Moss and air: biofiltration and moss as a fresh air generator
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Authors
Pepi, William
Issue Date
2024-08
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Architecture
Alternative Title
Abstract
This thesis addresses both indoor air quality (IAQ), the top environmental risk to human health, and building energy consumption, a principal driver of climate change. Plants can enhance both IAQ and building energy efficiency. Botanical biofilters host microbial populations that remediate a diversity of contaminants while plant photosynthesis may provide CO2-O2 balance of occupant respiration, enabling continuous clean air recirculation and HVAC energy savings – by reducing the supply and conditioning of outdoor air. In other words, beyond hosting microbial biofiltration, plants may be complete fresh air generators. Vascular botanical biofilters (state of the art) are a promising nascent technology; facing challenges regarding system size, grow light energy, CO2 assimilation, airflow, and root-zone drying, which can inhibit microbial bioremediation. Vascular biofilters show high VOC removal but insufficient evidence for photosynthetic CO2 assimilation of occupant respiration. Thus, current systems effectively remove VOCs but do not fully regenerate fresh air. This dissertation argues that moss biofiltration is a feasible alternative avenue towards complete indoor fresh air generation. We posit that moss – with its fractal structure, high surface area, porosity, water content, robust microbiotic consortia, mat-like morphology, and high chloroplast efficiency – can facilitate uniform air flux, rapid contaminant mass transfer, and high photosynthetic carbon assimilation in a compact and energy-efficient package. In addition to its (known) filtration efficacy, we hypothesize that moss photosynthesis occurs rapidly under high air flux and CO2 concentrations, potentially allowing for complete indoor air recirculation and resolution of energy-IAQ tradeoffs. We deploy three distinct methodologies. (1) A mini meta-analysis synthesizes botanical biofiltration studies into normalized metrics, such as filtration efficiency and clean air delivery rate, enabling quantitative comparisons with state-of-the-art systems. (2) Empirical experiments on moss biofilter prototypes investigate carbon assimilation at high air flux and CO2 concentrations, VOC and PM filter efficiencies, and evapotranspiration (moss’s cooling effect). Additionally, in vitro tests characterize dose-response inhibition of fungal and microbial activity by moss metabolites. (3) We present a parametric modeling framework that co-simulates air mass balance and building energy for arbitrary biofilter and building systems, enabling estimation of air quality and total energy consumption. We run a suite of modeling studies (over 30,000 individual variants) investigating the impact of climate, occupancy, metabolic rate, HVAC system types, biofiltration systems, future weather, and other parameters. (1) The statistical review of botanical biofiltration research highlights the field's incipient nature. Besides important parameters like airflow rate, the study itself significantly predicts biofilter efficiency, indicating varied experimental parameters and biofilter systems can yield diverse results. (2) Although typically observed to be low-light slow-growers, we observed that under high airflow (approx. > 3 m/s), light (PPFD > 250 µmol/m2/s) and CO2 (approx. > 1000 ppm), moss biofilter photosynthesis outperforms vascular systems (CADRCO2 > 0.5 m3air/m2moss/hr), in a package about ten times smaller (per person) and using a third of the light energy. Thus, moss photosynthesis may typically be limited by environmental parameters, not intrinsic physiology. (3) Our simulations reveal that biofiltration in general surpasses conventional methods for improving IAQ such as (abiotic) filtration and outdoor air dilution; and, in some cases, can resolve energy-IAQ tradeoffs. The indoor-to-outdoor temperature differential is the best predictor of energy savings, with extreme climates benefiting most from indoor air recirculation. Overall and in a detailed multizone energy-air-quality model, moss systems outperform vascular biofilters on net energy use intensity, air quality, and return on investment metrics. We thus provide some evidence that moss is an attractive platform for achieving complete and regenerative indoor air recirculation.
Description
August2024
School of Architecture
School of Architecture
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY