MICROCLIMATE
BUILDING DESIGN
THEORY
DEVELOPMENT
MICRO-CLIMATE
FOR BUILDING COMFORT
THE
WEATHER
CREATING
MICRO-CLIMATE
NATURALLY
OCCURRING MICRO-CLIMATE
USING
MICRO-CLIMATE FORCES FOR COMFORT
THE
BENEFITS
ECOLOGICAL
DEVELOPMENT
SUMMER
COMFORT WITH CROSS VENTILATION
SUMMER
COMFORT WITH CLERESTOREY VENTILATIONThe climate is characterised as `temperate', with temperatures outside the normal human comfort range principally in summer.
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
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.
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.
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.
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.
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.