EFFICIENT INTEGRATION OF DIRECT AIR CAPTURE WITH HVAC SYSTEM

Abstract

Direct Air Capture (DAC) is a pivotal negative emissions technology uniquely capable of capturing CO2 from unaddressed sources such as transportation, construction, and agriculture. This capability makes DAC integral to mitigating atmospheric CO2. However, its widespread implementation has been hindered by substantial energy demands and cost. This thesis explores the integration of DAC with Heating, Ventilation, and Air Conditioning (HVAC) systems to enhance DAC energy efficiency, reduce operational costs, reduce the cooling energy consumption of buildings and improve indoor air quality. Morever, Utilizing existing HVAC infrastructure significantly cuts the capital costs associated with deploying DAC technologies. Initial research reviews the DAC landscape, focusing on energy challenges and integration potential with building systems. Thermodynamic models assess various DAC configurations within an Air Handling Unit (AHU). Positioning the DAC unit after the exhaust fan markedly increases Direct air capture efficiency, from 5.3% to 27.19% on peak demand days. Experimental results with sorbents like SBA-15 functionalized with Tetraethylenepentamine (TEPA) show substantial increases in CO2 adsorption capacity. Under humid conditions, replacing Lewatit with S-TEPA decreases thermal energy consumption from 425 kJ/molCO2 to 325 kJ/molCO2, and using S-PEI-L reduces it further to 275 kJ/molCO2. The levelized cost of CO2 capture (LCOD) for standalone DAC systems using a benchmark material like Lewatit ranges from $349 to $429 per ton based on Qatar climate conditions. Integrating DAC with HVAC systems lowers this cost to about $219 per ton using Lewatit. Further advancements with SBA-15-TEPA in DAC-HVAC setup reduce the LCOD to $208 per ton, while using NbOFFIVE in amine free DAC system achieves the most economical rate at $184 (reduction by 58% of initial DAC LCOD) per ton. Additionally, this amine-free system is projected to reduce the building's cooling energy consumption by approximately 29.67%, significantly enhancing HVAC efficiency. These findings demonstrate the efficiency and cost benefits of alternative sorbents and integration strategies. Integrating DAC within HVAC not only optimizes economic and DAC operational efficiency but also bolsters indoor air quality and reduces building cooling energy. This research aims to transform DAC from a conceptual solution to a practical technology integrated within existing infrastructure.

Date of Award	2025
Original language	American English
Awarding Institution	HBKU College of Science and Engineering