Green Hollow Fiber Membranes for Energy-Efficient Dehumidification in HVAC Systems

Original Authors: Lakshmeesha Upadhyaya, Abaynesh Yihdego Gebreyohannes, Muhammad Wakil Shahzad, Usman T. Syed, Sandra L. Aristizábal, Radoslaw Gorecki, Suzana P. Nunes

Original paper is accessible at: https://doi.org/10.1016/j.memsci.2023.122215

Introduction

As climate change intensifies, extreme heat and humidity are becoming significant global health threats. The interplay between temperature and humidity reduces the human body's ability to cool itself, often leading to dehydration and cardiovascular stress. Consequently, Heating, Ventilation, and Air Conditioning (HVAC) systems have become indispensable worldwide. However, conventional air conditioning, particularly dehumidification processes, consumes vast amounts of energy and contributes to over 2 billion tons of CO₂ emissions annually. Dehumidification accounts for a substantial portion of this energy demand, prompting the need for more sustainable alternatives.

System Design and Membrane Concept

Membrane-based air dehumidification offers an isothermal, non-toxic alternative to traditional condensation or adsorption techniques. This study introduces a membrane system using hollow fibers fabricated from Ultem® (polyetherimide), coated with green polyphenol (tannic acid) and crosslinked with either m-phenylenediamine (MPD) or hyperbranched polyethyleneimine (PEI). These fibers enable selective water vapor transport while maintaining structural and thermal stability.

The membranes were designed to:

• Enhance energy efficiency by utilizing water vapor transport at constant temperatures,

• Avoid cross-contamination between air and water phases,

• Operate sustainably without toxic solvents or materials.

Materials, Methods, and Fabrication

Hollow fibers were produced via dry-jet wet spinning using a polymer solution of Ultem®, diethylene glycol (DEG), and NMP. The membranes were then coated with tannic acid, oxidized with sodium periodate, and crosslinked using MPD or PEI. These coatings increased hydrophilicity and selectivity, improving membrane performance.

Modules were assembled using 350–500 fibers per unit and tested under various conditions. Advanced characterization techniques (e.g., SEM, TEM, FTIR, XPS, contact angle measurements) confirmed successful coating and stability of the fibers.

Performance Evaluation and Results

Key findings included:

• Water vapor permeance: Up to 13,000 GPU.

• Water/N₂ selectivity: As high as 47,000 in optimized configurations.

• COP (Coefficient of Performance): 2.3–2.5 for large-scale modules, which is 4–5 times greater than conventional desiccant systems.

• Durability: Minimal decline (<10%) in performance after 390 days of continuous operation under real-world conditions.

The system showed stable operation across different temperatures (25–35 °C) and humidity levels (40–80% RH), simulating conditions common in hot, humid regions like Saudi Arabia.

Green Metrics and Sustainability

A comprehensive green assessment was performed:

• Eco-Scale Score: 75 (borderline green).

• Atom Economy: 90%.

• Carbon Efficiency: 90%.

Compared to previous studies, this fabrication process minimized the use of hazardous chemicals and solvents, favoring sustainable and scalable membrane production.

Conclusion

This study presents a highly efficient, green, and scalable membrane-based system for dehumidification in HVAC applications. With outstanding performance metrics and sustainability scores, the polyphenol-coated hollow fiber modules offer a promising route toward climate-resilient air conditioning. Their compact design, long-term stability, and environmental friendliness position them as a viable replacement for conventional dehumidifiers, especially in water- and energy-stressed regions.