How to keep your house cool in a heatwave

How to keep your house cool in a heatwave

By Wendy Miller, Queensland University of Technology

Should you open or close your house to keep cool in a heatwave? Many people believe it makes sense to throw open doors and windows to the breeze; others try to shut out the heat. Listen to talk radio during a hot spell and you are likely to hear both views.

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.

In contrast, a 9- or 10-star house in the same climate would deliver more “comfort” hours (85-95%) and would be above 30C less than 2% of the time. These houses are designed to slow down the transfer of heat, meaning they naturally stay cooler for longer. And there is no (or little) need for air-conditioning!

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.

The Conversation

Wendy Miller has conducted consultancy research for Metecno Pty Ltd, the Australian Glass and Glazing Association and Ergon.

She has also received funding from the Sustainable Built Environment National Research Centre and the Australian Government through the National Climate Change Adaptation Research Facility.

This article was originally published on The Conversation.
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Three new tech concepts you might actually use from CES 2014

Three new tech concepts you might actually use from CES 2014

By Dian Tjondronegoro, Queensland University of Technology

The massive Consumer Electronics Show (CES), hosted annually in Las Vegas, showcases the latest discoveries and innovations, including audiovisual, gaming, smartphones, computing, household appliances and in-car technologies.

While we see plenty of new hardware, software and gadgets which definitely have the “wow!” factor (such as a Bluetooth-enabled toothbrush) as well as the odd celebrity low point, we should focus on the bits and pieces which could actually be useful – and potentially change our lives for the better.

So here are my top three most practical themes from CES 2014 which, in my opinion, could be easily incorporated into daily life.

Ultra high definition, curved, glasses-free 3D screens

Just as most people start to fully embrace the beauty of high definition contents, the Ultra HD (4K) screens already promise four times the resolution of existing 1080p full HD screens.

There is a strong push from leading companies such as Samsung and LG for technologies, such as organic light-emitting diodes (OLEDs), to deliver next generation screens that suit human vision better. Features of these screens include a curved, bendable design, richer colour, more dynamic range of contrast and a more natural 3D depth vision without glasses.

The world’s first curved television – the LG Curved Ultra 108-inch HD TV – guarded by LG employees after being unveiled at CES 2014.
EPA/Michael Nelson

To help usher these screens into a new era of living room, new cameras and content providers (such as Netflix) will start the race to support the 4K resolutions. Next-gen gaming consoles such as PlayStation 4 are already 4K compliant.

The biggest question, though, is how would content be distributed? Blu-ray disc is no longer seen as a future-proof media to hold ultra HD audio visual contents.

(Perhaps the keynote by networking company Cisco later in the show will address streaming 4K contents over the internet, which means new services for renting and purchasing 4K videos.)

Refresh rate will continue to be a key requirement for comfortable viewing, especially for 3D viewing. High frame rate 3D has been used in some cinemas to show the latest blockbuster movie The Hobbit in 48 frames per second (rather than the usual 24 frames per second), which, according to director Peter Jackson, delivers a better 3D experience.

A higher frame rate also shows how future cinematic experience will feel closer to home theatre, but some reviews found the experience a little too real, like “watching a daytime TV show”.

Ultra realistic, near-lifelike visual experiences will continue to push technology, and future audio speakers, ranging from sound bars, headphones and multi-speaker systems will have to keep up by delivering equally high-definition audio contents.

Bluetooth 4.0 and AptX codecs are designed to deliver better quality audio over wireless.

Wearable tech fashion from head to toe

Tim Alessi from LG Home Entertainment introduces Lifeband Touch.
EPA/Michael Nelson

An infographic by Mashable portrays how Google Glass, smart watches (or wristbands) and smartshoes can form fashionable technologies. When connected to smartphones, they will allow us to harness the power of embedded computers using natural interactions such as speech, gestures and action recorders.

These wearable gadgets have the capability to record our actions and activities to better understand our characteristics, profile and preferences to provide smarter services.

CES 2014 also unveils Netatmo’s sun tracking bracelet that helps users to track their UV exposure.

To support real-time monitoring and processing of information, many gadgets will leverage from the computing power of smartphones which are equipped with better processors, evidenced by the increasing push for 64-bit mobile processing units by Intel and NVidia.

In addition to these wearable gadgets, there is also Withing’s Aura Smart Sleeping System for analysing body activity and records information including noise, room temperature and light level to optimise a room’s lighting and sound that helps people get a good nights’ rest.

Pervasive technologies that help with daily needs are attractive, but what’s overkill? For example, a Bluetooth-enabled toothbrush to help parents monitor children’s dental health is probably not going to be awfully useful.

Driverless cars – well, almost

Cars can already be connected to smartphones, enabling drivers to use speech to control features like GPS and streaming music. Apple’s voice-activated virtual assistant Siri helped revolutionise natural interaction and will soon work with new cars.

This year CES 2014’s keynotes feature Audi’s chairman Rupert Stadler. Audi will provide a large dedicated floorspace to showcase their future of driving, with driver assistance systems ranging from adaptive cruise control to lane-keeping assistance and automated steering, making cars nearly autonomous.

Manufacturers are committed to follow regulators in enabling gradual advances, as the key objective is to bring as many benefits as possible, such as helping to prevent road accidents, and more comfortable and safe driving experience.

Drivers remain in control, while built-in sensors, cameras and radars enable the car to take over much of the actual driving task.

What do these mean to us for now?

CES 2014 brings the emphasis to natural computing. It is now assumed that technology will become pervasive, wearable fashion and embedded in most of daily activities. People will embrace new gadgets that can help to make life easier, and bring imagination and creativity to reality.

The Conversation

Dian Tjondronegoro is a member of IEEE and ACM.

This article was originally published on The Conversation.
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