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.
How the Fluid Loop Works
A run-around (separated) coil uses two coils linked by a pumped fluid loop (water/glycol). Exhaust warms the fluid; the fluid warms incoming air in a second coil. Streams never meet — ideal when they are far apart or contaminated.
Pump & Freeze Care
- Glycol concentration set for the lowest expected temperature to avoid freeze.
- Pumps add parasitic load, so effectiveness is a little lower than direct plate/heat-pipe.
- Loop can route exhaust and intake across a building.
Run-around vs Heat Pipe
Both keep streams separate. Heat pipe is passive and needs tilt; run-around handles larger separation and is easier to route. Compare in run-around vs heat pipe and run-around for contaminated exhaust.
Applications
Contaminated or odorous exhaust (paint, sludge, food), distant supply/intake, pharma no-recirculation. See separated recovery hub.
FAQ
When do I pick run-around over plate?
When the two streams are physically separate, or the exhaust is contaminated and you want a clean fluid loop between them.
Request a Run-Around Design
Call 15753355505 or request a quote.
Related Separated / Run-Around Applications
Food & Agricultural Drying · Industrial Dryer · Paint Booth · Boiler Flue Gas.