EFFECTS OF FACADES IN GREEN BUILDING DESIGN
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The document discusses sustainable building facades and their design. It provides three key points: 1) Building facades play an important role in separating the interior and exterior environment and creating the building's image. Sustainable facades aim to reduce energy usage while maintaining comfort. 2) There are two main types of facades - opaque facades made of solid materials and glazed facades like curtain walls made primarily of glass. Material properties, insulation levels, and glazing choices impact a facade's thermal and visual performance. 3) Proper facade design considers the local climate and orientation to passively reduce energy usage. Elements like shading, natural ventilation, and daylighting should be optimized based on orientation.
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EFFECTS OF FACADES IN GREEN BUILDING DESIGN
- 1. A STUDY ON EFFECTS OF FACADES IN DESIGNING A GREEN BUILDING
- 2. The façade forms the external weatherproof envelope of a building. In modern buildings, the façade is often attached to the building frame and provides no contribution to structural stability. This type of façade can be referred to as a non-loadbearing vertical building enclosure. Building Facades
- 3. Building facades perform two functions: • They are the barriers that separate a building’s interior from the external environment • More than any other component; they create the image of the building.
- 4. Sustainable facades are defined as exterior enclosure that use least possible amount of energy to maintain a comfortable environment, which promotes productivity to certain material which has less negative impact on environment. The role of sustainable facades is to reduce buildings’ energy consumption. Lighting 14% Space heating 28% Space cooling 10% ventilation 6% Refrigiration 5% Water heating 7% Electronics 3% Computers 2% Equipment 14% Other 11% Energy use breakdown for commercial buildings
- 5. Essentially there are two types of facades: Opaque facades, which are primarily constructed of layers of solid materials, such as masonry, stone, precast concrete panels, metal cladding, insulation, and cold formed steel framing. Opaque facades may also include punched openings or windows. Glazed facades, such as curtain walls or storefront facades which primarily consist of transparent or translucent glazing materials and metal framing components.
- 6. Environmental conditions Thermal comfort Visual comfort Acoustic comfort Opaque facades Material properties of cladding Amount of insulation Effective heat resistance properties ( R – value) Wall to wall ratio Material selection and properties Glazing Orientation Number of glass layers Layer thickness Heat transfer coefficient (U- value) Visual transmittance Solar heat gain coefficient(SHGC) Orientation Window properties, size, location and shape Glass thickness and color Visual transmittance reflectance Number of layers Layer thickness Layer density Framed and supporting structure for glazed facades Thermal properties of the frames Material types Environmental conditions and properties of façade elements that effect thermal, Visual, and acoustic comfort.
- 7. Solid wall Warm façade Cold façade Solid wall constructed from monolithic or composite elements, with or without a separate layer to provide climatic protection Warm façades have a thermal insulation layer applied directly to the surface of the building. If the insulating layer is applied on the outside, it also has to be water- resistant to ensure that the insulating properties are not lost due to weathering. Cold façades are characterized by the presence of a cavity, ventilated internally, between the outer layer that offers protection against the weather and the thermal insulation layer. Opaque facades
- 9. Basic design ideas for façade as per climate Orienting and developing geometry and massing of the building to respond to solar position. Providing solar shading to control cooling loads and improve thermal comfort. Using natural ventilation to reduce cooling loads and enhance air quality. Minimizing energy used for artificial lighting and mechanical cooling and heating by optimizing exterior wall insulation and the use of day lighting.
- 10. North-oriented East-oriented West-oriented South-oriented The basic rules governing the orientation of rooms. Orientation:
- 11. Fenestration: Fenestration components like windows, curtain walls, clerestories, skylights are important elements of façade design. They allow natural light to enter into the building. They also transfer between outside and inside of the building. They effect building’s overall energy consumption. Fenestrations materials and their properties decide the amount of energy consumption and also the heat loss or gain of the building. The quality criteria that enable the choice of window components to be determined and identifies the factors that reduce solar gains.
