade. This can be the result of wind pressure, the chimney effect, or mechanical ventilation (Jackman, 1974). Factors such as leakage, the quality of materials, the age of the building, the environmental conditions, and the geometry of the building have an effect on infiltration (Ji et al., 2005). Infiltration occurs through the building envelopes (Powell et al., 1989). It is a significant aspect in heat loss calculations, which play a fundamental role in determining the thermal load caused by the entry of outside air into a building. Air infiltration, along with ventilation, has a considerable effect on indoor environment quality. The moisture carried by infiltrating air leads to failures in the performance of building materials.

        Airflow leakage also affects the distribution of indoor air pollutants and detrimental microbes (Lstiburek et al., 2002; Rantala and Leivo, 2009). Infiltration causes undesirable heating and ventilation conditions that lead to indoor overheating and excessive energy consumption (Liddament, 1986). In this context, it is possible to control the impact of the prevailing winds through the use of aerodynamic shells to minimize infiltration (Jokisalo et al., 2009). The static pressure at the outer surface of a building is produced by the interaction of the wind with the building shell, and this is influenced by wind speed and direction, air density, surface orientation, and environmental conditions. Depending on the wind angle and the building form, the pressure produced on the building exterior can be positive or negative, and this will influence the infiltration flow (Sherman, 1987). Thus, the building envelope would appear to have a significant influence on the infiltration factors. In this regard, buildings with glass façades are very important because of the direct interaction with outdoor environmental factors, such as sun radiation and wind velocity.

        The purpose of this study was to investigate the wind-driven infiltration rate on the geometries of building façades and to determine the optimal forms for reducing energy consumption. In buildings with glass façades, the leakage rate is higher because of the unique type of envelope. Therefore, infiltration plays a significant role in reducing heating and cooling energy consumption. The study examined the effects of four forms (simple, indented, convex, and concave) on the infiltration rates on building façades in four climates in Iran. This facilitated energy simulation and modeling on the basis of the obtained data in order to determine the optimal forms for façades. Accordingly, the study has proposed optimal energy consumption solutions.


Conclusion

        Sustainable development principles in the built environment have encouraged researchers to focus on more efficient building envelopes. Façades, as a principal constituent of building envelopes, have a vital role in protecting indoor environments and controlling the interactions between outdoor and indoor spaces. The design and implementation of façade building systems can have positive effectives on energy waste reduction and air leakage. Infiltration control through façade geometry plays an important role in building energy consumption. The purpose of this study was to investigate the effects of façade geometries on wind infiltration rates and heating and cooling energy consumption in buildings in four climates in Iran. Four models with convex, concave, simple, and indented geometries were simulated in Design Builder and studied in Yazd, Tabriz, Rasht, and Bandar Abbas, which are in the hotarid, coldarid, moderate, and hot–humid zones. The results confirmed that the interaction of the wind with the concave spaces in the double-skin façades with concave and indented geometry increased the wind pressure and air infiltration rates. In the convex model, the wind pressure and air infiltration rate were lower. The wind pressure was transferred to the exterior surfaces, and the total wind pressure on the exterior façade was reduced. In addition, the increase in the air infiltration rate increased cooling and heating energy consumption.

        The results indicate that the energy consumption in the analyzed cities was lowest in the convex model and highest in the indented geometry model. The annual cooling energy savings in the convex models for the Yazd, Tabriz, Rasht, and Bandar Abbas were 5%, 4.3%, 3.7%, and 5.3% more than the savings in the indented models, respectively. In addition, the annual heating energy savings for the mentioned cities in the convex model were estimated as 7.6%, 7.1%, 7.3%, and 9.5 greater than the indented model. In general, the unwanted infiltration related to the façade geometry had a much greater effect on heating energy consumption than on cooling energy consumption. In addition, the façade geometry had a significant effect on heating and cooling energy consumption in the hot climates.

        Four glass façade geometries were simulated in this study. Based on the results in the four climate regions, the designer must evaluate the available facilities and estimate the construction costs for the most appropriate geometry. Redesigning the glass façade is less costly, and it does not affect the interior spaces. Also, this method can be applied to existing buildings which reduces the need for mechanical heating or cooling systems and associated costs. Last, considering the quality of materials and their associated infiltration rates, designers can draft intelligent façades to increase the energy efficiency of new and existing buildings by adapting the geometries to account for wind pressure and direction.

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