Particulate fouling assessment in membrane based air-to-air energy exchangers

Samples of three different membrane transport media, extracted from commercial HVAC ERV exchanger cores, were loaded with graphite and NaCl aerosol nanoparticles. Accelerated loading experiments were conducted in a laboratory apparatus to simulate several years of fouling in the field. Initial and post-loading water vapor permeance through the membrane samples were experimentally determined for each loading to quantify the effects of fouling. The impact of relative humidity on the performance of loaded membranes was also studied by exposing membranes loaded with particles in dry air to an elevated RH of 75%, leading to surface condensation. The experiments show that the deposition of particles in dry air can only affect the membrane when the fouling is severe enough to form a cake layer on the membrane surface comparable to the thickness of the membrane. In the case of membranes loaded with hygroscopic salt particles, surface condensation at high RH values can lead to vapor permeance reductions of up to 15% well before the cake layer formation phase of fouling, whilst no permeance reduction was observed for membranes loaded with non-hygroscopic graphite particles. This indicates a net porosity reduction in the microporous substrate layer of exposed salt-loaded samples. A pore-narrowing process of the substrate layer, due to the mobilization of salt particles in aqueous form, is a potential explanation for these observations.