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The World's Coolest T-Shirt

Materials engineer Po-Chun Hsu is developing textiles that heat and cool at the personal level—a scaled-back approach to climate control that could help curb emissions in the U.S.

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M. Volborth: This is Rate of Change, a podcast from Duke Engineering dedicated to the ingenious ways that engineers are solving society's toughest problems. I'm Miranda Volborth.

M. Volborth: To tackle the really huge issues facing human civilization; climate change, disease, poverty, you have to be able to venture outside the established parameters, try different approaches, search out new paths. You have to be a bit of a rebel.

M. Volborth: Po-Chun Hsu isn't who you probably imagined when you think "rebel." He has short, hair-colored hair, nice shoes and no visible tattoos. But Po-Chun, at the age of 18, did something so crazy and so different from what was expected of him, that it made him kind of famous in his native Taiwan.

Po-Chun Hsu: Yeah, of course as a high schooler you are curious about everything. And what interested me the most ... that was sneakers. I remember there was a pair which has like a very beautifully special iridescent color, and I couldn't help but wondering what that was. What's the material inside?

M. Volborth: Do you still have those sneakers?

Po-Chun Hsu: No.

M. Volborth: It was that bewitching pair of holographic sneakers that set Po-Chun on on his path to rebellion.

Po-Chun Hsu: In Taiwan we have the so-called "entrance exam," which is kind of like SAT in the US. You take the test, get a score and apply for schools based on the scores, your GPA and other stuff. In Taiwan it's a department who gives the admission, not the university. So that means the high schooler really need to decide the major before entering the college. But most people just use their scores to apply to whatever school has the highest score threshold. So for me, I knew I liked material science very much, so I just decided to go straight to do that.

M. Volborth: Po-Chun will not say this outright, but he was the top student in his graduating year nationally. And he chose to go into materials science even though he would have been admitted to departments with higher thresholds, like medicine or electrical engineering.

M. Volborth: Pursuing one's passions, Po-Chun told me, was not the norm in Taiwan at that time. And people went crazy, telling him that he was wasting his high score and that he was going to regret the decision that he was making.

M. Volborth: Fast forward to 2019. Po-Chun is living the dream— his dream anyway—as a new faculty member at Duke University in the Department of Mechanical Engineering and Material Science. His research lab works on light and heat management focusing on dynamic controls.

Po-Chun Hsu: Imagine— so you can see things through a thermal camera. That means we are radiating a lot of heat, which can be captured by the infrared camera. And what I'm doing is, instead of just letting that radiation come out without any control, if we can block that radiation, then we can keep the heat around you, make you feel warmer. And if you can maximize that radiation freely transmitting to the ambient, meaning we can make you feel much, much cooler.

M. Volborth: Here's why this topic is so important and why Po-Chun's research holds so much potential to serve society. Right now in the US space heating and cooling accounts for 14% of our total energy consumption. That's 648 million tons of CO2 produced every year just from heating and cooling. Our dependence upon indoor climate control produces a very troubling feedback loop in which these huge CO2 emissions contribute to global warming, which in turn causes us to use more power to keep our environments cool, which leads to more emissions and more climate change.

Po-Chun Hsu: So the reason that space heating and cooling consume so much energy is because we are trying to heat up or cool down the entire building, which is gigantic compared to our body area and volume inside. So personal thermal management is really to locally regulate the thermal comfort around the residents and ignore the empty space and all of the objects.

M. Volborth: What he's saying is, that if we could just create our own little climate controlled bubbles, we'd save a ton of energy because we wouldn't be heating or cooling empty space.

Po-Chun Hsu: If you do the math and calculate what's required energy to provide the comfortable environment just around us, not the entire building, you get the number about 10 times off. That means what we are consuming, which is the 14%, we actually need just 1.4% use of that. So there's a huge room for improvement. And my approach is to engineer the textile so they have special properties that can either maximize or minimize the thermal radiation heat loss.

M. Volborth: He approaches textile engineering at the nano scale, making polyethylene into nano porous fibers that allow water and air to pass freely through the textile or using metal nano wires to trap heat.

Po-Chun Hsu: The reason we made it into nano porous is to make it soft enough and also breathable. So as long as we make into a fiber shade and we spin into yarns, the textile that's woven out of that, it's really soft and as comfortable as cotton.

Po-Chun Hsu: So again, mainly the wires are to provide an infrared or thermal radiation shield, so that can reflect your infrared back. And the reason of using nano wires, again, is to keep your textile breathable. Because now we are having a network which has not enough pores for water and for moisture to transport, but is small enough to reflect the radiation.

Po-Chun Hsu: And the principal is like— everyone has a microwave oven. And on the door there's a mesh of metal with tiny holes, so you can see through the tiny holes so you can see whether your food is cooked or not. The microwave cannot escape from the oven. So imagine those meshes are now nano scale. What we are doing is, we have those nano wire to block the infrared, and now the smaller things like a water molecule or air molecule can freely pass through. And wearing those textiles during wintertime or summertime means you can reduce the usage of space heating or cooling but still feel the same, similarly comfortable environment. And you are wearing very lightweight clothing.

Po-Chun Hsu: So, exactly how much energy is saving will depend on the climate zone you are in. But generally speaking, increasing the air conditioner setpoint or decreasing the heater set point by one degree Celsius can save about 10%. And our cooling textile can save about 30% of the energy and heating can save about 50% of the energy.

