Thursday, 9 June 2016

Passivhaus in the tropics?

Ultra-energy-efficient passive houses seem to work in cold climates. What about the tropics?

I was reminded about Passive Houses when I attended a talk at a recent Grand Designs Live exhibition by Janet Cotterell, an architect and author of The Passivhaus Handbook. The term Passive House, or to use the original German term, Passivhaus, refers to a standard for energy efficiency in a building. In a Passivhaus, very little energy is required to keep the interior at a comfortable temperature. Without getting into too much detail, this is achieved by making the building well insulated and airtight, with a ventilation system in which the incoming air is warmed or cooled. The system is so efficient that a Passivhaus dwelling does not require conventional radiators.

The concept originated in Germany in 1988, and the first Passivhaus buildings were constructed in Darmstadt in 1991. Since then the idea has spread, and although the majority of Passivhaus buildings are in Germany and Scandinavia, they have been built in other countries, including the UK. Most of these are relatively cold countries, where the main emphasis is on keeping warm in the winter. It is said that the concept can be applied to hot climates as well, but I did wonder how this might work in the tropics, in countries like Malaysia and Singapore, where it's hot and humid in the day, and not much cooler at night.

In a cold climate, insulating a house and making it airtight to eliminate draughts will keep it warm. Keeping a building cool in the tropics, on the other hand, traditionally involves providing shade from the sun to minimise heating, and ventilation to allow cross breezes to cool the rooms. Even then it often gets uncomfortably hot and stuffy. Fans help a bit, but these days air conditioning is used more and more, sometimes permanently, and at other times selectively.

There are several problems with air conditioning. It’s very energy-intensive, and it generates heat, which is radiated into the surrounding area outside. If a room is designed with air conditioning in mind, then this often results in poorer ventilation when the air conditioning is turned off and the windows are opened. This is the case with sliding windows in which the entire aperture cannot be opened fully, since part of it is always obstructed by a glass panel.

Traditional houses in that part of the world, with their open verandahs, slatted windows, and numerous wall apertures for ventilation are often not suitable for air conditioning without modifications. When air conditioning is installed, the openings are usually sealed off with glass, which prevents natural ventilation. I find that rather unfortunate.

I discovered one example of Passivhaus construction in the tropics. This is the Austrian Embassy in Jakarta, by Vienna-based Pos Architekten, completed in 2011

Here, thermal gain is reduced by a predominantly north-south window orientation, and by overhanging roofs and wooden screens. The building is air tight and thermally insulated, and instead of conventional air conditioning, it is cooled by “concrete core tempering”, in which cool water flows through pipes embedded in the concrete ceilings. Inside, the temperature is 24.5C–25.8C and the humidity is 55%-70%, while outside it’s 28C–35C, with a humidity of 80%-100%.

A different approach is adopted by Jason Pomeroy of Pomeroy Studio in Singapore, who built the first zero-carbon house in South East Asia in 2011. This is the Idea House, a prototype residence on the outskirts of Kuala Lumpur in Malaysia. The house uses the principles embodied in the traditional Malay kampong house, with deep overhanging roofs to provide shade. The house is oriented north-south with a narrow plan to minimise solar heat gain, and uses photovoltaic cells on the roof for energy production.

The principles are explained by the architect in this video:

He then built the B House in Singapore, completed in 2015 and named for its owner Belinda Young, utilising similar principles. The house generates more energy that the inhabitants are likely to use, and it is said that the temperature indoors is around 24C without the use of air conditioning.

While the Austrian Embassy in Jakarta is built according to Passivhaus principles, relying on an airtight insulated structure that is efficiently cooled and artificially ventilated, the Idea House and B House rely on natural ventilation, allowing the breeze to flow through. The Passivhaus standard seems like a technically complex and expensive way to build in the tropics. Ursula Schneider, the principal architect of Pos Architekten concedes that it “imposes western standards on to tropical climates and requires a separation of the interior climate from the exterior”, which is to me not the best way to go about things, and probably not one that can be extended beyond a few high end projects. It seems to me that encouraging natural ventilation and allowing breezes to blow through is preferable, and an approach that is more likely to be applicable on a wide scale.

In my opinion, of the problems in the tropics is, as Schneider has mentioned, the imposition of western, or temperate, climatic standards. Pos Architeckten’s picture of the embassy in Jakarta shows the men dressed as though they are in Vienna. Suits and ties make no sense whatsoever in that climate.

I have found that public buildings in Singapore are often excessively chilly, and I think that this level of air conditioning results to a sort of de-acclimatisation, in which the natural environment outdoors feels more uncomfortable than it ought to. To me, 24C is a comfortable temperature for a house in the tropics, especially with a gentle breeze blowing, but the author of the New York Times article about the B House (ref below) seemed to be suggesting that it was a little too warm. Perhaps she had come from a chilly air conditioned hotel in a chilly air conditioned car.

It is good to see architects and engineers working to design energy efficient buildings which provide a comfortable internal environment in hot and humid regions, but I think it's also important for the people in those countries to dress appropriately for the climate. The heat and humidity in these places is challenging enough as it is.

Links / references:

Divine insulation: passivhaus architecture
Paul Miles. 8 April 2016 Financial Times

In Singapore, a Home That’s Naturally Green
Jane A Peterson. 31 March 2016 New York Times

Pos Architekten

Pomeroy Studio

Passive House Institute

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