Eric Schuldenfrei pushes a button and sends plumes of white smoke through a floor of public housing. It rushes through corridors, spilling into bedrooms and living rooms before spilling out windows into the warm spring air.
This is not a real housing estate, of course – it’s a scale model depicting a cutaway view of a floor in a Y-shaped tower. And it’s not in Hong Kong but 9,100 kilometres away in Venice, where the official Hong Kong exhibition at the Biennale of Architecture is presenting 33 projects that examine the quintessential elements of Hong Kong’s built environment.
Among them is Schuldenfrei’s project “Airflow Archetypes: Visualizing Ventilation Phenomena in Hong Kong’s Public Buildings.” It’s part of an ongoing initiative to understand air quality and ventilation in the densely-packed living quarters of Hong Kong public housing, whose towers are home to just over 45 percent of the population. The smoke machine is a fun visual representation of how the wind flows through a building, providing fresh air and cooling rooms without the need for air conditioning. In real life, Schuldenfrei and his colleagues at the University of Hong Kong, where he is an associate professor in the Faculty of Architecture, use small, mobile sensors to analyse air flow. “We’ve been scaling up,” he says. “We can have up to 150 sensors at a time now.”
Most of Hong Kong’s public housing estates consist of several different types of buildings that are replicated over and over – a cost-effective way of providing a large amount of housing. There are cruciform towers, Y-shaped towers, square-shaped towers with central courtyards and more. Because the same building type is repeated in many different estates, it’s possible to study how they perform in different locations: in the middle of an estate versus its periphery, on a mountainside or in a low-lying valley, next to the sea or deep inland. “The questions we’re asking are, what is the optimal design?” says Schuldenfrei. “And beyond that, what is the optimal placement?”
Answering these questions could improve the quality of life of millions of people in the densely-packed vertical cityscape of Hong Kong. And in a city that is increasingly hot and ever more reliant on air conditioning, better natural ventilation could have a significant environmental impact, too, by reducing the need for climate control that consumes enormous amounts of energy, much of it produced by burning coal.
Schuldenfrei says the project has implications beyond Hong Kong, too. Asia and Africa are rapidly urbanising. “And most of those moving to cities aren’t wealthy,” he says. They’ll need low-cost places to live like Hong Kong’s public housing estates. And ideally, it won’t just be affordable housing: it will be healthy and comfortable too.
Stagnant air in a stifling city
Air flow has been a concern since Hong Kong’s earliest days as a city. When journalist George Wingrove Cooke visited in 1857, he wryly noted that the British had built their settlement on the wrong side of the island: in the sweltering summer months, the Peak blocked the prevailing southerly wind, turning the jam-packed streets of what was then known as Victoria City into fetid canyons of stagnant air.
“The climate of Hongkong has not presented itself to me with a pleasant aspect,” writes Cooke in his 1858 book China. “The city of Victoria is on the wrong side of the sugar-loaf. That Victoria Peak shuts out the south-west monsoon which blows in grateful breezes upon the southern coast; the heat, therefore, is a stagnant, up and down, fierce, often reflected heat — a heat there is no escaping — which finds you out in your hiding-place on a shady verandah, and shoots across from the white face of the opposite house, or up from the surface of the white road, or down at an obtuse angle from the dark cliff of decomposing granite.”
Summer had only just begun; things would get worse in August, Cooke was warned. He noted with approval that Macau did not share Hong Kong’s insufferable climate. Not only was the Portuguese colony open to the southerly breeze, its many leafy plazas and gardens offered a respite from the heat. Hong Kong, by contrast, was engineered to extract as much value out of its limited land area as possible. As early as the 1840s, “houses were thus erected with the object of providing as much living space as possible, as cheaply as possible,” noted longtime Hong Kong urban planner Edward George Pryor in a historical review of the city’s housing conditions. Unless you had access to the fresh air of the Mid-Levels or the Peak — or even a building with a verandah, like Cooke — you were probably squeezed into a squalid, airless tenement on a narrow street.
