Techno Optimisation of Fixed-Bed CO₂ Adsorption Technology for Energy-Efficient Heating Ventilation and Air Conditioning Systems

Ensuring both energy efficiency and indoor air quality in buildings remains a key challenge in heating ventilation and air conditioning system design. High ventilation rates improve air quality but increase energy consumption, while reduced ventilation enhances efficiency but may lead to elevated CO₂ concentrations, negatively affecting occupant well-being. This study investigates the integration of a CO₂ adsorption system within air-conditioning units as a novel approach to mitigate this trade-off. The selected sorbent material, epoxide-modified pentaethylenehexamine impregnated on activated carbon fibre, exhibited a high adsorption capacity of up to 101 mg/g under typical indoor CO₂ concentrations. Notably, it allowed efficient regeneration at low temperatures (50-60°C), making it suitable for continuous operation with minimal energy input. A thermodynamic model of a fixed-bed CO₂ adsorber was developed, incorporating detailed mass and energy balance equations to characterise adsorption, desorption, and thermal effects. The model was validated against experimental data, demonstrating its reliability in predicting CO₂ capture dynamics. A parametric analysis was conducted to optimise the design of the adsorption bed, identifying the best dimensions to ensure adequate CO₂ saturation time while minimising pressure drops and avoiding excessive energy costs. The study also explored system performance under various airflow rates to assess the feasibility of implementation across different heating ventilation and air conditioning system configurations. Additionally, alternative system layouts incorporating CO₂ adsorption technology were proposed to evaluate its integration potential. The results indicate that integrating CO₂ adsorption into heating ventilation and air conditioning system systems can significantly reduce the need for fresh air intake – by up to 91% in comparable studies – leading to lower fan power consumption and reduced heating and cooling loads. These systems are particularly relevant for applications where ventilation represents a major contributor to space conditioning energy demand. While CO₂ adsorption does not remove other indoor pollutants, a minimum air change rate must still be maintained to dilute contaminants such as volatile organic compounds and particulates.