19-minute listen/watch | 12-minute read
How do you keep a building comfortable without wasting energy? A Penn State team is tackling that question with an innovative smart window. Using a responsive polymer, the window can block visible light, infrared heat, or both—automatically, without sensors or electricity. The technology could dramatically reduce energy use in buildings while giving architects new freedom to design spaces that work with, rather than against, the sun.
Transcript
Patrick Mather
We like to live in buildings that are perfect temperature. And yet that comes with a cost because it's very expensive to heat or cool a building, and this stands opposed to our desire to have windows. We have a technology that will dynamically change how much light gets through, depending on how much sun is shining on it, and that will dramatically reduce the cost to keep a room or a building at a particular temperature.
Host
Welcome to Growing Impact, a podcast by the Institute of Energy and the Environment at Penn State. Each episode of Growing Impact explores the projects of Penn State researchers who are solving some of the world's most challenging energy and environmental issues. Each project has been funded by the Institute's Seed Grant Program that grows new research ideas into impactful energy and environmental solutions.
I'm your host, Kevin Sliman. In this episode, we explore a smart window that uses a polymer to block visible light, infrared light, or both, without sensors or electricity. This breakthrough could cut building energy use and inspire architects to rethink how windows shape our spaces.
Thank you all. Thank you, Nathan, Sebanti, and Pat. Thanks for coming on Growing Impact. I really appreciate you coming and discussing your project. Can each of you go around and introduce yourselves? Can you please tell us your name, your title, and provide a brief background on your research?
Nathan Keim
Sure. I'm Nathan Keim. I'm an associate professor of physics, and my research is focused on mechanical systems materials mostly, that can store and process information mechanically, like non-living, non-electronic. I'm just really fascinated by this idea of memory and information storage.
Sebanti Chattopadhyay
I'm Sebanti Chattopadhyay. I'm a postdoc in the physics department, and I work with Nathan, and we have been collaborating with Pat for over a year now. My background and research so far has been in studying how soft materials that you find in your life everyday around you — how they fill and deform when you apply forces small forces or change their temperatures, and so on.
Patrick Mather
I'm Pat Mather, I have two titles. Dean of Schreyer Honors College an undergraduate community here at Penn State. And I'm also a professor of chemical engineering and a professor of material science and engineering. My research over the years has focused on polymer science. And for those that don't know, polymers are long chain molecules. And for the past couple of decades, I've worked on an area that intersects with both Nathan and Sebanti, which is smart polymers or, in particular, shape memory polymer materials that change shape when environmentally cued to do so. So, this project that we'll be talking about fits squarely into my research interests.
Host
Fantastic. Thank you all. And thank you for that great segue, because that leads us right into our first question. So, what inspired this team to explore a polymer-based solution for smart windows? And what makes this material different from other technologies in the energy efficiency space?
Patrick Mather
I discovered quite a while back now that there was a type of polymer — a cross-linked polymer — that had an anomalous behavior relative to traditional thermal expansion. Most materials, when you heat them, they get bigger, and when you cool them, they get smaller. This material had just this... when we were testing it... type of shape memory polymer, and when we heated it at some particular temperature it dramatically shrinks.
Not only that, but it reverses when you cool it back down. At a similar temperature, it dramatically elongates so much. But with the naked eye, you see this occurring, and it's kind of like an artificial muscle, I guess you would say. But, instead of being in a human or another mammal with biochemical triggers, this is thermally triggered.
And I was always wondering, like, what could we do with this that would be useful? And so, you know, sketching on a napkin, conversations with others. And I always thought this has to have some application for optics in particular. If we could get this muscle, this shrinkage, etc., to, to cause one windowpane to shift relative to another – and we'll get into that more – I got to believe this would be useful because it intrinsically we wouldn't need a motor. We wouldn't need power. We would only need heat and windows experience heat, as soon as sun, shines on them.
Host
How does this smart polymer actually know? And I'll say, for those who are listening, know in quotation marks when to change shape and what role does temperature play in triggering its response?
Sebanti Chattopadhyay
So, this polymer that we are talking about, it's a semi-crystalline polymer. And so, it has a melting temperature. And here's the cool thing. This polymer has a melting temperature that can be engineered to be very close to the room temperatures — close to let's say 2530 degrees C. So, what happens is when we heat it up, the crystals will all melt, and due to rubber elasticity, the polymer would like to shrink.
