Climate specific design responses and passive cooling methods are different for:
- Hot humid climates where cooling only is required.
- Temperate and warm climates where both heating and cooling are required.
- Cool and cold climates where heating needs are predominant.
1) Hot humid climates requiring cooling only
- Due to the unique nature of hot humid climates, many state, territory and local governments in these regions have produced a range of excellent design resources and advice.
- Hot humid climates require a fundamentally different design approach.
- We focuses predominantly on climates requiring both summer cooling and winter heating.
- The most significant difference is in the size and orientation of windows or openable panels and doors. In these climates, modest amounts of well-shaded glazing can and should be positioned on every façade to encourage air movement.
- Windows or other openings should be located, sized and designed to optimise air movement, not solar access. As stated earlier, wind doesn’t blow through a building — it is sucked towards areas of lower air pressure.
- Locate larger openings on the downwind, or leeward, side of the house and smaller openings on the breeze, or windward, side.
- This is advantageous in these cyclone prone regions since cyclones and cool breezes commonly come from an onshore direction (see Orientation).
- Other elevations should also include openings because breezes come from a variety of directions and can be redirected or diverted through good design and appropriate window styles, especially casement windows.
- Another critical difference is that the designer needs to make an early decision about whether the home is to be ‘free running’, conditioned (mechanically cooled) or hybrid (a combination of both).
- Free running buildings should not be conditioned at a future date without substantial alteration: this includes reducing the size of openings, adding bulk insulation around the room(s) to be conditioned and condensation detailing.
i) Design responses to the challenges of hot humid climates
- High humidity levels in these climates limit the body’s ability to lose heat by evaporating perspiration.
- Sleeping comfort is a significant issue, especially during periods of high humidity where night temperatures often remain above those required for human comfort. While acclimatisation helps, it is often inadequate during the ‘build-up’ and wet season — especially in cities with highly transient populations such as Darwin.
- Design responses consider shading, air movement, insulation and construction methods.
- Permanently shade all walls and windows to exclude solar access and rain.
- Consider shading the whole building with a fly roof.
- Shade outdoor areas around the house with plantings and shade structures to lower the ground temperature and thence the temperature of incoming air.
iii) Air movement
- Maximise exposure to (and funnelling of) cooling breezes onto the site and through the building, e.g. larger leeward openings, smaller windward openings.
- Use single room depths where possible with large openings that are well shaded to enhance cross-ventilation and heat removal.
- Design unobstructed cross-ventilation paths.
- Provide hot air ventilation at ceiling level for all rooms with shaded openable clerestory windows, ‘whirlybirds’ or ridge vents.
- Elevate the building to encourage airflow under floors.
- Use higher or raked ceilings to promote convective air movement.
- Design plantings to funnel cooling breezes and filter strong winds.
- Install ceiling fans to create air movement during still periods.
- Consider using whole of house fans with smart switching to draw cooler outside air into the house at night when there is no breeze.
- Choose windows with maximum opening areas (louvres or casement) that can be tightly sealed when closed; avoid fixed glass panels. Openable insulated panels and security screen doors can be used instead of some windows.
- Use lighter colours on roof and external walls.
- Use insulation solutions that minimise heat gain during the day and maximise heat loss at night, i.e. use multiple layers of reflective foil to create a one way heat valve effect and avoid bulk insulation.
- Use low thermal mass construction generally.
- Consider the benefits of high mass construction in innovative, well-designed hybrid solutions.
2) Mixed climates requiring heating and cooling
- Well-designed homes do not require air conditioning in most climates.
- More than 50% of homes in warm temperate climates are mechanically cooled.
- This proportion is rapidly increasing — often because inadequate shading, insulation and ventilation, or poor orientation and room configuration for passive cooling and sun control, cause unnecessary overheating.
a) Warm humid climates
- Energy consumption for heating and cooling can account for up to 25% of total household energy use in this climate. In benign climates like the coastal areas of south-east Queensland and north-east NSW, achieving the high levels of passive thermal comfort required to reduce this by as much as 80% is a relatively simple and inexpensive task.
