CLIMATE RESPONSIVE BUILDING DESIGN
GENERAL
New South Wales is a portion of the land area situated on the central
eastern
coastline of the Australian continent. It is situated between the large
continental land mass to the west and the large ocean mass to the east.
As a result of solar inflow variation with latitude, in continental terms the
large land mass to the west typically is warm, and the water mass to the east is perpetually
cool the interior continental land mass is arid, the summer
winds flow over the substantial land area and are warm.
The ocean
infiltrates cool air changes across New South Wales in the general west to east
flow of weather patterns as a result the general weather patterns in NSW are typified by cool
winters with southwest winds and moisture, and hot summers with northerly winds,
either dry and dusty, or tropical.
The climate is characterised as `temperate', with temperatures outside the
normal human comfort range principally in summer.
Passive solar building design suits cooler climates where inflow of solar heat
gain creates comfortable interior space with limited additional interior space
heating.
This design approach has some applicability in the limited number of cool
climate locations in NSW.
In arid fringe climate areas the design of buildings for comfort must address:-
- resisting summer heat inflow from outside
- ejecting the heat build up
emanating from occupants and appliances inside the building
This approach is appropriate for comfort design for the majority of NSW.
Responsive building design for NSW is described in
separate information below about micro-climate, and building cross
ventilation using heat, wind and moisture forces common in areas of arid fringe
climate
Investigations about responsive building design in the NSW context are the synthesis of:-
- theoretical hypotheses
- backed by empirical
evidence
- applied to building designs both in concept and real life
applications.
The hypotheses used have been developed from basic meteorology and physics
theory as described above.
Empirical evidence is available from human use of weather forces in other
activities. In Australia about 1000 sailplanes achieve 150,000 flying hours in
convection weather conditions annually.
Convection weather conditions typify the
forces available in the climate and are applicable to building design. This is
one of the substantial empirical data bases available for the formulation of responsive building design principles.
Buildings designed to use these responsive principles are in operation
and are achieving the low energy comfort environments originally postulated.
Variations in weather occur everyday.
Even though it varies in detail from day to day, it is
nevertheless uniformly composed of three contributing influences:-
- sun heating
- wind
- moisture mixed to varying degrees
These forces are the components pieces of micro-climate.
A standard vacant house block can be envisaged as consisting of flat and open
ground, unfenced, and with neither structures nor vegetation on it. The climate
on such featureless land is the same as that of the surrounding general area
weather in which the site is located; that is - macroclimate and microclimate
are the same.
By erecting a building on that land, the climate
changes on the land.
This occurs with every building constructed on every site.
Now there is shade
cast by the building onto the ground to the south of that building, and the
portion of the site north of the building receives additional reflected heatload
from the building's walls
By constructing a building on the land, the site is segmented into a sun
side hot zone and a shade side cool zone.
This occurs as part of locating the
building on the land.
A simple example of the creation of microclimate.
Very seldom is land as featureless as is described above.
Existing features on
vacant land contribute to modifying the climate on the site from the general
area weather. Existing vegetation and structures on the land create shade and
moisture variations; land slope and soils change the heating load on areas of
the land.
On land with a north facing slope, compared with another with a south facing
slope, quite different house designs will be required for comfort.
Even where
this land is on adjoining allotments the local microclimate on these sites is
so different that on the south slope high solar inflow is required to achieve
comfort, on the north slope solar shading is needed.
Microclimate can be used to advantage.
Warm external spaces are pleasant places
to live in winter, cool outside spaces are comfortable in summer.
But these changes to the home site's microclimate also affect the interior
comfort of the building. By creating variations in heatload, wind pressure and
moisture on different faces of the home, the interior can be kept comfortably
warm in winter and ventilated and cool in summer.
This is described in detail in other
areas below.
Microclimate occurs on every home site, with the combination of the land's
existing features, and by placing the building appropriately on the site.
The first considerations in planning a home are:-
- which existing features on the land affect the microclimate, and determine
where the building is to be situated on the land for comfort,
- which way its wall faces and openings are to be oriented to
maximise comfort,
- and the heat, cooling and air flows which are created by the above for comfort as
covered in other areas on this site.
Buildings designed to use microclimate are achieving substantially lower energy
consumption to gain the same comfort levels as conventional buildings; anything
between a half and a sixth of normal energy use.
That is a lot of money saved on
annual operating and heating/cooling costs.
Microclimate is consistent with ESD principles because the
existing features and ecology of the land gives a sound guide to the
microclimate potential and features which should be incorporated in buildings
for comfort on each site.
Other areas on this site set out some of the detail design options available
to enhance the energy savings inherent in good microclimate building design.
Every day the sun tracks through the northern sky over Australia. Each building
casts its shadow on its southern eastern and western side, and reflects the sun's heat from its
northern wall and adjacent ground.
NSW is situated in an arid fringe zone, with a substantial summer
heat load where building cooling can be a major energy user.
The naturally occurring heat imbalance around buildings described above can be
used to improve comfort in buildings in NSW in summer.
Several
complementary actions are involved.
