"Exhaust Fan" generally refers to a total heat exchanger containing a new wind-wide heat exchange core, the exhaust ventilation equipment. Total heat exchanger working principle is: when the product is working, indoor ventilation and fresh air are a positive way to cross when passing through the heat exchanger core, since the airflow on both sides of the partition plate and the temperature difference between the air flow exists vapor partial pressure, two streams presented through the partition plate heat and mass transfer phenomena, causing total heat exchange process. Summer runs, get fresh air from the air exhaust cooling capacity, lowering the temperature, while being conditioned air drying, the moisture content reduced fresh air; in winter running, get fresh air from the air chamber exhaust heat, the temperature rises. Thus, through the whole process of the heat exchanger heat exchanger core, so that the new air-conditioned recovering energy from exhaust air.