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Building Envelope
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BUILDING ENVELOPE
Submitted By: Mukeshwaran B
M. Arch. (S. A.) 2014-16 Roll No. 14001506006 [email protected] 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.