The Window Sticker That Cuts Your Electricity Bill By 10%

A heat-blocking film that you can stick on your windows could replace the humble air conditioner.

Scientists say the see through material keeps out 70 per cent of the sun’s rays and automatically gets darker as temperatures rise to reject more heat on hotter days.

The team claims that if every exterior-facing window on your house were covered in this film, the building’s air conditioning costs could drop by 10 per cent.

In the US, it’s estimated that air conditioners use around six per cent of all electricity.

This costs $29 billion (£22 billion) annually – an expense that’s expected to grow as thermostats climb with global warming.

Researchers at the Massachusetts Institute of Technology (MIT) developed the heat-reflecting film.

It shrinks and becomes opaque when exposed to temperatures of 32C (89F) or higher.

Below 32C the film is fully transparent and does not reflect heat.

It is hoped that the material can be produced for homes and businesses to use on windows during summer month heatwaves.

In a trial, engineers applied a solution of the heat-shielding substance between two sheets of 12-by-12-inch glass to create a film-coated window.

They shone light onto the window to mimic incoming sunlight.

The film turned frosty in response to the heat, reflecting 70 per cent of the heat produced by the lamp.

The polymer material is thermochromic and will temporarily change phase or color in response to heat.

MIT Professor Nicholas Fang says the material provides an affordable and energy-efficient alternative to existing smart window technologies.

Prof Fang said: ‘We thought there might be room for new optical materials and coatings to provide better smart window options.

‘Smart windows on the market currently are either not very efficient in rejecting heat from the sun, or they may need more power to drive them, so you would be paying to basically turn windows opaque.

‘Meeting this challenge is critical for a metropolitan areas like Hong Kong, where they are under a strict deadline for energy savings.’

The research was published in the journal Joule.