In this post, David Warsinger, an assistant professor in the College of Engineering and a member of the Purdue Institute for a Sustainable Future, discusses his research “Dual-module humidity pump for efficient air dehumidification: Demonstration and performance limitations,” which was recently published in Applied Energy with the support of the Department of Energy Industrial Efficiency and Decarbonization Office, and the Oak Ridge Institute for Science and Education.
What did you want to know?
For almost a decade, researchers have been theoretically modeling a particular air dehumidification system, which we call the “Dual Module Humidity Pump” or DMHP. This system uses water vapor selective membranes (materials that allow water vapor to pass through while blocking air molecules), to dehumidify air for buildings. Cooling and ventilation accounts for nearly 10% of global electricity consumption, so it is crucial to develop more efficient technologies. So, with this in mind, while many research groups, including our own, had theoretically modeled the DMHP system, no one had successfully built a prototype in the open literature. Our ultimate goal for this study was build the DMHP and provide experimental performance.
So, in this work, we wanted to know, can we move this system out of the theoretical, on-paper concept stage, and into the real-world. If so, what are the limitations of this approach and what are the most important aspects for future experimental prototype development?
What did you achieve?
We built the first working prototype of the dual module humidity pump in the open literature, to the best of our knowledge. To be clear, many other experimental prototype exist for other membrane dehumidification systems (vacuum membrane dehumidification, vacuum sweep dehumidification, liquid desiccant membrane contactors). Our work is specifically on this “dual-module” design, which in theoretical modeling works is often regarded as the highest performing system. To have a working prototype is over coming a significant barrier that the technology has faced in terms of moving closer to commercial development.
Beyond simply building something that works, this experimental prototype also enabled some new scientific discoveries that could not be achieved by models. The membrane-based dehumidification systems rely heavily on having a high selectivity, where selectivity is a measure of how well the membrane blocks air while allow water vapor passage. Much of this field has heavily focused on further increasing the selectivity of membranes to improve energy efficiency. One major finding of this publication was that improving beyond the current state of the art membrane reported in literature, will not help improve efficiency very much. Currently, the main bottleneck of the technology is the water vapor compressor component and mechanical system design. It is our hope that these findings, only enabled thanks to the successful prototype, help researchers prioritize future work.
What is the impact of this research?
Ten percent of global electricity consumption is spent on cooling and ventilating buildings. Thirty-one percent of the GHG emissions associated with building cooling comes from dehumidification (only 27% is associated with actually cooling the air). Current air conditioning relies on condensing the water in air, which is very energy expensive. Meanwhile, countries are improving quality of living around the globe (air conditioner use is increasing), the climate is change (building cooling is becoming more needed), we are trying to widespread electrification (so we need our current electric technologies to be more efficient to “make room” for the new things, like electric vehicles, on the electric grid), and governments around the world are rapidly phasing out traditional refrigerants, which are efficient and reliable, but bad for global warming when they leak. So, the air conditioning industry is under great pressure from several directions to drastically improve the way we cool our buildings. We cannot rely on incremental change. We need drastic changes to the way to cool our buildings to meet our decarbonization goals. Dehumidification is a huge part of the emissions associated with cooling, and the membrane technology we are working on has the potential to nearly double to efficiency of our building cooling systems.