Reflective and insulative paints developed at Stanford University for cars and homes can reduce energy use.
Painting buildings white to keep them cool in hot climates is nothing new. Look no further than the Greek island of Santorini, with its stark — and picturesque — dwellings. The science behind it is simple: lighter colors reflect heat — or, more accurately, infrared light from the sun — while darker colors absorb it. But a team of scientists at Stanford University has invented a new type of paint that can be almost any color and still help buildings both stay cooler in summer and warmer in winter. Their invention has the potential to dramatically reduce the energy needed to heat and cool homes and commercial buildings, which accounts for almost twenty-five percent of the world’s annual energy use. The paints could help make a dent in global greenhouse gas emissions, roughly eleven percent of which are estimated to stem from the climate control of the places where people live, work, and play.
“For both heating and air conditioning, we must reduce energy and emissions globally to meet our zero-emissions goals,” said Yi Cui, the director of both the Precourt Institute for Energy and the Sustainability Accelerator at the Stanford Doerr School of Sustainability, and the senior author of a research paper that describes the development of the new paint. “How to reduce heat exchange between human living and work spaces and their surroundings is getting more attention, and new materials for enhanced insulation — like low-emissivity films for windows — are in demand.”
The Stanford team’s special paint consists of two layers. The lower layer contains aluminum flakes that reflect infrared light. Once it’s been sprayed onto a surface and has dried, it’s time for the second layer. This coat is super-thin, transparent (but can be colored), and contains inorganic nanoparticles that help reflect near-infrared light. This layer further boosts the paint’s cooling properties.
These paints could be used on the walls and roofs of buildings in hot climates; roughly eighty percent of the infrared light coming from the sun would reflect off the paint and would not be absorbed by the building as heat. If used on interior walls, the paint could serve as an insulative barrier and help keep a house cozy in winter by reflecting warmth into the room instead of letting the wall absorb the heat.
According to a Stanford media release, during tests in the lab, the paints “reduced the energy needed for cooling by almost twenty-one percent in artificial warm conditions. In simulations of a typical mid-rise apartment building in different climate zones across the United States, with the new paint on exterior walls and roofs, total heating, ventilation, and air conditioning energy use declined 7.4 percent over the course of a year.”
The scientists say that their reflective and insulative paint could also be used to keep cars and trucks cool. The biggest vehicular winners would be owners of trucks and trains that carry refrigerated goods – so-called “reefer trucks.” Keeping goods cool can gobble up as much as half of a transportation budget. If painting the trailer of an eighteen-wheeler that hauls fruit or ice cream will cut the long-haul refrigeration costs, a trucking company will probably do it.
But as promising as it sounds, the Stanford paint isn’t yet ready for prime (pun intended!) time.
“Our team continues to work on refining the paint formulations for practical applications,” said another of the study’s authors, Jian-Cheng Lai. “For example, water-based solutions would be more environmentally friendly than the organic solvents we used. That could facilitate the commercialization of the paints.”