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how does air to air heat exchanger work in fresh air system

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In a fresh air system, an air-to-air heat exchanger is used to recover heat from outgoing indoor air and transfer it to the incoming fresh outdoor air—without mixing the two airflows. This improves indoor air quality while reducing heating or cooling loads. Here's how it works step-by-step:

How It Works in a Fresh Air System:

  1. Stale indoor air is extracted from rooms like kitchens, bathrooms, or general living spaces. This air is typically warm in winter or cool in summer, depending on indoor climate control.

  2. Fresh outdoor air is drawn in simultaneously. This air may be cold in winter or hot in summer, requiring conditioning.

  3. Both air streams pass through the air-to-air heat exchanger, but in separate, sealed channels:

    • The warm outgoing air transfers its heat (or coolness in summer) to the metal or membrane surfaces inside the exchanger.

    • The incoming cold air picks up that heat from the exchanger surfaces before entering the building.

  4. The two air streams never mix, ensuring clean, filtered air is delivered inside.

Benefits in a Fresh Air System:

  • Energy efficiency: Recovers 60–90% of heat that would otherwise be lost.

  • Improved indoor air quality: Constant supply of filtered, fresh air.

  • Comfort: Reduces temperature swings from direct outdoor air intake.

  • Humidity control (if an ERV is used): Some units also transfer moisture to balance indoor humidity.

how does air to air heat exchanger work

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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.