From buildings to crops: a techno-economic and environmental analysis of DAC-HVAC integration for CO₂ enrichment in agricultural greenhouses

Arid regions face dual pressures of food security and decarbonization amid high cooling demand in buildings and built environment. This study presents an integrated techno-economic and life cycle environmental assessment of a carbon capture and utilization (CCU) system that combines Direct Air Capture integrated with Heating, Ventilation, and Air Conditioning (DAC-HVAC) and CO₂ utilization in agricultural greenhouses. The system captures CO₂ from indoor air in buildings to support controlled-environment food production, with a focus on deployment in arid regions such as Qatar. A Geographic Information System (GIS)-based spatial analysis was conducted to map a representative CO₂ source and potential greenhouse sinks, perform optimal source-sink routing, and group greenhouses into four spatial clusters for localized modeling and sensitivity analyses. The base model couples the GIS layer with (i) a DAC-HVAC thermodynamic model to evaluate the energy requirements and (ii) a greenhouse model that simulates CO₂ assimilation, water consumption, and HVAC energy demand in greenhouses at each cluster location, using site-specific climatic data. The results from system modeling were used to conduct a comprehensive economic analysis to assess system costs and financial viability, followed by a cradle-to-gate life cycle assessment (LCA) to quantify seven environmental impacts using ReCipe 1.08 midpoint method. Robustness was examined by varying cluster locations (transport distance and climatic conditions) and solar energy integration. The DAC-HVAC system achieved a levelized cost of capture (LCOC) of $202/ton CO₂, and when integrated with CO₂ utilization in greenhouses, resulted in a levelized cost of production (LCOP) ranging from $1.19 to $1.229/kg of produce, depending on the cluster location (as determined by GIS-based spatial clustering by proximity) and corresponding climatic conditions. Among the four greenhouse clusters, Cluster 2 has the most favorable performance, achieving the lowest LCOP ($1.19/kg), shortest discounted payback period (DPP) (4.25 years), and smallest break-even units (BEU) (488 tons), alongside the lowest environmental burdens, including a climate change impact of 0.945 kg CO₂ eq./kg. In contrast, Cluster 1 performed worst economically due to long CO₂ transport distances, while Cluster 4 incurred the highest environmental impacts due to elevated energy and water use. Integration of renewable energy sources, particularly solar, has proved to significantly enhance sustainability outcomes. Solar energy reduced climate change impacts by up to 66 % and lowered LCOP by up to 18 % compared to subsidized and 74 % compared to unsubsidized grid electricity. Accordingly, policy should prioritize CO₂ routing via spatial planning, account for site-specific climatic drivers of energy and water demand into planning future greenhouse locations, and accelerate solar adoption to realize the quantified reductions in cost and environmental impact.