Saving energy on site, part 2

Our cool building

This post is part of a series on CSIRO Newcastle’s energy-efficient office buildings. Read all the posts in the series here.

There’s a style of house that’s so common in the hotter, north eastern parts of Australia that it’s know as the ‘Queenslander’. It’s usually built on piers so cooling air can pass underneath, and has wide verandahs and awnings to keep out the hot summer sun. These old styles of house often keep themselves cool without the owner needing to use air-conditioning.

An example of a 'Queenslander' house (source: Wikimedia Commons)

This sort of clever building design was, until recently, par for the course. Designs that promoted cross-ventilation and shading were simply a necessity in warm climates. It was also possible to take things a step further – some grander residences enhanced the cooling effect by putting their houses on top of a smooth slope, behind a fountain. The warm air rising up the slope would create a constant breeze that would be cooled by the fountain before passing through the house. If this were designed today it would be considered an example of brilliant, modern, sustainable (not to mention rather flashy) architecture – but before the days of cheap air con it was simply sound design.

The mansion in the Park de Sceaux, near Paris, was air-conditioned simply by the clever placement of a slope and a fountain. The fountain was operated by the pressure of the water source on top of the hill.

Nowadays architects and engineers are resurrecting some of these ‘forgotten’ ideas when designing new buildings. This was the case when our buildings at CSIRO in Newcastle were being designed around ten years ago. Since most of the energy used in a typical office building is for heating, cooling and lighting, a lot of attention was paid to these areas. Many of the solutions (as you may have come to expect) are driven by the sun.

Firstly, cooling. As any sportsperson knows, evaporation is an efficient way to cool down – it’s why our bodies sweat. This is also the same principle that makes the fountain at Sceaux cool the air. At CSIRO we get the same effect by using plants.

Through the process of transpiration, leaves lose water vapour which cools them and the air around them. We have a rich leafy-green garden in the partly-shaded area between our lab and office buildings that helps cool the air in this way. In addition, there’s a cavity space under the office building where the air naturally stays at about 18°C all year around. Together these give us the first ingredient for natural air-conditioning: a source of cool air.

Computer image (left) and photo (right) of our garden atrium and where it's located.

The second ingredient is a way to get this air into the building. This part is easy: we have office windows that open, and ducts that draw the air up from under the building.

But something else is needed, and that’s a way to encourage this cool air to flow into the building and displace the warm air. This is where our stairwells come into play. They are essentially north-facing, glass-fronted columns designed to let the sun heat the air inside them. The warm air then rises up these ‘solar chimneys’ and passes out through vents in the roof. As this air leaves the building it pulls new, cooler, air in through the windows. This creates a stream of naturally cooled air through the workspace.

Left: air in the north-facing stairwell is heated by the sun and rises out of the rooftop vents. Cool air is drawn through the building to take its place (right).

When the windows are open and a cool breeze is passing through, we say the building is in ‘natural ventilation’ mode. This can save our building about 100 kW of power usage in the middle of the day, reducing our total site energy usage by up to a quarter at times.

A graph of power supplied to CSIRO Newcastle over a day. The red curve shows the office building in 'natural ventilation' mode; blue shows power on a similar day when air-conditioning was active. The difference indicates significant energy savings from natural ventilation.

One of the most basic design features for keeping a building cool in summer and warm in winter is the use of eaves over the north-facing windows (or south-facing, if you’re in the northern hemisphere). In summer when the sun’s higher in the sky the offices are shaded, and in the winter when the sun’s lower, some of the light angles in under the eaves to help keep things warm. Our eaves are as simple and inexpensive as wooden boards painted white and fixed over the windows.

Eaves provide shading on the north side of the offices.

These eaves, though, are more multi-purpose than your average white plank. You’ll notice they’re in pairs, with one at the top of the window and another a third of the way down. We call the lower ones ‘light shelves’ and they also help us maximise natural light in the offices. The white paint reflects sunlight into the building and up onto the ceiling, where it scatters down into the room in a diffuse glow, saving the need for some electrical lighting during the day.

The eaves (shown in right hand photo) do more than your average wooden board. The drawing at left shows how in addition to providing shade from direct light, they also reflect diffuse light onto the ceiling and into the room.

You’ll notice that these energy savings for cooling and lighting don’t require any gizmos more high-tech than a leafy plant and a plank. The benefit comes from just putting all the elements of a normal office building in the right arrangement. Our building engineers tell me that for this reason, our energy-efficent building costs no more than a standard office block – and it ends up saving energy and money.

Of course, we like gizmos as much as any other research organisation, and we use them to reduce energy too. More about them in the next post.

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