BUILDING ENVELOPE

Submitted By: Mukeshwaran B

M. Arch. (S. A.) 2014-16 Roll No. 14001506006 ar.mukeshwaran@gmail.com M: +91-9894926744

Department of Architecture Deenbandhu Chhoturam University of Science & Technology

Murthal, Sonepat (Haryana) (India)

BUILDING ENVELOPE

Opaque/solid elements

Translucent elements

Transparent elements

Energy production elements

Sunspaces

Atria

BUILDING ENVELOPE

In sustainable architecture the link between building performance and the

design of the envelope is critical.

Any well-built building enclosure is expected to keep out wind, damp

and rain, to let in light and air, to conserve heat and to provide security and

privacy.

In a sustainable building we may also expect it to mediate the effects of

climate on the users and the energy systems of the building, collect and store

heat, redirect light, control air movement and generate power.

Sustainable strategies for envelope design

Respond to orientation to provide for heating and cooling and daylight

strategies.

The world about the building is not symmetrical. Modify the envelope to

respond to the challenges and opportunities presented by different façade

orientations.

Design and detail the building envelope to minimize heat losses and achieve

thermal comfort with respect to thermal mass and insulation, avoid thermal

bridging and minimise air infiltration.

Design for durability. Specify for long life and low maintenance to minimise

the use of energy and materials over the life of the building.

Specify materials with low embodied energy –more significant as we move

towards carbon neutral buildings.

Minimise heat loss through infiltration and provide controlled energy

efficient ventilation with heat recovery.

Integrate appropriate passive components to enhance the performance of the

envelope.

Integrate active technologies to provide energy from renewable sources.

Keep it simple. Do as much as possible by architectural means before

resorting to service installations to fine-tune the indoor environment.

OPAQUE / SOLID ELEMENTS

The solid elements of the building envelope can perform both heating and

cooling functions through use of thermal mass, insulation and protection of the

internal environment from air infiltration.

Heating and cooling

For both heating and cooling functions, the thermal properties of an opaque

wall can be controlled by:

thermal conductivity and thermal storage capacity of material (thermal mass)

thermal insulation

good detailing.

Thermal Mass

Studies analysing passive solar design of non-domestic buildings found that:

high thermal mass is desirable to stabilise daytime temperatures and for

night cooling, but may marginally increase heating cost in some buildings;

thermal mass is best increased by maximising surface area, as increase in

thickness is relatively ineffective;

thermal mass delays the time at which peak temperatures occur;

thermal mass should not be thermally isolated from circulating air (e.g.

under a raised floor or above a suspended ceiling);

adopting a night cooling strategy can enhance the performance of thermal

mass.

Walls

Wall materials can be categorised in terms of low or high thermal mass.

In buildings occupied by day, thermal mass will absorb heat during the day

and release it at night, reducing peak day-time air temperatures.

Thermal comfort depends as much on mean radiant temperature as on air

temperature, and the surface temperature ofthermally massive elements will

be lower than the air temperature at peak times, contributing further to

comfort.

In buildings not occupied all day, in

cooler climates, a lightweight

envelope with low thermal mass may

be appropriate, as it can reduce

response time and the heat required to

provide comfort.

Floors

Suspended timber floors have less

embodied energy than concrete floors but a

concrete slab (provided that it is not covered

with a lightweight finish) can act as a

thermal store, as the cross-section through

the floor construction of the BRE building in

England illustrates.

Insulation

Walls, roofs and other opaque parts of a

building must be provided with thermal

insulation, both in cool climates to reduce heat

loss and to maintain internal surfaces at a higher

temperature than would otherwise be the case,

and in hot climates to reduce external gains and to

maintain internal surfaces at a lower temperature,

thus improving comfort levels.

Choosing the appropriate insulation

material depends on the application, placement in

element, life cycle analysis, and specific

requirements such as compressive strength and

environmental characteristics.

Walls

Insulation may be placed on the external or

internal face of a wall or within the wall without,

in theory, altering the overall insulation

properties. The optimal position will be

determined by the availability of thermal mass,

occupancy patterns, and the responsiveness and

control of the heating system.

Internal insulation

Internal insulation will separate the thermal

mass of the walls from the space, and reduce both

the response time and the energy required to bring

the room up to comfort levels. There may be

thermal mass available in other elements in the

space which will dampen temperature

fluctuations. Otherwise the application is

appropriate for intermittently heated buildings.

