Application of indirect non-invasive methods to detect the onset of crystallization fouling in a liquid-to-air membrane energy exchanger.

Highlights • Three indirect non-invasive methods are applied to detect the onset of fouling. • Two of the three methods can effectively detect the onset of fouling in a LAMEE. • The slope method is the most sensitive of the three methods. • A high moisture transfer rate through a membrane accelerates the initiation of fouling. • Fouling is detected earlier in the membrane with lower vapor diffusion resistance. Abstract Liquid-to-air membrane energy exchangers (LAMEEs) use semi-permeable membranes and are designed to transfer heat and moisture between air and liquid streams in heating, ventilating, and air-conditioning (HVAC) systems. However, crystallization fouling in membranes is possible in practical HVAC applications, and this may lead to severe degradation in the performance of LAMEEs. The main aim of this paper is to apply three indirect non-invasive methods to detect the onset of crystallization fouling in a LAMEE. The methods are used to detect fouling by analyzing experimental measurements of moisture flux and moisture transfer resistance. The experimental tests involve dehydrating varying concentrations of MgCl 2 (aq) desiccant solutions using two types of membrane with different vapor diffusion resistances (VDRs). The results confirm that two of the three methods can effectively detect the onset of crystallization fouling in the LAMEE. Thus, the methods can be used for online monitoring of operating LAMEEs in order to timely identify the initiation of fouling. The results also show that the membrane with a lower VDR produces a higher moisture flux which leads to a higher degree of fouling than the membrane with higher VDR. [ABSTRACT FROM AUTHOR]