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BedZED (Beddington Zero Energy Development), the
UK's largest and first carbon-neutral eco-community: the distinctive roofscape
with solar panels and passive ventilation chimneys
.
Sustainable architecture is architecture that utilizes environmentally
conscious design techniques. Sustainable architecture is framed by the larger
discussion of sustainability and the
pressing economic and political issues of our world.
In the broad context, sustainable architecture seeks to minimize the
negative environmental impact of buildings by enhancing efficiency and
moderation in the use of materials, energy, and development space. The idea of
sustainability, or ecological design,
is to ensure that our actions and decisions today do not inhibit the
opportunities of future generations.[1] This can be framed in the context of a
conscious approach to energy and ecologicalical conservation in the design of
the built environment.[2]
Contents
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Sustainable energy use
Main articles: Low-energy house
and Zero-energy building
K2 sustainable apartments in Windsor, Victoria, Australia by Hansen Yuncken (2006) features passive solar
design, recycled and sustainable materials, photovoltaic cells,
wastewater treatment,
rainwater collection
and solar hot water.
The passivhaus standard combines a variety of
techniques and technologies to achieve ultra-low energy use.
Following its destruction by a tornado in 2007, the town of Greensburg, Kansas
(USA) elected to rebuild to highly stringent LEED Platinum environmental
standards. Shown is the town's new art center, which integrates its own solar
panels and wind generators for energy self-sufficiency.
Energy efficiency
over the entire life cycle of a building is the single most important goal of
sustainable architecture. Architects use many
different techniques to reduce the energy needs of buildings and increase their
ability to capture or generate their own energy.
Heating, ventilation and cooling
system efficiency
The most important and cost effective
element of an efficient heating, ventilating, and air conditioning (HVAC)
system is a well insulated building.
A more efficient building requires less heat generating or dissipating power,
but may require more ventilation capacity to expel polluted indoor air.
Significant amounts of energy are flushed out of buildings in the water,
air and compost streams. Off the shelf,
on-site energy recycling technologies can effectively recapture energy from waste hot water and stale air and
transfer that energy into incoming fresh cold water or fresh air. Recapture of
energy for uses other than gardening from compost leaving buildings requires
centralized anaerobic digesters.
HVAC systems are powered by motors. Copper, versus other metal conductors, helps to improve the
electrical energy efficiencies of motors, thereby enhancing the sustainability
of electrical building components. (For main article, see: Copper in
energy efficient motors).
Site and building orientation have some major effects on a building's HVAC
efficiency.
Passive solar
building design allows buildings to harness the energy of the sun
efficiently without the use of any active solar mechanisms such as photovoltaic cells or solar hot water panels. Typically passive solar building designs incorporate
materials with high thermal mass that
retain heat effectively and strong insulation that
works to prevent heat escape. Low energy designs also requires the use of solar
shading, by means of awnings, blinds or shutters, to relieve the solar heat
gain in summer and to reduce the need for artificial cooling. In addition, low energy buildings
typically have a very low surface area to volume ratio to minimize heat loss.
This means that sprawling multi-winged building designs (often thought to look
more "organic") are often avoided in favor of more centralized
structures. Traditional cold climate buildings such as American colonial
saltbox designs provide a good historical model
for centralized heat efficiency in a small scale building.
Windows are placed to maximize the input of heat-creating light while
minimizing the loss of heat through glass, a poor insulator. In the northern hemisphere
this usually involves installing a large number of south-facing windows to
collect direct sun and severely restricting the number of north-facing windows.
Certain window types, such as double or triple glazed insulated windows with gas filled spaces and low emissivity (low-E) coatings, provide much
better insulation than single-pane glass windows. Preventing excess solar gain
by means of solar shading devices in the summer months is important to reduce
cooling needs. Deciduous trees are
often planted in front of windows to block excessive sun in summer with their
leaves but allow light through in winter when their leaves fall off. Louvers or
light shelves are installed to allow the sunlight in during the winter (when
the sun is lower in the sky) and keep it out in the summer (when the sun is
high in the sky). Coniferous or evergreen plants are often planted to the north
of buildings to shield against cold north winds.
In colder climates, heating systems are a primary focus for sustainable
architecture because they are typically one of the largest single energy drains
in buildings.
