Building Design
Materials, components and assemblies
South western facade showing the bioclimatic wall and collonade
The planning of the building responds to two basic accommodation types:
1. Teaching accommodation
in the from of classrooms and laboratory spaces;
2. Offices and administration spaces for academic and general staff.
The broad planning approach is to place the academic offices to the north and west with classrooms and laboratories to the south. Accommodation in the north east sector of the building is reduced to single story. The accommodation is wrapped around the courtyard with pedestrian circulation and access points on the north and south.
The planning approach is a sensible response to environmental conditions created by the site and the brief. The classrooms and laboratories are spaces that have higher heat loads due to higher occupancy rates and equipment needs as compared to the offices. Placing these spaces on the south, which receives less heat load from the external environment places less pressure on the passive environmental control system. In addition, placing the academic offices to the north and west, which receive higher heat gains in winter from the environment and cooling breezes in summer, gives optimum potential for passive systems.
The, single storey
massing of the building to the northeast allows access for ventilation to the
courtyard and spaces served by the courtyard. This gives a semi-enclosure to
this element, which is clearly aimed at improving its thermal performance. Furthermore,
the use of circulation routes as access 'ducts' for breeze into and out of the
courtyard is a further advantage of this planning strategy.
The north south section shows the principle aspects of the composition of the building and the environmental control intentions. The dominant space is the courtyard, which acts as the lungs and eyes of the spaces adjacent to it. There is a clear intention that light and breeze is drawn into these spaces via the courtyard. Recordings of air temperatures in the courtyard have found them to be lower than ambient temperatures suggesting the creation of a 'cool pool' in summer to improve thermal comfort for occupants in adjacent spaces (Rajapaksha, U. and Hyde R.A., 2001). The butterfly roof was chosen to shade the courtyard. This roof form has a number of advantages. First, it is orientated with the valley gutter aligned east west. This means that the high points of the roof rise to the north and south allowing light and breeze into the courtyard. Second, water collection from the roof is taken into a central collection point and can be used for irrigation of the landscape elements.
In the area of the academic offices a double loaded corridor is created. Ventilation through the circulation corridor is facilitated in section by the use of roof ventilators. Hence the massing and section of the building is highly perforated which is consistent with the need for summer cooling. Selected shading to the accommodation is provided for thermal defence in summer and solar access in winter. Furthermore a colonnade to the southwest provided further protection from westerly sun in summer.
The key issues
in the performance assessment of this building is concerned the disposition
of elements to achieve passive control of these elements
Materials, components and assemblies
The building construction is based on a two storey steel structure. The external envelope is a mixture of lift slab reinforced concrete panels, glass panels, and perforated aluminium and fibreglass louvres. The building has a steel roof with roof ventilators coupled to the internal corridors. The steel butterfly roof over the central courtyard provides shading to the space below whilst creating a space (with the main roof) for possible natural airflow coming through the courtyard. It is supported by the use of a steel, portal frame structural system.
The key aspects
of the material selection are to use low cost and low maintenance components
where possible.
Two key design concepts have been integrated into the building to develop a new generation of building form. First, The Central Courtyard allows spaces for relaxation and interaction of occupants, whilst providing for ventilation and natural light penetration. The courtyard is designed to operate as a large funnel drawing outdoor air through the walkways and openings creating a breeze in the occupied area particularly in the summer season. Second, The Bio-Climatic Thermal Envelope which is developed to its fullest extend on the northwest and northeast walls provides a shaded space of one metre width just outside the windows separating them from the heavy masonry outer wall. Thermal chimney vents located at the top of this space enhance vertical breezes through this space. A number of active (driven by electrical energy) and passive strategies (driven by natural energy) were used. The passive strategies are as follows:
· Courtyard
The courtyard is a semi open space with a shading roof to prevent solar access
in summer. It is intended to provide a 'cool pool' for cross ventilation of
adjacent spaces. The temperature of air drawn into the courtyard is maintained
or cooled by the elements of the courtyard - the mass, vegetation and absence
of solar gain.
In addition the use of the roof and shading diffuses the day lighting and reduces the heat load component. This is an important aspect of lighting in the subtropical climates, whilst high levels of daylight are available, the attendant high heat loads and glare are to be avoided. The courtyard is an ideal strategy to address these issues.
Courtyard showing the internal features for light and ventilation
·
Thin plan depths and open section
The building uses a thin-plan approach where possible. This means the distance
between openings in the building skin is minimised, no distance is greater than
6m. In addition the sections maximise connections between floor and roof.
