As global temperatures reach record highs, developers of cool, energy-efficient houses are in demand. Paul Miles provides an excellent article in the Financial Times in advance of the the 20th International Passivhaus Conference that will take place on April 22 and 23 in Darmstadt, Germany.
Divine insulation: passivhaus architecture
The period between 2011 and 2015 was the warmest on record, with 2015 the warmest year of all, according to the World Meteorological Organisation. As a result, “cooling energy use” — air-conditioners and devices of similar ilk — in residential and commercial buildings will grow 84 per cent between 2010 and 2050, the Intergovernmental Panel on Climate Change predicted in 2014.
“With rising average temperatures and improved lifestyles, the demand for cooling systems in many regions can only increase,” says Christoph Frei, secretary-general of the UN’s World Energy Council. The combination of a world that is warming up and a population that wants to cool down poses an architectural quandary: how to design buildings that can maintain a comfortable temperature without consuming quantities of energy that contribute to further climate change.
Could pioneering attempts to build energy-efficient “Passivhaus” buildings in the heat and humidity of the tropics provide answers? Passivhaus, which originated in Germany in the 1990s, is the fastest-growing — and most rigorous — low-energy construction standard in the world. Until recently, most Passivhaus buildings — some 30,000 — have been constructed in temperate climates, mainly in Europe, where the emphasis is on reducing heating bills by as much as 90 per cent. Now architects are applying Passivhaus design principles in hot climates, reducing buildings’ cooling bills by a similar degree.
The Austrian Embassy in the Indonesian capital Jakarta, completed in 2011, is an early example of a Passivhaus building in the tropics. The two-storey embassy uses 85 per cent less energy per sq metre than a conventional air-conditioned office in Indonesia, report the project’s energy consultants, New Energy Consulting. Not only does the 1,035 sq metre building cost less to cool and emit less carbon than an ordinary office block, but staff say it’s more pleasant to work in. “The old embassy building was very uncomfortable [temperature- and humidity-wise],” says Michael Jan Swoboda, counsellor and consul at the embassy until 2012. “This new Passivhaus building is far better. The building, the interior humidity and the temperature are excellent. Our staff and our guests are very pleased about the comfort,” he says.
Ursula Schneider, principal architect of Vienna-based Pos Architekten, which designed the embassy, attributes the “excellent indoor climate and energy performance” to “design that respects the principles of effective sun protection”.
She explains how all windows and doors are protected from direct sunlight by porch roofs and shading screens. Double-glazed windows, providing energy insulation, have tinted glass. Even opaque walls and the roof are shaded by wooden screens.
Rather than conventional air-conditioners that blast cold air — which can be uncomfortable as well as wasteful — the building is cooled by “concrete core tempering”. Cool water passes through pipes embedded in the ceilings, which retain the coolness. Meanwhile, hot, humid air is cooled and dried before entering the airtight, insulated building. This process is powered by solar energy harnessed from panels on the roof. The interior temperature and humidity ranges between 24.5C and 25.8C and 55-70 per cent humidity compared with an exterior temperature of 28C-35C and 80-100 per cent humidity.
Further from the equator, in subtropical Asia, German architect Peter Ruge has designed what he calls “the most energy-efficient building in southern China”. The five-storey Passive House Bruck is a complex of 46 apartments in Changxing, a city west of Shanghai. According to Ruge, the building uses about 95 per cent less energy for cooling and heating than conventional builds. Completed in 2014, the scheme was commissioned by real estate developer Landsea to demonstrate the Passivhaus standard as part of a commercial drive to develop low-energy homes. It houses Landsea employees and clients wishing to experience Passivhaus life.
Meanwhile, the first project in Africa that aims to gain Passivhaus certification is currently under way in the Democratic Republic of Congo. A new, shared Dutch and Belgian Embassy building is being built in Kinshasa, four degrees south of the equator. Here, the temperature ranges from 20C-32C and humidity from 50-96 per cent; the embassy will aim for 20C-26C and 40-60 per cent.
Computer modelling suggests the 5,800 sq metre building, due for completion this year, will use 70 per cent less energy for cooling than a conventional build, says architect Sebastian Moreno-Vacca, of Belgian firm A2M. The main principles of Passivhaus — orientation with regard to the sun, airtightness and insulation — reduce the amount of energy it takes to cool the building by 50 per cent. The design also considers limited local resources. “Everything in the building is as simple as possible so that it doesn’t need much technical maintenance, which can be hard to find in Kinshasa,” explains Moreno-Vacca. “Cantilevered and vertical sun blinds are fixed in place rather than electronically operated, for example.” This has also proved economical. “Our proposal was the least expensive,” says Moreno. “The building will cost €7m to construct. Other bids were between €13m and €19m.”
Indeed, constructing a low-energy building in the tropics need not be costly, especially where local conditions work in your favour. “There are places near the equator where it’s very easy for buildings to maintain a comfortable temperature range year-round with little or no energy demand,” says Jürgen Schnieders of the Passivhaus Institut in Darmstadt. “Locations such as Mexico City or around Lake Victoria where, because of the altitude of between 1,000 and 2,000 metres, the ambient temperature is rarely too hot, day or night.”
In fact Schnieders concedes that, here, many conventional buildings would meet Passivhaus standards without trying, maintaining a comfortable interior with little or no energy needed for temperature control.
Even architects who specialise in Passivhaus design acknowledge that it is not the only blueprint for low-energy buildings near the equator. “In tropical climates, two concepts can work sustainably,” argues Pos Architekten’s Schneider. “The first is the local traditional building technique, which includes shading and natural ventilation through the building in combination with an appropriate dress code and eating or drinking habits,” she says. “If one can also divide the active working hours and relaxation times according to the climate conditions — like having a siesta and working late — this model can still work today and does not require too much technology or energy.”
“The second concept [imposes] western standards on to tropical climates, which requires a [separation] of the interior climate from the exterior,” says Schneider. “Only with an airtight shell can the interior comfort be improved efficiently.”
However, a building’s airtightness can cause problems if occupants create unexpected amounts of heat and humidity. One of the first properties in China built to Passivhaus principles, Lychee Garden, was completed in 2013. It has not been a success, admits its Australian architect, Simon Laws: “The airtightness makes it very sensitive to any heat-source inside. Boiling a saucepan will raise the temperature. In hindsight we had little hope because [the building is] used as a communal space for 10 to 15 people, often more, with people constantly wanting to cook.”
Laws has yet to be convinced that Passivhaus is appropriate for small projects such as individual homes in the tropics. Effectively lowering humidity is too expensive and complicated for most small projects, he says; the technology used to dry and cool incoming air in the Austrian Embassy in Jakarta is very technical and needs lots of solar power to run. “Somewhere above 30 degrees of latitude is where I think [the Passivhaus standard] starts making sense year-round for small projects,” says Laws. “Here the humidity is not so high, which is the main challenge in designing a Passivhaus home in the tropics.” In his opinion, in such places it’s better to “open the windows and let the outside in or turn on the solar powered air-con”.
Laws has also designed a beautiful beach property in Australia. Drew House is 24 degrees south of the equator on the Queensland coast, where the temperature and humidity are similar to Lychee Garden. Rather than using Passivhaus principles, Laws designed this beach holiday home in 2010 following the “open the windows” method. “Keeping the direct sun out of the interiors in the warmer months is the key; with plenty of air movement, large shaded sliding doors and fans are enough to completely remove the need for air-conditioning, especially at night,” he says. “Being by the sea, where there are breezes, certainly helps.”
However it is done — high-tech or low- — designing buildings to minimise the energy we use for cooling is a hot topic.