In warmer climates where cooling is a primary concern, passive solar
designs can also be very effective. Masonry building materials with high thermal mass are very valuable for retaining
the cool temperatures of night throughout the day. In addition builders often
opt for sprawling single story structures in order to maximize surface area and
heat loss.[citation needed]
Buildings are often designed to capture and channel existing winds,
particularly the especially cool winds coming from nearby bodies of water. Many of these valuable
strategies are employed in some way by the traditional
architecture of warm regions, such as south-western mission
buildings.
In climates with four seasons, an integrated energy system will increase in
efficiency: when the building is well insulated, when it is sited to work with
the forces of nature,
when heat is recaptured (to be used immediately or stored), when the heat plant
relying on fossil fuels or
electricity is greater than 100% efficient, and when renewable energy is utilized.
Renewable energy generation
Solar panels
Main article: Solar PV
Active solar devices such as photovoltaic solar panels
help to provide sustainable electricity for any use. Electrical output of a
solar panel is dependent on orientation, efficiency, latitude, and
climate—solar gain varies even at the same latitude. Typical efficiencies for
commercially available PV panels range from 4% to 28%. The low efficiency of
certain photovoltaic panels can significantly affect the payback period of
their installation.[3] This low efficiency does not mean that
solar panels are not a viable energy alternative. In Germany for example, Solar
Panels are commonly installed in residential home construction.[4]
Roofs are often angled toward the sun to allow photovoltaic panels to
collect at maximum efficiency. In the northern hemisphere, a true-south facing
orientation maximizes yield for solar panels. If true-south is not possible,
solar panels can produce adequate energy if aligned within 30° of south. However,
at higher latitudes, winter energy yield will be significantly reduced for
non-south orientation.
To maximize efficiency in winter, the collector can be angled above
horizontal Latitude +15°. To maximize efficiency in summer, the angle should be
Latitude -15°. However, for an annual maximum production, the angle of the
panel above horizontal should be equal to its latitude.[5]
Wind turbines
Main article: Wind power
The use of undersized wind turbines in energy production in sustainable
structures requires the consideration of many factors. In considering costs,
small wind systems are generally more expensive than larger wind turbines
relative to the amount of energy they produce. For small wind turbines,
maintenance costs can be a deciding factor at sites with marginal
wind-harnessing capabilities. At low-wind sites, maintenance can consume much of
a small wind turbine's revenue.[6] Wind turbines begin operating when
winds reach 8 mph, achieve energy production capacity at speeds of
32-37 mph, and shut off to avoid damage at speeds exceeding 55 mph.[6] The energy potential of a wind turbine
is proportional to the square of the length of its blades and to the cube of
the speed at which its blades spin. Though wind turbines are available that can
supplement power for a single building, because of these factors, the
efficiency of the wind turbine depends much upon the wind conditions at the
building site. For these reasons, for wind turbines to be at all efficient,
they must be installed at locations that are known to receive a constant amount
of wind (with average wind speeds of more than 15 mph), rather than
locations that receive wind sporadically.[7] A small wind turbine can be installed
on a roof. Installation issues then include the strength of the roof,
vibration, and the turbulence caused by the roof ledge. Small-scale rooftop
wind turbines have been known to be able to generate power from 10% to up to
25% of the electricity required of a regular domestic household dwelling.[8] Turbines for residential scale use are
usually between 7 feet (2 m) to 25 feet (8 m) in diameter and produce
electricity at a rate of 900 watts to 10,000 watts at their tested wind speed.[9]
Solar water heating
Main article: Solar thermal power
Solar water heaters,
also called solar domestic hot water systems, can be a cost-effective way to
generate hot water for a home. They can be used in any climate, and the fuel
they use—sunshine—is free.[10]
There are two types of solar water systems- active and passive. An active
solar collector system can produce about 80 to 100 gallons of hot water per
day. A passive system will have a lower capacity.[11]
There are also two types of circulation, direct circulation systems and
indirect circulation systems. Direct circulation systems loop the domestic
water through the panels. They should not be used in climates with temperatures
below freezing. Indirect circulation loops glycol or some other fluid through
the solar panels and uses a heat exchanger to heat up the domestic water.
