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UBC Theses and Dissertations

Condensation in membrane-based energy exchangers Rahgozar Abadi, Iman


Using energy exchangers in winter conditions, and hot and humid summer conditions can result in condensation. Condensation might affect the performance of the exchanger, facilitate the growth of micro-organisms and be a precursor to frost formation at lower temperatures. As a result, information about the impacts of condensation on the performance of the energy exchanger and the operating conditions that result in condensation is essential for the design of ventilation systems and the selection of the proper exchanger. In this study, a widely used energy exchanger is experimentally tested under various operating conditions. The presence of condensation is inferred from visual observation, investigation of the sensible and latent effectiveness, and measurements of pressure drop. It is shown that condensation increases the sensible effectiveness of the supply side and decreases the sensible effectiveness of the exhaust side. Additionally, the latent effectiveness of both air streams increases when condensation occurs, although the increase in exhaust side latent effectiveness is more significant. Finally, the accumulation of water in the channels significantly increases the pressure drop in the exhaust side while it does not significantly impact the effectiveness. Additionally, a heat and mass transfer model is developed to investigate condensation in a wide range of operating conditions. The permeability of the composite membrane of the exchanger used in this study, is measured at various temperature and humidities and the effects of membrane orientation and the phase of water (liquid/vapor) on the permeability of the membrane are investigated. An empirical membrane model is then added to the heat and mass transfer model. The heat and mass transfer model is validated against experiments and is then used to determine the operating conditions resulting in condensation and to investigate the effect of variation in the permeability of the membrane on the occurrence of condensation. It is shown that assuming a constant permeability for the membrane can result in errors of up to 25% in the prediction of the rate of condensation. Furthermore, it is shown that condensation in the energy exchanger will be significant only when the indoor air temperature and humidity are high.

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