Smart Window idea

The problem

At latitudes where summer cooling and winter heating systems are installed in buildings, we are not making the most of solar gain.  That means right now there’s free heat being wasted.  We need to reduce the energy used for both heating in winter and cooling in summer.

I was working for an eco-house company and we had a dilemma selecting low-e films for the high-spec double-glazed windows.  Do you let the sun’s energy in, for more free heat?  Or protect the inside from infrared, to prevent overheating?  Passivhaus designs tend to have lots of south-facing (in the northern hemisphere) windows; triple-glazed, with low-e films that let a lot of IR pass through, but always with a brise-soleil outside, overhanging the window.   This way the sunlight can only enter the building when the sun’s fairly low in the sky.   But, a brise-soleil isn’t practical for a lot of buildings, so I started thinking about how the same principle might work within a window…

The idea

The earth’s angle of tilt is around 23.5 degrees, relative to the sun.  So, here in the south of the UK, where the sun only gets to around 15 degrees above the horizon at midday in mid-winter, it’s up at about 62 degrees (that’s double the angle of axial tilt higher) in midsummer.   Anywhere in the world this difference in the sun’s maximum angle of elevation will be the same: About 47 degrees between winter and summer, although the starting point depends on your latitude.  We can exploit this difference to give us variable shading.

By using infrared-reflecting strips in layers, on multiple sheets of glass (or miniaturised onto thinner films) with the right geometry  we can ‘shade’ the inside of a building from the sun at high angles, but still let most of the heat through when it’s low in the sky.  All done within the plane of the window.  Like this:

What next?

This one is patent applied for and now needs to be prototyped and developed.  I’m looking for

  • Collaborators – especially people or companies who know about window films, or coatings.
  • Sources of or ideas for funding or investment

Please contact me if you’d like to get involved!