External insulation

The higher internal thermal capacity

available as a result of locating the insulation on

the outside of the building means that fluctuations

in air temperature are reduced, but the

space will take longer to heat up and cool down.

Cavity insulation

The cavity may be either partially or fully

insulated depending on the details of

construction, and the climate. Cavity insulation

makes available some of the thermal inertia

within the wall and substantially reduces the risk

of air infiltration and condensation within the

building. It also reduces problems from thermal

bridges.

Roofs

Generally the position of insulation in the

roof will offer similar advantages and

disadvantages as mentioned for walls.

Flat roofs may be one of three types: the

‘cold roof ’ is ventilated above the insulation,

while in the ‘warm roof ’ the insulation layer lies

immediately below the roof covering and is

unventilated. The warm roof has less risk of

condensation, but as with external insulation, the

layers of finish on top of the insulation will be

subject to large temperature fluctuations, and to

thermal stress and movement. The inverted roof

uses a water-resistant insulant on top of (and

protecting) the weatherproof membrane.

Floors

There is evidence that heat losses through

solid ground floors are greater than standard

calculations suggest. Heat loss from the slab is

not constant over the whole area of the floor, the

greatest being from the edge. Studies have shown

that insulating the edges of the slab can have as

good an effect as overall insulation, and the U-

value calculation for the ground floor slab must

take into account both the size and edge

conditions of the slab.

TRANSLUCENT ELEMENTS Heating

Transparent insulation material (TIM) can

admit daylight but without the heat

lossassociated with conventional glazing.

In addition, its composition can still allow

useful solar gain.

Daylighting

Transparent insulation material sandwiched

between sheets of glass in a conventional frame

can replace traditional glazing where light but not

vision is required. There are several categories of

TIM and performance characteristics, such as

light transmission, total solar energy

transmittance (TSET) and thermal (Ug-values)

can be varied by using other constructions and

glass types. Ug-values of up to 0.4 W/m²K, light

transmission from 60% to 21% and TSET of up

to 12% are possible.

TRANSPARENT ELEMENTS

In a sustainable building the glazing

elements are often the most interesting and

complex

Good glazing and window design involves

finding a balance between demands which

are often conflicting such as passive heating and

cooling functions, e.g. allow solar gain

but keep out excessive solar heat, provide

sufficient daylight without causing glare, allow controllable ventilation into the

building but keep out excessive noise, allow visual contact with the surroundings

but ensure sufficient privacy and ensure safety.

Heating

Direct heat gain through correctly

oriented windows is the simplest and often

the most effective manifestation of ‘climatic’

architecture. Glazing design and orientation

should optimise useful solar gains and

minimise heat losses during the heating

season.

Thermal insulation

Glass is a poor thermal insulator. There are a

number of ways to decrease heat lost

through glazing:

low-energy coating on the glass (Low

E) decreases radiation heat loss;

gases such as argon or krypton may be

substituted for the air in the cavity to

further decrease the convective heat

loss of the pane;

triple-glazing with low-e coating, with

or without argon or krypton gas.

Cooling

Overheating in the cooling season is

one of the most serious problems related to

glazing and window design. The principal

passive cooling techniques include the use of

solar shading and ventilation.

Solar shading

Heat gain through conventional windows can be significant. Depending on

the orientation and geographic location, if sensible glazing ratios are adopted the

need forshading may be reduced. However, where solar radiation is excessive for

parts of the day in summer, the most effective way to reduce heat gain is to prevent

or block solar radiation by using external shading. A wide and ever-growing

competitive range of shading devices is available to the architect, including blinds,

shutters, louvres and structural or add-on devices.

Ventilation

Ventilation air may be supplied by natural or mechanical means, or a hybrid

system containing elements of both. Natural ventilation is driven by wind or by

buoyancy forces caused by temperature differences. To encourage cross-

ventilation, there should be vents or openable windows on opposite sides of the

building, without major obstructions to air flow in between. An open-plan layout is

good in this regard.

Daylighting

Artificial lighting accounts for about 50% of the energy used in offices, and

a significant proportion of the energy used in other non-residential buildings. In

recent years, use of daylighting combined with high performance lighting means

that between 30–50% savings can be easily

achieved while 60–70% savings are possible in

some cases.

Daylighting requirements will depend on

the function of the building, the hours of use, type

of user, requirements for view, need for privacy

and ventilation requirements as well as the energy

and environmental targets. The perception of

adequate and comfortable daylight is influenced

by the uniformity of daylight and the absence of

glare.

