If you feel bad about cranking up the air conditioning in summer, there鈥檚 a remedy on the way to reduce the temperature and boost your green credentials at the same time.
Engineers at in Tennessee have developed a system which can be installed in your roof and attic to soak up the sun鈥檚 heat during the day and then release it back into the sky at night 鈥� keeping houses cooler.
鈥淭his could reduce the cooling bill for houses by up to 8 per cent,鈥� says Bill Miller, a member of a team testing roof and attic energy-saving systems at Oak Ridge. 鈥淲e鈥檙e able to intercept 90 per cent of the heat energy that would otherwise penetrate into the living space through the attic floor,鈥� he says. In tests, the system reduced attic temperatures on sunny afternoons by more than 5 掳C.
Advertisement
There are four components to the system, three of which form a first line of defence in the roof by reflecting heat from the upper roof material. This is achieved using reflective tile surface pigments, reflective material under the rafters and novel tile shapes that vent warm air from the roofing cavity.
But the fourth component is the most innovative, intercepting heat seeping through these first three barriers into the attic space itself. Laid in sheets above the attic floor, the material soaks up energy as it begins to melt, at around 23 掳C. Its temperature remains constant until it has all melted, which keeps the surrounding air at the same temperature too, delaying the transfer of heat from the attic into the living space below.
At night when the outside temperature drops, the material re-solidifies and the heat absorbed escapes into the atmosphere. 鈥淎s the sun goes down, all the heat of fusion is released into the night sky,鈥� says Miller. A team led by his colleague Jan Kosny has tested several of these 鈥減hase-change鈥� materials, which include paraffin wax contained in microscopic beads. Others under test are based on crystals of calcium chloride hydrate packed in pouches of aluminium foil. Some firms say 1 litre of such material can absorb as much energy as 10 litres of water.
The system could work well in combination with other green technologies, says Matthew Burgess, a spokesman for , a UK-based solar panel supplier. He says houses with rooftop solar panels could use the Oak Ridge idea to avoid wasting their green electricity on air conditioning.