The two most common types of collector panels are Flat-Plate and Evacuated-tube.
The two work similarly except that evacuated tubes do not convectively lose
heat, which greatly improves their efficiency (5%-25% more efficient). With
these higher efficiencies, Evacuated-tube solar collectors can also produce
higher-temperature space heating, and even higher temperatures for absorption
cooling systems.[12]
Electric-resistance water heaters that are common in homes today have an
electrical demand around 4500 kW·h/year. With the use of solar collectors,
the energy use is cut in half. The up-front cost of installing solar collectors
is high, but with the annual energy savings, payback periods are relatively
short.[12]
Heat pumps
Air-source heat pumps (ASHP) can be thought of as reversible air
conditioners. Like an air conditioner, an ASHP can take heat from a relatively
cool space (e.g. a house at 70°F) and dump it into a hot place (e.g. outside at
85°F). However, unlike an air conditioner, the condenser and evaporator of an
ASHP can switch roles and absorb heat from the cool outside air and dump it
into a warm house.
Air-source heat pumps are inexpensive relative to other heat pump systems.
However, the efficiency of air-source heat pumps decline when the outdoor
temperature is very cold or very hot; therefore, they are only really
applicable in temperate climates.[12]
For areas not located in temperate climates, ground-source (or geothermal)
heat pumps provide an efficient alternative. The difference between the two
heat pumps is that the ground-source has one of its heat exchangers placed
underground—usually in a horizontal or vertical arrangement. Ground-source
takes advantage of the relatively constant, mild temperatures underground,
which means their efficiencies can be much greater than that of an air-source
heat pump. The in-ground heat exchanger generally needs a considerable amount
of area. Designers have placed them in an open area next to the building or
underneath a parking lot.
Energy Star ground-source heat pumps can be 40% to 60% more efficient than
their air-source counterparts. They are also quieter and can also be applied to
other functions like domestic hot water heating.[12]
In terms of initial cost, the ground-source heat pump system costs about
twice as much as a standard air-source heat pump to be installed. However, the
up-front costs can be more than offset by the decrease in energy costs. The
reduction in energy costs is especially apparent in areas with typically hot
summers and cold winters.[12]
Other types of heat pumps are water-source and air-earth. If the building
is located near a body of water, the pond or lake could be used as a heat
source or sink. Air-earth heat pumps circulate the building's air through
underground ducts. With higher fan power requirements and inefficient heat
transfer, Air-earth heat pumps are generally not practical for major
construction.
Sustainable building materials
See also: Green building
Some examples of sustainable building materials include recycled denim
or blown-in fiber glass insulation, sustainably harvested wood, Trass,
Linoleum,[13] sheep wool, concrete (high and ultra high performance[14] roman self-healing concrete[15]), panels made from paper flakes, baked
earth, rammed earth, clay, vermiculite, flax linnen, sisal, seegrass, cork,
expanded clay grains, coconut, wood fibre plates, calcium sand stone, locally
obtained stone and rock, and bamboo, which is one of the
strongest and fastest growing woody plants, and
non-toxic low-VOC glues
and paints.
Recycled materials
Recycling items for building
Sustainable architecture often incorporates the use of recycled or second
hand materials, such as reclaimed lumber
and recycled copper.
The reduction in use of new materials creates a corresponding reduction in embodied energy (energy used in the production of
materials). Often sustainable architects attempt to retrofit old structures to
serve new needs in order to avoid unnecessary development. Architectural
salvage and reclaimed materials are used when appropriate. When older buildings
are demolished, frequently any good wood is reclaimed, renewed, and sold as
flooring. Any good dimension stone is
similarly reclaimed. Many other parts are reused as well, such as doors,
windows, mantels, and hardware, thus reducing the consumption of new goods.
When new materials are employed, green designers look for materials that are
rapidly replenished, such as bamboo, which can be harvested
for commercial use after only 6 years of growth, sorghum or wheat straw, both of which are waste
material that can be pressed into panels, or cork oak, in which only the outer bark is removed
for use, thus preserving the tree. When possible, building materials may be
gleaned from the site itself; for example, if a new structure is being
constructed in a wooded area, wood from the trees which were cut to make room
for the building would be re-used as part of the building itself.