- 12. Material R-value (h-ft2 – F/Btu) Brick 0.14 – 0.40 per inch CMU, 8 in. (200mm) 1.11 – 2.0 CMU, 12 in. (300mm) 1.23 – 3.7 Concrete (sand and gravel aggregate) 0.05 – 0.14 per inch Concrete (limestone aggregate) 0.09 – 0.18 per inch Concrete with lightweight aggregate 0.11 – 0.78 per inch Stone ( quartzite and sandstone ) 0.01 – 0.08 per inch Stone (limestone, marble, granite) 0.03 – 0.13 per inch Mineral batt insulation, 6 in. (150mm) 22 Expanded polystyrene insulation 5 per inch Spray-applied foam 6.25 per inch Gypsum board, 0.500 in. (12.7 mm) 0.45 Gypsum board, 0.625 in. (15.9mm) 0.56 Thermal resistance (R-value) - It is an assembly’s or a material’s resistance to heat transfers, and is expressed in h-ft2 or m2-K/W. individual materials have specific R-value. Used typically to define the thermal performance of opaque areas of facades built up from multiple layers of materials.
- 13. Material Embodied energy Aluminum Cast virgin Cast recycled (33%) Extruded virgin Extruded recycled (33%) Rolled virgin Rolled recycled (33%) 497 55 471 75 477 62 Brick 6.6 Cement Portland Fly ash (6-20%) Fly ash (21-35%) Mortar 2.09 1.96 – 1.67 1.65-1.36 0.49 Concrete General Fly ash (15%) Fly ash (30%) Precast 2.2 2.13 1.96 3.3 Glass Primary Toughened 33 52 Paint 154 Steel Virgin Recycled Stainless steel 78 21 125 Stone Granite Limestone Marble Sandstone slate 24 3.3 4.4 2.2 0.2 to 2.2 Wood General Glue laminated Plywood 22 26 33 PV panels Monocrystalline Polycrystalline Thin film 10,450 8,954 2,871 Embodied energy is the total energy required for the extraction, processing, manufacture and delivery of building materials to the building site
- 14. Systems and components Embodied energy CMU Brick cladding, continuous insulation and polyethylene membrane 247 Steel cladding, continuous insulation and polyethylene membrane 370 Precast concrete cladding, continuous insulation and polyethylene membrane 291 Cast-in-place concrete Brick cladding, continuous insulation and paint 113 Steel cladding, continuous insulation and paint 236 Stucco cladding, continuous insulation and paint 99 Steel framed (16 in.) Brick cladding, continuous insulation, cold-formed steel framing, cavity insulation and polyethylene membrane, gypsum board and paint 96 Steel cladding, continuous insulation, cold-formed steel framing, cavity insulation and polyethylene membrane, gypsum board and paint 219 Wood cladding, continuous insulation, cold-formed steel framing, cavity insulation and polyethylene membrane, gypsum board and paint 61 Precast concrete cladding, continuous insulation, cold- formed steel framing, cavity insulation and polyethylene membrane, gypsum board and paint 141 Steel framed (24 in.) Brick cladding, continuous insulation, cold-formed steel framing, cavity insulation and polyethylene membrane, gypsum board and paint 91 Steel cladding, continuous insulation, cold-formed steel framing, cavity insulation and polyethylene membrane, gypsum board and paint 213 Wood cladding, continuous insulation, cold-formed steel framing, cavity insulation and polyethylene membrane, gypsum board and paint 55 Precast concrete cladding, continuous insulation, cold- formed steel framing, cavity insulation and polyethylene membrane, gypsum board and paint 135 Curtain wall Vision glazing and frames 148 Opaque glazing 135 Metal spandrel panel 138 Comparing the Embodied energy
- 15. ASHRAE’s requirements are categorized Energy codes ASHRAE Energy Standard for buildings provides recommendation for building facades based on building location and climate zone. ASHRAE’s requirements are categorized based on the basic building function and occupancy, ASHRAE identifies four types of exterior walls: Mass walls, generally constructed of masonry or concrete materials. Metal building walls, consisting of metal members spanning between steel structural members (not including spandrel glass or metal panels in curtain walls) Steel framed walls, with cavities whose exterior surfaces are separated by steel framing members. Wood framed and other walls.
- 16. ASHRAE requirements are prescribed in three ways for different climate zones: Minimum allowable thermal resistance (R-value) for different exterior walls. Maximum allowable heat transfer coefficient (U-value) for the façade assembly (including the thermal bridging effects of framing members) Maximum allowable solar heat gain coefficient (SHGC) for the glazed portions of a façade assembly.
- 17. Single Glazing: Absorbent or tinted glazing: Reflective glazing: Types of Single Glazing Heat transfer coefficient (U-value) - It is the inverse of R-value. It measures the heat transmission through a material or a façade assembly. U-values are expressed in Btu/hr-ft2-oF or W/m2-oK, and are usually used to define thermal performance of glazed parts of facades assemblies.
