Aerosol Transfer through Semi-Permeable Membranes used in Membrane Energy Exchangers
Date
2024-10-16
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Masters
Abstract
Air conditioning societies and indoor air quality committees in North America have recently released guidelines for control of infectious aerosols in indoor spaces after the COVID-19 pandemic, recommending that more outdoor air be supplied to indoor spaces. Bringing in more outdoor ventilation air requires additional energy for heating and cooling the air to a comfortable temperature and relative humidity. Energy recovery devices such as membrane energy exchangers (MEE), can be used to reduce the energy required to condition outdoor ventilation air. MEE’s use a semi-permeable membrane to transfer heat and moisture between the outgoing exhaust air and the incoming ventilation air. However, these membranes may also transfer aerosols from the building exhaust air to the outdoor ventilation air. Measuring aerosol transfer through membranes is challenging and has many sources of error. This research is a first attempt to conduct these difficult measurements.
In this thesis, a test method to measure aerosol transfer through membranes for energy exchangers was developed and experiments were conducted using two common types of semi permeable membranes (dense and porous membranes) and two types of aerosols (dust and bacteria aerosols). The dust aerosols were dry and bacteria aerosols were wet representing the two common types of aerosols found in the ambient air. The aerosol transfer was quantified using exhaust contaminant transfer ratio (ECTR), the ratio of the mass transfer rate of aerosols transferred from the exhaust air stream to the supply air stream normalized by the maximum possible mass transfer rate of aerosols between the two airstreams.
Aerosol size and shape were the two important properties affecting whether the aerosols were transferred or deposited within the membrane. Deposition within the membranes dominated transfer through the membranes tested. While additional improvements are recommended to accurately quantify aerosol contaminant transfer, the method developed in this thesis was able to conclude that dust (dry) and bacteria (wet) aerosol transfer through the porous (Tyvek) and dense (Polyamide) membranes that were tested was negligible.
Description
Keywords
aerosol, membrane energy exchanger, bio-aerosol, indoor air quality
Citation
Degree
Master of Science (M.Sc.)
Department
Mechanical Engineering
Program
Mechanical Engineering