A Breath of Fresh Air: Natural Ventilation

14 October 2010 (Last Updated October 14th, 2010 18:30)

Taking advantage of natural airflow should play an important role on any green build. Chris Lo looks at four innovative buildings pushing forward this aspect of eco-friendly design.

For many buildings, especially commercial and academic structures, which accumulate heat quickly through body heat and the low hum of dozens of personal computers, regulating temperature and indoor air quality is vital to comfort and productivity.

But this requirement has to be balanced with now-established concerns for the environment and the need to incorporate energy saving aspects into building design.

The dependence on mechanical air conditioning, which has been estimated to consume one out of every five kilowatt-hours of electricity produced in the US, must play a significant role in this effort.

Although many office workers operating in hot weather can relate to the misery of A/C malfunctions, designers around the world are working to reduce our reliance on energy-intensive HVAC systems by using natural ventilation. Some incorporate cutting-edge technology, while others adapt tried-and-true design methods that have been cooling buildings for centuries. Here we list four buildings harnessing natural airflow to keep occupants cool without becoming huge refrigerators.

"Designers around the world are working to reduce our reliance on energy-intensive HVAC systems by using natural ventilation."

Westarkade Tower, Germany

Westarkade, an expansion of German state bank KfW Bankengruppe's Frankfurt headquarters, is a fine example of an ultra-modern, technology-led approach to ventilation. Opened in July 2010, the 56m skyscraper has a glass façade with openable windows, traditionally a problematic feature in tall buildings due to high wind speeds. German architecture firm Sauerbruch Hutton, the building's designer, overcame this problem by installing 180 vertical ventilation flaps on the façade to create a "pressure-ring". A rooftop weather station and dozens of sensors throughout the building feed information on temperature and pressure to the flaps, which prompts the exterior flaps to open and close accordingly, creating consistent positive pressure to keep strong winds out.

The tower's heating and cooling system uses high technology to create a comfortable environment for employees without heavy energy usage, such as heat recovery from vented air and a basement data centre, as well as geothermal heat exchangers. During the spring and autumn months, the building's intelligent control system will advise staff when to open windows to create optimal air flow. KfW are predicting that all this innovation will limit the building's energy usage to 100 kilowatt-hours per square metre per year, only a third of the consumption of the average US office, according to an article by IEEE Spectrum contributing editor Peter Fairley. Oregon-based façade specialist Mark Perepelitza extolled the building's potential to Fairley, "This building represents a new generation," said Perepelitza.

Heelis – National Trust Central Office, UK

The National Trust is a conservation charity dedicated to protecting the UK's natural spaces and historic buildings, investing over £160m annually into the country's environmental infrastructure. It is fitting then, that the organisation sought to minimise carbon emissions in its new headquarters in Swindon, dubbed Heelis in reference to the married surname of author Beatrix Potter, one of the charity's most generous benefactors.

"During the spring and autumn months, the building's intelligent control system will advise staff when to open windows to create optimal air flow."

Ventilation specialist SE Controls was tasked with maintaining comfortable temperatures for the office while keeping energy usage and carbon emissions low.

The building management system (BMS) the company came up with was based on its OSO controller, which automatically adjusts airflow based on information fed to it by hundreds of actuators placed on windows and roof vents.

If the system detects that the interior temperature has risen beyond a set level, for example, roof vents are opened to allow rising warm air to escape rather than slowly fill the office space.

The BMS also operates night time cooling, actively channelling cool night air into the space and pushing hot air out.

The result has been a feted success, saving the charity around £550,000 a year in running costs and receiving multiple awards for sustainable design, including an "excellent" rating from the BRE Environmental Assessment Method, a RIBA Sustainability Award and an innovation prize from the British Council for Offices in 2006.

A judge from the latter panel was particularly impressed by the building's natural ventilation, saying: "It is blessed with a most ingenious and successful strategy for naturally ventilating and cooling the building. Visited by the National Panel on what was one of the hottest days of the year, it was clear the strategy was a proven success."

King Abdullah University of Science and Technology, Saudi Arabia

Completed in September 2009 and spanning over 5m square feet, the campus of King Abdullah University of Science and Technology (KAUST) is the world's largest LEED (Leadership in Energy and Environmental Design) Platinum-certified project. The campus, which regularly bakes in temperatures of more than 45°C, embraces historical techniques in its design principles to maximise cooling and air quality without creating a massive carbon footprint. 

In such an unforgiving climate, creating a comfortable indoor atmosphere is a major challenge. All campus buildings at KAUST meet air quality and temperature standards set by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). Clearly, traditional air conditioning is necessary, but the University has utilised natural ventilation and heat diffusion techniques as much as possible.

In the style of traditional Arabic cities, the campus is compressed into as small a space as possible to minimise exposure to the sun and reduce walking distances between buildings. The campus also drew inspiration from souks (Arabic marketplaces) and Bedouin tents to create shaded spaces with natural flows of circulation to create breezes. This traditional approach is also complemented by solar-powered wind towers that produce energy to create airflow in the campus walkways.

"The campus drew inspiration from souks and Bedouin tents to create shaded spaces with natural flows of circulation to create breezes."

Aldo Leopold Legacy Center, US

The Aldo Leopold Legacy Center, headquarters of US conservation organisation the Aldo Leopold Foundation. The building, located in Baraboo, Wisconsin, was conceived as both a central office for the organisation and a beacon of minimalist, environmentally sustainable design. On its completion in April 2007, it succeeded in both of those goals, with the highest LEED Platinum rating of any building built up to that time (61 out of 69 points awarded).

Insulation and ventilation contractor Thermal Energy System Specialists worked hard to build features into the building that would reduce energy-intensive ventilation.

The main building is air-conditioned by drawing outside air into the building through earth ducts, which use the stable ground temperature to warm up air in the winter and cool it down in the summer. Interior thermal loads are then regulated by radiant floors that are heated in the winter and cooled in the summer by connected ground-source heat pumps.

These kinds of energy saving techniques, along with the building's production of solar energy through photovoltaic solar panels on the roof, mean that the Aldo Leopold Legacy Center uses 70% less energy than a typical building of comparable size. Solar energy production also accounts for what little energy is used, making the centre a carbon-neutral (or better) operation. When the building received its LEED certification, US Green Building Council president Rick Fedrizzi emphasised the forward-thinking nature of the project: "This building does things that people are dreaming about," he said. "There are people out there saying, 'Somehow, somewhere, a building will be able to do that.' This building is doing it today."