Unlocking the potentials of integrating direct air capture with HVAC system

The increasing concentration of carbon dioxide (CO₂) in the atmosphere has compelled researchers and policymakers to seek urgent solutions to address the current global climate change challenges. In order to keep the global mean temperature at approximately 1.5°C above the preindustrial era, the world needs increased deployment of negative emission technologies. Among all the negative emissions technologies reported, direct air capture (DAC) is positioned to deliver the needed CO₂ removal in the atmosphere. DAC technology is independent of the emissions origin, and the capture machine can be located close to the storage or utilization sites or in a location where renewable energy is abundant or where the price of energy is low. Notwithstanding these inherent qualities, DAC technology still has few drawbacks that need to be addressed before the technology can be widely deployed. The main findings point to undeniable facts that DAC overall system energy requirement is high, and it is the main bottleneck in DAC commercialization. The proposal of this study is to unlock the potential of integrating DAC with HVAC systems. DAC with HVAC system integration can be proposed to allow for reducing indoor CO₂ levels to improve indoor air quality (IAQ), HVAC energy reduction using higher air recirculation ratios, a more efficient DAC system by capturing from more elevated CO₂ concentrated streams (indoor air), applying cooler adsorption, and adsorption at different relative humidity points. The expected reduction in the net present value of tons of CO₂ after 50 years is estimated to be 3000$/tonCO₂ compared to the highest in the literature of 1000 $/tonCO₂ [1]. This reduction in NPV is estimated based on possible energy recovery by quantifying only one benefit which is HVAC energy reduction using higher air recirculation ratios. Therefore, coupling DAC with HVAC can be economically favorable in comparison to only DAC. In the present work, a comparison between efficiencies of the stand-alone DAC unit and the one integrated with Air Handling Unit are quantitively evaluated based on validated mathematical model. The positions of direct air capture unit within the HVAC are chosen to maximize the possible benefits. The DAC unit efficiencies throughout the hot months in Qatar are improved to be within the range of 21% to 22% compared to the range of 16% to 21% by only positioning the DAC at point 2 in the Air Handling Unit.