- 18. Electrochromic glazing: Gasochromic glazing: Double Glazing:
- 19. Double-skin façade The double skin facade is an envelope construction, which consists of two transparent surfaces separated by a cavity, which is used as an air channel. This definition includes three main elements: (1) The envelope construction, (2) The transparency of the bounding surfaces and (3) The cavity airflow 0 10 20 30 40 50 60 70 Single skin façade Single skin façade with vertical fins Single skin façade withelectrochromic glazing Double skin glazing Infiltration People Equipment Lighting Solar heat gain
- 20. Energy-generating façades The concept of sustainable social and economic development is generating a new environmental technology culture that is centered on the current abuse and future extinction of fossil fuel energy. It is possible to take advantage of the solar energy reaching the surface of buildings in two different ways: Passively Actively
- 21. Green Facades Green facades are created through the growth of climbing plants up and across the face of a building, from either plants rooted in the ground, or those in containers installed at different levels up the face of a building. Parameter measured Outcome Effect of the green facade Difference in temperature in front of and behind the facade 1.4°C cooler in summer 3.8°C warmer in winter Absorption of light and heat energy by foliage keeps the cavity temperature lower Facade support system creates a microclimate/unstirred air layer next to the wall even when stems are bare Difference in surface temperature between bare wall and vegetated wall (summer) Average bare wall temperature is 5.5°C higher (Maximum temperature is 15.2°C higher) Full leaf cover provides effective shading and prevents heat gain by the building Difference in relative humidity in front of and behind the facade 7% higher in summer 8% lower in winter Evapotranspiration from leaves causes a local increase in humidity (and cooling) in summer which is not apparent when stems are bare Impact of a green facade on Building thermal performance
- 22. Sustainable Features of facades: • Minimize the area of its external skin. • For those offices with an external facade, very high levels of thermal insulation • Natural ventilation and daylight penetration are maximized. • Optimized Window sizes • Provide adjustable blinds. • large geothermal heat exchanger • The high thermal mass of the walls • photovoltaic cells have been integrated into the glazing. • Panel facade made entirely of untreated local timber, which is prototypical in Germany. The double-glazed windows in the outer facade have been provided with an additional pane of glass. These panels are located behind the opaque glass cladding. Fresh air reaches them through louvered opening in the deep window reveals. The total window area of the outer facade, that is, the transparently glazed part, comprises 35 percent. Sixty percent of the inner facade as a whole is glazed with transparent glass. Federal Environmental Agency’s
- 23. Sustainable Features of facades: • Windows use high U- value glass • Horizontal sunscreens. • The building sits on an east–west. • The parking lot surface and walkways surrounding the building use a light-colored concrete that reduces the heat island effect. • Construction waste recycling. • Recycled content materials. The Carl T. Curtis Midwest Regional Headquarters The high U- value glass used for the windows reduces the amount of incoming heat and harmful ultraviolet rays. The heavy massing and minimal windows in the west elevation block the intense afternoon sunlight, whereas on the east elevation, a combination of windows and walls prevent glare and solar heat gain from the early sun. Sun shades help block the summer sun while bouncing light deep into the open office areas. All of the artificial lighting can be controlled to increase com- fort for the building’s occupants while simultaneously saving energy.
- 24. Approach for designing of the sustainable building façade in the following steps: Climate considerations Building orientation Façade materials properties Wall assemblies N
- 25. Typical exterior environment conditions Climate consideration: In this climate air conditioning will always be required, but can be greatly reduced if building design minimizes overheating. Minimize or eliminate west facing glazing to reduce summer and fall afternoon heat gain. Orient most of the glass to the north, shaded by vertical fins, in very hot climates, if there are essentially no passive solar needs. Locate door and window openings on opposite sides of building to facilitate cross ventilation, with larger areas facing up-wind if possible.
