Tag Archive fresh air system

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:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.