In a modern house the
best advice is to shut up shop during the heat of the day, to keep the heat
out. Then, throw open the windows from late afternoon onwards, as long as
overnight temperatures are lower outside than inside.
But our research shows
that opening and closing doors, windows and curtains is just one of the factors
at play. To really stay cool when the heat is on, you also need to think about
what type of house you have, and what its surroundings are like.
The traditional
“Queenslander” house has long been seen as ideally suited for hot weather. Such
houses have great design features for cooling, including shady verandas and
elevated floors. But the traditional timber and tin construction provides very
little resistance to heat transfer.
If uninsulated homes
are closed up during a heatwave they would very likely become too hot. This has
led people to opening up their house, to stop them getting much hotter inside
than outside.
But in temperatures of
40C and above, one could argue that both strategies (opening and closing) in an
uninsulated house would result in very uncomfortable occupants. Such houses
would also not meet current building regulations, as insulation has been
required in new houses since 2003 (or earlier in some parts of Australia).
Our research explores the role of design
and construction on occupant comfort in hot weather. We have
looked at brick and lightweight houses, as well as those made from less common
materials such as structural insulated panels, earth, straw, and advanced glass
and roof coatings.
We found that three
factors influence the comfort of people inside a house: whether is it opened or
closed; its urban context; and its construction materials. Having a better
understanding of these factors could help you to keep cool this summer – or
prepare for the next one.
To breeze or not to breeze
Whether they have
air-conditioning or not, we found that people usually approach hot weather in
the same way: by opening doors and windows to capture breezes.
People in both groups
also tended to shut up the house if it gets hot outside, or if there is no
breeze, or before switching on the air-conditioner if they have one. Most
participants in our survey, which looked at homes less than 10 years old, also
used ceiling fans to create air movement.
Occupants tape foil to the inside of
windows to try to stop their home from overheating in Queensland.
But our research showed
that many people failed to take advantage of cooler overnight temperatures,
meaning their homes were hotter than the outside during the night.
This may mean that houses have not been designed to get rid of daytime heat. Or
that people aren’t opening the windows overnight to allow the house to cool
down.
The impact of context
The research shows
that occupants first try natural ventilation for achieving comfort. But the
success of this strategy depends on the urban
context of the house. This includes factors such as housing density,
street scape and microclimate.
For example, during a
hot spell in 2013 an Ipswich estate experienced minimum and maximum
temperatures that were 3-4C hotter than the local weather
station. Restricted air movement due to nearby buildings, and radiant heat from
hard surfaces such as concrete, can both drive temperatures up.
Built for comfort
Both the housing
industry and occupants seem to have little understanding of the impact design
and construction have on the temperature inside the building. As a result,
air-conditioning is now seen not as desirable, but as a necessity. This does
not have to be the case.
Most houses are built
to minimum regulations (5-6 stars out of 10). There is also evidence
that, with poor construction practices and virtually non-existent
compliance testing, many would fail to meet even this level.
What does this mean
for comfort year-round, and in a heatwave?
In inland southeast
Queensland, a 6-star home will have an internal temperature of 18-28C for
80-85% of the time. In a typical year, its temperature will be above 30C for
between 300 and 350 hours (3.5% of the time). Heat-wave conditions would result
in more hours above 30C.
This 9-star home uses 48% less electricity
than the south-east Queensland average.
A wide variety of
design and construction techniques and materials can be used to achieve such
high performance houses in every climate zone in Australia.
Open and shut case
So when facing a
heatwave, should we open up our houses or close them up? The answer is… it
depends.
If your home is well
insulated and shaded, it should be able to resist several days of extreme heat.
Closing doors, windows and curtains during the heat of the day can help the
house stay cooler than outside. Ceiling fans provide air movement to make you
feel cooler.
Opening the house as
much as possible from late afternoon to early morning is beneficial if
overnight temperatures will fall below your inside temperature.
Air conditioning a
poorly insulated house with little shading is expensive and futile. In a
well-insulated and shaded house, air-conditioning can be used quite efficiently
by using the same strategies as above. A higher thermostat setting (perhaps
26-28C), combined with ceiling fans, can provide comfort with lower running
costs. This can also reduce strain on the electricity network.
Whether
air-conditioned or not, houses can be designed specifically for their climate,
to limit the flow of heat between the outside and inside. The higher the star
rating of the house, the more effectively it stops unwanted heat from entering
the house. Different
strategies are required for different climates.
Of course, the
knowledge that you might be more comfortable in a different house is likely to
be cold comfort as you swelter through this summer. But perhaps you can prepare
a “cool comfort” plan for next summer.
