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The effects of temperature and humidity on the permeation properties of membrane transport media used in energy recovery ventilators

ASHRAE

We report on an experimental study of the effects of relative humidity and temperature on the transport of water vapor and CO² through a series of standard polymeric materials to determine their potential for use as membrane media in energy recovery ventilators (ERVs). Results are reported for four polymers of two major types (glassy and rubbery). The selectivity of water vapor over CO² is also evaluated from permeation experiments. Permeability results show that rubbery membrane samples, with glass transition temperatures well below the temperature range of experiments (30°C to 50°C), have a higher water vapor permeability and a much higher CO² permeability compared to glassy membrane samples. This is hypothesized to be mainly due to the higher diffusivity of water vapor and CO² in rubbery polymers with higher chain flexibility leading to a much lower selectivity for rubbery membrane samples. In all polymer samples, water vapor permeability increases with relative humidity (up to an order of magnitude) and decreases with temperature. This is attributed to the negative enthalpy of water vapor sorption dominating its activation energy of permeation, which is associated with a lower solubility at higher temperatures. In contrast, CO² permeability increases with temperature because of the positive activation energy of CO² permeation. CO² permeability decreases slightly with increasing relative humidity (up to 30%), which is hypothesized to be due to the competitive sorption between water vapor and CO² at higher humidity levels. Therefore, the selectivity of membrane samples for water vapor over CO² decreases with temperature and increases with relative humidity, and these trends are dominated by water vapor permeability variations. In general, the permeability results reported here suggest that ERV exchangers using polymer membranes can achieve high latent effectiveness (i.e. very high water vapor permeability) over a wide range of operating temperature and relative humidity while maintaining very low CO² permeability and crossover rates (<1%)

Conference Paper

eng

Vancouver : University of British Columbia Library

10.14288/1.0366216

Applied Science, Faculty of; Mechanical Engineering, Department of

A. Engarnevis, S. Romani, A. Sylvester, R. Huizing, S. Green, and S. Rogak, The effects of temperature and humidity on the permeation properties of membrane transport media used in energy recovery ventilators. in ASHRAE 2017 Annual Conference Proceeding, D-LB-17-C067 (ASHRAE, 2017)

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