Techno-economic and environmental evaluation of building-integrated direct air capture performance

Building-integrated direct air capture (BI-DAC) has been proposed as a decentralized approach to carbon dioxide capture in dense urban environments, leveraging existing heating, ventilation, and air conditioning (HVAC) infrastructure while improving indoor air quality (IAQ). Potential advantages of BI-DAC include decentralised deployment, use of existing HVAC airflow pathways, and integration of CO₂ capture with IAQ management at the building scale. This study focuses on a building-level CO₂ capture subsystem with potential relevance to carbon dioxide removal (CDR) when coupled to downstream storage and does not include compression, transport, storage, monitoring, reporting, and verification (MRV). Accordingly, the study evaluates capture performance, energy demand, life cycle greenhouse gas (GHG) emissions, and costs within the defined system boundary under realistic operating conditions. A dynamic multi-zone framework couples EnergyPlus building CO₂ simulations with a numerical adsorption model for a representative large office building in Portugal. Two adsorption-regeneration strategies were assessed to examine operational trade-offs between capture throughput, sorbent requirements, and energy use. Simulated gross CO₂ capture ranged from 3.73–5.29 tCO₂·y⁻¹, while indoor CO₂ concentrations remained within recommended IAQ thresholds. Sensitivity analysis identified occupancy and ventilation scheduling as dominant drivers influencing annual capture performance. After accounting for electricity- and sorbent-related emissions, the capture subsystem retained 89 per cent of gross captured CO₂. The levelized cost of capture was estimated at €969-€1037 per tCO₂. Results demonstrate the technical feasibility of BI-DAC and inform future work on system optimization, low-carbon energy integration, and pathways toward durable and verifiable CO₂ removal when coupled with storage and MRV systems.