The heat is on: Could next-gen building materials eliminate HVAC?
The heat is on: Could next-gen building materials eliminate HVAC?
Smart-building materials have come a long way in the last decade: They're less toxic, more durable and more energy efficient than their predecessors. But the smartest materials available today still can't accomplish something that even the most primitive life forms can do -- keep their internal environment stable as outside conditions change.
It's called homeostasis. Healthy humans, for example, maintain body heat of about 98.6 degrees as outside temperatures vary, manage their oxygen and carbon-dioxide levels and also keep their blood pressures, salt and sugar contents from falling too low or climbing too high. Even amoebas maintain their osmotic pressure at a livable rate. And cells in all living organisms manage their levels of ATP, the substance that enables the production and flow of energy internally from one set of biochemical reactions to another.
"If you look at living organisms, one of the most basic things they can all do is regulate their own internal conditions," says Ximin He, a post-doctorate fellow at the Harvard School of Engineering and Applied Science and the Hansjorg Wyss Institute for Biologically Inspired Engineering. "It's how organisms survive in different seasons and face the constant challenges life throws at them," she says.
Now researchers at Harvard University and the University of Pittsburgh -- including He -- hope to create a new class of materials that can do the same thing. After about two years of research, the scientists have come up with a platform for creating materials that can self-regulate many different factors, including temperature, light, pressure or pH balance. And they've already invented one prototype: a thin water-based gel, or hydrogel, that automatically heats up when it's cold (and stops heating when it isn't) to maintain a constant temperature.
The research, unveiled in Nature in July, could have huge implications for smart buildings. If future building materials could control their own temperatures, they might be able to eliminate the need for air conditioning and heating. Given that buildings account for nearly 39 percent of the U.S. energy use -- and heating, ventilation and air conditioning make up 64 percent of that 39 percent -- such a feat could significantly cut energy consumption and greenhouse-gas emissions.
It could also win these materials a piece of the booming sustainable-building market. Santa Monica, Calif.-based research firm IBISWorld expects the U.S. market will total $20.6 billion this year, up 7.3 percent from 2007, and reach $45.2 billion in five years.
Targeting corporate buildings
If self-regulating materials can truly deliver significant energy savings at a competitive cost, they have "great potential" to revolutionize the market for sustainable industrial and commercial buildings, said Deonta Smith, a construction and infrastructure analyst at IBISWorld. "It's a pretty innovative technology; pretty amazing," he says.
Cost will be a key factor determining whether self-regulating materials fulfill their potential. That could present a challenge, considering that new technologies usually cost more, Smith says. But if, aside from cutting energy bills, these materials can eliminate the cost of installing heating and air-conditioning ductwork and give companies more usable space in a building, they may be able to justify higher prices, he adds. "If it makes sense financially compared to other sustainable materials, then companies would be open to putting it in new construction," he says.
Even at the right price, though, these materials will still have plenty to prove. One of the biggest concerns will be how long they hold up, Smith says. Materials' lifespans -- or durability -- and reliability are critical to calculating their depreciation and total cost over time. As Smith puts it, "If it lasts a year and you have to keep changing it, it might not be cost-efficient." LEED certification would go a long way toward winning credibility with architects and contractors, he added.
If these materials do prove cost efficient, durable and sustainable, Smith predicts big corporations will be their first commercial customers. After that, he thinks the materials also could find a big market in new condos and apartments. But he expects the earliest adopter will be Uncle Sam. If the government tries the technology on federal buildings and finds that it cuts utility bills and lasts a long time, it could choose to introduce it into the private sector with a tax credit or other incentives, Smith says.
Moving out of the labs
Before getting in with Uncle Sam, though, self-sustaining materials first need to get out of the lab. They're only in early development now, and He estimates the heating gel remains at least three to four years away from becoming a market-ready product, such as windows or insulation. Still, she thinks the technology has a good chance of getting licensed.
Making the hydrogel is actually a "pretty simple" process that doesn't require costly equipment, she said. "We imagine it will not be difficult to scale up, make the first commercial prototype and optimize it into real industrialized fabrication," she said. "We think it should be really promising and not taking very long."
She admits that challenges exist. Making a material that can control its temperature in a lab is a far cry from making the material work the same way on a building. "In the lab, at a small scale, you don't have to consider the outside environment very much," He said. "In the window of a building, you need to consider the sunlight, wind and other very harsh conditions out of the lab. We'll have to find ways to protect [these materials] and make them sturdy enough."
Learning from the living
Even in a lab, of course, making a self-regulating material is no small feat. How did the scientists do it? Inspired by the feedback loops organisms use to maintain their internal environments, they've strung together a series of actions and reactions that interconnect like pieces of a Rube Goldberg machine. Instead of making a contraption that might start with, say, knocking over a domino and end with hammering in a nail, researchers have tied up mechanical and chemical reactions so that each responds to the other in an endless loop.
The hydrogel, for example, is made of two separate layers. The lower layer contains tiny hair-like microstructures made of a material that automatically swells -- causing them to stand up -- when the temperature drops below a set point. When that happens, the tips deliver a substance from that lower layer to the top layer, setting off a chemical reaction that creates heat. As the temperature rises, the microstructures lie back down, ending the heat-creating reaction.
This concept could work with a broad range of heat-producing chemical reactions, giving developers the flexibility to choose the reactions -- and chemicals -- that make the most sense for various applications. It seems the scientific possibilities are, well, if not endless, then only limited by what chemical reactions can accomplish. "This design can serve as a blueprint for a whole generation of self-regulating materials," He said.
She expects the lab will produce other materials with different abilities -- such as keeping cool when outside temperatures rise, creating light when darkness falls or maintaining specific pH or glucose levels -- in the next year. That could lead to all kinds of potential applications beyond temperature control in buildings.
Imagine materials that could help keep electronics cool without fans or other external cooling; that could enable biomedical devices -- many of which require specific pH levels, temperatures or other conditions -- to work in places they can't be used today, potentially helping far more people; and that could help purify water, such as in -- perhaps -- a self-cleaning water bottle. Those are just a few of the ideas that He envisions. "We have a lot of follow-up research to do," she said.