The air to air heat exchanger

Air-to-air heat exchanger, a component often used in ventilation systems to improve energy efficiency. You're correct that it’s typically an accessory integrated into devices like heat recovery ventilators (HRVs) or energy recovery ventilators (ERVs). These systems transfer heat (and sometimes moisture) between incoming and outgoing air streams without mixing them, helping maintain indoor temperature while ensuring fresh air circulation.

The use of hydrophilic aluminum foil is interesting—its water-attracting property likely enhances performance by aiding in moisture transfer or preventing condensation buildup, which is key in humid environments. The foil is usually pressed into thin, corrugated layers to maximize surface area for heat exchange within a compact design.