- Design and orientate to maximise the contribution of cooling breezes.
- Use earth-coupled concrete slab-on-ground.
- Provide high levels of cross-ventilation via unobstructed pathways.
- Use ceiling fans and convective ventilation to supplement them.
- Include a well-located and shaded outdoor living area.
- Use lighter colours for roof and external walls.
- Consider whole of house fans in this climate.
- Apply hybrid cooling principles where cooling is used.
- Passive solar heating is required during winter months and varies from very little to significant. Integrate passive heating requirements with cool breeze capture by providing passive or active shading (eaves or awnings) to all windows.
- Employ well-designed shading and insulation to limit heat gain and maximise summer heat loss in response to the specific microclimate (see Shading).
- Use high mass construction in areas with significant diurnal (day−night) temperature ranges (usually inland) to provide significant amounts of free heating and cooling.
- Use low mass construction where diurnal temperature ranges are low (usually coastal) to increase the effectiveness of passive and active heating and cooling.
- Elevate structures to increase exposure to breezes in warmer northern regions.
- Eliminate earth coupling in southern and inland regions.
- Use bulk and/or reflective insulation to prevent heat loss and heat gain.
- Use glazing with a low to medium solar heat gain coefficient (SHGC) and U-value.
b) Hot dry climates with warm winter
- Use courtyard designs with evaporative cooling from ponds, water features and ‘active’ (mechanical) evaporative cooling systems. They are ideal for arid climates where low humidity promotes high evaporation rates.
- Use evaporative cooling if mechanical cooling is required.
- Use ceiling fans in all cases.
- Use high mass solutions with passive solar winter heating where winters are cooler and diurnal ranges are significant.
- Use low mass elevated solutions where winters are mild and diurnal ranges are lower.
- Minimise east and west-facing glazing or provide adjustable external shading. High mass living areas are more comfortable during waking hours. Low mass sleeping areas cool quickly at night. High insulation prevents winter heat loss and summer heat gain.
- Consider high mass construction for rooms with passive winter heating and low mass for other rooms.
- Shade all windows in summer and east and west windows year round.
- Use well-sealed windows and doors with maximum opening area to optimise exposure to cooling breezes and exclude hot, dry and dusty winds.
c) Hot arid climates with cool winter
- Use high thermal mass construction to capitalise on high diurnal temperature ranges by storing both warmth and ‘coolth’.
- Use compact forms to minimise surface area.
- Maximise building depth.
- Include closeable stack ventilation in stairwells and thermal separation between floors in two storey homes.
- Use shaded internal courtyards with evaporative cooling features in single storey homes.
- Use smaller window and door openings designed for night-time cooling and cool thermal currents where available.
- Use low U-value double glazing with high SHGC.
- Ensure that the majority of glazing is north facing and passive solar shaded.
- Avoid west windows.
- Evaporative cooling and active solar heating systems reduce the need for large, solar exposed glass areas for heating (i.e. active rather than passive heating).
3) Traditional and innovative cooling methods for arid climates
- Specialist passive and low energy cooling systems have evolved for hot dry climate areas in other parts of the world which are also applicable to a large portion of the continent.
- They introduce moisture to building structures (such as roof ponds or water sprayed onto evaporative pads) and incorporate stacks or chimneys that use convection to exhaust rising hot air and draw cooler, low level air into the building.
- This air can be evaporatively cooled by being drawn over ponds, or through mist sprays or underground labyrinths (these towers are dominant elements and are therefore an integral part of the fundamental architecture of the building).
- Modern version of an Iranian Badgir cooling system where earth exchange and evaporation pre-cool incoming air drawn by a solar chimney.
4) Temperate climates
- With good design, temperate climates require minimal heating or cooling. Good orientation, passive shading, insulation and design for cross-ventilation generally provide adequate cooling. Additional solutions from the range explained here can be used where site conditions create higher cooling loads.
