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.