An air-to-air heat exchanger in a fresh air system transfers heat between incoming fresh air and outgoing stale air without mixing the two streams. Here’s how it works:
- Structure: The exchanger consists of a core with thin, alternating channels or plates, often made of metal or plastic, that separate the incoming and outgoing airflows. These channels allow heat transfer while keeping air streams isolated.
- Heat Transfer:
- In winter, warm indoor air (being exhausted) transfers its heat to the colder incoming fresh air, pre-warming it.
- In summer, cooler indoor air transfers its "coolness" to the warmer incoming air, pre-cooling it.
- This process occurs through conduction across the exchanger’s walls, driven by the temperature difference.
- Types:
- Cross-flow: Air streams flow perpendicularly, offering moderate efficiency (50-70%).
- Counter-flow: Air streams flow in opposite directions, maximizing heat transfer (up to 90% efficiency).
- Rotary (enthalpy wheel): A rotating wheel absorbs and transfers both heat and moisture, ideal for humidity control.
- Benefits:
- Reduces energy loss by recovering 50-90% of the heat from exhaust air.
- Maintains indoor air quality by supplying fresh air while minimizing heating/cooling costs.
- Operation in Fresh Air System:
- A fan draws stale air from the building through the exchanger while another fan pulls fresh outdoor air in.
- The exchanger ensures the incoming air is tempered (closer to indoor temperature) before distribution, reducing the load on HVAC systems.
- Moisture Control (in some models):
- Enthalpy exchangers also transfer moisture, preventing overly dry or humid indoor conditions.
The system ensures ventilation efficiency, energy savings, and comfort by recycling heat while maintaining air quality.
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