It wants to stay in a coiled state and a shorter. That makes it go short. And the reverse happens when you start cooling it. And so, I guess I should also mention that all this is happening with the stress applied to this polymer. So, if you hold this polymer and you apply a small stretch to it, and then you start cooling it, what happens is as it crystallizes, because of the stretch, the crystals would align along that direction, and it causes an elongation in the length.
Patrick Mather
The effect is large. You can see... we're talking about like 50% increase in length. We can tune that. And that's what we would do in engineering the device. But yeah, it's the melting of the crystals. And then they're recrystallization on cooling that gives the material its "intelligence”. And because that can be tuned by the chemistry of the, the making of the polymer, that would give us a lot of versatility.
We might want a hot window or a cooler window. And this could be tuned by the exact composition of the polymer that we would utilize in the window.
Sebanti Chattopadhyay
There's something else that's relevant to this polymer, which is it can do this shape change from going short to long. It can do this for many, many cycles, which is kind of cool. So, you can keep using it. It'll not degrade very soon. It'll hold this property for long enough time to be, well, economically viable, I suppose.
Patrick Mather
You know, it's funny and you think, well, how often would it do this in a real situation? Well, you think about, you know, in the afternoon, sun hits the building from the West. It depends where this building is. And maybe that's when the office or your bedroom will get really hot. And so, then this would kick in, and then the next, as the sun would go lower, we would let the light back in because that driving force would go away.
So, it'd be on the daily, and probably we would want this to last many years. And so, what Sebanti was saying, it is absolutely critical that it go back and forth predictably one or more times a day.
Host
Can you describe the real-world impact of this technology? How might it change the way buildings are designed, renovated or operated, especially in terms of energy consumption and sustainability?
Nathan Keim
Heating and cooling is a major driver of energy consumption. It's only going to continue to rise as more people can afford air conditioning and heating, which is, you know, wonderful. But also, as the climate keeps putting more stress on buildings and people. So, this is a great place to make an impact. And we kind of want something that is really cheap, right — and that can be retrofit and that is easy to maintain and can go maybe a decade or more with almost no maintenance. And these shape memory polymer smart windows have the potential to check all those boxes.
Patrick Mather
I think design is a really important part of the question. Once this technology is available, maybe closing the loop on okay, the normal way we where we place windows in a building, how they're shaped, how they're sized, this technology could change the design process. And I would love to have architects and architectural engineers play with this capability. That might lead to a new paradigm of window design, now that that the technology would be available
Of course we would, our initial prototypes will look like a normal window, is our plan here. But once that capability rolls out, I'd love to have architects scratching their head thinking, oh, this lets me change, you know, where we put the light and ability. Maybe the current designs that we think are just normal window designs would be reimagined, and that's exciting to us. And that's why it's great to have an architectural engineer as part of the team [Julian Wang].
Sebanti Chattopadhyay
We would like the polymer to be incorporated to windows as is, with minimal changes in what window designs we have so far. So, if we can just incorporate the polymer with minimal changes, that would I guess be maybe easier to implement.
Patrick Mather
What market we enter could depend on you know, is kind of interesting. We would we would love to like spread the word about this by presenting to companies at conferences, etc... And I think the boxes that are checked as we've talked about, may put us into a particular market, particularly low cost. Nathan mentioned it's inexpensive to prepare this polymer.
Absolutely correct. And if you combine that low cost with a large scale, we can make rolls and rolls of this that could be deployed. Maybe we're talking about greenhouses, or I might be talking about rural housing. My original mind goes to skyscrapers because, you know, the economic benefit could be huge, but when the cost of the technology is so low, who knows where this will land.
But I do believe low cost will be, probably one of the most important design constraints that would favor utilization of of this new technology.
Host
You're testing two different design approaches for the windows, one that changes transparency and another that modulates infrared transmission. So, what are the key advantages or tradeoffs of each and how might their uses differ in practice?
Nathan Keim
I think for most people, modulating infrared transmission is probably what you want. And like a residence or something. Already, if you buy a pretty good window for your home, it will already be engineered to block some of the infrared and let light through. So already, you can notice that it's not quite effective, right?
It still blocks some visible. If you just open the window, things get a little brighter.
Host
So, what is the benefit to blocking infrared?
Nathan Keim
A lot of the energy that comes from the sun, is not visible as light. It is at longer wavelengths, as infrared. And that's why sunlight feels hot. And that is a major contributor to what's heating up your building. And so, blocking infrared, you know, rejecting it in the summer is something you absolutely want to try to do as much as possible.
