An air-to-air heat exchanger works by transferring heat between two separate airflows—one hot and one cold—without mixing them. This is commonly used in ventilation systems to recover heat and improve energy efficiency. Here's how it works:

Basic Working Principle:

1. Two air streams:

   • One stream is warm, stale air from inside a building (exhaust).

   • The other is cool, fresh air from outside (intake).

2. Heat transfer surface:
   The two air streams pass through separate channels inside the heat exchanger, usually made of metal or plastic plates, or thin aluminum foils.

3. Heat exchange:

   • As the warm exhaust air flows past the heat exchanger surfaces, it transfers its heat to the material.

   • At the same time, the cool incoming air flows through adjacent channels and absorbs the heat from the surface.

4. Result:

   • The fresh incoming air is preheated before entering the building, reducing heating demand.

   • The exhaust air is cooled before being vented outside.

Key Features:

• No mixing of air streams (important for hygiene and air quality).

• Often used in heat recovery ventilation (HRV) or energy recovery ventilation (ERV) systems.

• Efficiency can reach 70–90% in modern systems.