Optimizing chemisorption based direct air capture unit efficiency in HVAC systems: A study on the impact of DAC location and adsorption conditions as a response to the climate crisis and indoor air quality

Abstract

Direct air capture (DAC) technology is still facing some challenges that need to be addressed before the technology can be widely deployed. One major challenge is the high overall system energy requirement, and it is the main bottleneck in DAC commercialization. This study aims to unlock the potential of integrating DAC with Heat Ventilation and Air Conditioning (HVAC) systems. A thermodynamic model is used to test the effect of varying the adsorption and desorption conditions on DAC unit performance, and to assess the characteristics of DAC unit positioned in six different locations within air the handling unit (AHU). The results show that by only locating the DAC unit in Position 6 (i.e., positioning the DAC unit after the exhaust fan in AHU) in comparison to a stand-alone unit, the efficiency of the DAC system is improved at varying times through the summer season in Qatar. Specifically locating DAC unit at Position 6 increases DAC efficiency from 5.3% to 27.19% for 8th of June 2022 at 11:00 am in Qatar. Additionally, using the DAC unit with other filters in AHU allows for full air recirculation for 10 h. Based on this scenario and the weather data for 20th of July at 12:00 pm, the hottest day in Qatar in 2022, a reduction of 44% in cooling load is achieved. Locating the DAC unit at a point before the air is supplied from AHU is the best, however, in case of full recirculation of air, positioning the DAC unit after the exhaust fan will achieve better performance.