Melting buildings

According to New Scientist, phase change materials - materials that melt at around room temperature - could revolutionise the way we cool our buildings.

The sun has risen, and a new building on the University of Washington’s campus in Seattle is slowly melting. Or at least parts of the building are anyway. Encapsulated within the building’s walls and ceiling panels is a fabric specially designed for climate regulation, called a phase change material (PCM).

The material – a gel, which New Scientist reports on in its 7 January issue, melts at around room temperature, and while melting absorbs lots of energy, helping the building stay cool. At night, when the temperature drops, molecular bonds within the gel are reformed and the material thus releases heat (which can easily be dissipated by opening the windows). The material is then being ‘recharged’.

Professor Andy van den Dobbelsteen, of the climate design and sustainability section (Architecture faculty), is familiar with this technique. “The materials are not being used much yet,” he says. “A lot of research effort is being put into optimizing these kinds of materials, however. They’re still very expensive, but as developments continue prices will drop.”

The professor believes the technique is especially promising for building light-weight constructions. Regarding their thermal behaviour, PCMs are in fact a kind of light version of rock and concrete, Prof. Van den Dobbelsteen explains: “Heavy buildings, like Romanesque churches, also stay cool thanks to the materials they’re made of. Their thick walls have a high thermal mass which helps to reduce indoor temperature fluctuations. What’s interesting about PCMs is that you can regulate the temperature using a lot less material.”

PhD student, Bas Hasselaar (Architecture faculty), agrees. But he also warns that PCMs are not the panacea they’re often taken for. “These materials can only help in fine tuning the temperature,” explains the researcher, who extensively studied the materials for his thesis. “PCMs do not have very high thermal mass overall, yet during their melting trajectory their heat absorbing capacity peaks. Once the temperature has risen above that melting range, say 25 ºC, they no longer cool the building.”

Another disadvantage of PCMs is that they do not have any supporting power, says Hasselaar. Consequently, one must always encapsulate them in other building materials.

If you want to make a building in which the climate is regulated energy efficiently, you have to set your priorities differently, Hasselaar concludes: “First of all, you need good sun blinders, you must ensure the building is constructed with material that has lots of thermal mass, and you need good ventilation. When these requirements are met, then you can wind up with PCMs.”