Energy transfer and energy saving potentials of air-to-air membrane energy exchanger for ventilation in cold climates

Frosting occurring inside heat exchangers degrades the exchangers' performance and reduces energy recovery in cold climates. The moisture transport in membrane energy exchangers (MEE) provides a great potential to increase frost tolerance and decrease energy consumption by the air handling units (AHU). In addition, the moisture recovery in MEEs tends to improve the thermal comfort by adding moisture to the indoor dry air. However, applications of MEEs for cold climates are less known compared to their use in hot and humid climates as independent cooling and dehumidification. The open literatures dealing with heat and mass transfer of the MEEs for cold climates are scarce and acute. This research aims to investigate heat and moisture transfer, and energy saving potentials of MEEs compared to the sensible-only heat exchanger (HE). The applicability of transforming heat and moisture transfer analysis carried out for hot and humid conditions to cold climates is examined. The study attempts to “translate” conventional sensible-only HE correlations to the MEEs. Knowledge and data of heat exchangers are transformed to MEEs through analysing the boundary conditions of heat and mass transfer in both MEE and HE. This transformation can reduce needs of relying on computational fluid dynamics (CFD) to analyse heat and mass transfer in MEEs. As one of most important advantages of adopting MEE in cold climates, frosting reduction by the MEE is determined and compared for a specific MEE and HE in the heating season of Oslo (Norway). The energy consumption by the AHU equipped with the MEE is compared to the AHU with HE under different airflow rates. The MEE is able to significantly reduce the energy consumption by preheating and post-conditioning (reheating and humidifying) when there is frosting risk in MEE or HE for Oslo climate.