- 26. Building orientation •Building should be facing south west for visual access to the sea side. •But the problem of west facing façade in these type of climatic conditions is that, it will consume large amount of heat energy. Therefore maximum percentage of west side surface area should be opaque. •North east facing façade can be designed with maximum glazing percentage. Glazing type Centre of glass Edge of glass Aluminum frame without thermal brake Aluminum frame with thermal brake Double glazing 12 mm air space 2.73 W/m2-oK 3.36 W/m2-oK 4.14 W/m2-oK 3.26 W/m2-oK Double low-e glazing with 12mm argon fill 1.70 W/m2-oK 2.62 W/m2-oK 3.26 W/m2-oK 2.38 W/m2-oK Façade materials properties: Type of material to be used in the building should have minimum heat transfer coefficient and should have minimum embodied energy in its construction and installation of framing. Façade should have maximum thermal resistance which can prevent building from heating. Here for example choosing on a glass façade and its framing component materials: For choosing glazing type Case A:Using double glazing façade with 12mm air space. Case B: Using double low-e glazing (coating on glass surface 2 or 3) with 12 mm argon fill. Comparing heat transfer coefficients for glazing. (U-value)
- 27. Embodied energy for using curtain wall Aluminum - rolled recycled 62 MJ/lbs. Insulation - fiber glass 62 MJ/lbs. Glass - toughened 52 MJ/lbs. Steel - recycled 21 MJ/lbs. Wall assemblies: Due to wind velocity and hot weather conditions in this region using a single glazing is not feasible solution because the building absorbs an immense amount of heat. Therefore double skin façade is proposed to be used. We can use double glazing with 6mm air space for the inner façade and double low e- glazing with 12mm argon fill on the exterior façade which require relatively better strength to bear wind load on the building. By doing this we can maintain the embodied energy of the building material used. We can also reduce the peak heating/cooling loads and use of natural daylight instead of artificial as much as possible.
Editor's Notes
- Heating cooling spaces account for more than half of the energy use. The performance of the building façade can significantly affect the energy consumed by the building systems.
- The basic rules governing the orientation of rooms. A cylindrical projection of the sun’s path viewed from Paris provides a link between orientation and solar elevation through the seasons. The azimuth is given by the cardinal points and solar elevation is measured using concentric circles. A percentage indicates the fraction of solar radiation available compared with south – considered to equal 100% - with respect to the 8 main orientations. North-oriented rooms benefit from even light and diffuse solar radiation all year round. In summer, they may suffer from direct sunlight in the early morning and evening because the sun is low and its rays cause unmanageable glare. East-oriented room’s benefit from the morning sun but the light is difficult to regulate because the sun’s rays are low on the horizon. Insolation is low in winter but, in summer, it is higher than for a southerly orientation, which is not useful. West-oriented rooms have identical characteristics: potential visual discomfort due to glare and excessive sunshine in summer. In addition, in summer, these rooms being exposed to intense solar radiation which, on top of high temperatures towards the end of the day, makes it difficult to prevent overheating. South-oriented rooms benefit from more manageable light and from maximum sunshine in winter but minimum in summer. In fact, the low sun in winter comes further into a house whereas in summer, the solar elevation is greater and the sun comes less far inside. South is the orientation that enables the best passive regulation of sunlight. Solar heat gain on a vertical surface (a window) are also far lower on the south side because they are reduced by a factor equal to the cosine of the angle of incidence.
- Material selection has an environmental impact. It is becoming increasingly important to select materials that have the least negative effect on the environment. The life-cycle assessment approach can be used to determine environmental impacts of material selection, where material contents, production methods, energy requirements, and waste are analyzed to identify the real cost of material, reflecting the total amount of its environmental impact.
- When comparing the embodied energy of façade systems, the measurements are based on area (ft2 or m2) instead of mass or volume. The embodied energy of individual components and material of the façade must be considered.
- Metal building walls, consisting of metal members spanning between steel structural members (not including spandrel glass or metal panels in curtain walls) Steel framed walls, with cavities whose exterior surfaces are separated by steel framing members(including typical steel stud walls and curtain walls)
- Absorbent or tinted glazing: is glass to which a chemical additive has been added which modifies its color and therefore its physical properties. It is specially designed to maximize the absorption of all or part of the solar spectrum. Reflective glazing: If a lower solar heat gain factor than that achieved by using tinted glazing is required, a reflective coating can be applied to the glazing, which increases its reflection coefficient.
- Currently, there are three different basic approaches to improving the energy performance of glazing: 1. Modifying the glass itself by changing its chemical composition or its physical characteristics. This is the case for tinted glass, for example. 2. Applying a thin coating to the surface of the glazing. Reflective coatings or films have been developed to reduce heat gains and glare and, more recently, low-emissivity or spectrally selective coatings have been developed as a response to the specific conditions of cold or hot climates. 3. Assembling multiple panes and exploiting the properties of or the gaps between the panes. Altering a window’s light transmission factor If 6mm thick clear single glazing has a light transmission factor of 89%, combining two panes in double glazing will result in a light transmission factor of 89% x 89% = 79%. Electrochromic glazing: Each transition between a colored state and a bleached one is caused by applying an electronic and ionic charge across two thin layers using an electrolyte. The transmittance of this type of glazing remains the same until a new charge is applied. By reversing the polarity, it returns to the initial state of transparency and light transmission. Gasochromic glazing: A gasochromic unit is made up of gasochromic insulating glazing, a gas supply unit and a control unit. The active component of a gasochromic system is, as for electrochromic glazing, a tungsten oxide film (WO3). This is located on the inner side of the exterior triple-glazing pane.
- Reduction of heating demand during winter Reduction of cooling demand during summer Reduction of peak heating/cooling loads Use of natural daylight instead of artificial as much as possible Use of natural instead of mechanical ventilation when possible, using the Double Skin Façade cavity Exterior Glazing: Usually it is a hardened single glazing. This exterior façade can be fully glazed. Interior glazing: Insulating double glazing unit (clear, low E coating, solar control glazing, etc. can be used). Almost always this layer is not completely glazed. The air cavity between the two panes. It can be totally natural, fan supported or mechanically ventilated. The width of the cavity can vary as a function of the applied concept between 200 mm to more than 2m. This width influence the way that the façade is maintained. The interior window can be opened by the user. This may allow natural ventilation of the offices. Automatically controlled solar shading is integrated inside the air cavity. As a function of the façade concept and of the glazing type, heating radiators can be installed next to the façade
- Passively: According to the orientation of the building and the materials used in its outer layer: this energy can be used to heat the building and at the same time to provide natural light inside. Actively: Solar energy can be used for heating (thermal solar energy) or to generate electricity (photovoltaic solar energy).
- The use of plants on building surfaces has a long history, stretching back at least to the legendary Hanging Gardens of Babylon. Incorporation of vegetation on the surfaces of "Green buildings" has a more recent pedigree, revolving around the functional benefits of plants to building performance.
- Sustainable Features of facades: • The building has been designed to minimize the area of its external skin. For those offices with an external facade, very high levels of thermal insulation of walls and windows help to reduce heat loss. • Natural ventilation and daylight penetration are maximized. • Window sizes have been optimized according to each office’s specific location to profit from daylight while limiting solar gain. • Operable window and retractable blinds provide adjustable solar shading. • On days of high or low external temperature a large geothermal heat exchanger naturally conditions fresh air before it reaches the interior spaces. • The high thermal mass of the walls and ceilings together with night ventilation of the offices enables further cooling of the offices in the summer. • 20 percent of the building’s energy needs are met from renewable sources. 250 m2 of photovoltaic cells have been integrated into the glazing of the forum roof and a local landfill site provides energy for a gas turbine. • All building materials were selected for ecological and biological suitability. The most visible of these material choices is a panel facade made entirely of untreated local timber, which is prototypical in Germany.
- Windows use high U- value glass that allows daylight in but greatly reduces the amount of incoming heat and harmful UV rays. • Extensive utilization of natural lighting. • Levels two and three of the building have horizontal sunscreens on the south and east sides to further increase thermal efficiency. • The building sits on an east–west axis—this provides access to exterior views for more than 90 percent of the interior workspaces. • The project uses light- harvesting technology with sensors that mea- sure the natural light in occupied spaces and adjust the electrical lighting accordingly. • The parking lot surface and walkways surrounding the building use a light-colored concrete that reduces the heat island effect. • More than 60 percent of construction waste from demolition, construction, and land clearing was diverted by means of recycling. • More than 10 percent of the total project materials and products were made from recycled content materials. Thermopane glass with low- E coating, deep sunshades, and sunscreens minimizes heat gain and helps maintain the thermal comfort of the occupants.
- In this climate air conditioning will always be required, but can be greatly reduced if building design minimizes overheating. Minimize or eliminate west facing glazing to reduce summer and fall afternoon heat gain. Orient most of the glass to the north, shaded by vertical fins, in very hot climates, if there are essentially no passive solar needs. Locate door and window openings on opposite sides of building to facilitate cross ventilation, with larger areas facing up-wind if possible.