· Buffer
zoning
Buffer zoning as the name implies is a form of shading applied to buildings
to provide solar defence to internal spaces. Traditionally this has been carried
out through the use of external rooms such as the colonnade and the pergola.
In this case a ventilated cavity is used on the north and west facades of the
academic offices. The intention is to reduce the heat load on the internal skin
of the envelope.
· Fixed
shading
Horizontal and vertical shading elements are used to protect glazed area to
reduce the effects of direct solar gain. The angle of inclination of this shading
is designed to reducing glare.
Bioclimatic wall
· Sub-sill louvres and horizontal sliding windows
The function of openings in the building envelope is to regulate the amount
and direction of airflow for ventilation. The use of sub-sill louvres allows
air to be directed from a low point across the occupant to be extracted at high
level. This uses the natural thermosiphon principles of air movement in conjunction
with the pressure driven effects of cross ventilation. These louvres and windows
control the input of air into the space.
· Roof ventilators
Roof ventilators work with the louvre and window strategies. Essentially these
are designed to control the exhaust or outflow of air from the building
· Ceiling and corridor ventilators (academic offices)
Purpose designed ventilators are used to control ventilation and provide acoustic and visual privacy to the academic offices. As the corridor is used for ventilation to allow air to exhaust to the roof ventilators a further set of louvres is used in the corridor wall. The air has two pathways dependent on the acoustic privacy required by the occupant. For high acoustic and visual privacy conditions the door and louvres in the corridor are closed and air passes through a ceiling vent, ducting space and to the corridor at high level. Acoustic absorbent material in the ceiling void is designed to reduce sound attenuation through the duct. For conditions where visual privacy but no acoustic privacy is required the door is closed and the louvres in the wall can be opened. Finally the door and the louvres can be opened to allow full interconnection of the corridor and the office.
· High ceilings
(classrooms only)
The ceiling height in offices is increased to 2.8m to allow for ventilation
in the classrooms. This allows more effective stack cooling to high level louvres.
Cross ventilation between the louvres can remove hot air whilst avoiding high
levels of airflow at desk level.
The active strategies
are as follows:
Office cooling system and lighting
· Ceiling
and wall mounted fans
Fans have been provided as a back up strategy for cooling in still conditions
and for periods of high humidity. The type of fans that are provided give a
cooling effect similar to a 2-3 degree Celcius reduction in air temperatures.
· Light
sensitive louvres
Light sensitive louvres are used in the bioclimatic wall to automatically control
the amount of daylight to reduce glare. The louvres are perforated to allow
light penetration yet reduce glare. In days of high illuminance the louvres
are closed, occupants can still see through the louvres. Additional vertical
blinds are provided for additional daylight control.
The building was assessed using spot lighting measurements (Hyde R.A. 2000). Lighting grids were set up in selected spaces and measurements taken with respect to the external conditions. In a similar way air temperature and wind speed measurements were taken. These were logged over a three weekly period. External conditions were assessed based on meteorological data from Maroochy Airport.
Daylighting levels
on the ground floor; the yellow denotes high levels of day lighting reducing
to red for low levels, note the effect of the courtyard is to maximise natural
lighting
Daylighting first floor; the shaded courtyard and buffering to the exterior
reduce direct sunlight and allow diffused light to the offices and classrooms
Different daylighting effects are found from the climate responsive strategies used. The sky conditions are characterised by clear sky weather events. On average the site receives seven hours of sunshine a day. In these conditions high levels of sky brightness occur at the zenith decreasing to the horizon. As a consequence the effects of shading can significantly reduce the available day lighting. In addition sunlight has high intensity with up to 100,000-150,000 lux with a heat load of 1000 W per m2. Hence there are significant environmental penalties for direct sun penetration into buildings.
Consequently the shading of windows is designed to avoid penetration of sunlight and direct solar radiation thus reducing glare and heat load. The diagrams above are colour-coded to represent the penetration of natural light into the building. Lighter colour denotes areas with higher levels of illuminance. As the level of illuminance decreases the spectrum changes to indicate areas with less natural light in colour red.
The overall effects show the benefits of the courtyard to the day lighting levels. The classrooms receive lighting from two sides reducing the need for electric lighting. In the offices area the lighting levels in the corridor are acceptable but low, as light is not borrowed from the office space. The replacement of the solid opaque louvres with light emitting material could address this problem. The bio-climatic weather wall limits penetration of light. The amount of diffused light entering the building through the perforated aluminium louvres, in some cases, is insufficient as indicated in the results of testing.
