A rotary heat exchanger (energy-recovery wheel) rotates a porous matrix through both air streams so the wheel stores heat from the exhaust and releases it to the supply on the next sector. Because it can carry moisture as well as temperature, a wheel delivers the highest total-recovery effectiveness of any air-to-air device. This guide covers wheel types, the carryover issue, and where a wheel is — and is not — the right call. For the overview see the complete guide.
How a Wheel Works
The matrix is split into supply and exhaust sectors as it turns. A purge sector between them pushes any trapped exhaust back out, cutting carryover to roughly 0.5–2%. An enthalpy (desiccant-coated) wheel adds moisture transfer; a sensible (aluminium or polymer) wheel moves temperature only.
Wheel Variants
| Variant | Recovery | Effectiveness | Note |
|---|---|---|---|
| Sensible wheel | Temperature | 70–85% | Aluminium / polymer |
| Enthalpy wheel | Sensible + latent | 70–85% S / 60–80% L | Desiccant-coated |
| Purge-sector wheel | Both (+ carryover cut) | As above | Lower carryover |
Where Wheels Win — and the Hard Limits
Wheels are the best geometry for large commercial and institutional buildings and for continuous industrial process where a large latent load makes total recovery worthwhile and the exhaust is clean. The selection rules are explicit about where a wheel is not acceptable: mines and tunnels must use heat pipe or plate, never rotary; data centers use plate or free-cooling, not rotary; and any exhaust that must not be recirculated — pharmaceutical sterile zones, contaminated or explosive streams — must use a separated (run-around / desiccant) system instead. Respecting these rules is what keeps a wheel installation safe and code-compliant.
Sizing and Carryover Control
Size the wheel for face velocity and pressure drop; a deeper matrix and a purge sector reduce carryover but add cost and fan load. Compare geometries in plate vs rotary and size from the sizing article; effectiveness numbers should be read per the effectiveness guide.
EN159 Wheel Products
See It Applied
Jump to rotary wheel applications, or compare with plate, heat pipe and separated recovery.