Lower volatile organic compounds
Low-impact building materials are used wherever feasible: for example,
insulation may be made from low VOC (volatile organic
compound)-emitting materials such as recycled denim
or cellulose insulation,
rather than the building
insulation materials that may contain carcinogenic or toxic
materials such as formaldehyde. To discourage insect damage, these alternate
insulation materials may be treated with boric acid. Organic or milk-based paints may be
used.[16] However, a common fallacy is that
"green" materials are always better for the health of occupants or
the environment. Many harmful substances (including formaldehyde, arsenic, and
asbestos) are naturally occurring and are not without their histories of use
with the best of intentions. A study of emissions from materials by the State
of California has shown that there are some green materials that have
substantial emissions whereas some more "traditional" materials
actually were lower emitters. Thus, the subject of emissions must be carefully
investigated before concluding that natural materials are always the healthiest
alternatives for occupants and for the Earth.[17]
Volatile organic compounds (VOC) can be found in any indoor environment
coming from a variety of different sources. VOCs have a high vapor pressure and
low water solubility, and are suspected of causing sick building syndrome
type symptoms. This is because many VOCs have been known to cause sensory
irritation and central nervous system symptoms characteristic to sick building
syndrome, indoor concentrations of VOCs are higher than in the outdoor
atmosphere, and when there are many VOCs present, they can cause additive and
multiplicative effects.
Green products are usually considered to contain fewer VOCs and be better
for human and environmental health. A case study conducted by the Department of
Civil, Architectural, and Environmental Engineering at the University of Miami
that compared three green products and their non-green counterparts found that
even though both the green products and the non-green counterparts both emitted
levels of VOCs, the amount and intensity of the VOCs emitted from the green
products were much safer and comfortable for human exposure.[18]
Materials sustainability
standards
Despite the importance of materials to overall building sustainability,
quantifying and evaluating the sustainability of building materials has proven
difficult. There is little coherence in the measurement and assessment of
materials sustainability attributes, resulting in a landscape today that is
littered with hundreds of competing, inconsistent and often imprecise
eco-labels, standards and certifications. This discord has led both to
confusion among consumers and commercial purchasers and to the incorporation of
inconsistent sustainability criteria in larger building certification programs
such as LEED.
Various proposals have been made regarding rationalization of the
standardization landscape for sustainable building materials.[19]
Waste management
Waste takes the form of spent or useless materials generated from
households and businesses, construction and demolition processes, and
manufacturing and agricultural industries. These materials are loosely
categorized as municipal solid waste, construction and demolition (C&D)
debris, and industrial or agricultural by-products.[20] Sustainable architecture focuses on
the on-site use of waste management,
incorporating things such as grey water systems for
use on garden beds, and composting toilets
to reduce sewage. These methods, when combined with on-site food waste
composting and off-site recycling, can reduce a house's waste to a small amount
of packaging waste.
Building placement
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One central and often ignored aspect of sustainable architecture is
building placement. Although the ideal environmental home or office structure
is often envisioned as an isolated place, this kind of placement is usually
detrimental to the environment. First, such structures often serve as the
unknowing frontlines of suburban sprawl.
Second, they usually increase the energy consumption
required for transportation and lead to unnecessary auto emissions. Ideally,
most building should avoid suburban sprawl in favor of the kind of light urban development articulated by the New Urbanist movement. Careful mixed use zoning
can make commercial, residential, and light industrial areas more accessible
for those traveling by foot, bicycle, or public transit, as proposed in the Principles
of Intelligent Urbanism. The study of Permaculture, in its holistic application, can
also greatly help in proper building placement that minimizes energy
consumption and works with the surroundings rather than against them,
especially in rural and forested zones.
Sustainable building consulting
A sustainable building consultant may be engaged early in the design process,
to forecast the sustainability implications of building materials,
orientation, glazing and other physical factors, so as to identify a
sustainable approach that meets the specific requirements of a project.
Norms and standards have been formalized by performance-based rating
systems e.g. LEED[21] and Energy Star for homes.[22] They define benchmarks to be met and provide metrics and
testing to meet those benchmarks. It is up to the parties involved in the
project to determine the best approach to meet those standards.
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