Carbon, Indoor Air, Energy and Financial Benefits of Coupled Ventilation Upgrade and Enhanced Rooftop Garden Installation: an Interdisciplinary Climate Mitigation Approach

Building energy use contributes to urban carbon dioxide (CO2) emissions while inadequate ventilation can yield indoor CO2 build up from human respiration. However, increasing ventilation rates can add to energy costs and climate burdens. Our objective was to quantify changes in emissions, energy, and financial cost when rooftop garden and ventilation upgrades are done simultaneously, with an opportunity to enhance plant growth from exhausted CO2. We measured indoor CO2 concentrations, calculated ventilation rates, and modeled five scenarios to assess these impacts. The indoor CO2 concentration maximum was 2210 ppm, median was 840 ppm, and 33% of the daytime was spent above 1000 ppm. The estimated ventilation rate was 4 L/s. Our model calculations show that increasing ventilation to recommended levels (7 L/s) would increase total CO2 emissions, energy use, and cost (1-4%), but this could be counterbalanced by rooftop garden installation benefits, which yielded a net decrease of 23-46% in CO2 emissions, 12-13% in energy use, and 12-16% in cost. This novel integration of data collection and modeling provides support for the co-benefits of simultaneous improved installation ventilation systems and indoor CO2-enhanced rooftop gardens.