Date of Award

12-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Jianshun Zhang

Keywords

Dynamic Botanical Air Filtration, DBAF, Air Purification

Subject Categories

Mechanical Engineering

Abstract

A dynamic botanical air filtration (DBAF) system was developed, tested and modeled for indoor air purification. The DBAF system consisted of an activated-carbon/hydroculture-based root bed for potted-plant, a fan for driving air through the root bed for purification, and an irrigation system for maintaining proper moisture content in the root bed. Results from test conducted in a full-scale open office space indicated that the filtration system had ability to supply clean air equivalent to 80% of required outdoor air supply for the space. The DBAF was effective for removing both formaldehyde and toluene at 5 to 32% volumetric water content of the root bed. It also performed consistently well over the relatively long testing period of 300 days while running continuously.

In order to improve the understanding of the mechanisms of the DBAF system in removing the volatile organic compounds, a series of further experiments were conducted to determine the important factors affecting the removal performance, and the roles of different transport, storage and removal processes. It was found that passing the air through the root bed with microbes was essential to obtain meaningful removal efficiency. Moisture in the root bed also played an important role, both for maintaining a favorable living condition for microbes and for absorbing water-soluble compounds such as formaldehyde. The role of the plant was to introduce and maintain a favorable microbe community that effectively degraded the VOCs that were adsorbed or absorbed by the root bed. While the moisture in a wet bed had the scrubber effect for water-soluble compounds such as formaldehyde, presence of the plant increased the removal efficiency by about a factor of two based on the results from the reduced-scale root bed experiments.

A mathematical model was also developed for predicting the short and long term performance of the DBAF with model parameters estimated from the experiments. The simulation results showed that the model could describe the pressure drop and airflow relationship well by using the air permeability as a model parameter. The water source added in the model also lead to the similar bed moisture content and outlet air RH as that in real test case. The simulation results also showed that the developed model worked well in analyzing the effect of different parameters. It was also found that the critical bio-degradation rate constant was 1×10-5 s 1, below which the DBAF would not be able to sustain the formaldehyde removal performance. The bio-degradation rate constant of the reduced scale DBAF tested was estimated to be in the range of 0.8-1.5×10-4 s 1.

Whole building energy simulation results showed that using the DBAF to substitute 80% of the outdoor air supply without adversely affecting the indoor air quality could result in 30% saving in heating, 3% in cooling and 0.7% in pump energy consumption per year at the climate of Syracuse, NY (Zone 5). A higher percentage of energy savings was found to be achievable for climate zones with a higher annual heating load (e.g., climate zone 6 and 7).

Access

Open Access

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