Air-to-air heat recovery captures energy from exhaust air and uses it to precondition incoming supply air. The question is what gets recovered: temperature only, or temperature and moisture. That distinction separates an HRV from an ERV.
Sensible recovery
Sensible recovery transfers only dry-bulb heat. A plate or heat-pipe exchanger moves temperature but not humidity — moisture passes through independently. Sensible effectiveness of 70–85% is typical.
Enthalpy (total) recovery
Enthalpy recovery transfers both heat and moisture. A rotary wheel or a membrane plate (ERV core) carries water vapour along with energy. This is essential in humid climates where you want to recover cooling without importing outdoor humidity indoors, or recover heat without over-drying supply air in winter.
HRV vs ERV
| HRV | ERV | |
|---|---|---|
| Transfers heat | Yes | Yes |
| Transfers moisture | No | Yes |
| Best climate | Cold/dry winters, balanced humidity | Hot-humid or very cold-dry |
| Typical use | Northern HVAC, warehouses | Humid commercial, residences |
Why effectiveness drives savings
Recovered power ≈ exhaust mass flow × cp × (exhaust temp − supply temp after recovery). At 80% effectiveness the supply air arrives 80% of the way from outdoor to exhaust temperature, so the heating/cooling plant works far less. In a cold-climate school, that can mean 30–50% lower ventilation heating load.
Frost, condensate and defrost
- Frost formation occurs when exhaust drops below 0 °C on the plate; it blocks channels and destroys effectiveness.
- Defrost strategies: exhaust-only bypass, preheating, or recirculation. ERV membranes that pass moisture reduce frost risk because they transfer latent heat too.
- Condensate in summer (cooling recovery) must be drained; plate cores need a condensate tray.
Choosing HRV vs ERV
Pick HRV when indoor and outdoor humidity are already balanced and you only need temperature recovery. Pick ERV when humidity control matters — humid summers, or very dry winters where you don't want to over-dry already-dry supply air. See our selection guide for the full checklist, and applications by industry for real-world examples.
HeatRecoveryHub is an independent knowledge base by Zibo Qiyu.