Monday, December 19, 2005

Beyond just white roofs and roads

Black roofs vs. White roofs are the topic of discussion over at Worldchanging. Worldchanging has a post about the environmental value of white roofs. Three simple approaches to reducing the cooling needs are plant trees, paint roofs white, use lighter colored pavement.

Treehugger points out that just changing roofs to white could actually have a significant enough effect to cancel out the expected effect of global warming. They use a very simple model to demonstrate this, but the data is enough to warrant using a more exact model to better estimate the impact.

I have always had the idea of taking this approach one step further. What if the surface (roof or pavement) turned black when it was cold outside and white when it was hot? In the summer the surfaces would reflect solar radiation and keep the surface from heating up, saving on cooling costs. In the winter the surface would be cold and remain black, absorbing enough radiation to melt snow or ice. This is especially important for my driveway this time of year.

Since I am an idea man, I just have to suggest the idea not perform the difficult implementation task. However, I do wonder if such a surface would just equilibrate to a grey color as it heated up from cold and black or cooled down from hot and white. Such a static result would lack the dynamic adaptation to temperature to produce the desired effect.


whirdly said...

With the high costs of gas these days, I'd rather have a black roof. You would use less energy to heat your home.

Richard Koehler said...

The issue is not heating the home. It also costs a lot of money to air condition a house or office building with a black roof. Think about cooling an office building on a hot sunny summer day when it is surrounded by a +10 degree microclimate caused by the black parking lot that surrounds it.