The day lighting strategy in the classrooms is considered adequate in terms of maximising the use of natural light. The result of testing shows the minimum back ground level of illuminance to be at 320 lux in the centre of the room given clear sky conditions. The appropriate background lighting for reading purposes is considered to be between 190 and 500 lux.
In both the offices and the classrooms the use of electric lighting for task lighting is an option and can be required depending on the time of day, the external climatic conditions and the task being undertaken in this tutorial room. The minimisation of direct sunlight into places where visual tasks are performed is an appropriate lighting strategy, however, the dull uniformity of diffused light, particularly in the internal courtyard, produces the opposite effect in a place intended for relaxation, reflection and interaction.
The result of testing in a typical office shows similar levels of daylighting in the office and classrooms. Automated light responsive louvres prevent the user from adjusting the penetration of natural light according to their needs. Vertical blinds are provided to achieve this kind of adjustment.
With shading systems, an anti-glare device is located on the southwest façade. This allows light from different directions into the colonnade preventing drastic contrast in brightness. On the other hand, it falls short in providing shade, particularly on summer afternoons, when direct sunlight accesses the classrooms with its consequent heat problems. Internal shading systems reduce these heat problems. The courtyard roof and bio-climatic weather wall are suitable devices in terms of shading.
Lighting levels across the section showing the available natural light
The macro climatic data demonstrates a need for airflow to achieve thermal comfort in summer given the high humidity. The Bioclimatic Chart for Brisbane shows that the comfort zones for still-air is seen to be about 26 degrees C with humidity at 60 per cent. To extend the comfort zone for higher humidity and higher temperatures, higher airflow rates are required. This is quite extensive given the humidity, up to 1 m/sec.
At the time when the spot measurements were made indicated this level of wind speed was found in the courtyard but not in the offices or classrooms. This is mainly due to the shading strategies and the orientation used. The building is orientated so that the longest façade facing north-north- east. The breezes at the time of measurement are oblique to the northerly facade and funnel through the courtyard. The consequence of this is that wind-driven ventilation is not the major source of ventilation and there is a strong reliance on stack effect.
There are a number of deficiencies with the stack systems for cooling. First, it is necessary that the internal temperatures are higher than external temperatures for the natural buoyancy of the air to rise. A minimum temperature difference of about 1degree C is required for the thermal siphon effect to take place. This means that where temperatures are above the comfort zone the building has to get hotter than outside to provide cooling.
Second, the pressure forces generated by stack systems are lower than wind driven ventilation, hence wind can override and negate stack, blowing hot air back into the building. This was a concern with the courtyard were high wind speeds were recorded and this could be setting up positive pressures at roof level blowing rain and hot air back into the building.
Additional spot measurements have been taken with winds from the southeast and northeast. In these conditions the airflow was found to be as predicted, the control of the louvres could control the ventilation to the office spaces. In some case though reverse airflows were found with air movement from the ceiling vents.
This identifies
one of the lessons learnt from this building; natural ventilation in buildings
is unpredictable and hence adequate methods of control are required.
Internall and shade air temperatures in the office areas showing the temperatures
remain at or near ambient. This is an inidicator of good performance in passive
buildings
Air temperatures and high humidity showing problems with microclimate conditons
in summer
Ventilation and day lighting can be controlled passively though the building form and fabric. Humidity, on the other hand, is very difficult to control by the use of passive systems. This is due to the need to dehumidifying of the air.
Informal discussion with users identified discomfort from overheating and humidity. The effects of humidity provide problems with the operation of electrical equipment, which undermines productivity. Most users consulted followed the appropriate dress code for the climate, that is, light, loose fitting clothes.
Recordings on the site during February 2000 revealed that although the air temperatures were particularly high, the microclimate of the site created difficult humidity conditions. The tropical shower weather conditions, which comprised periods of sunshine and heavy rain, raised the humidity levels inside the building to 100 percent on some days.
The lessons learnt
from this are that a passive mode building has limits to way that thermal comfort
serviced. The back up systems of fans and a thermal refuge, that is a place
which provides personal cooling, such as air-conditioned common spaces can be
used to provide additional services for these periods. In this way the costs,
energy and health benefits of the passive building can be achieved whilst providing
an appropriate level of service in extreme weather conditions.