Two Recovery Paths
Air-to-air devices (plate, rotary, heat pipe) move energy directly between the two airstreams. Air-to-water devices use a coil to dump recovered heat into water for domestic hot water, process heating, or a buffer tank.
Comparison
| Air-to-Air | Air-to-Water | |
|---|---|---|
| Best when | Streams are co-located | Heat is needed elsewhere (water) |
| Complexity | Lower | Higher (pump, tank) |
| Use | Pre-condition supply air | DHW, process, storage |
Decision
If the recovered energy can be used to condition the incoming air, air-to-air is simplest. If you need hot water or process heat, or the streams are distant, air-to-water (or a run-around coil to water) is the better fit.