When two air streams must never mix, you cannot share a core. A separated recovery system transfers heat (and, with desiccant, moisture) through an intermediate loop instead. The two proven geometries are the run-around coil (two coils linked by a glycol loop) and the desiccant / membrane separation system. This guide covers both, and why separation is sometimes mandatory — context in the complete guide.
Run-Around Coil
An exhaust coil and a supply coil are joined by a pumped glycol loop. Heat moves from exhaust to supply through the fluid; the streams themselves stay fully separate, with no carryover and no purge sector. It is the standard answer for retrofit and for streams that are far apart or at different pressures.
Desiccant / Membrane Separation
Where moisture recovery is wanted but mixing is forbidden, a desiccant wheel or a selective membrane transfers latent energy while keeping the airstreams apart. This reaches total recovery without the cross-contamination a shared matrix would allow.
When Separation Is Mandatory — the Selection Rules
Pharmaceutical and cleanroom exhaust must not be recirculated into supply; the rule is explicit. The same applies to exhaust that may carry solvent, pathogen or explosive vapour. In all these cases the only compliant recovery geometry is separated (run-around coil or desiccant / membrane) — not a plate core, not a rotary wheel. Compare with heat pipe, which also keeps streams apart but is sensible-only.
Effectiveness and Cost
Run-around coils return about 40–65% of the sensible load; the pump and loop losses trim effectiveness below a direct core, but the separation is worth it. Size the coil pair and loop from the sizing article and read effectiveness per the effectiveness guide.
EN159 Separated-Recovery Products
See It Applied
Jump to separated recovery applications, or compare with plate, heat pipe and rotary wheel.