Design and performance assessment of a modular carbon capture-algal utilization retrofit for residential heating

Abstract Rising carbon emissions from fossil-fuel-based space heating highlight the need for retrofit solutions deployed at scale. This study presents a modular carbon capture and utilization (CCU) system designed for integration with residential and light-commercial HVAC&R infrastructure. The system captures post-combustion CO₂ using a multi-stage filtration and pressure swing adsorption (PSA) unit, then feeds the captured gas to a photobioreactor (PBR) cultivating Chlorella vulgaris. The resulting algal biomass is processed into biodiesel, enabling on-site conversion of emissions into usable fuel. Modelled for a standard 20-kW natural gas boiler, the system demonstrates the capacity to capture over 7 metric tons of CO₂ per heating season while generating appreciable quantities of biomass and renewable fuel. This biodiesel production contributes significantly to reducing the annual heating energy demand. The biodiesel provides 10,798.4 kWh of fuel energy, contributing 8638.86 kWh to heating demand at 80% boiler efficiency. While the system displaces 1.74 tCO₂e/year of fossil natural gas through fuel substitution, the ~ 7.78 t of CO₂ captured per season is cycled through the biological loop rather than permanently sequestered. Techno-economic analysis, estimates a capital cost of approximately $5,900, a simple payback period of approximately 22 years, and a 10-year present value of the net-benefit stream of approximately $1,660. These results demonstrate the technical feasibility of small-scale CCU retrofits for reducing emissions from existing heating systems, while showing that single-household economics are not yet cost-competitive; centralized, cluster-scale deployment is identified as a promising direction for closing this gap.