As air temperature increases locally, that air parcel expands and reduces in
density. Such a low density air parcel has a higher temperature than ambient,
and is forced upward by the surrounding ambient air temperature and pressure.
This takes the form of thermal convection a common meteorological
phenomenon.
On the northern side of a building, this temperature imbalance can be
extenuated by constructing hard wall and ground surfaces which reflect solar
heat, and these can be formed into a sunken or walled courtyard configuration to
maximise the temperature imbalance created.
As air humidity increases, the density of that air parcel increases and the
temperature decreases because the latent heat capacity of the air also
increases.
Buildings cast shadows to their south. The air in this external area abutting
the building is cooler than ambient. This air temperature can be further
contained by adding more shade in the form of verandah or pergola, and adding
humidity with vegetation, spray or drip irrigation or water features including
fountains.
Buildings designed with both these
microclimate features are suited to
summer cross ventilation. Opening of windows on north and south sides allows
cool and humidified external air from the southern side to infiltrate the
building while the building air volume is drawn out to the north by the thermal
convection.
The calculated effect of this mechanism in an effective installation is up to
9 air changes per hour. The effect is to create air changes within the building
with cooler than ambient air suitable for comfort in summer conditions. The
pre-cooled low volume cross ventilation is created with little on-going or
recurrent operating costs.
Microclimate generated cross ventilation is based on simple and well
understood meteorological phenomena.
Their application to individual buildings should however be undertaken with
care.
Poor building and landscape design in relation to the building's unique
site and location can negate the effects being sought.
For a new building, the site should be assessed with a view to the naturally
occurring hot and cool spaces. North facing slopes, depressions created by both
landform and vegetation, soils, rock outcrops; all form favourable hot spaces.
In existing developments, adjacent overshadowing by other development, and heat
absorbing building facades reduces adjacent hot space potential.
Surfaces suitable for heat reflection should be selected and sited to reflect
heat into the external space, not to the building. Light colour matt surfaces
are more effective than dark colours. Both high thermal mass and heat
reflectance materials are suitable.
Sunken paving with retaining walls or walled courtyard
extenuate heating by
avoiding wind chill cooling of the space, and minimising air inflow directions,
a wall of vegetation can be also be suitable.
For cool spaces, shading by both built enclosure and vegetation are suitable
Pergolas, trellis, and vine. Verandah materials should resist heat transfer
through the roof. Light colour and insulation or proprietary reflectance
surfaces are suitable.
External ground level raised in relation to the building allows the cooled air
to descend, extenuating throughflow. Walls and vegetation barriers are not
beneficial
To maximise cross ventilation, large opening areas in the building faces to both
spaces should be possible.
Written operating directions for occupants assist in maximising the
effectiveness of the installation.
A clerestorey is high level openable glazing, resulting in the room having a
high or sloping ceiling, and associated with it a high, sloping or curved roof
on the building.
This high level glazing can be situated over the centre of a room or building
to introduce natural daylight into the house in addition to daylight through
windows on the perimeter walls.
The result is a greater amount of and more uniform distribution of natural
daylight within the room or building, reducing the need for daytime artificial
lighting and thereby reducing energy use.
The clerestorey lighting offers privacy, and daylight clear of vegetation as a
result of its elevated situation.
In cold climates, clerestorey can face the sun with a northern aspect,
reducing winter heating costs.
The majority of NSW is situated in an arid fringe climate where
summer cooling is the major energy use.
In this climate clerestorey faces south, allowing full daylight inflow without
direct sunlight or heat.
The clerestorey also can contribute to ventilation and cooling of the home in
summer
Because clerestoreys can generate airflow, their use in bushfire prone areas
must be considered carefully. In situations where they can encourage fire
ingress to the home they should not be used; where fire ingress potential is
less extreme their use is conditional on other fire resistant features including
wired glazing, metal mesh screens, shutters and frames being incorporated.
Ventilation through clerestorey is generated by the variations in air
pressure from windflow around the home
It can also operate in concert with thermal venting as described in `Summer Comfort with Cross Ventilation'.
As air flows around the building, upwind surfaces dam air to higher than
atmospheric pressure. Downwind and sheltered areas contain air at atmospheric or
lesser pressure
South facing clerestorey is situated in a sheltered area relative to NSW prominent northern summer winds. The combination of sheltered area
between high and low roof, the reducing air pressure over the sloping or curved
roof results in air outflow from the building when clerestorey windows are
opened.
Effective ventilation depends on replacement air being drawn from elsewhere
around the building. In summer the north winds are hot, dry and dusty, and
direct ventilation is undesirable.
The south downwind side of the home encompasses shaded air which can be cooler
than ambient temperature as well as at dust free atmospheric pressure.
This is suitable replacement air by opening south windows in concert with the
clerestorey.
During summer weather changes characterised by south-west `cool change'
conditions, opening the clerestorey to act as an air-in ram bringing cool air
into the home to rapidly cool the structure.
The effectiveness of this action depends on opening a north window laterally in
the home to encourage air throughflow.
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