- Design for compact form in cooler zones, extending the east−west axis in warmer zones (see Orientation).
- Prefer plans with moderate building depth — two rooms is ideal.
- Design for the impacts of climate change and consider highly efficient heat pump systems to cope with increases in extreme weather events.
- Use thermal mass levels appropriate to the amount of passive cooling available (cool breezes, consistent diurnal variations) and use thermal mass to delay peak cooling needs until after the peak demand period.
- Choose window opening styles and position windows to ensure good cross-ventilation.
- Orientate for passive solar heating and divert breezes.
- Employ larger northern and southern façades.
- Design for moderate openings with the majority to the north.
- Use minimal west-facing glazing (unless well shaded).
- Use moderate east-facing glazing and moderate south-facing glazing except where cross-ventilation paths are improved by larger openings.
- Use bulk and reflective foil insulation.
- Use low to medium U-value and SHGC glazing in milder areas and double glazing where ambient temperatures are higher.
- Temperate climates call for good orientation, passive shading and cross-ventilation.
5) Cool and cold climates where heating dominates
- Zone requires careful consideration of cooling needs because climate change modelling indicates that it is likely to be impacted by climate change more than most other zones.
- This necessitates a shift from the current high thermal mass design practices to moderate or low mass designs with carefully calculated glass to mass ratios to avoid summer overheating. Higher mass solutions remain useful in higher altitude and colder regions where significant diurnal ranges are likely to continue to provide reliable cooling in all but extreme weather events.
- Winter heating remains the predominant need in all but the warmest regions in these zones.
- Passive solar orientation and shading is critical.
- On sites where passive heating or cooling access is limited, consider low mass, high insulation solutions with highly efficient reverse-cycle heat pumps.
- Give increased attention to the design of high level cross-ventilation for night cooling.
- Low U-value double glazing with high SHGC is highly desirable due to its effectiveness in both summer and winter.
- Use a well-designed combination of reflective foil and bulk insulation.
- Use modest areas of glazing with the majority facing north where solar access is available.
- Minimise west-facing glazing.
- Passive and/or active shading of all glazing is essential.
- Applicable in all climates, especially hot humid and hot dry, ‘adapting lifestyle’ means adopting living, sleeping, cooking and activity patterns that respond to and work with the climate rather than using mechanical cooling to emulate an alternative climate.
- High humid climates present the greatest challenge in achieving thermal comfort because high humidity levels reduce evaporation rates.
- Adapting lifestyle’ means working with the climate rather than using mechanical cooling to emulate an alternative one.
- Acclimatisation is a significant factor in achieving thermal comfort. Most people living in tropical climates choose to do so. They like the climate and know how to live comfortably within its extremes by adopting appropriate living patterns to maximise the outdoor lifestyle opportunities it offers.
- Sleeping comfort at night during the hottest and most humid periods is a significant issue for many people living in tropical climates. Sleeping comfort generally should be a high priority when choosing, designing or building a home. Different members of a household have different thermal comfort thresholds. Children often adapt to seasonal changes more easily than adults do.
- Understanding the sleeping comfort requirements of each member of the household can lead to better design, positioning or allocation of bedrooms — and increased thermal comfort for all with less dependence on mechanical cooling.
- Live outside when time of day and seasonal conditions are suitable — particularly in the evenings. Radiation by the body to cool night skies is an effective cooling mechanism, especially in the early evening when daytime heat loads have not been allowed to escape from the interior of the house.
- Cooking outside during hotter months reduces heat loads inside. This lifestyle tradition developed to suit our climate is not often directly connected to thermal comfort. Locate barbeques outdoors, under cover in close proximity to the kitchen, with good access either by servery or screened door. Shaded barbecue and outdoor eating areas (insect screened where required) facilitate outdoor living and increased comfort.
- Sleep-outs are an ideal way to achieve sleeping comfort and can provide low cost additional space for visitors who often arrive during the hotter Christmas period.
- Vary active hours to make best use of comfortable temperature ranges at different times of the year.