Experimental investigation on the scaling stability of membrane-based energy exchanger cores under proportional airflow and numbers of layers

To conserve energy consumed by building heating, ventilation and air-conditioning systems, an increasing number of buildings have employed air-to-air energy recovery ventilators (ERVs) to recover energy from exhaust air. As a critical component of the ERV, a membrane-based energy exchanger (MEE) core undertakes the heat and mass exchange process between fresh and exhaust air streams. In engineering practices, MEE cores with different numbers of layers are manufactured for ERVs at different nominal flowrates. This study is to investigate the scaling stability of MEE core efficiency: whether performance remains consistent when the airflow rate and the number of layers are scaled proportionally. Three MEE cores were manufactured with identical materials, identical layer structures, and different numbers of layers. Their efficiencies were tested at four flowrate levels. At each flowrate level, the ratio of core flowrates equals the ratio of their number of layers. Experiment results indicate that (1) the measurement results are reliable according to heat and mass balance check. (2) In winter conditions, the uncertainty of latent efficiency is considerable, mainly due to the low temperature and humidity ratio (the “small denominator” effect). Except for the latent efficiency in winter conditions, all efficiency uncertainty values are much less than efficiency values. (3) Efficiency deviations across cores are close to combined expanded uncertainties. When modeling/estimating the MEE core efficiency, it is acceptable to assume that MEE core efficiency is stable (especially under summer conditions) when air flowrate and number of layers are scaled proportionally.