A cooling paint that could easily deliver buildings a significant temperature drop could help cut down on expensive air-conditioning, one research team is suggesting. The light-reflecting material gives ancient advice to paint buildings white in order to reflect away heat a high-tech upgrade.
Just like wearing a white shirt on a hot day can keep you cooler than wearing a dark shirt, so the same goes for building finishes in sunny climates. You may not necessarily understand the theory behind it, but you’ll almost certainly be aware of the repercussions. The white reflects away the heat energy, while the black absorbs it and thus warms the building.
The new paint was developed by applied physicists at Columbia University, based on earlier work integrating light-reflecting particles into other materials. The team, led by Yuan Yang and Nanfang Yu of the Materials, Energy & Environment group, discovered a way to create tiny pockets of interconnected air voids by using a fairly straightforward polymer and some special treatment.
First, they mix the polymer – known as PVDF-HFP, or Poly(vinylidene fluoride-co-hexafluoropropylene), and typically used for wire and cable coatings, corrosion-resistant tubing, or lining pipes and tanks – with acetone and water. When applied to a surface, the acetone evaporates and then the polymer separates from the water. As the droplets of water then evaporates, the space they occupied forms the network of gaps.
Painted onto a building, the new material stayed around 6 degrees Centigrade cooler than the surrounding air, according to a research paper published this week. Indeed, the “voids” the water droplets leave behind after evaporating can reflect up to 99.6-percent of light, the researchers found, across the IR, visible, and UV spectrums.
It’s not the first highly-reflective material that has been suggested as a way to passively cool buildings. Previous efforts have led to even more efficient materials, including embedded tiny beads of glass into plastic films, which can deliver up to 10 degrees Centigrade of cooling. What sets this particular paint apart, however, is its durability and ease of application.
Although commercial efforts with prior research is underway, this new passive cooling paint is straightforward to apply and – though it will reduce its efficacy – can be dyed, too. Though likely to be more expensive than regular exterior paint, the longer-term implications of being able to rely less on active cooling technologies like air conditioning could offset that upfront cost, too.