Windows

As a rule of thumb, daylighting within a

building will only be significant within about

twice the space height of a glazed façade. Thus

shallow-plan buildings provide more opportunities

for daylighting (as well as natural ventilation and

cooling) than deep-plan arrangements. The level

of daylighting at a point in a space depends to a

large extent on the amount of sky visible through

the window from that point. Thus the provision of

a significant amount of glazing near the ceiling is

beneficial from a daylighting point of view. For

example, tall narrow openings will provide a

better daylight distribution in a room than low

wide ones. For spaces with dual aspect or on the

top floor, openings in more than one façade or

roofl ights will also improve daylight distribution.

In the design of glazed areas, pay

attention to:

• window size and orientation;

• glazing type;

• frame type and detailing at junctions to prevent

infiltration;

• means of solar control;

• means of night insulation;

• openable sections for occupant comfort and

satisfaction.

Daylight systems and devices

Light re-directing systems include:

• Scattering the light: such as special glasses and

holographic optical elements

• Re-directing the light: such as re-directing glasses,

light shelves, laser cut panels ,

louvers and louvered blinds, heliostats, lightpipes

• Transporting the light: fibre-optic or other elements

Shading

If glazed openings have fixed overhangs to

minimise solar gains in summer, these will also

reduce daylight entry throughout the year. Movable

shading or blinds will reduce daylight only while they

are in place. While direct sunlight can be an attractive

feature in a room (particularly in winter), if it falls

directly on occupants or worktops it may be

undesirable. Venetian blinds may be used to reflect

sunlight towards the ceiling, thus avoiding discomfort

due to direct sunlight and achieving greater

penetration of daylight at the same time. Occupants

may need instruction on how to use such blinds to

best effect.

Ventilation

Where opening lights in glazing present

problems, operable vents, whether located in

opaque elements or integrated in a window assembly,

are worth considering. With air flow control, insect

and dust screens or acoustic baffles, they can provide

a relatively inexpensive solution where noise or air

pollution create difficult site conditions. Openable

opaque panels can enhance ventilation rates in

summer while avoiding excessive glazed areas.

Insulation

Insulating shutters which are closed after dark

can be useful in reducing heat loss. Creating a well-

sealed air-gap between shutters and glazing increases

their effectiveness, but can be difficult to achieve.

External shutters are preferable; internal shutters may lead to condensation on the

glass during cold conditions, or, if left closed while the sun shines, set up thermal

stresses which probably cause the glass to break. However, managing the operation

of external shutters is not easy; in cold weather the occupants are unlikely to open

windows to close the shutters. A louvred shutter operated from the inside can

overcome this problem, but it may also interfere with light penetration during the

day.

ENERGY PRODUCTION ELEMENTS

Photovoltaics

Photovoltaic technology represents a

decentralized electricity generating system that

can help a building provide its own energy

requirements directly from sunlight.

Solar thermal panels

A typical solar panel consists of a flat

collecting plate sandwiched between an

insulating backing and a glazed front; evacuated

tubes represent an important alternative. The

optimum orientation in the northern hemisphere

is south-facing on roof or walls, though any

orientation within about 30º of south will

perform almost as well as a southfacing

collector. The optimum inclination depends on the application. For water heating

an angle with the horizontal of less than the latitude of the site is usually best, to

make good use of energy from the high-altitude summer sun. For space heating a

higher inclination angle is best, since the sun is lower in the sky during the heating

season. The path of the sun is not the only consideration in choosing collector

inclination – diffuse solar radiation from the sky is also important .

Heating and Cooling

The sunspace acts as a buffer zone for a house, significantly reducing heat

loss. Even in the absence of direct solar gain it is a functional energy efficient

device.

SUNSPACES

Familiar to many in the form of the traditional

domestic conservatory, the sunspace is a combination

of both direct and indirect gain approaches to passive

solar heating.

ATRIA Heating and Cooling

Atria function as inter mediate buffer spaces,

and their ambient temper ature levels

depend on the specific losses from the glazed space

to the outside , and the specific gains

from the buildings to the glazed space .

Ventilation

Solar shading and ventilation is an effective combination to reduce atrium

temperatures during summer, but natural cross-ventilation has to be carefully

evaluated in order to ensure comfort on critical days.

Daylighting

Atria can noticeably improve the quality of

the adjoining internal spaces, which can enjoy all

the advantages of daylight, without the

accompanying climatic extremities. Improved

technologies allow the architect greater freedom

regarding the choice of construction, design and

materials; even where longer payback periods are

indicated there may be a strong case for employing

such a system.