Bryoremediation integrated oxygen module (BIOM)

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Pepi, William
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Electronic thesis
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(Problem) Indoor air quality (IAQ) poses a severe and often overlooked threat to human health and wellbeing. Even in the United States where air quality is relatively good, air pollution accounts for 4% of all death and $70 billion in lost workdays and productivity, annually. The increasingly common practice of sealing building envelopes to improve energy efficiency can exacerbate poor IAQ by trapping pollutants; and increasing outdoor air ventilation to improve IAQ increases HVAC loads. Thus, there exists a tension between energy efficiency and indoor environmental conditions. Currently, this tension can be resolved with (1) mechanical methods such as the use of heat exchangers and mechanical air filters, or with (2) vascular phytoremediation technologies (i.e., AMPS) where clean air is generated within the enclosure. Heat exchange methods are effective but thermodynamically limited (approximately at ϵ = 85%); mechanical filters require regular replacement, disposal, and are likely insufficient given the large numbers of death and illness attributable to indoor air pollution; and extant vascular phytoremediation systems require complex air flow dynamics (to the rhizosphere), are normally physically and permanently integrated into HVAC systems, and need regular plant maintenance and nutrient supplies. (Hypothesis) Mosses are ecological pioneer species known for robust growth, extremely high leaf surface area (approximately equal to pure peat), and minimal metabolic requirements, making them a potentially low-maintenance, resilient and effective alternative to the vascular phytoremediation techniques first developed by Bill Wolverton at NASA. The enormous leaf surface area of moss and the biofilm it supports on its rootless mat-like surface make it a potentially high-efficiency filter capable of remediating PM and VOCs. That surface area is also photosynthetic, thus this thesis argues that moss can generate a building’s oxygen requirements from within the enclosure by balancing photosynthetic biomass with human respiration, while filtering prevalent pollutants. This would radically reduce the energy needed to condition outside air (less energy generation likely lessens total air pollution as well) while directly improving indoor air quality for occupants. (Methodology) Although mosses have demonstrated some ability to ameliorate high CO2 ppm, PM, VOCs, and heavy metals, there is a dearth of research focused explicitly on their potential benefit on IAQ as an indoor biofilter, and these promising results are often tangential to the focus of their respective studies. Thus, this thesis investigates the most basic metabolic plant function––photosynthetic oxygen production––as well as the VOC degradation capacity of moss, as VOCs are prevalent in the indoor environment and poorly adsorbed by MERV and HEPA filters. Leveraging moss’s mat-like growth, a desktop ‘BIOM’ unit houses a surface-area-maximizing scaffold that radically increases total biomass compared to a 2-dimensional moss wall. Control logic for wirelessly integrated electronic sensing and data driven HVAC operation has been developed to intelligently mediate air and energy exchange across building enclosures, optimizing for air quality and energy savings due to reduced outdoor air ventilation and associated conditioning loads. Preliminary energy models attempt to quantify the potential energy savings a building equipped with BIOM might realize due to HVAC load reduction. (Impact) Nonvascular phytoremediation of indoor air is an understudied and desirable biological building technology. Preliminary results suggest reasonable areas of moss can support indoor ecosystem respiration (plant photosynthesis ∝ human respiration), reducing the need for outdoor air ventilation with indoor fresh air generation, while filtering harmful and prevalent indoor contaminants. The energy savings associated with reducing outdoor air ventilation are dependent on variables such as climate and envelope infiltration rate: savings increase as balance point diverges from design temperature and envelopes get tighter. But for a high-performance office building in New York City, the model suggests an annual energy use intensity (EUI) reduction of 10% and 30% compared to a baseline with and without energy recovery ventilators (ERVs) respectively. This model assumes zero outdoor air ventilation as BIOM theoretically eliminates that requirement; however, it is the position of this thesis that a completely “closed” or “sealed” world is neither desirable nor feasible. Instead, wirelessly HVAC-integrated IAQ-data-driven negotiation of air and energy across the building envelope optimizes indoor air quality and positions the building as a participatory ecological agent rather than a chamber hermetically sealed from the outside world.
August 2021
School of Architecture
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Rensselaer Polytechnic Institute, Troy, NY
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