A STUDY ON EFFECTS OF FACADES IN DESIGNING A GREEN BUILDING

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

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.

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.

Lighting14%

Space heating28%

Space cooling10%

ventilation6%

Refrigiration5%

Water heating7%

Electronics3%

Computers2%

Equipment14%

Other11%

Energy use breakdown for commercial buildings

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.

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 layersLayer thicknessLayer 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.

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

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.

North-oriented

East-oriented

West-oriented

South-oriented

The basic rules governing the orientation of rooms.

Orientation:

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.

 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.

Material Embodied energy AluminumCast virginCast recycled (33%)Extruded virginExtruded recycled (33%)Rolled virginRolled recycled (33%)

 497554717547762

Brick 6.6CementPortlandFly ash (6-20%)Fly ash (21-35%)Mortar

 2.091.96 – 1.671.65-1.360.49

Concrete General Fly ash (15%)Fly ash (30%)Precast

 2.22.131.963.3

Glass Primary Toughened

 3352

Paint 154SteelVirginRecycledStainless steel

 7821125

StoneGraniteLimestoneMarble Sandstoneslate

 243.34.42.20.2 to 2.2

Wood GeneralGlue laminatedPlywood

 222633

PV panelsMonocrystallinePolycrystallineThin film  

 10,4508,9542,871

Embodied energy is the total energy required for the extraction, processing, manufacture and delivery of building materials to the building site

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 113Steel cladding, continuous insulation and paint 236Stucco 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

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.

  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.

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.

Electrochromic glazing:  

Gasochromic glazing:

Double Glazing:

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

Single skin façade Single skin façade with vertical fins

Single skin façade withelectrochromic

glazing

Double skin glazing0

10

20

30

40

50

60

70

Infiltration People Equipment Lighting Solar heat gain

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

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 facadeDifference 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

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

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.

Approach for designing of the sustainable building façade in

the following steps:

Climate considerations

Building orientation

Façade materials properties

Wall assemblies

N

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.

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)

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.