Airflow was rarely a concern as Hong Kong developed through the 20th century. After World War II, the urban environment grew ever denser, the buildings ever more massive. With its many mountains and extensive shoreline, Hong Kong is naturally predisposed to having a plethora of microclimates. The increasingly dense and vertical nature of its cityscape added another layer of artificial topography to the already complex natural one. Not only has urban development made Hong Kong hotter — especially at night — it has made it up to 67 percent less windy at street level. Between 1968 and 2005, according to the Hong Kong Observatory, average wind speeds in urban areas dropped by 0.57 metres per second every decade. In the heart of Kowloon, the average wind speed is a paltry 7.1 kilometres per hour: barely enough to ruffle a feather.
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- Heng On Estate. Photo by See Ming Lee
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- “Airflow Archetypes” in Venice
The wall effect
The SARS epidemic of 2003 finally raised public awareness about the importance of good natural ventilation. And it highlighted how many parts of Hong Kong had been deprived of the wind. Around the turn of the 21st century, a new crop of private housing estates emerged with towers so tightly packed, they cut off ventilation to the neighbourhoods around them – like a wall.
“Wall effect buildings are ruining the health of our citizens,” declared environmental activist Roy Tam in 2007. His concern group, Green Sense, had conducted a study of 138 newly-developed private housing estates and found that 104 of them contributed to the so-called wall effect. In an editorial for the South China Morning Post, Tam noted that the wall of private housing estates built on the reclaimed waterfront of Tai Kok Tsui in the early 2000s had restricted airflow in the old neighbourhood beyond the towers. Residents there reported higher rates of respiratory illness since the new buildings had been completed.
Subsequent research confirmed the impact of the wall effect: one study published in 2011 found that high-rise waterfront buildings could reduce inland air flow by as much as 76 percent. The Planning Department issued voluntary guidelines for ventilation in new developments in 2005, but it was the public and media outcry in the late 2000s that seems to have made the biggest difference: many new developments now undergo a ventilation assessment as part of their design process.
Incidentally, the so-called “dragon gates” found in a number of high-rise buildings weren’t a response to concerns about ventilation – at least not originally. These distinctive openings made their debut in 1986 with the construction of The Repulse Bay, an upmarket residential tower built on the site of the landmark mansion Eucliffe. In 2018, its developer told CNN that the hole had been conceived purely as an aesthetic device — a way to make the building stand out — but a certain mythology had developed around it, claiming that it was to enable dragon spirits to pass through the building in order to improve its feng shui.
Feng shui master Raymond Lo has debunked the claim, telling The Guardian “this is nothing to do with feng shui.” But the opening sparked a trend, with dragon gates appearing in a number of Hong Kong buildings, notably The Arch in West Kowloon and Bel-Air in Cyberport. In most cases, improving air flow seems like a happy byproduct of the openings, although in the case of Causeway Bay shopping and office complex Hysan Place, several sky gardens were designed to mitigate the tower’s wall effect on the adjacent low-rise neighbourhood.
Facing the wind
For all the talk about the wall effect, dragon gates and urban airflow, there still isn’t much data on the relationship between specific buildings and the wind. That’s what Schuldenfrei and his team hope to change. So far, they have performed a statistical analysis of all 2,635 Hong Kong Housing Authority buildings, and this summer they will put scale models of seven common building types in a wind tunnel to see how they perform.
They’ve already been able to draw some conclusions from their research. “Overall building shape greatly impacts the wind flow around and through the buildings,” says Schuldenfrei. He says the best performers are Y-shaped towers, also known as Trident blocks, which were mostly built between 1984 and 1992. “This has an impact on both the residents within those buildings — since they have better airflow into their flat — and on the airflow arriving to the neighbouring buildings, since the shape allows the air to flow around the building more effectively and to be able to reach the neighbouring buildings.”
Schuldenfrei hopes his low-cost sensors could one day become a standard tool used to measure ventilation in buildings throughout Hong Kong. And when he finishes his research, he hopes it will change the way the city develops. “The intent is to inform planning policy, as it could significantly improve the airflow for Hong Kong,” he says – a breath of fresh air in an increasingly stuffy city.