Energy efficiency of botanical systems for the remediation of indoor CO2

• First quantification of lighting energy needs for plant-based CO 2 drawdown. • Crop plants outperformed ornamentals in CO 2 removal. • Supplementary lighting makes plant systems less efficient than ventilation. • Naturally light botanical biofilters could reduce ventilation energy use. Various indoor plant systems have been proposed to have the capacity to supplement building ventilation, however, the use of artificial lighting and its energy requirements to achieve this has not previously been considered for its contribution to plant-ventilation system energy balances. To test the capacity of plant systems for ventilation system energy reduction, the light energy required per unit of photosynthetic carbon dioxide (CO 2 ) drawdown was recorded in sealed chambers for several ornamental and one crop plant under two light levels. All species were capable of CO 2 removal, although one ornamental species demonstrated net CO 2 emission under low light, and the crop species ( Pak choi ) substantially outperformed the ornamental species. Green walls and potted plants performed equally, dependant on the foliar area of the plants. To assess the ventilation energy savings capabilities of plant systems, their CO 2 removal capacities (‘ventilation equivalence’) were compared to the modelled performance of a mechanical ventilation system, with performance metrics based on various building standards. It was found that the mechanical system was far more energy efficient than any plant systems, if supplementary lighting was required by the latter. We conclude that botanical systems may play a role in reducing building ventilation energy use, but only if the plant systems are provided with natural rather than supplementary light. We propose a concept design for the integration of naturally lit, plant-based systems into the heating, ventilation and air conditioning systems (HVAC) of future buildings for the purposes of reducing the energy requirements of the built environment.