The fact that ambient air temperature, lad surface and sea surface temperatures are rising across the Australian continent can no longer be denied.
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| GRAPH: Australian Bureau of Meteorology |
In New South Wales generally average maximum temperatures in the month of January 2024 ranged from around 24°C to 36-39°C, spiked by days on end of heatwave temperatures which often broke temperature records for individual localities.
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| MAPPING: Australian Bureau of Meteorology |
In the north-east coastal zone of the state the minimum air temperature was 1°C higher and maximum air temperature 1-2°C higher than they were between 1981-2010.
In January the highest Northern Rivers region minimum & maximum recorded daily temperature range was:
Evans Head 24.8—38°C
Grafton 24.5—37.6°C
Yamba 25.6—37.2°C
Murwillumbah 27.1—36.2°C
Casino 27.1—36.2°C
Lismore 24.5—35.6°C
Tabulam 23.0—34.9°C
Byron Bay 25.6—32.7°C
Ballina 24.9—34.2°C
Note: These are the nine official Bureau of Meteorology weather stations in the Northern Rivers region.
Yet despite all this new subdivision schemes and housing designs are paying little more than lip service to sustainability and mitigating the thermal load of both the internal road networks of these subdivisions or the collective & individual loads of dwelling contained there in.
Apparently, multi-dwelling structures that increasing look like a collection of boxes are skating through BASIX requirements on the presumption that each individual box within these boxes will be fully air conditioned at some point before occupation or that if ceiling fans are fitted to some of the rooms then this will mitigate heat.
An assumption which:
(i) takes no account of the increasing stress air conditioning places on a household's cost of living. Because the price per kilowatt hour & associated charges of residential electricity supply continues to rise and commonly these multiple dwelling boxes are not built with any rooftop solar power grid to mitigate cost;
(ii) completely ignores the increasing risk of destructive storms causing levels of damage to power supply infrastructure that cuts power supply to both collections of streets or entire towns for days/weeks at a time. As occurred in heatwave conditions in 2024; and
(iii) appears to leave the thermal load of closely clustered internal roads out of the equation completely.
I expect the latest collection of boxes being considered by Clarence Valley Council will also get the nod because I have yet to see this local government apply the full suite of climate change policies to every development application before deciding consent. The heat footprint of an application rarely rates a mention in Council-in-the-Chamber debates or elicits questions to senior staff attending. Neither are there many mentions of the heat island affect caused by new roads, pavements and driveways. Nor does the wind resistance factor of a proposed building arise - and given the entire Clarence Coast is now in a cyclone risk zone that borders on the negligent when assessing new development applications.
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| Artists impression of street view of 6 Yamba Road, Yamba proposed subdivision. IMAGE: BDA |
Set out below are some basic facts about how the freestanding houses, town houses, duplexes, units and flats we live in attract and retain heat.
Australian Government, Your Home, retrieved 19 February 2024:
Passive Design
What is thermal mass?
In simple terms, thermal mass is the ability of a material to absorb, store and release heat. Materials such as concrete, bricks and tiles absorb and store heat. They are therefore said to have high thermal mass. Materials such as timber and cloth do not absorb and store heat and are said to have low thermal mass.
In considering thermal mass, you will also need to consider thermal lag. Thermal lag is the rate at which heat is absorbed and released by a material. Materials with long thermal lag times (for example, brick and concrete) will absorb and release heat slowly; materials with short thermal lag times (for example, steel) will absorb and release heat quickly.
Thermal mass
Thermal mass, or the ability to store heat, is also known as volumetric heat capacity (VHC). VHC is calculated by multiplying the specific heat capacity by the density of a material:
Specific heat capacity is the amount of energy required to raise the temperature of 1kg of a material by 1°C.
Density is the weight per unit volume of a material (ie how much a cubic metre the material weighs).
The higher the VHC, the higher the thermal mass.
Water has the highest VHC of any common material. The following table shows that it takes 4186 kilojoules (kJ) of energy to raise the temperature of 1 cubic metre of water by 1°C, whereas it takes only 2060kJ to raise the temperature of an equal volume of concrete by the same amount. In other words, water has around twice the heat storage capacity of concrete. The VHC of rock usually ranges between brick and concrete, depending on density. Most common building materials with high VHC also tend to be quite conductive, making them poor insulators.
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Thermal lag
How fast heat is absorbed and released by uninsulated material is referred to as thermal lag. It is influenced by:
heat capacity of the material
conductivity of the material
difference in temperature (known as the temperature differential or ΔT) between each face of the material
thickness of the material
surface area of the material
texture, colour and surface coatings (for example, dark, matte or textured surfaces absorb and re-radiate more energy than light, smooth, reflective surfaces)
exposure of the material to air movement and air speed.
To be effective in most climates, thermal mass should be able to absorb and re-radiate close to its full heat storage capacity in a single day–night (diurnal) cycle.
In moderate climates, a 12-hour lag cycle is ideal. In colder climates subject to long cloudy periods, lags of up to 7 days can be useful, providing there is enough solar exposed glazing to ‘charge’ the thermal mass in sunny weather.
Embodied energy
Some high thermal mass materials, such as concrete, cement-stabilised rammed earth, and brick, have high embodied energy when used in the quantities required. This highlights the importance of using such construction only where it delivers a clear thermal benefit. When used appropriately, the savings in heating and cooling energy from the thermal mass can outweigh the cost of its embodied energy over the lifetime of the building. Consideration should be given to using high thermal mass materials with lower embodied energy, such as water, adobe or recycled brick.
Why is thermal mass important?
When used correctly, materials with high thermal mass can significantly increase comfort and reduce energy use in your home. Thermal mass acts as a thermal battery to moderate internal temperatures by averaging out day−night (diurnal) extremes.
In winter, thermal mass can absorb heat during the day from direct sunlight. It re-radiates this warmth back into the home throughout the night.
In summer, thermal mass can be used to keep the home cool. If the sun is blocked from reaching the mass (for example, with shading), the mass will instead absorb warmth from inside the home. You can then allow cool breezes and convection currents to pass over the thermal mass overnight to draw out the stored energy.
Conversely, poor use of thermal mass can reduce comfort and increase energy use. Inappropriate thermal mass can absorb all the heat you produce on a winter night or radiate heat to you all night as you try to sleep during a summer heatwave.....
