Science Interviews


Sun, 10th Feb 2008

Rising Stars - In-Wall Wax for Comfy Climate

Matthew Richardson

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Thermal imaging of a Passive House, with a conventional building in the backgroundMatthew Richardson - Energy saving is big news.  We’re asked to turn off computers and ditch the car for buses and bikes.  Did you know that a third of the world’s energy is used in buildings, much of it on heating and air conditioning?  It takes a lot of energy to keep you at a steady 20 degrees come rain or shine.  But there’s plenty of heat and cold out there already it just tends to be at the wrong place at the wrong time.  In Cambridge we’re looking at the ways that natural ventilation can help.   Air in buildings expands when it’s heated and hot air rises, just like smoke from the tip of a cigarette.  In the theatre, for example, the heat from the audience drives an air flow.  In the lab we can use simple water models to understand where the heat goes and ways to control it to keep everyone comfy.  Sometimes it can be as simple as opening a window to draw in cold air from the outside.  Then automatic controls could slash energy use, without you even noticing.

Pannonhalma ArchabbeyMuch of natural ventilation is borrowed from history, the Romans used to build under-floor furnaces in their baths and air would rise through chimneys in the walls and out to the roof.  Using this method they could heat the baths up to 50 degrees.  Natural heat flows keep cathedrals cool at the height of summer.  Heavy stone walls take far longer to heat up and cool down so chunky buildings can protect you from extreme temperatures just as the sea protects coastal areas from extremes of winter and summer.  Nowadays though, builders often want to build frame buildings with paper-thin walls.  Here we’re experimenting with putting tiny wax capsules into walls to create a similar effect.  Wax may not be as heavy as stone but it can absorb a huge amount of energy when it melts.  If fact, a couple of kilos of melting wax absorbs the same amount of energy as it takes to boil a kettle.  By adding wax we hope to turn your house into a cathedral.

While these methods show promise understanding air flows can be complex and sometimes we’re just tempted to turn on the aircon and forget the cost.  Increasingly though, natural ventilation will have a vital role to play in maintaining the climate outside our buildings as well as comfort within.


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