The passive way to do it, is to make a window that blocks as much infrared as you can, while letting as much visible light through. But the sort of ideal solution is, well, there are really just a few hours a day when you really need the best performance. I think there might be other applications where you just want shade, right?
You just want to block, visible light too at some times of day if it's just too bright for a setting. I thought, you know, for maybe aesthetic reasons and, and obviously material that blocks everything, including infrared is the cheapest.
Patrick Mather
The design complexity is different for these two different scenarios, in our initial estimation. The dynamic infrared that Nathan was talking about would require us to do smaller scale back and forth motion, which we call actuation. I won't get into the details about why that's the case, but it is the case, and it would make it a little more complicated for just shading all of the light back and forth — that's from a design point of view, easier, simpler. I'd just say simpler. And so there is that tradeoff between or just difference between infrared, switching and reversible shading just as we implemented in the actuation design. But we're interested in both, so, we're going to pursue both.
Host
Looking ahead, what challenges remain before this technology could be implemented in homes or commercial buildings? And what excites you about its potential? And one more thing. Are there other areas that maybe this solution could be applied to?
Sebanti Chattopadhyay
We are not the first people who have come up with a design that uses smart material to make a smart window, but one of the challenges that these prototypes face is when you try to commercialize them, they often don't pan out. It doesn't work out. So, I guess that will also be something that we would want to keep in mind that how can we make that process better for our design?
Patrick Mather
Yeah, that's a great point, Sebanti. And I think probably just consistent with what you just said is a challenge of modifying something as so every day prevalent in our lives as a window. It's actually hard. Windows are designed to maximize the amount of glass and minimize the amount of other stuff, the frame and so forth. And we're proposing to add something to a window, which is going to take up “real estate” in the area that we would prefer to be just glass.
And so, for us, the challenge is going to be from version one to version two to version three, to take some clunky add-ons and make them thinner and narrower to the point where the consumer or the occupant of the building or the viewer of the exterior doesn't even know it's there. And that's a huge challenge. And that's a challenge we love, because it forces us to be creative geometrically with where we place things.
Host
Are there other areas where maybe you could see this technology being applied?
Patrick Mather
Interactive art is like an emerging thing that you might see at museums. If you walk around and see something that notices that you're there and I've seen a few of these really modern technologies coming out. And so, for us, we're imagining dynamic stained glass that maybe isn't there simply for minimizing energy consumption, but also for artistic value. And so, we imagine being able to work with artists and this technology to design things that change in a way that they might have artistic vision to implement.
And that would be a wonderful space. And at a place like Penn State, where we have not just physicists and engineers, we also have amazing artists. We picture working at the intersection of science and art as well.
Host
30 seconds: do you have an elevator pitch ready? Why should I invest in it or pay any attention to it?
Patrick Mather
Well, first of all, there's a problem in our society where we like to live in buildings that are perfect temperature. And yet that comes with a cost because it's very expensive to heat or cool a building. And, this stands opposed to our desire to have windows. And so, we have a technology that will dynamically change how much light gets through depending on how much sun is shining on it. And that will dramatically reduce the cost to keep a room or a building at a particular temperature.
Nathan Keim
No motors, no electronics is what I'd add.
Sebanti Chattopadhyay
A switch that operates based on the temperature outside, you don't have to do anything, just enjoy the ambient conditions inside the room.
Host
Thank you, Nathan. Thank you, Sebanti. Thank you, Pat, for coming on here and talking about this. It's really been a pleasure listening to you explain the challenges and these potential solutions. So, I appreciate your time now.
Nathan Keim
Thank you. Kevin, this is very fun, and it's really exciting to have IEE's support for this.
Sebanti Chattopadhyay
Thank you so much.
Host
This was season six, episode one of Growing Impact. Thanks to Nathan Keim, Sebanti Chattopadhyay, and Patrick Mather for joining me.
To watch a video version of this episode, and to learn more about the research team, visit iee.psu.edu/podcast. Once you're there, you'll find previous episodes, transcripts, related graphics, and so much more. Our Communications Director is Chris Komlenic, with graphic design and video production by Brenna Buck, marketing and social media by Tori Indivero, and web support by John Stabinger.
Join us next time as we continue our exploration of Penn State research and its growing impact. Thanks for listening.
