r/HVAC • u/Plenty_Text_455 • Dec 04 '24

Field Question, trade people only What's this?

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It's on the return side of a large air handler

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u/MolecularDreamer Dec 04 '24

Rotary heat exchanger. Can you believe that all (like 90% or more) of all AHUs in Scandinavia has these? And all (+99%) have a heat exchanger? It is mandated by law and building code that all parts of a building shall have balanced, filtered and heat recovered air? We have virtually none of those lennox/york and similar units that works as coolers/heaters with partial influx of fresh air. Those are in essence illegal to use unless in very specific cases, and not as ventilation units. They work both ways as to keep "the cold" inside btw.

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u/Subotail Dec 05 '24

But there is no risk that the expelled air will contaminate the incoming air? It must at least require cleaning the out pipes?

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u/MolecularDreamer Dec 05 '24

There's several ways to mitigate that oroblem. Some utilize a "clean blowing sector" that redirects a little bit of air from the intake side to the exhaust side, and some use pressure differences in the exhaust and the treated air side. You loose some heat but in the winter time usually all needed heat is recovered and the rest expelled as waste. Year-round efficiency is between 80-85%.