Po-Chun Hsu’s groundbreaking research delves into the realm of thermal comfort, photonics, multispectral photonic energy, and renewable energy. With 15% of energy and carbon emissions directed towards thermal comfort, his work addresses this challenge from two perspectives. Firstly, by harnessing multispectral photonic energy from the sun and the universe, he pioneers low-carbon building heating and cooling methods, using passive radiative cooling that channels excess heat to cold deep space. His adaptive solar heater and radiative cooler (ASHARC) revolutionize smart building envelopes, offering energy-efficient, weather-responsive heating and cooling. Secondly, through wearable technology like the variable emitter device (WeaVE), Hsu pioneers human body thermoregulation.

Which wall does your research break?

Around 15% of our energy and carbon emissions are for one single purpose: thermal comfort. After all, maintaining a constant thermal environment is one of the most fundamental survival needs and is closely related to productivity, health, and welfare. Traditionally, fossil fuel-intensive heating and air conditioning are used to regulate the temperature of the entire building, which is slow, inefficient, and not focused on individual needs. Therefore, it is critical to push the boundary of science and technology in this human-building-energy nexus to mitigate energy consumption while maximizing personal thermal comfort and health. My research aims to accomplish this goal from two thrusts: (i) Utilize multispectral photonic energy from the sun and the universe to achieve low-carbon-footprint building heating and cooling, (ii) Develop an ultra-efficient multimodal wearable thermoregulation device to manage the heat exchange between the human body and the surrounding. The first thrust aims to shift the paradigm from traditional solar heat management to passive radiative cooling by losing heat to cold deep space. Thermodynamically, air conditioning must be done actively by external work, which is why the enormous energy consumption. By directly tapping the cooling potential of the universe that is only 3-kelvin-cold, we can achieve sub-ambient cooling without any energy input. Our electrochemically driven devices, adaptive solar heater and radiative cooler (ASHARC) can be used as the smart building envelope to further modulate the heating and cooling based on the weather conditions and occupants’ needs, completely using renewable heating and cooling sources. The second thrust focuses on the human body thermoregulation, in which our wearable variable emitter device (WeaVE) can modulate the radiative heat exchange with the surrounding. Compared with conventional wearable thermoregulation devices that actively generate or pump the heat, our device controls the human body’s heat loss to the ambiance, leading to orders-of-magnitude better energy efficiency. A single coin cell can operate the device for weeks, and a typical smartphone battery can last for months. We also incorporate sensors and electronics to use the device from smartphone Bluetooth, showing a close-loop personalized thermoregulation. I will further combine the two thrusts to complement and communicate with each other, ultimately bringing energy sustainability to the human-building-energy nexus.

What inspired or motivated you to work on your current research or project?

As a scientist trying to contribute to energy sustainability, I was genuinely shocked when I first learned that thermal comfort plays such an essential role in greenhouse gas emissions and yet has been significantly underexplored. Compared to generating more renewable energy via solar and wind, I realized that transforming and decarbonizing the current thermoregulation technologies will have an imminent and significant impact, which is precisely what we need to solve the urgent global warming issue. Therefore, I aspired to use my multidisciplinary expertise in nanoscience, photonics, heat transfer, and electrochemistry to provide innovative solutions. I was fortunate to be exposed to these concepts through inspiration from established researchers. When I began my independent research career, I tried to connect the dots by using reversible electrochemical reactions as a highly powerful, precise, dynamic, and versatile tuning knob for photonic and thermal properties. This tunability is extremely important because both building and personal thermoregulation aim to stabilize the temperature against external fluctuations. The technological challenges are to achieve the goal with minimal carbon footprint. I was also intrigued by the fundamental scientific findings while interrogating the mechanisms. Innovation cannot be done correctly without fundamental understanding. Realizing my research can become part of the effort to tackle climate change has always driven me to go further and deeper.

In what ways does society benefit from your research?

The first immediate outcome of my research for society would be an adaptive system with integrative building envelopes and wearable devices that can regulate the optical and thermal properties to help maintain the heat balance. The electricity required by my thermoregulation devices is less than 1% of current consumption, but the thermal energy tapped from the sun, the sky, and the ambiance, is tremendous, leading toward a great reduction of carbon emission associated with indoor temperature control. Wearable thermoregulation also helps avoid temperature-related illnesses, such as heat stroke, heart attack, and even influenza. With the exacerbating global warming, human adaptation to the extreme temperature and weather events has become more and more critical. Current wearable technology can sense physiological signals related to these illnesses, and I aim to close the loop by providing the ideal health-oriented thermal environments. On the other hand, the underlying reversible electrochemistry and photonic principles can be extended broadly to solve critical issues in other applications, too. For example, my research aims to study the structure-synthesis-property relationship of the electrodeposited metal nanostructure, which coincides with a holy grail of the energy storage research community that strives to use pure lithium or other metals as the battery anode for higher energy density. The tunable multispectral photonics aspect also provides a unique and powerful approach for displays and sensors in virtual/augmented reality devices and self-driving cars.

Looking ahead, what are your hopes or aspirations for the future based on your research or project?

I envision that the coalition of electrochemistry, nanophotonics, and thermal science can inspire new opportunities in how we manipulate light and heat in a scalable fashion, ultimately changing how we use energy. Several missing gaps are yet to be amended to bring costly photonic concepts to reality in energy science. Global warming is the largest challenge we humans need to solve together. No step is too small, but we must set the right direction. Heat illness is another increasingly important issue that would also demand more research efforts. I also picture that, in the future, when extraterrestrial travel and colonization become common activities, adaptive solar heating and radiative cooling technology would become more essential because there is no atmosphere and convection.

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