M. Volborth: Has anybody tried to wear that textile?

Po-Chun Hsu: Yeah, we actually put those raw material and ask the outside factory to make a real woven textile for us. From my personal point of view, it's not distinguishable between our textile and traditional cotton textile.

M. Volborth: Really?

Po-Chun Hsu: It's soft, it's lightweight. I think the only difference is you feel much cooler.

M. Volborth: So do you have your own T-shirts at home?

Po-Chun Hsu: It was probably $1,000 to make, so I don't keep one. It still comes down to whether these processes can be compatible with the current milling and fiber spinning factories. But we are quite confident that with a given market search and given a volume... problem, this really can combine with traditional textile industry and in a scalable way.

M. Volborth: After working on ultra heating and ultra cooling, he took it a step further and started working on reversible textiles that can heat on one side, and when you flip them over they can cool on the other side.

Po-Chun Hsu: Radiation is a surface property, just like colors. We know things can have different colors, although they have the same bulkiness and same porosity. So this reversible thermal textile is the first demonstration how radiation heat management can achieve something that cannot be done by traditional textile.

Po-Chun Hsu: And that leads us to the next stage of research, which is to expand this to an ability and tuneable range to become even smarter than similar textile and to take advantage of the dynamic environment for more energy saving. Why it's simple is to combine some radiation control with sunlight control. And when we place those textile to, for example, the rooftop or tent material, it can absorb the sunlight and reduce thermal radiation loss for heating during wintertime. And in the summertime you can do the opposite, which is to reflect sunlight and promote some radiation loss for efficient cooling. And this dynamic smart textile material can save energy from a different approach by manipulating a different special property, which is sunlight and thermal radiation.

M. Volborth: So that material in that application would need to be tuneable by somebody controlling it, right?

Po-Chun Hsu: Right. Because we are living a constantly changing environment. Winter, summer, and even daytime, fluctuation can be something like 20 degrees Fahrenheit sometimes. So it's really important to have something that's smart enough to maintain, to keep up with the change. And you can provide the maximum comfort for human being or the maximum energy saving for the building.

M. Volborth: Can you tell me about the different ways that that material could be tuneable?

Po-Chun Hsu: Yeah, so we are exploring a variety of different options. For example, we can do it in a mechanical way by stretching or compressing. We can have different optical properties and we also try to use electricity to control or to induce such change.

M. Volborth: Where do you expect your research to be five years from now?

Po-Chun Hsu: Yeah, so of course we're going to push the performance higher and higher, making them hotter or cooler, but I also anticipated to combine the dynamically controlled thermal textile with a wearable sensor to provide optimal thermal comfort to the users. Or we can sort of close this controlling loop by feeding those physiological and environmental data to the textile and then the textile itself to adjust the optimal thermal property to fit the preference of the users.

M. Volborth: At this point in my conversation with Po-Chun I started daydreaming about things like blankets that adjusted my body temperature throughout the night. It just seems that there are so many possibilities that haven't been explored.

Po-Chun Hsu: Yeah. Whenever I think about this textile research I have a very strange feeling, because I know textile has been around with us for thousands of years. And if you compare that with electronics, say smartphone laptops, which is only decades, but we expecting more out of electronics than our textiles. So for us it's really interesting to say, "Okay, what if we put our effort which is in the electronic, but now we're putting it into textile? How much can we achieve?" One example would be, let's say if your textile can be linked to your calendar. Who knows where you are traveling next, what's the weather there? And what's the temperature? So the textile can warm up or cool down before you really arrive. Or it can sense your blood pressure or sense your health condition, so when you wake up in the middle of night, it will warm up so you won't catch cold.

Po-Chun Hsu: 20 years from now. I want to see our textile development is as progressive as the electronics and other smart technology right now. One of the most important thing is for cardiovascular diseases, which is I think still a top one or two fatal diseases globally. And for those kinds of diseases really important to prevent the happening compared to curing it. And I think one of the approaches is to really provide a comfortable and the stable thermal environment, so there's no sudden increase of blood pressure and there is no sudden change in those in those the environment. And I think I want to use this textile as a preventive medicine kind of like combining with the health sensors so it can really prevent the occurrence of those a heart attack and brain stroke and that kind of diseases.

M. Volborth: Remember how I said that Po-Chun is kind of famous in Taiwan? Right after he started at Duke there was a massive spike in the number of views to his faculty webpage. So many in fact that we initially thought our web traffic data was wrong. Most of the traffic originated in Taiwan where people are tracking Po-Chun's career, eager to see how the choices this rebellious researcher made 15 years ago are now playing out. And there was a lot of chatter online about how his career was shaping up.

Po-Chun Hsu: When you do something different you expect a lot of different opinions. And some people of course were happy for me, finally seeing some young person fulfilling his dream. I've heard some other people feel like even though I'm doing research, I'm a professor right now, they still kind of judge me based on the, for example, the salary and other stuff that I don't really care about. So it's really about the values that people people have in their mind. But I feel like if I can set a small example of what you can possibly also achieve if you are as rebellious and as stubborn enough like me, then you can one day do whatever you like. And don't take other critics too seriously, because they're not the one who was going to live your life, you are.

M. Volborth: So what do you think is the future of Po-Chun's research? A few years from now will you own a jacket whose properties you control with your smartphone? Will our tuneable rooftops help keep our offices a stable 70 degrees? Will Po-Chun have made a dent in the world's energy consumption?

M. Volborth: Thanks for listening. Subscribe for updates from Duke Engineering. And if you learned something from this podcast, please share it with others.

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