Modelling condensation in energy exchangers with variable permeability membranes

Using membrane energy exchangers (also referred to as energy recovery ventilators, or ERVs for short) in winter conditions, and extremely hot and humid summer conditions, can result in condensation of water vapor. Condensation will affect the performance of the exchanger, facilitate the growth of microorganisms and is a precursor to frost formation at lower temperatures. Developing models that predict the onset of condensation and the performance of the exchanger under condensation conditions is therefore essential for the design of ventilation systems and the selection of the proper exchanger. Membrane permeability typically depends on water concentration and temperature. In this study, a heat and mass transfer model that accounts for the variations in the permeability of the membrane due to temperature, concentration and condensation is developed to predict the occurrence of condensation in membrane energy exchangers. The model is validated against experiments and is then used to investigate the effect of variation in the permeability of the membrane on the occurrence of condensation and to determine the operating conditions resulting in 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. (C) 2022 Elsevier B.V. All rights reserved.