A new generation of energy-efficient HVAC technologies using organic materials

Researchers at Texas A&M have improved the dehumidification performance of a polymer, which could be used to develop more efficient systems that are lower in energy and carbon footprint.

Heating, ventilation, and AC systems (HVACs) provide relief from the heat and humidity during hot summer afternoons. These systems are often equipped with dehumidifiers and consume around 76% of electricity in residential and commercial buildings.

Researchers at Texas A&M University have discovered a polyimide-based organic material that requires less energy to dry the air. Researchers also found that polyimide-based HVAC systems can be cheaper than those priced at thousands of dollars.

“In this study, we took an existing, rather strong polymer and then improved its dehumidification efficiency,” Hae-Kwon Jeong (McFerrin Professor in Artie McFerrin Department for Chemical Engineering). These polymer-based membranes will be a key to developing next-generation HVAC and dehumidifier technology that is more efficient than existing systems and less carbon-intensive.

The Journal of Membrane Science describes the results of the study.

Dehumidifiers dry out the air and remove moisture to make it dry. This can improve air quality and eliminate dust mites. Refrigerants are the most common dehumidifiers. These chemicals dehumidify the air by cooling it and decreasing its ability to transport water. Refrigerants, despite their popularity, are a significant cause of global warming.

Zeolites, a naturally occurring material that can dry quickly, are a viable alternative to dehumidification. Unlike refrigerants, zeolites are desiccants that can absorb moisture in their water-attractive or hydrophilic pores. These inorganic materials are very green and have excellent dehumidification capabilities. However, zeolite-based humidifiers present their challenges.

Jeong stated that scaling up is a significant problem with zeolite membranes. First, zeolites can be expensive to synthesize. The mechanical properties of Zeolites are another problem. They are fragile and require concrete support structures. This can increase the overall cost.

Jeong and his team looked for a cost-effective organic material called Polyimides. These are well-known for being rigid and resistant to heat and chemicals. These high-performance polymers’ basic unit is a series of repeating, ring-shaped, imide groups connected in long chains. Jeong stated that the attractive forces between imides give the polymer strength, an advantage over mechanically weaker zeolites. The polyimide material’s dehumidification capabilities needed to be improved.

Researchers first made a film by applying small amounts of polyimide molecules to a few nanometer-wide alumina plates. The researchers then put the movie in a concentrated sodium hydroxide solution. This caused hydrolysis. This caused the imide molecular group to become hydrophilic and break down. The researchers discovered hydrolysis reactions could lead to water-attractive percolation canals or highways within the polyimide materials.

Jeong and his team found that the polyimide membrane they had developed for dehumidification was highly permeable to water molecules when they tested it. The membrane could extract excess moisture from the air, trapping them within the percolation channels. According to the researchers, these membranes can be used continuously without needing to regenerate. The trapped water molecules are released from one side by a vacuum pump mounted within a standard humidifier.

Jeong stated that his team meticulously designed their experiments for partial hydrolysis, where a controlled number of imide groups becomes hydrophilic.

Jeong stated that polyimides’ strength comes from the intermolecular forces they have between their chains. We want to hydrolyze only a few imides. Hydrolysis that is too low will result in the material not being effective at dehumidification.

Jeong stated that polyimide membranes are promising in dehumidification. However, their performance is still behind zeolite membranes.

Jeong stated that this is a novel approach to improving the properties of a polymer for humidification. He added that many optimizations are needed to enhance the membrane’s performance further. It must be affordable, especially for homeowners. Although we have yet to arrive, we are progressing in this direction.

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