In the ever-increasing global average temperatures, HVAC systems provide relief from the intense heat and humidity. However, the comfort humans enjoy from these systems comes at a price - more than three-fourths of power consumption in commercial and residential buildings.
Researchers from the Texas A&M University are looking into the potential of a class of organic materials called polyimides, which could potentially revolutionize heating, ventilation, and air conditioning (HVAC) systems. In a new study, researchers propose that dehumidifiers based on these polyimides could become cost-effective alternatives to conventional dehumidifiers used in HVAC systems, costing thousands of dollars on average.
The Texas A&M University team presented their reports in the latest Journal of Membrane Science, titled "Enhancing air-dehumidification performance of polyimide membranes by generating hydrophilic Poly(amic acid) domains using partial hydrolysis."
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Improving an Existing Polymer for HVAC Systems Applications
"In this study, we took an existing and rather robust polymer and then improved its dehumidification efficiency," said Hae-Kwon Jeong, one of the authors of the study and the McFerrin Professor in Texas A&M's Department of Chemical Engineering. In a news release from the University, Jeong expresses optimism that new membranes based on these polyimides will "help develop the next generation of HVAC and dehumidifier technologies" that are better in terms of both efficiency and carbon footprint.
As a critical part of modern HVAC systems, dehumidifiers are in charge of removing moisture from the air to an acceptable level of dryness. This is done to improve air quality, eliminate dust mites, control mold growth, and more. Commonly used dehumidifiers require refrigerants, which dry up the air and reduce their ability to carry water vapors. However, these refrigerants are a source of greenhouse gases, which contribute to global warming.
To help reduce the greenhouse emissions from the materials, various efforts have looked into natural alternatives. One example is a material called zeolite, a microporous material known for its dehumidifying capabilities. Its characteristics as a molecular sieve allow it to absorb moisture without the greenhouse emissions from conventional refrigerants. Zeolite, however, is not a perfect alternative, posing its own challenges for practical use.
Jeong explains that scalability is an issue with zeolite membranes. The first is that they are relatively expensive to synthesize. The other is from their mechanical properties; zeolites are weak and require support, which adds materials and costs.
Turning to polyimides
To overcome the cost problem that inhibits zeolite, researchers turned to another organic material: polyimides. These materials are repeating, ring-shaped imide groups that together constitute a long chain on a molecular scale. With a structure like this, polyimides are considerably stronger compared to zeolites, although they remain not as good as dehumidifiers as the latter.
Working on the polyimides' ability to dry air up, researchers fabricated a film from carefully laid out polyimide molecules on nanoscale alumina platforms. The resulting film was then placed in a solution of sodium hydroxide to encourage hydrolysts, causing the imide groups in the organic polymer to break down and become hydrophilic or water-resistant. Additionally, researchers discovered that the process also created water-attracting channels inside the polyimide.
"This is a new approach to improve the property of a polymer for dehumidification, and a lot more optimizations need to be done in order to further enhance the performance of this membrane," Jeong said.
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